© IMechE 2023.Plug-in hybrid electric vehicles (PHEV) have the potential of combining the benefits of a renewable electric mix with biofuels. More recently, PHEV have been designed to be equipped with a small combustion engine known as range extender (RE), thus allowing an improvement in vehicle’s range while converting fuel energy through a highly efficient path. Despite being a convenient strategy for decarbonizing light vehicles, the intermittent operation of the engine may create issues regarding the catalytic conversion of pollutants, yielding an increase in local harmful emissions. This drawback may be intensified depending on the used fuel. Hydrous ethanol is a promising alternative for gasoline and is already available in some countries, such as Brazil. However, ethanol has a great enthalpy of vaporization and it results in a charge cooling, affecting the catalyst warm-up and making the intermittent operation with ethanol more challenging. Hence, this study was motivated by the need of improving the catalytic efficiency of flexfuel RE operating with both gasoline and hydrous ethanol. Thus, a calibration was firstly performed to shorten the warm-up phase with ethanol. Then, an electrical heater was employed for accelerated catalyst heating, further improving emissions from ethanol operation, aiming at attaining future emissions regulations. Experimental tests were conducted in a vehicle under FTP72 cycle using a chassis dynamometer. The calibration adjustments resulted in a warm-up phase for ethanol <10 s longer than that for gasoline. The stable operation phase resulted in similar emissions for both fuels. On the cycle average, a reduction in CO for ethanol was observed, and although the methane and NOx emissions were slightly increased due to colder catalyst operation, significant improvements were obtained on a well-to-wheel (WTW) analysis. The use of an electrically heated catalyst (EHC) improved the emissions during the warm-up phase, significantly reducing the emission of NOx and non-methane organic compounds.

© 2024 SAE International. All rights reserved.Plug-in hybrid electric vehicles have the potential of combining the benefits of electric vehicle in terms of low emissions and internal combustion engine vehicles in terms of vehicle range. With the addition of a renewable fuel, the CO2 potential reduction increase even more. The last trends for PHEV are small combustion engine known as range extender, with battery package between full hybrid and electric powertrains. Thus, allowing an improvement in vehicle's range, reducing battery materials while converting fuel energy through a highly efficient path. Although these vehicles have been proved to be a convenient strategy for decarbonizing the light vehicles, the use of alternative fuels is poorly studied. In this work, hydrous ethanol is chosen because is already available in some countries, such as USA and Brazil, and have an ultra-low well-to-tank CO2 emission. The study combines experimental and numerical tools for the development of an ultra-efficient and ultra-low emission powertrain in a range extender BMW i3 fueled with hydrous ethanol. Experimental tests were conducted in an engine test bench and a chassis dynamometer under FTP72 emission cycle. The vehicle simulation was performed in AVL Cruise M for the control strategy optimization and vehicle test under different driving conditions. For comparison, the vehicle was also tested with the battery electric version. In summary, this study demonstrates that the utilization of hydrous ethanol as a range-extender fuel in plug-in hybrid electric vehicles can significantly enhance vehicle range while reducing well-to-wheel CO2 emissions. The range-extender configuration, particularly with E100, exhibits promising potential, making it a competitive choice for drivers concerned about range limitations and environmental impact. The research emphasizes the adaptability of hydrous ethanol-fueled PHEVs across various driving scenarios, contributing to the ongoing global initiative to decarbonize light vehicles and combat climate change.

© 2024Producer gas from biomass gasification offers a renewable alternative to fossil fuels. However, its low energy density results in low conversion efficiency in engines. Blending producer gas with higher-ranked fuels such as hydrogen has been proposed to overcome this issue. This study investigates the combustion of artificially made producer gas and hydrogen mixtures in an optical SI engine. The molar fraction of hydrogen in producer gas ranged from 14 to 62%, which simulated additions of hydrogen to a low calorific producer gas. The experiments are conducted at a constant speed and stoichiometric ratio. The spark timing is varied to achieve the highest power for each mixture. Results include data on emissions, thermodynamics, and flame morphology. The molar fraction of 33% hydrogen on producer gas improves the flame morphology of the mixture to resemble that of pure natural gas, while 24–36% was found to be the optimal range for engines initially designed to run on natural gas with lower NOx and UHC emissions.

© 2023 Elsevier LtdOne way to achieve a fast track for the decarbonization of the transportation sector is through the usage of biofuels. Among the many biofuels available for transportation, ethanol is one of the most promising, especially when combined with direct-injection spark-ignited engine technologies. The present work aims to validate 3D Computation Fluid Dynamics (CFD) ethanol spray and combustion models with the calibration of specific model parameters using experimental data obtained with optical measurements. Focus is given on the investigation and determination of the Extended Coherent Flame Model parameters for hydrous ethanol turbulent spray combustion. To characterize the spray produced by the injector, measurements obtained with a Phase Doppler Interferometer system are used. Natural luminosity and in-cylinder pressure are acquired on a single-cylinder research engine with optical access. The work also considers results obtained from 1D and 3D CFD models to supplement the acquired experimental setup. From the comparison between experimental and numerical results, it comes out that a correction of the Extended Coherent Flame Model turbulence stretch parameter can be done according to a ratio of flow and combustion length scales obtained at the spark time. In this sense, an expression is proposed to allow the correction of such a parameter in different engine operating conditions. Accordingly, in-cylinder mean effective pressure calculated with 3D CFD simulations show a good agreement with the experimental data for all studied cases.

© 2023, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.The Turbofan engine represents the type of propulsive technology mostly used in commercial aircrafts, and until that the new disruptive technologies take place, researches to optimize this propulsive system shall be continued to reduce the environmental impacts. The aim of this paper is to propose a methodology for the low-pressure system preliminary design (fan/low-pressure turbine), based on aircraft cruise thrust adjustment from commercial off-the-shelf turbofan engine, focusing on reducing specific fuel consumption for the individual aircraft mission. This work is carried out according to the following steps: (i) model development with calculation methodology for velocity diagram flow angles applied to the low-pressure system; (ii) estimation of baseline low-pressure system design parameters from limited engine data (an integrated engine aircraft model developed in the Gasturb and MATLAB commercial softwares are applied); (iii) evaluation of the strategies to increase the low-pressure system component efficiencies and their implementation by computer simulation; (iv) reapplication of the calculation methodology for estimation of the velocity diagram flow angles considering the adjusted low-pressure system components; and (v) analysis of the adjustment proposal results considering the matching between the lowest specific fuel consumption and the net thrust required for the cruise flight phase of the aircraft. As a final result, it demonstrates that the proposed strategies are promising for the adjustment of the low-pressure system in the preliminary design scope, and this approach may be considered feasibility from the standpoint of the engine manufacturer implementation, since the engine core and its external sizing do not affected.

© IMechE 2022.Thermal processes and power generation systems may employ producer gas generated through gasification as an alternative to replace natural gas with lower carbon footprint. However, pure producer gas in engines is associated with a significant power derating that can be mitigated by blending it with other biofuels. This work evaluated the effects of methane and producer gas blends on the performance of a SI engine. The additions of methane were 10%, 25% and 50% on a molar basis. The results demonstrated that adding 25% methane to producer gas is enough to sustain the combustion reaction with good stability and a power derating of 10.8%. The addition of 50% methane to producer gas attains efficiency and combustion characteristics remarkably similar to pure natural gas with a power de-rating of 5.4%. Emissions indicated that carbon monoxide (CO) has decreased with the addition of methane to producer gas from 85 to 3.43 g/kWh, while nitrogen oxides ((Formula presented.)) emissions have increased from 0 to 8.85 g/kWh. In the case of unburned hydrocarbons (UHC), emissions did not considerably change before adding 25% methane to producer gas and stayed constant at approximately 10 g/kWh. Engines designed to run on natural-gas could use this mixture without significant modifications to the combustion chamber while decreasing NOx emissions.

© IMechE 2022.The mandatory migration from fossil to renewable energy sources requires the characterization of new alternative fuels. One important step in fuel characterization is the test in optical engines, which allows the morphological characterization of flames. This analysis requires the post treatment of images by using segmentation. In many cases, an automatic threshold presents shortcomings as the flames may present different regions with variable luminosity, as also reflections from valves and cylinder liner. Consequently, a time-consuming manual image processing is required and, therefore, an automatic procedure would be welcome. The use of deep learning techniques for image segmentation is a promising alternative for such task, which has showed excellent results in several applications. In this study, two different models were trained to identify flames in images obtained from an optical engine operating at various conditions. The dataset used to train the models was generated by using images from tests with several types of fuels and combustion modes. The effects of image resolution and the generalization capabilities for different fuels and combustion operation were investigated. After analyzing the results, the use of deep learning methods to identify and characterize flames was validated as a mean for improving processing time.

© 2023, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.This paper aims to specify a methodology for an optimized inerting system conceptual design based on fuel tank flammability analysis defined by rules for commercial aircraft certification proposal to evaluate the impact on engine bleed consumption in a modernized commercial long-range aircraft model. This work was carried out according to the following steps: (1) estimation of aircraft geometric tank features from limited data; (2) development of tank thermal model to estimate bulk fuel temperature based on flight performance aircraft, fuel consumption/transfer in the tank, presence of heat sources and external airflow heat exchange; (3) flammability analysis based on Federal Aviation Administration (FAA) certification requirement methodology; (4) conception of an inerting system model as a flammability reduction means based on tank gas mixture model, onboard inert gas generation system publicly available data from FAA previous studies and proposed inerting gas distribution model; (5) incorporation of inerting system in the flammability model and reassessment of the fuel tank flammability; (6) analysis of the impact in engine bleed air consumption and specific fuel consumption due to the designed inerting system. As a final result, a methodology to increase the safety in aircraft operation was obtained, considering the current most common technology used to reduce the fuel tank flammability in commercial aircraft, the inerting system. This strategy is applicable for new aircraft in a development phase and also allows the accomplishment of modernizing designs for existing aircraft following current safety regulations.

© 2022 Elsevier LtdThe high environmental impact of fossil fuels combined with the rise of carbon dioxide in the atmosphere has made the search for renewable fuels imperative. The study assesses the technical and economic viability of replacing heavy fuel oil (HFO) with green hydrogen (H2) in industrial plants for high temperature generation (>1100 K). The study also estimates the emissions generated by the plants after the fuel switch in terms of particulate matter (PM), SO2, NOx and CO2 emissions. To illustrate the feasibility of this replacement, an assessment of a calcination furnace at a pulp plant in Chile in 2022 was carried out, taking into account two electricity generation scenarios for H2 production by water electrolysis. Replacing HFO with a mixture of H2 + HFO was beneficial in terms of emissions. The financial assessment showed that blending H2 with HFO of up to 20 % is the best solution, considering current fuel prices, and that full substitution of HFO with H2 after 2030 is economically viable.

