Combustion and emission characteristics of a DME (dimethyl ether)-diesel dual fuel premixed charge compression ignition engine with EGR (exhaust gas recirculation)

In this study, effects of DME (dimethyl ether) pre-mixing ratio and cooled external EGR (exhaust gas recirculation) rate on combustion, performance and emission characteristics of a DME-diesel dual fuel PCCI (premixed charge compression ignition) engine were investigated in a 2105 engine. PCCI combustion at a high pre-mixing ratio exhibited a three-stage-combustion behavior. The peak values of heat release rate and pressure rise rate increased in HCCI (homogeneous charge compression ignition) combustion stage and decreased in diesel diffusion combustion stage. A higher DME pre-mixing ratio caused lower smoke and NOx (nitrogen oxides) emissions but higher HC (hydrocarbons) and CO (carbon monoxide) emissions. Adopting EGR, the peak values of in-cylinder pressure and calculated mean charge temperature decreased. Meanwhile, the crank-angle positions corresponding to the maximum heat release rate and maximum pressure rise rate lagged respectively. Equivalent brake specific fuel consumption increased. With an increase in EGR rate, NOx emission decreased sharply, however, smoke, HC and CO emissions increased. Nevertheless, decreasing levels in maximum values of in-cylinder pressure and temperature, heat release rate and pressure rise rate, as well as lagging degrees in crank-angle positions corresponding to the above-mentioned maximum values, gradually weakened with an increase in DME pre-mixing ratio.