抄録
This study tried to improve ignitability of intermittent CNG jet for gas-fuelled engines. Fundamental experiment was carried out using a constant volume combustion chamber. CNG was directly injected into the combustion chamber by a gas injector and the jet was ignited by a spark plug. The effect of injection control and spark position on ignition and combustion of CNG jet was investigated by high-speed schlieren photography, combustion pressure measurement, and analysis of gas flow employing laser sheet technique and numerical calculation. Results show that ignitability of CNG jet is improved by controlling jet velocity. Ignition near injector at jet boundary is effective to reduce jet velocity, resulting in improvement of ignitability. Multiple injection was applied to CNG jet combustion. At the multiple injection, CNG is ignited after the end of the first injection. The second injection supports the development of initial flame, and CNG is supplied to the flame during the third injection. Multistage injection is effective to reduce initial jet velocity and promote initial flame development, leading to high ignitability of CNG jet with high injection pressure. Moreover, when CNG jet is impinged to the spark plug, jet velocity is further reduced and flame development is also improved, which produces higher ignitability and prevents wall quenching.