© 2023 American Society of Mechanical Engineers (ASME). All rights reserved.To attend the high demand for high performance, low fuel consumption, and low emissions, ethanol has become a potential candidate to replace gasoline applications worldwide. In this scenario, ethanol market share has increased in two spaces, blended with gasoline, where the goal is just to increase the knock limit during engine operation, and then leverage the thermal efficiency, or in its pure form, where the benefits of its green characteristics contribute significantly to Green House Gas (GHG) credits benefitting car manufacturers. The objective of this research is to analyze the effects of different spark plug conditions, representing nominal and outwearing conditions, on flame propagation in engine-like conditions applying numerical modeling. The commercial software STAR-CD is adopted for the 3D Computational Fluid Dynamics (CFD) model mimicking the Direct Injection Spark Ignition (DISI) optical engine adopted for the experimental tests. The numerical model adopts a 3-Zones Extended Coherent Flame (ECFM-3Z) and Imposed Stretch Spark Ignition Model (ISSIM), for the combustion and the spark plug modeling, respectively. The engine operating conditions adopted consist of direct injection of ethanol (E100) partial load and low speed. The model was built and validated according to experimental measurements. Afterward, the tuned model was used to study a set of cases intended to evaluate how different spark plug discharge energy and electrode gaps influence flame propagation in engine-like conditions. The results obtained identified the influence of non-optimal spark plug conditions in combustion propagation and indicated the influence of the parameters studied in engine performance.

© 2023 by the authors.Global gas markets are changing as natural gas (NG) is replaced by biomethane. Biomethane is produced by upgrading biogas, which can have a molar concentration of methane to over 98%. This renewable energy has been injected into the pipeline networks of NG, which offers the possibility to increase its usage in industrial and residential applications. However, the expectation of the increase in biomethane proportion on the NG grids could increase the fluctuations on the composition of the NG–biomethane mixture in amplitude and frequency. In this context, the injection of biomethane into the existing network of NG raises a discussion about the extent to which variations in gas quality will occur and what permissible limits should exist, as variations in combustion characteristics can affect the operation of the combustion processes, with consequences for consumers, distributors and gas producers. This study describes a gas quality analysis with regard to the use of biomethane in industrial equipment, mixed or not mixed with NG, taking into account the indicators for gas interchangeability and provides a discussion on the necessary gas quality level to be achieved or maintained for efficient combustion in equipment originally designed to operate with NG. NG and biomethane real data collected for 92 consecutive days in 2022 and provided by two different companies in Brazil were used for this study. It is shown that the maximum deviation of the Wobbe Index (WI) of 5%, which is allowed for industrial plants, does not work for the operation of furnaces at temperatures of 1200 °C or more. In addition, it is shown that the WI, as defined in relation to the calorific value of the fuel, may allow inappropriate substitution of fuel gases, which is likely to reduce the range of blending of biomethane in NG pipelines. The results can be assessed to analyze how the addition of biomethane to NG grids will impact the WI and the equipment operation parameters such as the air-to-gas ratio, products-to-gas ratio, adiabatic flame temperature and furnace temperature.

© 2021 Taylor & Francis Group, LLC.A reverse vortex flow gliding arc discharge in a fuel-rich premixed mixture was applied to a high swirl fuel-lean global combustion to accelerate fuel oxidation. Both the discharge and flame were generated in natural gas and air. To evaluate the role of the gliding arc in the process, a gas analysis of the exhaust gas was performed in the same operational conditions with and without plasma. The chemical measurements show that the plasma reduces carbon monoxide and unburned hydrocarbons contents with a low impact on the NOx level. Furthermore, the comparison of the relative decrease of the hydrocarbon emissions shows that the hydrocarbons have different sensitivities to the plasma application.

© 2022 Elsevier LtdEthanol is a renewable fuel and can be used in electric hybrid vehicles concepts, especially for countries capable of producing such fuel in a sustainable way. A strategy to enhance these concepts is the use of lean-burn combustion, which is an effective way to improve the fuel economy from spark-ignition engines, while obtaining low pollutant emissions. However, these improvements are complicated to achieve in a practical way because lean combustion has low rates of reaction, extinction, and misfire cycles, leading to cyclical variability for the engine operation. The drawback becomes even greater when lean combustion is associated with commercial ethanol fuels and direct injection. Therefore, the objective of the present work is to provide an experimental analysis of spray guided direct injection with commercial fuels used in a consolidated market for the use of ethanol such as the Brazilian one, in particular hydrous ethanol (E95W05) and ethanol-gasoline blends (E27G73). The experiments were conducted in an optically accessible spark-ignition engine and the lean combustion effects on engine cycle variability, performance, flame morphology, and exhaust emissions were assessed. In general, the results indicated that combustion instabilities can be correlated from thermodynamic and optical analyses. Flame instabilities for E95W05 were associated with the lower flame propagation speed caused by the temperature reduction during lean combustion. Additionally, exhaust emissions contained the presence of unburned ethanol which increased when combustion became leaner. Moreover, the lower flame propagation speed was one of the factors responsible for reducing engine performance and increasing combustion variability. The results indicated that vaporization was a relevant phenomenon affecting ethanol combustion in the direct injection mode. The cooling effect of fuel vaporization presented itself as a powerful means for the reduction of NOx and aldehydes, even for the lean operation. Higher emissions of CO and THC were also observed for the engine operating with E95W05 when compared to E27G73. The results of the present work showed that special attention must be paid to the use of commercial fuel with a high ethanol content in spray-guided direct injection engines, especially during lean-burn combustion, in order to not compromise the performance nor increase pollutant emissions.

© 2022, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.Solid propellants are usually characterized by their ballistic and mechanical properties. However, these properties are seldom homogeneous. Processing factors such as multi-batch, casting, curing and post-curing dynamics induce transfer of loads and defects along the propellant. This propellant heterogeneity is responsible for different ballistic and mechanical properties in the grain. This paper presents a novel experimental procedure to characterize the elastic properties of single- and multi-batch solid propellants based on the use of the two-dimensional digital image correlation (DIC) method. The proposed experimental procedure has been applied to two different specimen configurations namely SBIP (single-batch inert propellant) and MBIP (multi-batch inert propellant) propellants. The SBIP specimen was manufactured in a single shot aiming at a more homogeneous mechanical behavior and uniform degree of cure along the propellant length. On the other hand, the MBIP specimen was manufactured in three different stages where each stage has a different degree of cure. Both specimens have a diameter-to-length (L/D) ratio equals to 19, which is an aspect ratio representative of typical large-scale solid-fuel grain rocket configurations. Additionally, in order to validate the in-situ measured properties, tests at small coupon level were also carried out using small cylindrical coupons taken from the same regions of interest used to measure the mechanical properties of the SBIP and MBIP specimens. A very good agreement between the measured local and global (in-situ) strain fields and mechanical properties was found in both testing scales, thus validating the proposed testing procedure based on the DIC technique. Results showed an increase in the elasticity modulus in the specimen bottom due to gravity effects.

© 2022, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.With increasing regulations for pollutant emissions and greenhouse gases on spark-ignition engines, there is a need for improvement on engine fuel efficiency and investment in potential alternate biofuels, such as ethanol. There are several technologies available to increase fuel efficiency in gasoline engines, but further development is still needed for flex-fuel direct injection and ethanol-optimized applications. By operating a research spark-ignition engine with optical access, at partial load and low-speed condition, combustion performance was evaluated by means of cylinder pressure and heat release analysis, along with high-speed cycle-resolved direct visualization of flame propagation. Direct fuel injection (DI) technology was primarily utilized; tests were performed with port fuel injection (PFI) to obtain baseline results for comparison. Commercially available fuel mixtures of hydrous ethanol (95% vol ethanol, 5% vol water) and gasoline-ethanol blend (73% vol gasoline, 27% vol ethanol) were tested. On PFI engine tests, lower cylinder pressures were registered for ethanol due to higher charge cooling effect. Air-guided DI showed higher cyclic variation and delayed combustion for both fuels, related to a combination of less time for fuel vaporization on DI and cylinder wall-wetting, which is undesirable especially emissions-wise. Spray-guided DI presented improvements in rate of burn and cyclic performance over air-guided DI system, in view of a more favorable fuel injector position, enabling better fuel spray development and less wetting of the cylinder wall, despite still occurring impingement over the piston surface. Optical investigations revealed a tendency for gasoline flames to show more center of mass displacement throughout propagation, probably linked to the faster vaporization of gasoline and interaction with in-cylinder air flow. Flame circularity indicated higher values for ethanol on DI operation; this is aligned with other authors’ results but requires further investigation as to completely understand the causes.

© 2022 SAE International. All rights reserved.Restrictions on emissions have been made to guide society into a more sustainable development. The impasse between regulations and the expectation of a growing demand for aviation exposes the need for decarbonization of the sector. In this way, the utilization of hydrogen associated with fuel cells stands out as means to eliminate emissions during flight. This study evaluates the feasibility of using cryogenic liquid hydrogen (LH2) tanks as both energy source and cooling advantage for a small aircraft with electric propulsion. First, a propulsion system powered by a hybrid setup with Proton-Exchange Membrane Fuel Cells (PEMFC) and batteries is proposed for a small aircraft replacing an Internal Combustion Engine (ICE) and fuel tanks. Then, the new powerplant is integrated into the aircraft and simulated using the SUAVE tool. Next, a heat management analysis is performed to assess heat generation within the aircraft and heat requirements in the cryogenic tanks to meet the hydrogen consumption throughout a mission profile. Later, a sensitivity analysis explores the behavior of this heat balance with the variation in cruise duration. It is found that additional cooling capacity is required beyond that the provided by the cryogenic LH2 for this size of aircraft and mission profile, which is proposed as the additional liquid cooling system that was added to the simulation to obtain the final powerplant configuration.

Copyright © 2022 by ASME.The present study aims to evaluate the intrinsic differences in in-cylinder combustion in low load and low-speed conditions by applying experimental and numerical techniques. The experimental apparatus consisted of an AVL5406 SI-PFI single-cylinder with optical access operating under two different fuel delivery methods: Port Fuel Injection (PFI) and Direct fuel Injection (DI) with anhydrous ethanol (E100) and hydrous ethanol (E96W4). The outcomes of the engine-like conditions tests were evaluated based on the quantitative analysis of the flame propagation and on the thermodynamic data obtained using INDICOM. A Video Scope VS4-1845HS high-speed camera providing cycle resolved UV-visible digital image captured the natural emission of the flame for each test. Forthwith image acquisition, the flame propagation characteristics were post-processed through image segmentation techniques. Finally, relevant literature was revised to support the results and findings obtained at this time. The contribution of this study to the internal combustion engines research remains in gathering more information about in-cylinder flame front propagation and combustion stability for E96W4 and E100 ethanol under partial load and stoichiometric and lean conditions.

