Impact of Ethanol Droplet Size and Methane Addition on the Combustion Performance of Ethanol/LOx Bipropellant Systems: Insights from Reactive Molecular Dynamics Simulations

Abstract

Copyright ©2025 by the International Astronautical Federation (IAF). All rights reserved.Tins study investigates the influence of ethanol droplet size on the combustion performance of an ethanol/hqmd oxygen (LOx) brpropellant system using reactive molecular dynamics (RMD) simulations, with an additional focus on the effect of methane addition to larger ethanol droplets to enhance combustion efficiency. Liquid propulsion systems utilizing ethanol as a fuel offer advantages such as lower toxicity and environmental impact compared to traditional hypergohc propellants. However, the combustion efficiency of ethanol/LOx systems is highly dependent on the atomization and vaporization processes of the fuel, which are directly influenced by droplet size. This work employs RMD to model the molecular level interactions and reaction dynamics between ethanol droplets of varymg sizes (ranging from 20 to 100 Angstroms) and LOx under high-pressure and high-temperature conditions representative of rocket combustion chambers. Additionally, the study explores the incorporation of methane into larger ethanol droplets (50 and 100 Angstroms) to improve then combustion performance. The simulations reveal that smaller ethanol droplets (e.g., 10 A) exhibit faster vaporization rates and more efficient mixing with LOx, leadmg to enhanced combustion performance. Specifically, the ignition delay time for 10 A droplets was found to be 300/c shorter compared to 100 A droplets, while the heat release rate increased by approximately 250/c. For larger droplets, the addition of methane (10% by mass) resulted in a 15% reduction in ignition delay time and a 20% increase in heat release rate, demonstrating its potential to compensate for the lower efficiency of larger droplets. The presence of methane also altered the reaction pathways, promoting the formation of key intermediate species that enhanced overall combustion kinetics. These findings underscore the importance of precise fuel atomization in liquid propulsion systems and suggest that the strategic addition of methane can significantly improve the performance of ethanol/LOx-based engines, particularly when droplet srze minimization is challenging. Future work will focus on validating these results through experimental studies.

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