Laser ignition of methane-air mixtures with a rapid compression machine

We present here a study of laser ignition in a rapid compression machine (RCM). Laser induced ignition of natural gas-air mixtures at various test conditions was investigated. An Nd:YAG laser (1064 nm, 12 ns pulse duration) was employed as the laser source. Methane-air mixtures ranging from stoichiometric conditions to equivalence ratio of 0.4 were ignited using the laser as part of a lean limit study where the fuel-energy was kept constant for all cases. A study of minimum laser spark energy (MSE) and minimum ignition energy (MIE) was also conducted. We show that both MSE and MIE exhibit a stochastic behavior and, as a consequence, results can only be interpreted statistically. For our conditions, we found MSE at 90 % probability of MSE₉₀=2.3 mJ. The MIE study was conducted at an equivalence ratio of φ=0.4 yielding an MIE (90% probability) of MIE₉₀=7.2 mJ.