Simulation Study on the Combustion and Emissions of a Diesel Engine with Different Oxygenated Blended Fuels

Abstract

Aiming to achieve the goal of efficient and clean combustion in internal combustion engines, simulations are used to change the physicochemical properties and molecular configuration of fuels by adding oxygenated fuels such as alcohols, esters, ethers, etc., so as to achieve the purpose of improving combustion and reducing emissions. In this paper, blends of oxygenated fuels, including n-butanol, DME, DMC, and diesel fuel with different oxygen-containing functional groups, were selected for simulation to reveal the chemical mechanisms of fuel oxygen on combustion and pollutant generation in the combustion system and to deeply explore the mechanism and influence law of the different forms of oxygen bonding on the generation and oxidation of carbon smoke. At the same fuel oxygen content, the differences in the fuel physicochemical properties and reaction paths resulted in different effects of the different oxygenated fuels on the in-cylinder oxidative activity and different inhibition abilities of carbon smoke precursors. Compared with pure diesel, n-butanol, and DME, which promoted OH generation, DMC inhibited OH generation, so the oxidation activity of diesel/n-butanol was the highest, and that of diesel/DMC was the lowest; meanwhile, the two O atoms in the DMC molecule formed CO2 with one C atom, which reduced the utilization efficiency of the O atoms, whereas each O atom in the n-butanol and DME fuels took away one C atom, so the utilization efficiency of O atoms was higher. The individual oxygenated fuels themselves had different abilities to contribute to carbon smoke precursors, and the above combined factors led to reductions of 8.7%, 32.6%, and 85.4% in soot emissions from the addition of DMC, DME, and n-butanol compared to pure diesel fuel, respectively, at the same oxygen content. At a medium load, the addition of n-butanol, DME, and DMC reduced NOx emissions by 0.5%, 1.7%, and 3.3%, respectively. Thus, it is shown that DMC has a more significant effect on NOx emission reduction.