Research On The Diesel Engine Cylinder Pressure Recovering Methods

Measuring and analyzing the cylinder pressure of the diesel engine is import to improve the diesel engine performance, control the injecting timing , condition monitor and fault diagnosis. The ordinary library method to obtain the cylinder pressure is making a hole in the cylinder cover, measure directly using the pressure transducer. In this method the transducer endure high pressure and high temperature gas' impact, it's difficult to use in practice. The indirect recovery method using other easy testing signal may provide practical utility. On the basis of such background, this dissertation intends to study the vibration identification methods.1. At first test the fourth cylinder pressure signal, vibration signal, top dead center signal of the 4135 diesel engine. Then the characteristics of the excitation and vibration response of cylinder cover are analyzed. The cylinder cover system is regarded as a multi-input/single-output linear system, The experiment data are denoised by time statistic averaging, which could improve the signal noise ratio, then the measurement signal is split up into several sequences related to the combustion pressure using time domain windows and high frequency noise using a FIR low-pass filter, The transfer function of the system is used to recovery the cylinder pressure. Time statistic averaging and the right position of testing the vibration response signal is vital to improve the identification precision. Compare the raw pressure and the identification pressure at the position of eigenvalue, Demonstrate the applicability of transfer function method.2. Identify the cylinder pressure of the diesel engine using the cepstral analysis. And compare the raw pressure and the identification pressure at the position of eigenvalue which reflect the combustion performance, analyzing the characteristic of the cepstral method.3. The non-linear characteristic of the excitation and vibration response of cylinder cover are analyzed in this paper, expound a diesel engine cylinder pressure recovery method based on BP neural network. It was proposed to process the acceleration signal due to the combustion pressure with denosing method of timestatistic average, and remove high frequency noise using a lowpass filter, then train BP neural network using the adaptive grads algorithm, adaptive adjust the learning speed, improve the precision of the network, identify the cylinder pressure. Analyze the effect on cylinder pressure recovery caused by the middle layer neural network and the input layer neural network.