Optimization design of the ignition system for Wankel rotary engine considering ignition environment, flow, and combustion

To improve the poor in-cylinder combustion condition of the spark ignition (SI) Wankel rotary engine (WRE) and improve its efficiency, this paper optimized the traditional SI system into an in-cylinder spark ignition (ICSI) system. The ICSI system achieves direct ignition inside the combustion chamber rather than inside the ignition chamber by optimizing the structure and installation position of the spark plug. The cathode was arranged on the moving rotor, and the anode was located on the modified spark plug on the cylinder surface. To maintain a constant spark gap between the cathode and the anode during the rotor motion, a constant distance profile for the rotor was proposed for the first time in this paper. For in-depth analysis of changes in in-cylinder flow, ignition environment, flame propagation, and combustion parameters, a three-dimensional computational fluid dynamic (CFD) model of the WRE based on the reasonable turbulent model and the reduced chemical kinetic mechanism for gasoline was established, and its reliability was validated by comparing to experimental results. The calculation results indicated that the introduction of the ICSI system increased the peak pressure up to 24%, which greatly improved the engine performance. The turbulence intensity was increased during intake and decreased during ignition and combustion. In addition, it was proved that the structure of the cathode and the spark timing of the ICSI system had effects on combustion, emissions, and engine performance, which is of great design and research value. The ICSI system proposed in this paper greatly optimized the in-cylinder flow and combustion, providing a new direction for the performance optimization of the WRE.