© 2020 by the authors. Licensee MDPI, Basel, Switzerland.Sugarcane bagasse has a great potential to be used as biofuel; however, its use as feedstock in fluidized bed reactors is hampered due to its fibrous nature, low apparent density, high moisture content, and difficulties with its fluidization. The present study evaluated the torrefaction of sugarcane bagasse to propose suitable process conditions that balance the properties of the fuel obtained in the torrefaction and the process’s energy requirements. Based on the thermogravimetric analysis and previous reports, two final process temperatures (230 °C and 280 °C) and residence times (35 and 45 min) for the same heating rate (5 °C/min) and nitrogen flow (1 L/min) were evaluated. Within the experimental conditions evaluated, it can be concluded that for 30 min of residence time, the average target temperature of 230 °C should be high enough to produce a stable torrefacted bagasse with a 3.41% reduction in the volatile content and obtain 98.85% of energy yield. Higher temperatures increase the feedstock’s carbon content and energy density, but the reduction in energy yield and the fraction of volatiles do not justify higher temperatures or longer residence times for pretreating the sugarcane bagasse.

© 2021 SAE International.Compression ignition engines are widely used in the cargo and passenger transport sectors, this is due to their high energy efficiency and can operate with renewable fuels. The search for increased efficiency in internal combustion engines and reduced emissions are increasingly stringent, so to meet regulatory emission standards, new technologies are being studied and developed to reduce emissions generated by engines, in the case of diesel engines compression ignition, studies of techniques to reduce NOx and soot have been carried out. One of the techniques studied is the application of the DFI - Ducted Fuel Injection concept, which makes the fuel spray pass through a small cylindrical duct installed upstream of the injection orifice of the injector nozzle, thus improving the air/fuel, making it more homogeneous and allowing a more complete combustion. This work addresses a study of this application of DFI with different compression ratios. To carry out the tests, a thermodynamic single-cylinder engine was used where its compression ratio is 16.0:1 in its normal condition, when the ducts are installed in the combustion chamber the engine starts to operate with a compression ratio of 16.5:1, thus, this study is necessary so that it is possible to visualize the behavior of the engine when the compression ratio changes, aiming at the thermodynamic behavior and emissions. CO, HC and NOx emissions were measured with FTIR spectroscopy equipment, and soot was measured by Laser Induced Incandescence - LII. The difference in compression ratio between DFI and free spray causes soot levels to increase considerably with increasing load in free spray mode, while for DFI the indices are almost unchanged.

© 2021 SAE International.Hybrid vehicles have been developed for improving efficiency and the consequent reduction of fossil fuels consumption in the transportation sector. The complexity of such vehicles allows for countless architectures, being one of them the range extender concept, which corresponds to an electrically powered vehicle equipped with a small combustion engine to improve the vehicle range. In the literature there is no current consensus whether range extenders should adopt simple engine technology aiming at cost reduction, or should they incorporate complex systems in order to achieve a remarkable thermal efficiency and low emissions. In the context of exploring the advanced options for range extenders, the combustion characterization is a fundamental step, which provides information on combustion behavior for several fuel types under a wide range of combustion modes. That information can both yield useful insights for engine development and provide combustion datasets for engine simulation. This study proposes the characterization of the flame morphology of hydrous ethanol combustion under port fuel injection mode and mixture dilution with synthetic exhaust gas recirculation (EGR) on a spark ignition, optically accessible engine. Flame natural luminosity was recorded by a high speed camera and their post-processing provided the flame morphology, which was correlated to the in-cylinder pressure data and indicated parameters. The gaseous emissions were measured using FTIR technique, for three engine speed conditions (1500, 2250 and 2500 rpm) and three conditions of EGR dilution (5%, 10% and 15%) besides the baselines conditions with no dilution, under a constant load of 5 bar IMEP. Thermodynamic results indicate that there was no power de-rating with EGR dilution. However, the optical analysis revealed that dilutions rate beyond 10% of EGR led to a slower combustion and lower combustion stability. Specific emissions of NOx, aldehydes and CO were reduced with increasing EGR rates, while the unburned ethanol increased.

© 2021, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Aircraft electrification is subject of several studies in the aeronautical field, due to the increasing need to enhance efficiency and to reduce the contribution of the aviation sector to climate change. In this scenario, the use of hydrogen fuel cells (FCs) is one means to explore new designs for propulsion electrification. Thus, this study aims to assess the feasibility of using gaseous hydrogen with proton-exchange membrane FCs (PEMFC) to provide electric power for the propulsion of a small aircraft. Firstly, current commercially available FC and hydrogen storage systems were analyzed to obtain data of these systems. Secondly, FC powered hybrid-electric propulsion system (PEMFC and batteries) was proposed, considering versions with 700 bar and 350 bar hydrogen tanks, and then compared with versions having an internal combustion engine (ICE) and another having just batteries. For a fair comparison, the propulsion system for each version was size-fitted for the defined mission profile. The aircraft aerodynamics, weight, propulsive efficiency, sizing parameters and other aspects were modeled and simulated in a virtual environment (SUAVE). The result evidenced that the ICE version has the lowest aircraft mass throughout the cruise duration range (60 min to 120 min), also having the best performance, in terms of Energy Specific Air Range (ESAR), for cruise longer than 65 min. For the airplanes with electric propulsion, the hybrid versions are more suitable in longer missions, being able to double the cruise duration of the battery version, while the battery version has the best ESAR for cruise shorter than 65 min. Therefore, the propulsion hybridization with PEMFC, gaseous hydrogen and batteries is feasible for small airplanes in flights longer than 65 min, when compared to an electric propulsion with only batteries. However, although having a range extender potential, hybrid versions need great improvements in order to outperform the ICE version.

© 2021, American Institute of Aeronautics and Astronautics Inc.. All rights reserved.Aircraft propulsion electrification is currently considered by industry and academia as one of the most promising strategies to reduce air transport emissions and to increase overall efficiency levels. In the past decade, a multitude of papers was published in this subject, most of them indicating encouraging fuel burn benefits versus conventional, fossil-fuel based propulsion systems, when incorporating future technologies and especially when novel aircraft configurations and synergistic propulsive-airframe integration are used. However, a much smaller effort has been applied to the economical aspects of hybrid and full electric propulsion, which is crucial for a successful product introduction. The present paper describes the modelling of a baseline general aviation type aircraft and its electrified propulsion derivatives, exploring different electrification strategies. Analyses are performed at aircraft level, comparing recurring and cash operating costs of the considered concepts for several cost and durability scenarios. It is shown that while considerable CO2 reductions may be achieved in some electrification strategies, important improvements on economical figures of merit are needed in order to make electrified propulsion competitive on a cost perspective. This is because electric architectures tend to increase costs: turboelectric increases recurring equipment costs, while hybrid-electric increase direct maintenance costs, especially at higher degrees of energy hybridization.

© 2021 AIAA.Aircraft propulsion electrification is currently considered by industry and academia as one of the most promising strategies to reduce air transport emissions and to increase overall efficiency levels. In the past decade, a multitude of papers was published in this subject, most of them indicating encouraging fuel burn benefits versus conventional, fossil-fuel based propulsion systems, when incorporating future technologies and especially when novel aircraft configurations and synergistic propulsive-airframe integration are used. However, a much smaller effort has been applied to the economical aspects of hybrid and full electric propulsion, which is crucial for a successful product introduction. The present paper describes the modelling of a baseline general aviation type aircraft and its electrified propulsion derivatives, exploring different electrification strategies. Analyses are performed at aircraft level, comparing recurring and cash operating costs of the considered concepts for several cost and durability scenarios. It is shown that while considerable CO2 reductions may be achieved in some electrification strategies, important improvements on economical figures of merit are needed in order to make electrified propulsion competitive on a cost perspective. This is because electric architectures tend to increase costs: turboelectric increases recurring equipment costs, while hybrid-electric increase direct maintenance costs, especially at higher degrees of energy hybridization.

© 2021 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.This paper presents a conceptual study of a regional aircraft with a turboelectric propulsion system and boundarylayer ingestion. The aircraft has an additional electric propulsor installed at the aircraft tail cone, which is driven by generators installed on both underwing engines, aiming to ingest the fuselage boundary layer and improve the aircraft overall performance. The proposed configuration is an aircraft reengining of the reference aircraft platform, the Embraer 175-E1, targeting minimizing airframe modifications. Parametric variations of the thrust split ratio as well as the electric fan pressure ratio were performed in order to create a design space of possible solutions for the proposed concept and also to provide insights of the aircraft key variables trends. From that, a feasible and optimized configuration in terms of efficiency was selected and compared to the reference aircraft. As the main conclusion, it was determined that the studied propulsion system has the potential to provide specific air range benefits in the order of 4 to 7%, which may not be enough to justify a new development.

© 2019 SAE International. All rights reserved.Recently, the advance of computational fluid dynamics simulation applied on design of internal combustion engines (ICE) has highlighted the need of reliable chemical kinetics models for most common fuels applied on ICE operation, such as ethanol, gasoline and blends. Therefore, the mainly motivation for this study is determine and evaluate the influence of the water content on ethanol flames for laminar flame speed and chemical kinetics. For this goal, laminar flame speed measurements by OH-Emission and OH-PLIF were conducted on anhydrous and hydrous ethanol premixed flames at atmospheric pressure. Distinct fuel samples were evaluated at several equivalence ratios. Chemical kinetic simulation considering Marinovs mechanism was performed in order to match velocities obtained from experimental data versus values obtained through numerical simulation, and to verify the characteristics of hydroxyl production at conditions studied. A sensitivity analysis for defined species was performed for the test conditions and the images obtained by laser techniques were correlated to simulated cases.

© 2019 AIAA.This paper presents a conceptual study of a regional aircraft with a turboelectric propulsion system and boundary layer ingestion. The concept was designed by the installation of an additional electric propulsor at the aircraft tail cone, which is driven by generators installed on both underwing engines, aiming to ingest the fuselage boundary layer and improve the aircraft overall performance. The proposed configuration can be considered an aircraft reengining, targeting minimal changes on the reference aircraft platform, the Embraer 175-E1. Parametric variations of the thrust split ratio as well as the electric fan pressure ratio were done in order to create a design space of possible solutions for the proposed concept and also to provide insights of the aircraft key variables trends. From that, an optimized configuration not only in terms of efficiency but also regarding the concept feasibility was chosen and compared to the reference aircraft. It was determined that the studied propulsion system has a potential to provide specific air range benefits in the order of 4% to 7%.

