Abstract
Abstract
A reduction in the compression ratio can adversely affect the cold-start and idling performance of diesel engines. The problems and potential solutions have been investigated. Studies have been carried out to compare the indicated performances and heat release characteristics of a direct-injection diesel engine during low-speed cold operation at compression ratios of 18.4:1 and 15.4:1. The test engine was a naturally aspirated single-cylinder design with a swept volume of 0.5l. Tests covered start temperatures between 10°C and 20°C. At around 300r/min, the indicated work output was higher at the lower compression ratio as a result of lower blow-by, and the cycle-by-cycle stabilities of the heat release and work output were similar at both compression ratios. The cycle-by-cycle stability deteriorated with increasing engine speed. At 1000r/min idling conditions, the stability was relatively poor and was worse for the low-compression-ratio case. At the high compression ratio, the cycle-by-cycle stability was improved by introducing multiple pilot injections and using metallic glow plugs operating at about 850°C. At the low compression ratio, improvements in stability could not be achieved without switching to glow plugs operating at about 1100°C.
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