Experimental Investigations on the Effects of Low Compression Ratio in a Direct Injection Diesel Engine

In this experimental study, the effects of reducing the compression ratio on the performance, emission, combustion, and startability of a 0.55 L single cylinder, direct injection diesel engine were studied in detail. Engine compression ratio (CR) was reduced from 16.5:1 to 15:1 and then to 14:1 by suitably modifying the geometry of the combustion chamber. Low compression ratios led to a reduction in both nitric oxide (NO) and smoke emissions with a marginal increase in fuel consumption. A special experimental setup with a motoring arrangement and a cold air and coolant conditioner unit was done, for investigating the cold starting ability of the engine. Also, a detailed analysis was made to characterize the transient behavior (cycle-to-cycle variations) of the engine with two compression ratios namely 14:1 and 16.5:1 during starting at different ambient conditions. The analysis showed that cold starting phenomenon of engine with a compression ratio of 14:1 got affected at reduced ambient temperature. The causes of misfiring during cold starting were investigated, and it is seen that the sequence of misfiring cycles was not entirely random.