A space-time averaged steady-state heat transfer model and its application in Wankel rotary engines

In response to energy efficiency and emissions reduction demands, downsized Wankel rotary engines (WREs) are used in applications like vehicle range extenders and unmanned aerial vehicle power sources due to their high power-to-weight ratio. Addressing performance and lifespan issues under thermal loads is crucial. However, there is still no efficient solution for the definition of thermal boundary in Wankel rotary engine cooling research. Determining the thermal boundary through one-dimensional simulation is simple and accurate, which is very necessary for the study of cooling problems based on conjugate heat transfer (CHT). This study investigates thermal boundary definition using an one-dimensional to three-dimensional (1D-3D) simulation model under steady state heat transfer, and innovatively uses a space–time averaging method to simulate the temperature distribution according to the thermal load characteristics of the WRE. The results show that the temperature data obtained by this method are in good agreement with the experiments, and the maximum temperature deviation under 4500 rpm is only 1.09 %, which indicates that the temperature distribution of the WRE can be accurately obtained by using the 1D-3D simulation model and the space–time averaging method. This study puts forward the generalized application of this method and the empirical formula for determining the thermal boundary conditions, which provides theoretical guidance and reference for the determination of thermal boundaries in the study of WRE cooling.