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Based on NVH tests conducted on a heavy-duty turbocharged DI diesel engine, noise relevant differences between steady-state and transient operating condition were investigated. A vehicle drive-by test simulating the effects of vehicle mass and inertia was performed, followed by transient NVH measurements in a semi-anechoic test cell. Steady-state noise was exceeded by 5 dBA during transient operation due to broadband increase of noise excitation combined with structure resonance amplification. Transient noise results mainly from “harsher” combustion as a consequence of enlarged ignition delay indicated by significant increase in maximum cylinder pressure gradient. Variation of geartrain excitation and combustion excitation revealed that geartrain noise is of minor importance in this context.

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.