Conduction-strain model for heat transfer characterization in internal combustion engines

Abstract

Heat transfer between combustion gases and walls is one of the most important phenomena for internal combustion engines; however, its mechanisms have not yet been elucidated. This study proposed a new model based on one-dimensional heat conduction to characterize and predict engine heat transfer. This model assumes a conduction thickness of a thermal boundary layer determined by heat conduction and strain. Through comparison with numerical simulation, it was found that the heat flux from the conduction-strain model was comparable to that in laminar heat transfer. The heat flux calculated with the conduction-strain model is considered to be the minimum heat flux under each operating condition and engine specification. Therefore, the ratio of the measured heat flux to modeled heat flux indicates the intensity of convection and radiation, particularly turbulent mixing. It was also found that the conduction-strain model reproduced the measured heat flux well with a single coefficient, exhibiting a small error of 10.2%; meanwhile, the errors of Woschni and Annand models were greater than 20%, suggesting that the proposed model has good potential in predicting the instantaneous heat flux more accurately than conventional models.