© The Author(s) 2018.In the present work, a numerical and experimental study of the thermoacoustic instabilities of a combustor is performed. The numerical model is represented by the one-dimensional linearised Euler Equation and an n-τ formulation for flame transfer function that describes the unsteady combustion response to these acoustic disturbances. This approach is similar to other simplified models present in the literature. However, most theoretical works assume a constant density and speed of sound in the medium, which is not realistic for combustion chambers, as the mean temperature is expected to decrease spatially as one moves away from the combustion area. Hence, to compare with experiments where chamber temperature is spatially varying, we developed a numerical solution procedure, seeking eigenvalues (complex-valued frequencies ω) indicating the stability characteristics of a given mode. Due to the non-linear dependence of the flame transfer function with ω, eigenvalues are found with a non-linear root-finding method. The acquired results met those obtained experimentally, indicating that the proposed model is capable of predicting the thermoacoustic behaviour of the combustion chamber.

© 2019, The Brazilian Society of Mechanical Sciences and Engineering.The aim of this paper is to define a methodology to minimize the adjustment effort required to comply with aircraft design performance requirements, when commercial off-the-shelf turbofan engines are installed, which is a challenge to aircraft manufactures. In order to achieve an efficient operation, a reasonable proposal is to adapt the propulsive performance by turbofan engine optimization. This work is carried out according to the following steps: (i) creation of estimated performance curves for a gas turbine from limited data; (ii) analysis of the impacts on performance and propulsive integration, applying computer simulation of the most promising engine components configuration; and (iii) matching between the lowest specific fuel consumption and the net thrust required for the cruise flight phase of the aircraft. The technical feasibility and the possible predisposition of engine manufactures to perform the implementation were also considered as critical points in this procedure. As a final result, an evaluation that presents the most suitable turbofan engine component modifications proposal to comply with engine/aircraft performance integration to be applied in the conceptual design phase was obtained.

© 2019 by American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This paper presents a conceptual study of a regional aircraft with a turboelectric propulsion system and boundary layer ingestion. The concept was designed by the installation of an additional electric propulsor at the aircraft tail cone, which is driven by generators installed on both underwing engines, aiming to ingest the fuselage boundary layer and improve the aircraft overall performance. The proposed configuration can be considered an aircraft reengining, targeting minimal changes on the reference aircraft platform, the Embraer 175-E1. Parametric variations of the thrust split ratio as well as the electric fan pressure ratio were done in order to create a design space of possible solutions for the proposed concept and also to provide insights of the aircraft key variables trends. From that, an optimized configuration not only in terms of efficiency but also regarding the concept feasibility was chosen and compared to the reference aircraft. It was determined that the studied propulsion system has a potential to provide specific air range benefits in the order of 4% to 7%.

© 2019 SAE International and © 2019 SAE Naples Section. All Rights Reserved.Despite syngas is a promising alternative fuel for internal combustion engines (ICEs), its extensive adoption has not been adequately investigated so far. The dedicated literature offers several fundamental studies dealing with H2/CO blends burning at high pressure and room temperature, as well as preheated mixture at low pressure. However, these thermodynamic states are far from the operational conditions typical of ICEs. Therefore, it is essential to investigate the syngas combustion process at engine-like conditions to shed light on this fuel performance, in order to fully benefit from syngas characteristics in ICE application. One of the key properties to characterize a combustion process is laminar flame speed, which is also used by the most widespread turbulent combustion models. In the first part, a database of premixed laminar burning rates at engine-like conditions for different syngas (H2/CO) blends is created based on one-dimensional unstretched flame simulations using two validated chemical mechanisms. Then the resulting laminar flame speed values are fitted using a validated in-house method based on logarithmic correlations. In the second part of the paper, these are implemented in the G-equation combustion model and three-dimensional simulations of a four stroke Spark Ignition (SI) optical access engine fueled by syngas are carried out. The combustion characteristics of two H2/CO blends (50/50 and 75/25 volume fraction, respectively) are investigated and the simulation results are compared to the available experimental data for the same fuels. This joint numerical/experimental study allows to investigate and optimize the syngas combustion for ICEs and it provides general guidelines to further understand the feasibility of this alternative fuel in terms of ICE utilizations.

Copyright © 2019 by the American Institute of Aeronautics and Astronautics, Inc.Research has shown that oxidizer swirl injection and liquefiable fuels, such as paraffin wax, can increase regression rates in hybrid rockets. However, there are few studies published on motors that use both these strategies simultaneously. This paper presents an exhaustive experimental investigation on the performance of a lab-scale hybrid rocket motor using paraffin wax and gaseous oxygen under a number of different conditions, including five different oxidizer injectors with varying levels of swirl. Prechamber length, fuel grain length, burn duration, oxidizer mass flow rate, and fuel grain geometry were modified from a baseline, and the influence on fuel regression and thrust oscillations was evaluated. Swirl injection increased regression rates up to 2.4 times that of the baseline axial injection configuration, while providing smoother operating conditions. The results show that thrust density of a hybrid rocket can be increased simultaneously by the use of a liquefying fuel and swirl injection. The results obtained also provide a unique experimental observation of the influence of several motor parameters on its performance, revealing that prechamber length and the angle of an entry slope on the grain do not contribute significantly to the performance or stability of the motor with swirl injection.

© 2019 by the authors.To mitigate the increasing concentration of carbon dioxide in the atmosphere, energy production processes must change from fossil to renewable resources. Bioenergy utilization from agricultural residues can be a step towards achieving this goal. Syngas (fuel obtained from biomass gasification) has been proved to have the potential of replacing fossil fuels in stationary internal combustion engines (ICEs). The processes associated with switching from traditional fuels to alternatives have always led to intense research efforts in order to have a broad understanding of the behavior of the engine in all operating conditions. In particular, attention needs to be focused on fuels containing relatively high concentrations of hydrogen, due to its faster propagation speed with respect to traditional fossil energy sources. Therefore, a combustion study was performed in a research optical SI engine, for a comparison between a well-established fuel such as methane (the main component of natural gas) and syngas. The main goal of this work is to study the effect of inert gases in the fuel mixture and that of air dilution during lean fuelling. Thus, two pure syngas blends (mixtures of CO and H2) and their respective diluted mixtures (CO and H2 with 50vol% of inert gases, CO2 and N2) were tested in several air-fuel ratios (stoichiometric to lean burn conditions). Initially, the combustion process was studied in detail by traditional thermodynamic analysis and then optical diagnostics were applied thanks to the optical access through the piston crown. Specifically, images were taken in the UV-visible spectrum of the entire cycle to follow the propagation of the flame front. The results show that hydrogen promotes flame propagation and reduces its distortion, as well as resulting in flames evolving closer to the spark plug. All syngas blends show a stable combustion process, even in conditions of high air and fuel dilution. In the leanest case, real syngas mixtures present a decrease in terms of performance due to significant reduction in volumetric efficiency. However, this condition strongly decreases pollutant emissions, with nitrogen oxide (NOx) concentrations almost negligible.

© 2018 Hydrogen Energy Publications LLCIn recent years, hybrid and fully electric vehicles have received significant consideration since they represent an alternative sustainable transport to the conventional fossil-fuel powered vehicles. However, a worldwide implementation of this alternative propulsion can induce large and undesirable peak demands in distributed power systems. In this context, natural gas spark ignition engines are a promising form of technology to supply part of the energy demand. The main limitations related to low laminar flame propagation speed and poor lean-burn capabilities of natural gas can be overcome by using hydrogen as additional fuel. In this paper, a comparison was carried out between methane and different CH4/H2 mixtures. Specifically, low levels of hydrogen addition were used (5%, 10%, 20% volumetric basis) in stoichiometric and lean burn conditions. The measurements were carried out in an optically accessible single-cylinder port fuel injection spark ignition engine. Optical measurements were performed to analyze the combustion process with high spatial and temporal resolution. In particular, optical techniques based on 2D-digital imaging with two different combustion chamber views were used. Macroscopic (global) and microscopic (local) post-processing tools were implemented to provide a detailed analysis of the flame front propagation process. Moreover, an in-depth analysis was performed to study the flame penetration in the piston top-land crevice. Exhaust gas emissions were also characterized and linked with thermodynamic and optical data. In order to evaluate the combustion process in similar fluid-dynamic conditions, all measurements were performed under steady-state conditions at fixed engine speed, load and spark advance. All the results highlight fast combustion promotion due to the hydrogen addition. In addition, hydrogen reduces the preferential propagation of the flame in a certain direction and increases the flame front wrinkling. Flame propagation in the top-land crevice region was measured for methane and its blends with hydrogen, which represents an original contribution to the literature. An inverse trend was seen between flame penetration in the crevice and unburned hydrocarbon emissions. Lastly, tests in lean conditions demonstrate the potential to decrease nitrogen oxides emissions when methane and methane-hydrogen blends are used.

© CopyrightEPLA, 2018.Plasma-assisted combustion is a growing field of applied physics. In this study, a DC gliding arc plasma reactor used as part of a swirler stabilized burner was characterized to evaluate the discharge repetition frequency as a function of process parameters. The discharge was generated in fuel-rich premixed mixtures of air and natural gas. The repetition frequency was determined by applying a fast Fourier transform to the voltage waveforms. The results show that the mean voltage and mean current of the gliding arc remain almost constant as a function of the total gas flow rate. The increase in fuel concentration promotes a drop in the breakdown voltage, which leads to a rise in the discharge repetition frequency. However, for a fixed natural gas flow rate, the repetition frequency grows with the increased total mass flow rate due to a higher arc velocity.

© 2018 SAE International. All Rights Reserved.Uncertainty of fuel supply in the energy sector and environmental protection concerns have motivated studies on clean and renewable alternative fuels for vehicles as well as stationary applications. Among all fuel candidates, hydrogen is generally believed to be a promising alternative, with significant potential for a wide range of operating conditions. In this study, a comparison was carried out between CH4, two CH4/H2 blends and two mixtures of CO and H2, the last one taken as a reference composition representative of syngas. It is imperative to fully understand and characterize how these fuels behave in various conditions. In particular, a deep knowledge of how hydrogen concentrations affect the combustion process is necessary, given that it represents a fundamental issue for the optimization of internal combustion engines. To this aim, flame morphology and combustion stability were studied in a SI engine under lean burn conditions. The engine was fuelled with CH4, CH4/H2 (75-25%vol and 50-50%vol) and H2/CO (50-50%vol and 75-25%vol). The engine was operated at fixed rotational speed and wide open throttle. Lean operation was studied in detail through combined methodologies based on thermodynamic analysis and optical diagnostics. Specifically, cycle resolved UV-visible digital imaging was applied to follow flame front propagation. Image processing was applied to evaluate flame speed and other morphology parameters, including flame displacement and centroid motion. Moreover, a detailed study of local curvature was presented. The excess air ratio was raised from 1.4, to values close to the flammability limit for each fuel. In order to maintain roughly the same fluid dynamic conditions (swirl, tumble, turbulence intensity, among others) spark timing was set according to the maximum brake torque of the baseline case (CH4) in the condition of lambda 1.4.

