In order to investigate the influences of coupling effect of the complex turbulent field and ignition positions in the unique combustion chamber of an X-type rotary engine on the mixture combustion process,a three-dimensional CFD model of the X-type rotary engine was established and validated with the test results.The in-cylinder combustion process of the X-type rotary engine under different ignition positions was numerically investigated,revealing the influences of ignition positions on the flame propagation,combustion characteristics and pollutant formation.Results show that at the late stage of compression stroke,the complex turbulence fields including vortex and unidirectional flow are formed in the combustion chamber of the X-type rotary engine,which significantly affects the flame propagation process by the coupling effect with the ignition position.In order to obtain the high flame propagation speed,the ignition position is not suitable to be located at the vortex region.When the ignition position is located in the middle of the recess,the flame propagation can be accelerated by taking full advantage of the surrounding space and the higher velocity field formed at the transition between the vortex mass and the unidirectional flow field,thus advancing the center of gravity of combustion and increasing the rate of heat release.And the peak pressure is increased by 25％,with an indicated thermal efficiency of more than 30％and low emissions of HC and CO.However,due to the larger peak in-cylinder temperature,it leads to an increase in NO emissions.
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