The purpose of this study is to improve ignitability and combustion stability of CNG intermittent gas jet for gas-fuelled engines. The effect of spark position and H_2 addition on ignition and combustion of CNG was investigated by high-speed schlieren photography with the constant volume combustion chamber, burned gas measurement and analysis of gas flow employing laser sheet technique. It has been shown by the results that ignitability of CNG jet is improved by controlling jet velocity. Ignition near injector and at off-set position of jet axis is effective to reduce jet velocity and improve ignitability. H_2 addition improves stability of combustion.