A Cylinder Pressure Correction Method Based on Calculated Polytropic Exponent

The acquisition of more authentic cylinder pressure data is the basis of engine combustion analysis. Due to the multiple advantages, quartz piezoelectric pressure transducers are generally applied to the measurement of the cylinder pressure. However, these transducers can only produce dynamic cylinder pressure data which may be significantly different from the actual values. Thus, the cylinder pressure data need to be corrected through a certain method, while different cylinder pressure correction methods will cause result divergences of the combustion analysis. This paper aims to acquire a proper cylinder pressure correction method by carrying out theoretical analysis based on the polytropic process in the compression stroke as well as the experimental research of the cylinder pressure of a turbocharged eight-cylinder diesel engine. The method presented in this paper can not only get a polytropic exponent with higher accuracy by calculation but also revise the cylinder pressure curve at the same time. A further experimental research on this engine shows that the value of the polytropic exponent fluctuates from 1.33 to 1.38 at different working conditions, and is hardly associated with the engine load. However, the value of the polytropic exponent becomes bigger along with the increase of the engine speed.