New insights into the carbon chain structure of alcohol on the combustion of diesel surrogates using ReaxFF molecular dynamics simulations

Abstract

Achieving clean and efficient combustion of diesel fuel is the main trend in the development of diesel engines in the future. Adding oxygen-containing alcohol to diesel fuel is an effective way to improve diesel combustion efficiency and reduce carbon smoke emissions, which is of great significance for reducing the consumption of traditional fossil fuels and reducing environmental pollution. In this work, the reactive molecular dynamics (RMD) simulations are conducted to compare the combustion of diesel without/with various alcohols, focusing on the intermediates and product distribution, oxygen consumption, ignition delay time, initial combustion pathways, and the related kinetics. It can be found that the addition of alcohols can significantly improve the combustion of diesel with the promoting order being n-pentanol > n-butanol > ethanol > cyclopentanol. The longer ignition delay of the diesel/ethanol is related to the lower cetane number of ethanol compared to other alcohols. The promoting combustion effect of alcohols can be attributed to higher reaction rate of their unimolecular bond dissociations and hydrogen abstraction reactions. In addition, the straight-chain alcohols have higher oxygen consumption and perform better in reducing soot than cyclic alcohols with the same number of carbon atoms. A significant decrease in activation energy is observed in the diesel/n-pentanol combustion system compared to the pure diesel combustion based on the RMD Arrhenius parameters from the first-order kinetic analysis. From the RMD simulations on the diesel/n-pentanol with different oxygen concentrations, it can lead to the conclusion that when the oxygen amount in the system reaches stoichiometric combustion, adding more oxygen does not produce a significant promoting effect on the diesel combustion process.