A Holistic Approach to Develop a Common Rail Single Cylinder Diesel Engine for Bharat Stage VI Emission Legislation

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 (NO_x) 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. Intake air boosting using a mechanically driven supercharger could overcome the penalty in HC and CO emissions. However, the mechanical frictional losses of the supercharger resulted in a further penalty in the fuel economy. The reduced cylinder pressure due to lower compression ratio and the increased air availability due to intake air boosting could be utilized to improve the full-load performance of the engine by 28%. Further, the advantage of improved engine performance was utilized to down-speed the engine by optimizing the transmission gear ratios without compromising the acceleration performance of the vehicle. Overall, with this holistic approach, soot emission could be reduced by a significant margin of 83% whereas the NO_x emission is reduced by 5.8%. Moreover, the HC and CO emissions could be reduced by 17.6% and 30.9% respectively. Furthermore, the fuel economy at the vehicle-level could be improved by 5.4% while improving the in-gear acceleration performance by 9%. Thus, the proposed approach is found to be extremely beneficial to develop small, light-duty diesel engines with compliance on future emission regulations. The reasons behind the observed benefits are explained in detail based on the measured in-cylinder pressure and calculated heat release data.