Experimental and numerical studies on the effect of spark ignition engine fueled with different fractions of CNG-CO2-H-2 blend were conducted. The results show that with the increase of CO2 fraction, the effect of vortex on the flame wrinkle is weakened, and the flame development period increases. With the increase of the volume fraction of hydrogen in the mixture, the flame development period shortens and the flame instability trend increases. With the increase of engine speed, the turbulence intensity in the cylinder increases. The different ignition positions have great influence on the development form and combustion efficiency of the flame surface. The reasonable selection of ignition position will be beneficial to optimize and improve the performance of the whole machine. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.