Combustion and emission characteristics of laser-ignited pure methane in a rapid compression machine

In this study, effects of number of consecutive laser ignition pulses on combustion and particle emission characteristics of CH4/Air mixtures were investigated in a rapid compression machine (RCM) by using a passively Q-switched Nd:YAG laser ignitor. To that end, ignition kernel formation and flame evolution characteristics were analyzed with the instrumentality of a high-speed camera (Schlieren setup), while combustion and emission properties were examined by measuring pressure and particulate emissions, respectively. The variation of pressure was also recorded to calculate (with a MATLAB code) indicated work, indicated mean effective pressure and efficiency. Results of this study revealed the linear dependence of ignition possibility to the number of pulses. Ignition possibility increased with the increasing number of pulses. It was 72.72% at 1 pulse and became 92.10% at three pulses. However, number of pulses differently affected other measured or calculated parameters. Depending on the number of pulses, improvements and deteriorations were observed in performance metrics.