Experimental investigation on the effects of compression ratio on performance, emissions and combustion characteristics of a biodiesel-fueled automotive diesel engine

The present study examines the effects of compression ratio (CR; 19:1 base, 17:1 and 21:1) on performance, emissions and combustion characteristics of a 5.5-kW direct-injection automotive diesel engine fueled with biodiesel (B100). The results show that increasing CR improves the thermal efficiency of the engine. The change in CR from 19:1 to 21:1 for the biodiesel enhanced the brake thermal efficiency by about 9.5% and 4.63% at full load with engine speeds of 2200 (power output of 3.9 kW at 17 Nm torque) and 3000 rpm (4.9 kW at 15 Nm), respectively, compared to the base CR of 19:1. However, emission of oxides of nitrogen increased from 8.71 and 7.73 g/kWhr with CR of 19:1 to 9.25 and 8.92 g/kWhr with increased CR of 21:1 at speeds of 2200 and 3000 rpm, respectively. But the NOx emission at 2200 rpm can be reduced to 7.34 g/kWhr with 3 degrees crank angle retarded injection timing. A biodiesel-fueled engine with increased CR (21:1) and retarded injection timing could give improved performance and emissions compared to base diesel and biodiesel with base CR (19:1).