Energy balance analysis, combustion characteristics, and particulate number concentration-NOx trade-off of a heavy-duty diesel engine fueled with various PODEn/diesel blends

Abstract

Polyoxymethylene dimethyl ethers (PODEn) are promising diesel additives that have been widely evaluated and display many advantages for improving the combustion and emissions of diesel engines. There have been few investigations, however, that have performed an energy balance analysis of diesel/PODEn blends. Such an analysis would provide new insights into understanding the energy flow distribution and help further improve the energy conversion efficiency of diesel engines fueled with diesel/PODEn blends. For this reason, an energy balance analysis was conducted on a heavy-duty China VI diesel engine fueled with various diesel/PODEn blends (mass fractions of 10%, 20%, and 30%). In addition, combustion characteristics, as well as the particulate number concentration (PNC)-NOx trade-off relationship, were also examined. The results revealed that as the PODEn blending ratio increased, the effective work ratio (i.e., the brake thermal efficiency) gradually increased, while the exhaust loss ratio, cooling loss ratio, and incomplete combustion loss ratio decreased under each given operating condition. Therefore, fueling with diesel/PODEn blends caused the energy distribution to be superior and optimized compared to fueling with diesel fuel. Moreover, the PODEn addition reduced the peak in-cylinder pressure, mean in-cylinder temperature, and maximum heat release rate. Also, both the ignition delay and combustion duration were shortened, and the heat release process became both more concentrated and closer to the top dead center. This significantly improved the brake thermal efficiency, with the maximum increment reaching 3.29%. The trade-off between the NOx and PM emissions was significantly improved by blending PODEn during all operating conditions. In conclusion, diesel blending with PODEn effectively improved the energy conversion efficiency and combustion process of a test engine, resulting in a reduction of energy losses, especially under high load conditions.