Injector fouling was accelerated by reducing the injector needle opening pressure by 20 in a modified Perkins direct injection diesel engine operated at 75 rated speed and 75 of maximum torque. This resulted in a 20 mm test (including 5 mmidling pre-check) which produced accelerated 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 the totalorifice 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 individual injector orifices (4 orifices perinjector; 100-200μm diameter) from the inside with a light source thus producing a sharp, easily detectable difference between the now illuminated orifices and the darker background of the nozzle. An injector Fouling Index (FI), based on the ratiobetween the fouled and clean orifice areas, was developed 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{sup}-2) SRO - 5.1472(10{sup}-4) SRO{sup}2 +3.1008(10{sup}-6) SRO{sup}33 (R{sup}2 = 0.86; SRO = SRO in the fuel blend), showed that the injector orifice blocking increased with increasing SRO inclusion rates. For example, a 25 (v/v) SRO/diesel oil blend had a Fouling Index of 0.64 compared with0.38 for diesel fuel only, i.e., the SRO fuelled nozzle was approximately two thirds more blocked (i.e., 0.64/0.38) than when diesel only was used. Preliminary analysis of conventionally fouled direct injection diesel injectors has shown that this 20 minaccelerated injector fouling test using diesel fuel is approximately equivalent to 2500 h of conventional engine use also using diesel fuel (R{sup}2 = 0.68). Further work is required to substantiate the predicted capabilities of accelerated injectorfouling using longer term engine tests.
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