Copyright © 2017 SAE International.Pressures on vehicle manufacturers to reduce emissions have resulted in an increased interest to improve fuel economy and enable use of fuels developed from renewable sources that can achieve a net reduction in the CO2 output per vehicle. The use of bio-gas fuels in internal combustion engines has become a real alternative to traditional liquid fuels derived from petroleum. To extract the maximum benefits from these emergent fuels through optimized engine design and calibration, a deep understanding of the behavior is necessary. The combustion process of a single cylinder research engine with optical access, four stroke PFI-SI, was experimentally investigated. High spatial resolution cycle resolved digital imaging, in the visible and UV spectral range was used to characterize the flame front propagation. A post-processing routine was developed to evaluate flame areas and various local and global morphology characteristics to have a detail understanding of the flame behavior in an engine combustion chamber. The engine was fueled with Methane as baseline fuel and compared with an equivalent syngas mixture (blend of hydrogen, methane, carbon monoxide, carbon dioxide and nitrogen). It was operated at 900 rev/min, under partial load condition. For the equivalent syngas blend the results suggest an increase in the combustion duration. The flame speed propagation was higher to methane, with a difference of 1.9 m/s. Also both fuels present a preferential flame center movement in direction of the intake valves, and the average curvature was negative. The cyclic variations in the combustion process were around 1% for syngas and 0.5% for methane, indicating a stable combustion process.

Copyright © 2017 SAE International.In the last few decades a significant effort has been stablished in the automotive industry as well as in academic community towards increasing the renewable fuels applications in internal combustion engines, such as alcohol and gas derived sources. Meanwhile, turbo charging direct-injection spark-ignition engines have become fundamental features to achieve downsizing purposes, increasing power generation efficiency and attending high restrictive emissions regulations that have being taking place recently. For this study, experimental tests were carried out in a single cylinder research engine considering direct injection (DI) and port fuel injection (PFI) operations with anhydrous ethanol. The aim of this paper is to present a review and conduct further investigation about methodologies applied for imaging post processing considering chemiluminescence technique applied in an optical research engine. Crank angle resolved OH∗ and CH∗ flame chemiluminescence images were acquired in cycle based temporal evolution for consecutive engine cycles. Distinct intensification setups were adjusted based on an intensifier usage to evaluate its influence on radicals' evolution and on flame front determination. Forthwith image acquisition, a post processing routine was conducted in order to determine flame radius, and speed through distinct image segmentation and algorithms techniques. Finally, former researches are referenced and compared to current results in order to better correlate the study conducted. The contribution of current research work within the state-of-the-art in optical engines researches remains in the adoption of different cameras set up and post-processing methods for the characterization of flame behavior in an optical spark ignition (SI) engine fueled with anhydrous ethanol.

©2017 Sociedade Brasileira de Química.In this work the presence of soot in laminar diffusion of diesel and blends diesel/biodiese flames were investigated in the following proportions: 5, 10, 20 and 50% of biodiesel. The techniqu of laser-induced incandescence (LII) was used for the soot detection. Horizontal mapping wer performed at two heights (80 and 260 mm above the burner) to investigate the distribution of soo along the studied flames. The experiment was performed with a pulsed Nd:YAG laser with th wavelength of 1064 nm. The results have shown that the soot emission decreases as the amoun of biodiesel increases in the blends.

© 2017, The Brazilian Society of Mechanical Sciences and Engineering.There has been an ever increasing demand for research into alternative and environmentally friendly fuels since the oil crisis in the 1970s. Nowadays, with increasing energy demands and tightening environmental constraints, the need for research into these alternative fuels is mandatory. The use of microturbines for distributed power generation is already a reality and presents some environmental and operational advantages. However, this kind of thermal machine is designed for operation using hydrocarbons. The difference of the physical–chemical properties between hydrocarbons and alcohols impacts strongly the characteristics of the spray and hence the performance of combustion. In this context, an investigation about the behavior of the atomization process for an atomizer designed for ethanol operation and feasibility is mandatory. This study is divided into two parts: the characterization of the atomizer and spray in a laboratory environment and the assessment for pollutant emissions and combustion efficiency determination. The designed atomizer was machined and the main atomizer and spray characteristics data were acquired and then assembled on a gas generator operating with hydrous ethanol.

© 2017 IMEKOThe combustion process of a single cylinder research engine with optical access, four stroke with port fuel injection (PFI) and spark ignition (SI), was experimentally investigated. It was fueled with methane as baseline fuel and compared with a mixture of Syngas (blend of hydrogen, methane, carbon monoxide, carbon dioxide and nitrogen). The in-cylinder pressure and the related parameters were analyzed as indicators of the combustion behavior. Digital imaging measurements with OH filter were performed to evaluate the flame propagation. Therefore, UV chemiluminescence is applied to follow the OH radicals formation in the flame front from spark ignition to the cylinder walls through an optical access in the combustion chamber. The engine was operated at 900 rev/min, with the throttle being held in the partial-open position to get 7 mbar inlet pressure. The spark timing was set at 7° crank angle (CA) before top dead center (BTDC), and a stoichiometric air/fuel ratio was considered. For syngas blend the results suggest an increase in the combustion duration, with a difference in peak pressures and center of combustion location of 1.81ºCA and 1.99ºCA respectively, compared with methane. The cyclic variations in the combustion process were around 3% for both fuels, indicating a stable combustion process.

© 2017 by the authors. Licensee MDPI, Basel, Switzerland.Lean fueling of spark ignited (SI) engines is a valid method for increasing efficiency and reducing nitric oxide (NOx) emissions. Gasoline direct injection (GDI) allows better fuel economy with respect to the port-fuel injection configuration, through greater flexibility to load changes, reduced tendency to abnormal combustion, and reduction of pumping and heat losses. During homogenous charge operation with lean mixtures, flame development is prolonged and incomplete combustion can even occur, causing a decrease in stability and engine efficiency. On the other hand, charge stratification results in fuel impingement on the combustion chamber walls and high particle emissions. Therefore, lean operation requires a fundamentally new understanding of in-cylinder processes for developing the next generation of direct-injection (DI) SI engines. In this paper, combustion was investigated in an optically accessible DISI single cylinder research engine fueled with gasoline. Stoichiometric and lean operations were studied in detail through a combined thermodynamic and optical approach. The engine was operated at a fixed rotational speed (1000 rpm), with a wide open throttle, and at the start of the injection during the intake stroke. The excess air ratio was raised from 1 to values close to the flammability limit, and spark timing was adopted according to the maximum brake torque setting for each case. Cycle resolved digital imaging and spectroscopy were applied; the optical data were correlated to in-cylinder pressure traces and exhaust gas emission measurements. Flame front propagation speed, flame morphology parameters, and centroid motion were evaluated through image processing. Chemical kinetics were characterized based on spectroscopy data. Lean burn operation demonstrated increased flame distortion and center movement from the location of the spark plug compared to the stoichiometric case; engine stability decreased as the lean flammability limit was approached.

Copyright © 2016 SAE International.Since 70′, ethanol has risen as an alternative and ecological fuel, it has also been pointed as a potential candidate for replacing partial, or even totally, oil derived fuel application on internal combustion engines, supporting automotive industry. Ethanol is obtained from renewable sources and contributes to pollutants emission reduction in the atmosphere. In Brazil, it is obtained from sugarcane, but it can be obtained from others vegetable growing, such as beet or corn, common in other countries. For Brazilian automotive applications two types of ethanol are commonly applied: anhydrous, that contains at most 0.4% water in volume and has been used in gasoline blends up to 27%; and hydrous, with a maximum water content of 4.9% in volume, used as a substitute to gasoline on flex fuels engines. Although the widely application of ethanol, there is still lack of data available in literature regarding the fuel properties. The purpose of this research work is to gather the information published until now regarding anhydrous and hydrous ethanol as well as its blends. Furthermore, the investigation is enhanced with new data obtained at laboratory for respective fuel properties.

© 2016 Elsevier Ltd. All rights reserved.The effects of a non-steady state plasma discharge on flammability limits and flame structure of air-natural gas mixtures are investigated. As plasma power increases, flame structure is changed and flammable range is extended. In the absence of a visible flame, a higher hydrogen production is observed, revealing that the discharge is a source of molecular hydrogen. The reduction on hydrogen production inside the flammable range suggests a burning of hydrogen in the flame.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Three standard rocket motor tests (Lg/Dg ≈ 3.2 and 10 kg of propellant mass) casted with same HTPB/AP/Al solid propellant were conditioned at three different temperatures (20°C, 50°C and 72°C) in order to be fired at an horizontal bench test and investigate the influence of a thermal gradient appearance on the propellant grain by reducing its time of conditioning. The motors were instrumented with thermocouples placed over the case, nozzle and over the propellant spoke. The temperature levels were acquired prior and during the firing. Additionally, pressure and thrust profiles measured from the firings were plotted emphasizing the instant of membrane rupture and other important ballistic aspects. It was observed an important increasing on the Isp of the Motor Test #03 (72°C) and a thermal gradient induction of 2.9 °C, which led to slight variations on its pressure and thrust profiles with augmentation of progressive shape of the curves. Due to it, higher gradients must be investigated in new tests.

© 2016 Elsevier LtdA detailed literature review of laminar burning velocity and flammability limits of biogas mixtures combustion is presented. Biogas alone and in mixtures with other fuels is particularly significant because of its capability of application as fuels for internal combustion engines (ICEs). Therefore, a strict determination of the fundamental combustion characteristics required for their application in ICEs is crucial. Producing energy from biogas has the additional advantage of preventing its release into the atmosphere, where it results into significant air pollution. CH4 and CO2 are the main compounds of biogas, such as landfill, agricultural and sewage gas, after the removal of the trace amounts of organic compounds. For the same equivalence ratio, the presence of CO2 in the fuel feed results in substantial reduction of the laminar flame speed and flammability limits. Several research projects have shown that the decrease in the laminar flame speed of a fuel mixture containing dilution components is caused by the increase in specific heat capacity and the decrease in heat release, flame temperature and thermal diffusivity. The most promising strategies to increase the laminar burning velocity and the flammability limits of biogas are revised and discussed. The thermodynamic conditions under which these properties are determined are analyzed and the work still required for a comprehensive laminar burning velocity and flammability limits determination, at typical ICEs thermodynamic conditions, is addressed. The article provides a brief review of pollutant emissions of ICEs running on biogas and the current and future technological solutions to meet the increasing strict regulation.

© 2015 IEEE.Gliding arc discharges have been utilized in plasma-assisted combustion processes, among various other applications, due to their chemical properties. In this paper, an ac-powered gliding arc discharge having a reverse vortex flow configuration (tornado) was experimentally studied in air and in air-natural gas mixtures. A new method is proposed for the generalization of power characteristics of this type of discharge, based on similarity theory. The application of this method is demonstrated to be efficient for gliding arc discharges with tornado effect, using dimensional numbers. Regression dependences for discharges in air and in mixtures of air and natural gas were obtained in a form of simple power function equations (using the concept of equivalence ratio), which can be applied for the design of different gliding arc equipments for plasma-assisted combustion and related technologies.

