Research Method For Evaluation Engine Combustion Uniformity Based On Crankshaft Angular Acceleration

Cylinder pressure, as one of the best indicators of the characterization of the enginerunning state, could be used to analyze the engine combustion. But due to the complexCylinder pressure measuring process, the high cost and poor durability of cylinderpressure sensor, the application of the cylinder pressure in the evaluation of enginecombustion is limited. Taken the crankshaft angular acceleration as the alternativeparametric of cylinder pressure, engine combustion uniformity is analyzed in this paper.This method, which can reliably evaluate the engine working condition and improve theengine uniform combustion, does not produce any influence on engine combustionprocess, and it is simple and low in cost.The original data ,which are collected by Crankshaft Position Sensor are processed inMATLAB to confirm the zero-crossing point of the raw data, and fill in the zero points ofmissing teeth. Crankshaft angular velocity is calculated according to the zero-crossingpoints and the crank angle, and crankshaft angular acceleration is computed by splinenumerical differentiation.In this paper Wavelet threshold de-noising method is used to filter noise of thecrankshaft angular velocity and acceleration. According to the characteristics of thecrankshaft signal, different wavelet functions and filtering effect differences underdifferent break-up scales are analyzed aiming at obtain the optimum filtering effect, andthe optimum mode for wavelet threshold filtering is confirmed.In line with the characteristics of the signal, which are collected by CrankshaftPosition Sensor, the original data is analysed under different scales and different waveletsin order to obtain the optimal filtering effect,and determine the best mode of the waveletthreshold filtering.The relevant statistical parameters are calculated in angle domain. The correlationrelationship between the statistical parameters of crankshaft angular acceleration andstatistical parameters of cylinder pressure is analyzed, and then the indicators and themethods which are used to assess the non-uniform of engine combustion are determined. The condition of engine combustion at a mode are evaluated using this analysis method.Using the graphical visualization interface in Matlab, the interfaces are developed forsignal processing of crankshaft and the wavelet threshold filtering. The user interface notonly can calculate crankshaft angular velocity, angular acceleration and their statisticalparameters also can set parameters of wavelet threshold de-noising.