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The upcoming Bharat Stage VI (BS VI) emission legislation has put enormous pressure on the future of small diesel engines which are widely used in the Indian market. The present work investigates the emission reduction potential of a common rail direct injection single cylinder diesel engine by adopting a holistic approach of lowering the compression ratio, boosting the intake air and down-speeding the engine. Experimental investigations were conducted across the entire operating map of a mass-production, light-duty diesel engine to examine the benefits of the proposed approach and the results are quantified for the modified Indian drive cycle (MIDC). By reducing the compression ratio from 18:1 to 14:1, the oxides of nitrogen (NOx) and soot emissions are reduced by 40% and 75% respectively. However, a significant penalty in fuel economy, unburned hydrocarbon (HC) and carbon monoxide (CO) emissions are observed with the reduced compression ratio.

It is well established that reducing the compression ratio (CR) of a diesel engine leads to a significant increase in hydrocarbon (HC) and carbon monoxide (CO) emissions, especially in cold and transient conditions. Hence, it is essential to find new strategies to reduce the HC and CO emissions of a low compression ratio (LCR) diesel engine in transient conditions. In the present work, a detailed evaluation of different warm-up technologies was conducted for their effects on transient emissions characteristics of a single-cylinder naturally aspirated LCR diesel engine. For this purpose, the engine was coupled to an instrumented transient engine dynamometer setup. A transient cycle of 160 seconds with starting, idling, speed ramp-up and load ramp-up was defined, and the engine was run in automatic mode by the dynamometer. The experiments were conducted by overnight soaking the engine at a specified temperature of 25 deg.C.