CubeSats are tiny satellites shaped in cubic structures. The usage of a parallel interface for data exchange between on-board microcontrollers is not likely useful as it uses several pins. Therefore a serial interface is needed. Within this context, this work presents the CAN (controller area network) protocol, originally developed for automobile use, applied into a CubeSat for on-board subsystem communication. A pattern was defined for the 11 bits CAN message ID featuring priority, origin and message identification. Then, reception can be made independently for each property or as usual for a specific message. This way messages are received based on events of CAN hardware. The verification of the proposed CAN protocol is done using specific prototypes developed for these tests. The observed results suggest this protocol fits into the requirements of data transmission rate and reliability suitable for applications on the aerospace environment.

© Copyright 2015 SAE International.The use of numerical simulations in the development processes of engineering products has been more frequent, since it enables prediction of premature failures and study of new promising concepts. In industry, numerical simulation has the function of reducing the necessary number of validation tests prior to spending resources on alternatives with lower likelihood of success. The internal combustion Diesel engine plays an important role in Brazil, since they are used extensively in automotive applications and commercial cargo transportation, mainly due to their relevant advantage in fuel consumption and reliability. In this case, the most critical pollutants are oxides of nitrogen (NOx) and particulate matter (PM) or soot. The reduction of their levels without affecting the engine performance is not a simple task. This paper presents a methodology for guiding the combustion analysis by the prediction of NOx emissions and soot using numerical simulation. The methodology includes the use of 1D flow analysis using GT-Power and a three dimensional (3-D) computational fluid dynamics (CFD) to model flow inside the cylinder (using KIVA code), including models for turbulence, jet break-up process and models to predict emissions using kinetic chemistry. Injector design parameters were varied in order to evaluate the fidelity of the model through the qualitative trends found in tests. The effects of variations in engine load and fraction of dilution were also considered. The models were used to evaluate the sensitivity to variation of injector parameters. The results show good success in determining the qualitative trends in the simulated emissions values, especially regarding NOx estimation, for which the model correctly predicted the emissions trends in 93% of the cases.

© 2015 The Authors. Published by Elsevier Ltd.The present paper presents an experimental investigation about a double-stage swirl combustor for future application in gas turbine, in which the unfavorable conditions for pollutant formation (CO, UHC, NOx) are achieved by reagents and burned gases flow dynamics control into the combustor. The lean global combustion regime takes place in two chambers and is controlled by the parameters: global equivalence ratio (Ö), fuel jet Reynolds number (Rej) and swirler blades angle (á). The results have showed that when these parameter contribute to recirculation zone intensification formed at secondary chamber, ie, higher swirler angles and smaller Reynolds numbers, CO and UHC are reduced. For NOx this behavior is also observed, the only exception is the swirler angle, i.e,; the NOx increases when the swirler angle also increases. In addition, as expected, when the equivalence ratio increase the CO e UHC emissions reduce, on the other hand, the NOx emissions increase.

© 2015 The Authors. Published by Elsevier Ltd.The present paper presents an experimental investigation about a double-stage swirl combustor for future application in gas turbine, in which the unfavorable conditions for pollutant formation (CO, UHC, NOx) are achieved by reagents and burned gases flow dynamics control into the combustor. The lean global combustion regime takes place in two chambers and is controlled by the parameters: global equivalence ratio (Ö), fuel jet Reynolds number (Rej) and swirler blades angle (á). The results have showed that when these parameter contribute to recirculation zone intensification formed at secondary chamber, ie, higher swirler angles and smaller Reynolds numbers, CO and UHC are reduced. For NOx this behavior is also observed, the only exception is the swirler angle, i.e.; the NOx increases when the swirler angle also increases. In addition, as expected, when the equivalence ratio increase the CO e UHC emissions reduce, on the other hand, the NOx emissions increase.

© 2014 The Brazilian Society of Mechanical Sciences and Engineering.This paper presents the analysis of ecological and economical availability for using syngas from gasification of biomass waste or other solid fuels into diesel with ICE-based combined cycle (CC). The new approach is proposed to improve the ecological efficiency of the CC system and decrease the cost of electricity which can be produced with electric generator. For optimization of design of the combined system the new diagrams were obtained to determine characteristics of mixed fuel (diesel + syngas) for the engine at varied syngas fuel parameters after the gasifier with steam agent (plasma or other type). Based on these diagrams it is possible to obtain total reducing CO2emission in atmosphere of ~1.5 times in the CC system with biomass gasifier.

© 2014 by Nova Science Publishers, Inc. All rights reserved.Diesel engines are not only among the most applicable internal combustion engines today, but they are also one of the biggest polluters. There is great concern, in particular, with the emissions of NOx and particulates; EGR (Exhaust Gas Recirculation) is among the techniques used to reduce NOx emissions. This technique involves, besides a detailed study of integrated devices, accurate calibration regarding the achievement of the ideal EGR rate. This is because in addition to the NOx emissions, particulate matter emissions should also be evaluated without losing sight of their performance parameters. This work will present a detailed experimental study carried out with ACTEON, a four-cylinder engine that meets Euro III emission standards. This engine has an urban application, i.e., it works most of the time at low rotational speeds. In this important, operating range, a high rate of EGR is required for emission levels to be met. Different EGR configurations were studied by varying the EGR rate from 2.5 to 28 %. The values of emissions and performance will also be presented. The definition of the study conditions was carried out after the application of the Design of Experiments (DoE) technique. Findings are detailed for the most critical operating conditions.

© 2014 by ASMEFor copious levels of exhaust gas recirculation (EGR) (>30%), oxides of nitrogen (NOx) emissions can be reduced from Euro V to Euro VI regulated levels at the expense of fuel economy and soot emissions. The Lifted-Flame Concept (LFC) has been demonstrated by several researchers to be successful in reducing NOx, while minimizing soot emissions and impact to fuel economy. By simultaneously applying increased EGR and fuel pressure the LFC extends the lift-off length of a diffusion flame and enhances fuel-air entrainment leading to improved fuel and oxygen utilization. When combined with advanced turbocharging and EGR systems the LFC applied to a modern light duty (LD) diesel engine can result in improved fuel economy and lower soot emissions and shows good potential for meeting low soot engine-out targets. In the proposed paper a computational study was conducted using a multi-dimensional engine model. A modified 3D CFD KIVA code with detailed chemistry solver was used to model the diesel fuel spray, droplet breakup, vaporization, mixing, auto-ignition and subsequent heat release and emissions. The model uses inputs from 1D Amesim electro-hydraulic solver to generate the rate of injection (ROI) profile to raise pressure of 1800 bar to 2500 bar as well as to include a simulated post-injection. A 1D model using GT-Power was developed and utilized to provide air system boundary conditions for the 3D CFD model. Post-processing optimization was conducted using Matlab to identify minimum fuel economy and soot emissions for the study of several parameters. The objective of the study was to demonstrate Euro VI emissions levels on a 3.2 L LD diesel engine without NOx aftertreatment and minimal impact to fuel economy using the lifted flame concept. The engine-out NOx emission level was targeted at 0.4 g/kWh and the soot levels were targeted at 0.2 g/kWh assuming diesel particulate filter would be used for after-treatment. The results of the computational study successfully demonstrate the potential of the lifted flame concept to meet Euro VI without the use of NOx aftertreatment technology.

Soot particles usually cause respiratory diseases and other problems to human health. To prevent or at least reduces soot emissions it is necessary to know its formation mechanism. Laser-Induced Incandescence (LII) has been used to detect soot and its precursors, known as polycyclic aromatic hydrocarbons (PAHs), in diffusion flames. In this work, several mixtures of diesel/biodiesel blends were investigated using two laser wavelengths, at 532 nm, which excites both soot and PAHs, and at 1064 nm, which excites only soot. Thus, the difference of intensity between both LII signals provides the proportion of soot/PAHs in the irradiated regions of flames, and it can be associated to the evolution of soot formation along the flame.

The liquid-liquid bipropellant pressure swirl atomizers have been widely used in rocket engines to take advantage of their high mixing efficiency within the short length of the combustion chamber. In this kind of engine, the uniform mass distribution and propellant mixture ratio have great influence on combustion efficiency and instability. The present work investigates the effect of the number of tangential passages on the spray cone angle, mass distribution, and propellant mixture ratio of a bipropellant atomizer. Thus, three atomizers were designed, manufactured, and evaluated experimentally. The results showed that the number of tangential passages has some influence on the circumferential mass distribution; however, spray angle and propellant mixture ratio have not presented significant variations. © The Brazilian Society of Mechanical Sciences and Engineering 2013.

The performance and emissions behavior of a Rover 1S/60 turboshaft engine when operated with several blends of aviation kerosene and ox tallow ethyl-ester are shown in this article. The tests were performed with a compressor shaft coupled to an hydraulic dynamometer where data of power and mass fuel flow were collected to determine the brake specific fuel consumption. A flue gas analyzer was positioned at the exhaust duct to collect oxygen, carbon dioxide, carbon monoxide and nitrous oxides. An increase in the specific fuel consumption was observed due to the lesser lower heating value of the most oxygenated blends. However, reductions of CO, CO2 and NO x have been observed and no-significant ill effects have occurred in the turbine operation. © 2013 The Brazilian Society of Mechanical Sciences and Engineering.

The main focus of the present work is to evaluate the performance of the Helmholtz resonators to control acoustic instabilities inside combustion chambers. In the present stage of this work, some tests were conducted with non-reactive flow inside the combustion chamber. This paper presents a methodology to design the resonators and the calculations to theoretically determine the acoustic performance of damp instabilities, an experimental setup especially developed to study instabilities in reactive and non-reactive flows, and the experimental results for non-reactive situation with and without flow. The results show that the resonator has an exceptional capacity to damp the oscillations in the frequency of the design; but, it has a narrow range of actuation close to the design frequency. In addition, the experiments show that the resonator presence can modify the spectrum of frequencies, and in some cases it amplifies the oscillations, having the flow velocity inside the chamber some considerable influence in the performance attenuation. © 2013 Elsevier Ltd. All rights reserved.

