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

Abstract

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 phenomenon 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 combustion 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 combustion 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 improvements on such parameters were detected depending on the air–fuel-equivalence ratio λ.