Experimental observation of lean flammability limits using turbulent jet ignition with auxiliary hydrogen and methane in pre-chamber

The combustion characteristics of CH4-air mixture under the lean-fuel conditions ignited by different methods including SI, unfueled pre-chamber ignition and fueled pre-chamber ignition were investigated experimentally in a constant volume combustion chamber (CVCC) through high-speed schlieren photography. And a self-designed fueled pre-chamber turbulent jet ignition (TJI) combustion system with a single orifice configuration and small volume was employed. Results show that TJI could enhance combustion including the rapid increases of flame tip velocity and flame area growth rate, which also was manifested by increasing peak pressure and shortening time to peak. The pre-chamber ignition fueled with hydrogen can greatly extend the lean flammability limit in the main chamber and reduce the sensitivity of flame development with the excess air coefficient. However, the oscillations in flame propagation and pressure evolution due to the flame-shock interaction were obvious under the pre-chamber fueled with hydrogen. Overall, in the present work, the turbulent flame development in the main chamber depends on the flame consumption velocity in pre-chamber, orifice size of pre-chamber, and the mixture concentration in main chamber. These results are of great help to achieve the highly-efficient combustion and to shorten the combustion duration in practical SI engines.