Diesel engine technology has been driven by increasingly stringent environmental legislation. To comply with these laws, emissions-control systems are being rapidly improved. Within this context, development of exhaust gas after-treatment systems undertakes a significant role. Among the techniques used is selective catalytic reduction (SCR), which converts nitrogen oxides (NO x) into diatomic nitrogen (N2) and water (H2O). A reducing agent containing ammonia (NH3) is added to the flow and absorbed by a catalyst. Different reducing agents are currently used, principally anhydrous NH3, aqueous NH3, and urea. This study analyzed behavior of different urea- and formamide-based agents to SCR. Results are compared to those obtained with Adblue. In relation to the SCR system as well as to NOx reduction, we concluded that urea-based mixtures are the most efficient, although they present higher values of NH 3 slip. Formamide-based mixtures are significantly less efficient than urea-based mixtures, but the NH3 slip levels produced by these mixtures are virtually none. A challenge is to find new reducing agent for SCR applications, considering that the deposits of urea formed during certain work conditions are a significant problem. © Copyright 2013, Mary Ann Liebert, Inc.

Because of the scarcity of nonrenewable natural resources, such as petroleum and natural gas, the use of biofuel is needed. Gasification is a major process used to obtain renewable fuels from biomass; however, the gas cleaning system is a constraint for its broad utilization. During the pyrolysis process, a mixture of organic compounds in the gas phase is produced and must be removed from the gases before it is used in the most practical applications. In order to remove such organic compounds, which are known as tar, large, sophisticated, problematic, and expensive gas cleaning systems are added to the gasifier gas exit. Previous papers have shown that the plasma torch has the potential to destroy produced tar, being a simpler and less-expensive system than traditional gas cleaners. This work presents a qualitative and quantitative evaluation of a microwave plasma system running on tar destruction and its reforming. In order to evaluate a 1 kW microwave plasma system performance, an apparatus was developed and installed at ITA Laboratory of Plasmas and Processes (LPP-ITA). The system runs at atmospheric pressure with nitrogen and argon as carrier gas under a large range of flow rates. Experiments were performed using a gas mixture of N2, H2O, ethanol, and tar at controlled concentration in order to simulate the gases produced by a gasifier. The injected tar was obtained from pine pyrolysis and characterized for energy purposes. In order to reduce tar viscosity, it was diluted in commercial ethanol (92.5% ethanol and 7.5% water) and its concentration varied from 0.8 g tar/Nmgas3 to 4.2 gtar/Nm gas3. Species formed in the microwave plasma torch were identified using an optical spectrometer. The reactor exit gases had their composition evaluated on tar content as well as for noncondensable gases. As a result, this paper shows that no tar content was detected at the reactor outlet, indicating that all supplied tar was destroyed in the plasma reactor. The main detected products were CO and solid carbon (C(s)). Furthermore, neither NO nor CO2 were detected, and an indication of H2 formation was obtained. This paper concludes that the microwave plasma system is capable of destroying and reforming tar efficiently and produces mainly H 2, CO, O2, and C(s) as byproducts. © 2012 American Chemical Society.

Diesel engines are among the most effective engines in the world. Known as strong, economical and robust, they are also recognized for their traditional smoke and high level of nitrous oxides, NOx emissions. In the present study, a basic diesel engine that meets Euro III emissions standards with NOx concentration limited to 5.0 g/kW h and the particulate matter limited to 0.100 g/kW h was performed in order to evaluate its potential of attending Euro VI standards by developing Exhaust Gas Recirculation (EGR) technique. Euro VI will be used in the European community only in 2013 with NOx limited to 0.4 g/kW h and particulate matter to 0.01 g/kW h. The main idea is to achieve Euro VI emissions level, changing the EGR components and tuning the injection system. In order to reduce the investigation phase, statistics evaluation were used to define one specific speed and load that render the worst condition to create a high EGR volume at lower speed. The study was driven in two steps. Firstly, it was identified the components of EGR system which had more influence towards NOx reduction associated with fuel consumption and the particulate matter. Secondly, the components improved were implemented to analyze the engine potential. In total three different EGR configurations were performed and the best results obtained with the last version was NOx value equal 0.58 g/kW h, what means 8.6 times less than the start values and MIRA, one indicative of particulate matter, which reached 0.1 g/kW h, 62.96% smaller than 0.27 g/kW h at the beginning. Also, the specific fuel consumption achieved of 208 g/kW h was less than the value early defined as a goal which was of 210 g/kW h. After these results were obtained in the worst operational condition, it was assumed that the engine had potential to reach Euro VI. Thus, it was submitted to one integral test, the same as the one done during the certification process. The final test showed satisfactory results which means that the strategies used in the present study can be applied to get some insight into engines nowadays and in the future. © 2010 Elsevier Ltd. All rights reserved.

The technical evolution of turbofan engines has been accomplished by increasing the engine thermal and propulsive efficiencies. The former is mainly a function of component efficiencies, cycle temperatures and pressures, while the latter is basically related to the engine BPR and FPR. However, several technological challenges are faced to increase those levels of efficiencies. In the thermal efficiency side, higher pressure ratios, for a given stage loading, are obtained by increasing the number of compressor stages, adding weight and size penalties to the engine, and increasing the compressor delivery temperature. Higher cycle temperatures, mainly those found in the burner exit and the stator outlet require higher cooling flows, for a given blade material technology level. Higher cooling flows lead to penalties in the engine efficiency, since the air used in the cooling is bled from the compressor. In the propulsive efficiency side, higher bypass ratios can be achieved by larger fans or smaller, more thermal-capable cores. The latter is aimed to the concept of engine downsizing, targeting the design of smaller and lighter engines. However, small cores present the technical challenge of maintaining high component efficiencies while the Reynolds number is decreased and the effects of tip clearances are increased. In order to investigate the effects of the previous discussion, this paper integrated an engine simulation software with models of engine cooling and component efficiencies, allowing the investigation of component size and cooling flows on the performance, weight and dimensions of turbofan engines, sized to meet a constant thrust requirement. © 2013 SAE INTERNATIONAL.

In the last decade the hybrid propulsion has been considering as a viable alternative of chemical energy conversion stored in propellants into kinetic energy. This energy is applied in propulsive systems of manned platforms, maneuvering procedures and even in the repositioning process of micro satellites. It is a system of minimum environmental impact and lower cost than traditional systems based on liquid or solid propellants. Paraffin based grains are the hybrid solid fuels appointed as polymeric fuel substitute. The liquid layer formed on the burning surface ensures high regression rate when driven into the flame front. Paraffin grains allow row material recovery and reduce the risk of explosion in the presence of erosive burning. The structure of the grain and the control of the liquefying burning surface layer depend on the additives concentration, such as carbon black, which are added to the fuel matrix during the production process. In the solid propellant paraffin based grain a cylindrical center port developed during the centrifugation tends to concentrate carbon black in the outer region of the grain. During solidification 15% of shrinkage occurs and appears hardness gradient in the longitudinal and transverse directions. The influence of carbon black distribution and hardness gradient in paraffin based grain were evaluated in this work. The study suggests that multiple thin layers grain may generate burning surfaces with hardness and carbon black concentration almost constant. The ballistic properties and propulsion efficiency of a hybrid lab rocket scale with 150 N of thrust were evaluated in the pressure of 2.8 MPq with 140 Kg (sm2) gaseous oxygen (GOX) mass flux, the results show up the nozzle operation and motor-propellant relationships. Copyright © 2012 by ASME.

In recent years, Hybrid Propulsion is turning into a significant alternative to Liquid and Solid Propulsion Systems, it presents attractive features and good balance between performance and environmental impact. Thus, paraffin based propellant grains are indicated as a substitute for hydroxyl-terminated polybutadiene (HTPB), the actual solid propellant fuel grain. Despite being a wellknown material, scarce data on the relation of activation energy (Ea) and molecular weight (WC H ) of paraffin is available. In this work, the kinetic parameters (activation energy and pre-exponential factor) of microcrystalline 140/1450F paraffin have been raised through Thermo Gravimetric Analysis in conjunction with the Arrhenius kinetic mechanism, according to ASTM-E1461 and the dependence of molecular weight with melting point from Etessam and Sawyer approach. The 140/1450F paraffin activation energy calculated in this study was compared with different activation energy from alkanes and substances used as fuel in the propulsion systems field. The analysis indicated that the microcrystalline 140/1450F paraffin, manufactured by Petrobras, presents activation energy of 224 KJ.mol-1 and pre-exponential factor of 5.48x1022 min-1. Ignition was achieved with a 50 W pyrotechnic igniter. The firing test with 140/1450F paraffin fuel and gaseous oxygen (GOX) mass flux of 130 Kg.s- 1m-2 at pressure above 0.80 MPa, was easily sustained. Copyright © 2012 by ASME.

In the present paper, a hybrid version of the Generalized Extremal Optimization (GEO) and Evolution Strategies (ES) algorithms [1], developed in order to conjugate the convergence properties of GEO with the self-tuning characteristics present in the ES, is applied to the estimation of the temperature distribution of the film cooling near the internal wall of a thruster. The temperature profile is determined through an inverse problem approach using the hybrid. The profile was obtained for steadystate conditions, were the external wall temperature along the thruster is considered as a known input. The Boltzmann's equation parameters [2], which define the cooling film temperature profile, are the design variables. Results using simulated data showed that this approach was efficient in recuperating those parameters. The approach showed here can be used on the design of thrusters with lower wall temperatures, which is a desirable feature of such devices. © 2011 by ASME.

Gliding-arc discharges have been utilized in plasma-assisted combustion processes, among various other applications, due to their properties of high electron density and chemical selectivity in a transitional regime. However, basic characteristics relative to the relations between the fundamental parameters of discharge, like mass flow rate, breakdown voltage, and frequency of repetition (number of discharge breakdowns per half cycle), have not been completely studied. In this paper, an ac-powered gliding-arc discharge having a reverse vortex flow configuration is built to carry on a basic investigation on discharges in air, natural gas, and mixture of both. Electrical measurements, optical emission spectroscopy, and mass spectrometry are the techniques used for these investigations. The results presented in this paper describe the dependence of the breakdown voltage, frequency of discharges, and conversion rates of methane and molecular oxygen with respect to the variation of the mass flow rate (directly related to the residence time) and discharge current. © 2010 IEEE.

The pulsating combustion process has attracted interest in current research because its application in energy generation can offer several advantages, such as fuel economy, reduced pollutants formation, increased rate of convective heat transfer and reduced investment, when compared with other new techniques of combustion. An experimental study has been conducted with the objective of investigating the effects of combustion driven acoustic oscillations in the emission rates of combustion gases, especially carbon monoxide and nitrogen oxides, and soot presence in partial premixed flames in confined partially premixed liquefied petroleum gas flames. The results basically showed that a more uniform fuel/air mixture due to the presence of an acoustic field increases the NOx emissions in operations close to stoichiometric equivalence ratios and the frequency is the most important parameter. Carbon monoxide and soot reduced significantly. © 2009 Energy Institute.

The present paper shows experimental results about soot suppression on a laboratorial scale jet free diffusion flame of liquefied petroleum gas submitted to acoustic oscillations. The experiments were conducted to verify the influence of amplitude and frequency of oscillations in the regions of soot formation and suppression through the flame. To quantify the soot presence the laser induced incandescence was utilized. The results show combinations of frequency and amplitude of oscillation which the presence of soot is close to zero. © 2009 by ABCM.

