The European as well as U.S. market share of modern Diesel engines has increased significantly in recent years, due to their excellent torque and performance behavior combined with low fuel consumption. The overall improved noise and vibration behavior of modern Diesel engines has also contributed to this trend. Despite overall improvements in Diesel engine noise and vibration, certain aspects of Diesel engines continue to present significant challenges. One such issue is the presence of Diesel knocking that is prevalent during cold start and warm-up conditions. This paper discusses a technique used to optimize the cold start noise behavior of modern Diesel engines.
The methods used in this study are based on optimizing the engine calibration to improve the vehicle interior and exterior (engine) noise, even at low ambient temperatures. Initially, the engine's combustion noise behavior is characterized by measuring the cylinder pressure (under various operating conditions) and developing appropriate transfer functions. Various engine calibration iterations are carried out using a structured Design of Experiments (DOE) and for each iteration, the measured cylinder pressure is used to calculate the combustion noise influence (based on existing transfer functions). At the end of this study, the influence of key calibration parameters on improving the cold start noise characteristics is demonstrated.
The acoustic optimization achieved in this way has no detrimental effects on the engine's ability to start, combustion stability, visible black or white smoke and emissions. Finally, the potential of using the developed technique in conjunction with other new technologies, such as exhaust gas after treatment systems and alternative preheating and boosting concepts, is discussed.