Numerical study of effects on combustion characteristics and emissions of an X-type rotary engine by ignition location under wide open throttle conditions

The coupling of ignition position with chamber structure significantly affects combustion performance of an X-rotary engine (XRE). In the work, a three-dimensional simulation model of the XRE was established, and effects of ignition location on combustion characteristics and emissions were numerically investigated. Results showed that at the later stage of compression stroke, a complex vortex was formed in the recess of the XRE at medium to high engine speeds, which significantly affected ignition kernel development and flame propagation. The ignition location situated in the middle of the recess accelerated flame propagation by fully utilizing surrounding space and higher velocity field formed at the transition between the vortex and the vortex-free flow field, thus significantly shortening combustion duration. Meanwhile, this ignition scenario had the largest peak pressure, which increased by more than 30% over the worst scenario. Moreover, this ignition scenario had higher indicated thermal efficiency and indicated mean effective pressure at high-speed conditions, but also higher NOx generation. Peak pressure was reduced with increasing engine speed. The maximum peak pressure at 4500 RPM was 26.2% lower than that at 1500 RPM. Notably, ignition location had a slight effect on formations of Soot and CO in the XRE.