Experimental Investigations on the Performance and Cold Starting Characteristics of a Low Compression Ratio Diesel Engine

In this experimental work, the potential advantages of lowering the Compression Ratio (CR) of a diesel engine in terms of performance, combustion and emission related parameters along with the analysis and improvement in its cold starting characteristics are presented. The CR of a single cylinder direct injection common rail diesel engine used for light-duty automotive applications was lowered from 18:1 to 14:1 by suitable modifications to the combustion bowl while retaining its shape. The engine with both the CRs was tested on a dynamometer rig under similar operating and fuelling conditions. Additionally, experiments were carried out to determine the extent to which in-cylinder smoke emissions can be reduced when the Nitric Oxide (NO) levels of 14 CR are matched to the higher levels seen in 18CR.

In order to evaluate cold start ability and idling stability of the engine with a reduced CR (14:1), the engine was instrumented inside a cold chamber. The engine was soaked at different low temperatures ranging from 25 °C to -7 °C and experiments were performed to determine its cold start ability. The effects of injection scheduling and injection quantity on cold start ability are determined with the help of an open engine controller. Further, the improvement on start ability with the help of a grid heater was also evaluated.