An adapted heat transfer model for engines with tumble motion

In the last years, a growing interest about increasing the engine efficiency has led to the development of new engine technologies. The accurate determination of the heat transfer across the combustion chamber walls is highly relevant to perform a valid thermal balance while evaluating the potential of new engine concepts. Several works dealing with heat transfer correlations that consider the swirl motion are found in the literature; however, there is a lack of works dealing with heat transfer correlations which take into account the effect of the tumble movement. In this work, a heat transfer model accounting for the tumble motion is presented. A two stroke HSDI Diesel engine with high tumble and no swirl is used to perform the theoretical study, the model development and its final calibration. Initially, a theoretical analysis of the gas movement phenomena is carried out based on CFD results and then, a model is developed and calibrated based on a skip-fire testing technique. Finally, a sensitivity study focused on evaluating the model robustness is performed. The results confirm an average RMSE reduction of 70% with respect to the Woschni model, being this consistent improvement qualitatively evidenced in the instantaneous heat transfer evolution.