Sensitivity of diesel engine thermodynamic cycle calculation to measurement errors and estimated parameters

Abstract

The use of thermodynamic models for the calculation of the heat release law from the experimental in-cylinder pressure signal has been a common practice as a way to study the combustion process of internal combustion engines. However, the results of this procedure depend mainly on two factors: the validity of the assumed hypothesis and the quality of the measurement of the experimental parameters (both mean and instantaneous ones) used as input data. In this work a sensitivity study of a thermodynamic diagnostic model is presented, with the objective of evaluating the influence of errors in the measuring techniques or in the estimation of parameters on the main results, such as mean gas temperature, heat release and rate of heat release. In order to eliminate the effect of the uncertainty associated with the combustion process itself, the study focused on motored engine conditions. Otherwise, the effect of the inadequacy of the assumed hypothesis was eliminated by using as input in the diagnostic thermodynamic model the results from a predictive thermodynamic model with the same hypothesis as the diagnostic one, instead of an experimental pressure signal.