Comparative investigations of flame kernel development in a laser ignited hydrogen–air mixture and methane–air mixture
Abstract
Concerns about energy availability and pollutant emissions, such as oxides of nitrogen and particulates have driven concerted efforts toward the design of next generation internal combustion engines, capable of using newer fuels, delivering higher efficiencies and lowering emissions. Among various new engine designs and concepts, laser ignition is one of the promising approaches to attain these objectives. In this research, experimental investigations are carried out to study the laser ignition of hydrogen–air mixtures, which are compared with the baseline data of laser ignited methane–air mixtures. Experiments were carried out in a high pressure constant volume combustion chamber (CVCC) to investigate the flame kernel development and visualization, and flame speeds. The initial operating conditions of the experiments were set to 373 K chamber temperature and 10 bar chamber filling pressure. The flame kernel growth was investigated for different hydrogen–air mixture strengths ranging from λ = 2.0–5.0 and compared with the baseline of methane–air mixtures of λ = 1.2. A Q-switched Nd: YAG laser at 1064 nm wavelength with pulse duration of 6–9 ns was used for ignition by generating laser plasma inside the CVCC. The results indicate that the phenomenon of micro-explosions in the wave-front of hydrogen–air mixtures lead to significantly different flame front evolution and higher flame speeds compared to methane–air mixtures.