Effect of Optimizing of the Start of Injection Timing for Improving NOx/PM Trade-Off in DI Diesel Engine Fueled with Rapeseed Methyl Ester 2020-01-2132

Pollutant emissions are a major issue from all existing internal combustion engines, especially from Diesel engines, with nitrogen oxides (NO_x) and particulate matter (PM) receiving particular attention. Simultaneous reduction of NO_x and PM often presents a challenge to Diesel engine researchers because of the inherent trade-off between them due to their contradictory responses to oxygen content in a fuel. The use of liquid or gaseous biofuels in internal combustion engines, benefits in the reduction of life-cycle CO₂ emissions, but suffers from unfavorable NO_x/PM emissions trade-off. Hence, it is essential to moderate NO_x/PM emissions trade-off in order to effectively use the Rapeseed Methyl Ester (RME) fuel as an alternative to the fossil Diesel fuel in Diesel engines. In this study, the trade-off relations among PM and NO_x from a four-cylinder, direct injection (DI) Diesel engine fueled with fossil Diesel, RME, and their blends, in conjunction with various start of injection timing were investigated. It is known that when the oxygen content of the fuel increases, the PM density decreases while NO_x emissions increase. But in the present study, we have proven that an improvement in NO_x/PM trade-off can be achieved for pure RME fuel (B100) by adjusting the start of injection timing. The optimization of the start of injection timing (SOI) can minimize the amount of NO_x emitted and reduce the density of PM produced. These results are corroborated by the use of a feedback law applied to control NO_x emissions, from combustion of pure RME fuel (B100). By retarding the combustion process through optimizing the start of injection timing, this controller has proven its efficiency to track the desired trajectory of NO_x and reduce the density of PM produced.