In a pressure-swirl atomizer a swirling motion is imparted to the fuel leading it, under the action of centrifugal forces, to spread out in the shape of a hollow cone as soon as it leaves the exit orifice. This kind of atomizer is used in gas turbines and liquid-propellant rockets. The need to minimize the combustor length usually leads to spray angles around 90 deg. The present work presents a procedure to design and verify the experimental behavior for low pressure-swirl atomizers. This atomization condition is especially important, for example, in the case of gas turbine operation under idle regime. The Sauter mean diameter and the spray-cone angle are evaluated and made to fit the calculated atomizer dimensions. The Sauter mean diameter is obtained through the use of a model originally developed for fan-spray atomizers and extended for pressure-swirl atomizers. A pressure-swirl atomizer was manufactured following this design procedure. The discharge coefficient, the spray-cone angle, and the Sauter mean diameter were evaluated experimentally and compared with the theory used to design the atomizer displaying a good matching. The spray Sauter mean diameter was measured with a laser scattering system. Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

This paper shows the experimental results for changes in the flame structure when acoustic fields are applied in natural gas Delft turbulent diffusion flames. The acoustic field (pulsating combustion) generates zones of intense mixture of reactants in the flame region, promoting a more complete combustion and, consequently, lower pollutant emissions, increase in convective heat transfer rates, and lower fuel consumption. The results show that the presence of the acoustic field changes drastically the flame structure, mainly in the burner natural frequencies. However, for higher acoustic amplitudes, or acoustic pressures, a hydrogen pilot flame is necessary in order to keep the main flame anchored. In the flame regions where the acoustic field is more intense, premixed flame characteristics were observed. Besides, the pulsating regime modifies the axial and radial combustion structure, which could be verified by the radial distribution of concentrations of O2, CO, CO2, and NOx, and by the temperature profile. The experiments also presented the reduction of flame length with the increase of acoustic amplitude. © 2008.

An experimental study has been conducted with the objective of investigating the effects of the flame structure in the combustion oscillation conditions into a laboratorial scale cylindrical chamber. The experiments were conducted in a water-jacketed 1-m long by 25-cm internal diameter stainless steel vertical tube. The combustor operated with liquefied petroleum gas (LPG) in both oscillatory and non oscillatory conditions, under the same input conditions. Part of the reactant mixture was excited acoustically, before the burner exit, by a speaker positioned strategically. The burner was aligned with the chamber longitudinal axis and positioned at its bottom. The experiments were conducted for 0.16 g/s of LPG burning in stoichiometric equivalence ratio. To analyze the flame structure the image tomographic reconstruction process were used, and the resultant images were associated to the oscillatory conditions (frequency and amplitude) into the combustion chamber. The main conclusions were: 1) when the flame premixed condition increase, for example 60% of the total air flow rate is premixed with LPG, the region of intense energy released is close to burner exit and strong amplitudes of oscillation (close to 50 mbar) were obtained into the chamber; 2) for long flames, predominantly diffusive flames, just weak amplitudes were detected, in the spite of the speaker exiting the premixed flow; 3) when the energy is released distributed through the combustion chamber, the long flame acts like a baffle. Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

The use of oxygen to enrich the combustion air can be an attractive technique to increase capacity of an incinerator originally designed to operate with air. If incinerator parameters such as operation temperature, turbulence level and residence time are fixed for a certain fuel supply rate, it is possible to increase the residue consumption rate using enriched air. This paper presents the thermal analysis for operation with enriched air of an aqueous residue experimental incinerator. The auxiliary fuel was diesel oil. The theoretical results showed that there is a considerable increase in the incineration ratio up to approximately 50% of O2 in the oxidiser. The tendency was confirmed experimentally. Thermal analysis was demonstrated to be an important tool to predict possible incinerator capacity increase. © 2005 Published by Elsevier Ltd.

The effects of combustion driven acoustic oscillations in carbon monoxide and nitrogen oxides emission rates of a combustor operated with liquefied petroleum gas (LPG) were investigated. Because the fuel does not contain nitrogen, tests were also conducted with ammonia injected in the fuel, in order to study the formation of fuel NOx. The main conclusions were: (a) the pulsating combustion process is more efficient than the non-pulsating one and (b) the pulsating combustion process generates higher rates of NO x, with and without ammonia injection, as shown by CO and NO concentrations as function of the O2 concentration. An increase in the LPG flow rate, keeping constant the air to fuel ratio, increased the acoustic pressure amplitude and the frequency of oscillation. The injection of ammonia had no influence on either pressure amplitude or frequency. © 2005 Elsevier Ltd. All rights reserved.

The pulsating combustion process has won interest in current research due to indications that its application in energy generation can offer several advantages, such as: fuel economy, reduced pollutants formation, increased rate of convective heat transfer and reduced investment, when compared with conventional techniques. An experimental study has been conducted with the objective of investigating the effects of combustion driven acoustic oscillations in the emission rates of combustion gases, especially carbon monoxide and nitrogen oxides. The experiments were conducted in a water-jacketed 1-m long by 25-cm internal diameter stainless steel vertical tube. The combustor operated with liquefied petroleum gas (LPG) in both oscillatory and non oscillatory conditions, under the same input conditions. Part of the reactant mixture was excited acoustically, before the burner exit, by a speaker positioned strategically. The burner was aligned with the chamber longitudinal axis and positioned at its bottom. The experiments were conducted for 0.16 g/s of LPG burning in stoichiometric equivalence ratio. The main conclusions were: a) the pulsating combustion process produces more uniform fuel/air profile than the non pulsating process, b) close to stoichiometric equivalence ratio the pulsating combustion process generates higher rates of NOx; c) the frequency has a strong influence in NOx emission, but the pressure amplitude has a weak influence; d) the presence of the acoustic field may change drastically the combustion gas emissions in diffusion flames, but in pre-mixed flames the influence is not as strong.

The air enrichment in a combustion chamber designed to incinerate aqueous residues was investigated. In this experiment diesel fuels, and liquified petroleum gas (LPG) were used as fuels. It was found that an increase of 85% in the incineration capacity was obtained with nearly 50% O2 in the oxidant gas. It was also investigated that the CO concentration which was measured near the flame front decreased drastically with the increase of O 2 content in the oxidant gas. The experiments showed that NO x emissions could be controlled without damage in the increase of the incineration capacity by enrichment.

The use of oxygen to enrich the combustion air can be an attractive technique to increase capacity of an incinerator originally designed to operate with air. If incinerator parameters such as operation temperature, turbulence level and residence time are fixed for a certain fuel supply rate, it is possible to increase the residue consumption rate using enriched air. This paper presents the thermal analysis for operation with enriched air of an aqueous residue experimental incinerator. The auxiliary fuel was diesel oil. The theoretical results showed that there is a considerable increase in the incineration ratio up to approximately 50 % of O 2 in the oxidiser. The tendency was confirmed experimentally. Thermal analysis was demonstrated to be an important tool to predict possible incinerator capacity increase.

The influence of burner-port geometry in the mechanisms of hydrocarbon oxidation and NOx formation from a 50kW industrial-type methane-fired burner was investigated experimentally. Imaging and tomographic reconstruction techniques were used to assess the effects of port geometry upon flame visible length and C2 chemiluminescence distribution in the recirculation zone. C2 emission of methane flames depicts that low fuel jet velocities allow very rich conditions at recirculation zone and lead methane oxidation through O2-scarcity mechanism. Higher velocities imply that methane oxidises via a path including dissociation into free radicals. In-furnace measurements were performed from a refractory-lined vertical furnace. NOx concentration results revealed that NO formation is closely connected with the dissociation process, suggesting that prompt-NOx mechanism is more important than hitherto supposed. © 2001 Elsevier Science Ltd. All rights reserved.

The use of oxygen to enrich the oxidizer can be an attractive alternate to increase incineration rates of a combustion chamber originally designed to operate with air. For a certain fuel flow rate, if some incineration parameters are held constant (as combustion chamber temperature, turbulence level, and residence time), an increase of incineration rates becomes possible with injection of oxygen. This work presents a theoretical evaluation of combustion air enrichment in a combustion chamber designed to incinerate aqueous residues using methane as fuel and air as oxidizer. Detailed chemistry was employed to predict pollutants formation. The overall process was investigated using the PSR routine from the CHEMKIN library.The use of oxygen to enrich the oxidizer can be an attractive alternate to increase incineration rates of a combustion chamber originally designed to operate with air. For a certain fuel flow rate, if some incineration parameters are held constant (as combustion chamber temperature, turbulence level, and residence time), an increase of incineration rates becomes possible with injection of oxygen. This work presents a theoretical evaluation of combustion air enrichment in a combustion chamber designed to incinerate aqueous residues using methane as fuel and air as oxidizer. Detailed chemistry was employed to predict pollutants formation. The overall process was investigated using the PSR routine from the CHEMKIN library.

This paper presents a case study of air enrichment in an industrial rotary kiln type incineration unit. The study is based on mass and energy balances, considering the combustion reaction of a mixture composed by the residue and the auxiliary fuel with air enriched with oxygen. The steps are shown for the primary chamber (rotary kiln) and secondary chamber (afterburner). The residence times in the primary and secondary chamber are 2.0 and 3.2 sec, respectively. The pressure is atmospheric in both chambers. Based on constant chamber gas residence time and gas temperature, it is shown that the residue input rates can be increased by one order of magnitude as air is substituted by pure oxygen. As the residue consumption rate in the rotary kiln is also dependent on residue physical characteristics (mainly size), the study was also carried out for different percentages of oxygen in the oxidiser gas. © 1998 Elsevier Science Ltd.

Pulsating spray combustion in a Rijke tube was characterized. A specially designed Y-type atomizer and a commercially available solid-cone atomizer were used. Both were characterized in terms of spray Sauter mean diameter using a phase Doppler particle analyser. The operating regions for which acoustic oscillations were excited in the Rijke tube were identified. These regions are characterized by atomizing air, fuel and combustion air flow rates, atomizer position in the tube, and spray mean droplet diameters. With the Y-type atomizer, oscillations did not have a defined structure, and the pressure amplitudes varied without control. Pulsations were generated only in fuel-rich combustion. With the solid-cone atomizer, operating regions for which acoustic oscillations occurred in the combustor were also identified. In this case, pulsations were generated at near-stoichiometric combustion. Sound pressure amplitudes for the oscillating cases, though present, were much more difficult to control and of lower magnitude than in similar studies related to the pulsating combustion of solid (coal, wood, agricultural residue) and gaseous (propane, natural gas, acetylene) fuels in Rijke combustors. © 1997 Elsevier Science Ltd.