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This paper presents two closed-loop control methods for monitoring and improving the combustion behavior and the combustion noise on two 4-cylinder diesel engines, in which an in-cylinder pressure and an accelerometer transducer are used to monitor and control them. Combustion processes are developed to satisfy the stricter and stricter regulations on emissions and fuel consumption. These combustion processes are influenced by the factors such as engine durability, driving conditions, environmental influences and fuel properties. Combustion noise could be increased by these factors and is detrimental to interior sound quality. Therefore, it is necessary to develop robust combustion behaviors and combustion noise. For this situation, we have developed two closed-loop control methods. Firstly, a method using in-cylinder pressure data was developed for monitoring and improving the combustion noise of a 1.7L engine. A new index using the values calculated from the data was proposed.

In this study, a correlation between the maximum heat release rate and vibrations from a diesel engine block was derived, and a methodology to determine the maximum heat release rate is presented. To investigate and analyze the correlation, an engine test and an actual road vehicle test were performed using a 1.6-L diesel engine. By varying the engine speed, load and main injection timing, the vibration signals from the engine block were measured and analyzed using a continuous wavelet transform (CWT). The results show that the maximum heat release rate has a strong correlation with the magnitude of the vibrations. A specific bandwidth, the vibration signals between 0.3∼1.5 kHz, was affected by the variation in the heat release rate. The vibrations excited by combustion lasted over 50 CAD; however, the signals during the period of 35 CAD after the start of injection had a dominant effect on the maximum heat release rate.