Combustion characterization of commercial ethanol fuels in an optical research SI ignition engine for different injection strategies

Resumo

© 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.

Palavras-chave