Abstract
Fuel injection control is effective to improve the thermal efficiency of a diesel engine. In order to predict the gas temperature at the start time of fuel injection, the authors have previously developed an on-board polytropic index prediction model for the compression stroke with low calculation load based on physical principles. However, to estimate the indicated mean effective pressure (IMEP) required in its model, the diagram factor has been assumed to be a constant. In this study, a regression equation for diagram factor was derived based on numerical simulation results. Since the diagram factor depends on the centroid of heat release rate (CA50), a regression equation to estimate the CA50 based on operational conditions was determined. The average error between the IMEP estimated using the regression equations and experimental results was 1.2%, and the usefulness of the regression equation was confirmed.
