Evaluation of On-board Heat Loss Prediction Model and Polytropic Index Prediction Model for CI Engines Using Measurements of Combustion Chamber Wall Heat Flux 2019-32-0543

Diesel engines need to optimize the fuel injection timing and quantity of each cycle in the transient operation to increase the thermal efficiency and reduce the exhaust gas emissions through the precise combustion control. The heat transfer from the working gas in the combustion chamber to the chamber wall is a crucial factor to predict the gas temperature in the combustion chamber to optimize the timing and quantity of fuel injection. Therefore, the authors developed both the heat loss and the polytropic index prediction models with the low calculation load and high accuracy. In addition, for the calculation of the heat loss and the polytropic index, the wall heat transfer model was also developed, which was derived from the continuity equation and the energy equation. The present study used a single cylinder diesel engine under the condition of engine speed of 1200 and 1500 rpm, and measured the local wall temperature and the local heat flux of the combustion chamber. The measured data were compared with the prediction results of the heat loss and the polytropic index and evaluated the prediction accuracy of those models. The average relative errors for the heat loss and the polytropic index prediction models were evaluated to be 6.6% and 0.3%, respectively.