Characteristics of SACI combustion in a diesel rotary engine based on combined 1D and 3D comprehensive transient simulations

Abstract

Wankel rotary engines (WREs) are widely used in aviation equipment, vehicles, micropower systems, etc. Diesel WREs are well suited for military and aerospace applications due to great safety features of the diesel fuel. In this paper, the transient in-chamber flow and combustion processes of a spark-assisted compression-ignition (SACI) direct injection diesel WRE were numerically simulated. Firstly, an effective method of using two rotating vectors is proposed to calculate the crank-angle-based instantaneous position of each location on the rotor surface in the rotor housing, which defines the law of dynamic boundary changes, to realize transient simulation. Secondly, the one-dimensional (1D) simulation results were used as the initial boundary conditions of the three-dimensional (3D) simulation, which improves the accuracy of the simulation and reduces the number of computational cycles during the validation of the 3D simulation model. Thirdly, model reduction and dynamic mesh control were used in the numerical simulation. The time of one calculation cycle was reduced from 223 h to 125 h, which is a 43.95% reduction. Finally, the 1D simulation revealed that ignoring the leakage between two adjacent combustion chambers was one of the main reasons for the error between the 3D simulated in-cylinder pressure and the experimental result. Based on the simulation methodology developed in this paper, the SACI combustion characteristics of a direct-injection diesel WRE were revealed. This paper provides an efficient simulation method for optimizing the design of novel WREs.