PERFORMANCE AND EMISSION CHARACTERISTICS OF OFF-ROAD DIESEL ENGINE OPERATING ON RAPESEED OIL AND PETROL BLENDS

This article presents the bench testing results of a four stroke, four cylinder, direct injection, unmodified, naturally aspirated diesel engine operating on neat rapeseed oil (RO) and its 7.5 vol % blend with petrol (PRO7.5). The purpose of this research was to investigate the effect of petrol addition in the RO and preheating temperature on biofuel viscosity, brake mean effective pressure developed by the engine, its specific fuel consumption, the brake thermal efficiency and emission composition changes, including NO, NO2, NOx, CO, CO2, HC and smoke opacity of the exhausts. It was determined that addition in the RO 7.5 vol % of petrol the blend viscosity at ambient temperature of 20 degrees C diminishes by 31.7 % and the biofuel flow in the fuelling system improves. During operation of the fully loaded engine under constant air-to-fuel equivalence ratio, lambda=1.6, at the maximum torque 1800 min(-1) and rated 2200 min(-1) speed blend PRO7.5 ensures the brake mean effective pressure lower correspondingly by 2.6 % (bmep=0.750 MPa) and 0.5% (bmep=0.736 MPa) than that of neat RO case (0.770 and 0.740 MPa). The bsec at maximum torque (9.34 MJ/kWh) and rated power (9.08 MJ/kWh) determined when fuelling the engine with blend PRO7.5 is higher by 2.1 % and lower by 0.7 % and the brake thermal efficiency lower by 1.5 % and higher by 0.3 %, respectively, comparing with that of neat RO. The test results indicate that when running of the fully loaded engine at rated 2200 min-1 speed, petrol addition in the RO up to 7.5 vol % increases NO (18.2 %), NO2 (2.8 times), NOx (19.6 %), NO2/NOx (2.4 times), CO (33.4 %), HC (by 9-11 ppm) emissions and exhaust gas temperature (2.4 %) and diminishes simultaneously CO2 ( 2.6 %) emission and smoke opacity (2.4 %) of the exhausts.