Improvement of DME HCCI engine combustion by direct injection and EGR

Abstract

To extend the operating range of a homogeneous charge compression ignition (HCCI) engine fuelled with DME, direct injection and exhaust gas recirculation (EGR) were used to investigate their effects on the change of combustion characteristics in this experiment.Single cylinder engine was used with port fuel injector and direct injector. EGR line was connected from exhaust pipe to intake pipe. The experimental result for direct injection was compared with that for port injection. The gross indicated mean effective pressure (IMEPgross), which represented the operation region, for direct injection was higher than that for port injection due to late combustion resulting from lower temperature combustion induced by evaporating latent heat of injected DME in the cylinder. There was optimal direct injection timing for DME HCCI engine because the combustion characteristics were changed from overall lean combustion to locally rich combustion. IMEPgross was increased by EGR. It was because EGR made tardy combustion and increased positive work during expansion stroke. Consequently, direct injection with optimal injection timing and EGR increased the IMEPgross by 22% and 55% compared to port injection case, respectively.