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Diesel engine noise is classified into mechanical noise, flow dynamic noise and combustion noise. Among these, combustion noise level is higher than the others due to the high compression ratio of diesel combustion and auto ignition. The injected fuel is mixed with air in the ignition delay process, followed by simultaneous ignition of the premixed mixture. This process results in a rapid pressure rise, which is the main source of combustion noise. The amount of fuel burned during premixed combustion is mainly affected by the ignition delay. The exhaust gas recirculation (EGR) rate has an impact on ignition delay, and thus, it influences the combustion noise characteristics. Therefore, during the transient state, the combustion noise characteristics change as the EGR rate deviates from the target value. In this study, the effect of the EGR rate deviation during the transient state of the combustion noise is examined. A 1.6 liter diesel engine with a VGT was used for the experiment.

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.