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The source of the combustion noise of diesel engines was investigated in this paper. In the development of exhaust emission and combustion noise, we must optimize the injection parameters at the cell where engine noise can not be measured. To solve this problem, it is necessary to identify a method for developing combustion noise through in-cylinder pressure measurements. It is known that the combustion noise of a diesel engine is generated mainly in the phase of premixed combustion and depends on the rate at which the pressure increases. The combustion noise was analyzed by measuring the in-cylinder pressure and engine noise. Our results show that the combustion noise has a low correlation with the maximum rate of pressure increase. For this reason, a new index called the combustion noise index was developed based on the cylinder pressure level. This paper describes an advanced method for developing combustion noise and illustrates some examples of the results obtained.

Most research of internal combustion engine focuses on improving the fuel economy and reducing exhaust emissions to satisfy regulations and marketability. Engine combustion is a key factor in determining engine performance. Generally, engine operating parameters are optimized for the best performance and less exhaust emissions. However, abnormal combustion results in engine conditions that are far from an optimized operation. Abnormal combustion, including a misfire, can happen for a variety of reasons, such as superannuated vehicles, extreme changes in the driving environment, etc. Abnormal combustion causes serious deterioration of not only noise, vibration and harshness (NVH), but also the fuel economy and exhaust emission. NVH stands for unwanted noise, vibration and harshness from the vehicle. The misfiring especially deteriorates vehicle comfortability. Abnormal combustion at one cylinder breaks the exciting force balance between cylinders and causes unexpected vibration.