Effect of compression ratio on combustion stability and performance of a DI diesel engine under cold conditions

摘要

In recent years, there has been a design trend towards using lower compression ratios for light duty automotive diesel engines. The potential effect of this on cold start performance is of concern. A comparison of experimental results for high and low compression ratios is presented in this paper, for various fuel injection strategies and temperatures down to - 20°C. The magnitude and stability of indicated work output at fixed engine speeds between cranking and idle speeds are used as performance measures. The test engine was a single cylinder DI diesel with HPCR fuel injection. The compression ratio was lowered from 18.4:1 to 15.4:1 by modifying the piston bowl volume; the bore and stroke were unchanged. The reduction in compression ratio generally produces an increase in peak specific indicated work output around cranking speeds. The coefficient of variation of work output increases with increasing engine speed and decreasing load; stability is most prone to deteriorate at low compression ratio. Multiple pilot injections could be used to reduce variations in work output at high compression ratio but were not so effective at low compression ratio. At low compression ratio, stability could be improved by using high temperature glowplugs.