ACCELERATED INJECTOR FOULING USING RAPESEED OIL DIESEL BLENDS IN A DIRECT-INJECTION ENGINE

lnjector fouling was accelerated by reducing the injector needle openi ng pressure by 20% in a modified Perkins direct injection diesel engin e operated at 75% rated speed and 75% of maximum torque. This resulted in a 20 min test (including 5 min idling pre-check) which produced ac celerated injector fouling when using Semi-refined Rapeseed Oil (SRO)/ diesel blends ranging from zero to 75% SRO inclusion rates. The extent of fouling, which ranged from approximately 40% to 80% blockage of th e total orifice area compared with a clean injector was determined by measuring the reduction in individual orifice diameters using a novel technique based on image analysis, This was achieved by lighting the i ndividual injector orifices (4 orifices per injector; 100-200 mu m dia meter) from the inside with a light source thus producing a sharp, eas ily detectable difference between the now illuminated orifices and the darker background of the nozzle. An injector Fouling Index (FI) based on the ratio between the fouled and clean orifice areas, was develope d for direct injection diesel engines. A regression model relating FI to SRO inclusion rates was established. This model, where FI = 0.19156 + 2.8879(10(-2)) SRO -5.1472(10(-4)) SR02 + 3.1008(10(-6)) SRO3 (R-2 = 0.86; SRO = % SRO in the fuel blend), showed that the injector orifi ce blocking increased with increasing SRO inclusion rates. For example , a 25% (v/v) SRO/diesel oil blend had a Fouling Index of 0.64 compare d with 0.38 for diesel fuel only, i.e., the SRO fuelled nozzle was app roximately two thirds more blocked (i.e., 0.64/0.38) than when diesel only was used. Preliminary analysis of conventionally fouled direct in jection diesel injectors has shown that this 20 min accelerated inject or fouling test using diesel fuel is approximately equivalent to 2500 h of conventional engine use also using diesel fuel (R-2 = 0.68). Furt her work is required to substantiate the predicted capabilities of acc elerated injector fouling using longer term engine tests. Keywords. In jector fouling, Biodiesel, Image analysis, Fouling Index model D. I. e ngines, Alternative fuels.