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An experimental investigation has been carried out to compare the indicated performance and heat release characteristics of a DI diesel engine at compression ratios of 18.4:1 and 15.4:1. The compression ratio was changed by modifying the piston bowl volume; the bore and stroke were unchanged, and the swept volume was nominally 500cc. The engine is a single cylinder variant of modern design which meets Euro 4 emissions requirements. Work output and heat release characteristics for the two compression ratios have been compared at an engine speed of 300 rev/min and test temperatures of 10, -10 and -20°C. A more limited comparison has also been made for higher speeds representative of cold idle at one test temperature (-20°C). The reduction in compression ratio generally produces an increase in peak specific indicated work output at low speeds; this is attributable to a reduction in blowby and heat transfer losses and lower peak rates of heat release increasing cumulative burn.

An experimental investigation of combustion cycle-by-cycle stability under cold idling conditions has been carried out on a Dl diesel to examine the influence of pilot fuel injection strategy. The engine is a single cylinder variant of a multi-cylinder design meeting Euro 4 emissions requirements. The engine build had a swept volume of 500cc and a compression ratio of 18.4:1. Work output and heat release characteristics have been investigated at test temperatures of 10, 0, −10 and −20°C and speeds in the range from 600 to 1400rpm. At the lowest temperature, −20°C, stability is sensitive to the timing of main injection and is prone to deteriorate with increasing engine speed. The influence of the number of pilot injections and pilot fuel quantity on stability has been explored. Best stability was achieved by increasing the number of pilot injections as temperature is lowered, from one at 10°C to two at −10°C and between two and four at −20°C.