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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.

The spatial and temporal characteristics of the non-evaporating diesel sprays injected into the atmosphere through two pump-pipe-nozzle systems used in small DI diesel engines have been investigated by laser-single-beam deflection and phase-Doppler anemometry (PDA). The injectors used for these tests comprised a single-spring and a prototype two-spring multihole-type nozzle. The results provided quantitative information about the effect that the second spring exerts on injection duration and spray characteristics, i.e. it increases injection duration and, at the same time, improves fuel atomisation during the main injection period.