Laser and pre-chamber ignition, combustion and flame propagation characteristics of CH4/air mixtures in a constant volume combustion chamber

The most important stages determining the qualitative and quantitative characteristics of a combustion process are mixture preparation, ignition, combustion itself and pollutant emissions. Among these, the ignition phe-nomenon stands out in terms of ensuring a reliable operation under every working condition (which also affects subsequent stages). In this study, the influence of the properties and the type of the ignition source on com-bustion and flame propagation characteristics of methane/air mixtures were investigated by using a passively Q-switched Nd:YAG crystal laser and a pre-chamber ignitor in a constant volume combustion chamber. The number of consecutive pulses and the air-fuel-equivalence ratio are studied parameters. With the laser ignition system, it was possible to ignite fuel-air mixtures at very lean conditions. However, as flow conditions in the combustion chamber varied due to the protruding part of the pre-chamber ignitor, ignition possibility decreased and com-bustion metrics worsened. The number of pulses affected combustion parameters such as the ignition delay time, the combustion duration, the rate of pressure rise etc. in a non-monotonic manner. Deteriorations and im-provements on such parameters were detected depending on the air-fuel-equivalence ratio lambda.