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 0.5 l. Tests covered start temperatures between 10 uC and 220 uC. At around 300 r/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 1000 r/min idling conditions, the stability was relatively poor and was worse for the low-compression-ratio case. At the high compression ratio, the cycle-bycycle stability was improved by introducing multiple pilot injections and using metallic glow plugs operating at about 850 uC. At the low compression ratio, improvements in stability could not be achieved without switching to glow plugs operating at about 1100 uC.
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