Development of the Euro 5 Combustion System for Volvo Cars' 2.4.I Diesel Engine

The development of a new combustion system for a light-duty diesel engine is presented. The soot-NO_x trade-off is significantly improved with maintained or improved efficiency. This is accomplished only by altering the combustion chamber geometry, and thereby the in-cylinder flow. The bowl geometry is developed in CFD and validated in single cylinder tests. Tests and simulations align remarkably well. Under identical conditions in the engine the new combustion chamber decreases smoke by 11-27%, NO_x by 2-11%, and maintains efficiency as compared to the baseline geometry. The injector nozzle is matched to the new bowl using design of experiments (DoE). By this method transfer functions are obtained that can be used to optimize the system using analytical tools. The emissions show a complex dependence on the nozzle geometry. The emission dependence on nozzle geometry varies greatly over the engine operating range. Finally, the system's robustness is optimized using a Monte Carlo simulation approach, to maximize the distance from the failure mode.