A Linear Least Squares Algorithm for Double Wiebe Functions Applied to Spark Assisted Compression Ignition

Abstract

An algorithm for determining the four tuning parameters in a doubleWiebe description of the combustion process in sparkassisted compression ignition engines is presented where the novelty is that the tuning problem is posed as a weighted linear leastsquares problem. The approach is applied and shown to describe well an extensive data set from a lightduty gasoline engine for various engine speeds and loads. Correlations are suggested for the four parameters based on the results, which illustrates how the doubleWiebe approach can also be utilized in a predictive simulation. The effectiveness of the methodology is quantified by the accuracy for describing and predicting the heat release rate and predicting the cylinder pressure. The rootmean square errors between the measured and predicted cylinder pressures are 1bar or less, which corresponds to 2% or less of the peak cylinder pressure.