Flame kernel characterization of laser ignition of natural gas–air mixture in a constant volume combustion chamber

In this paper, laser-induced ignition was investigated for compressed natural gas–air mixtures. Experiments were performed in a constant volume combustion chamber, which simulate end of the compression stroke conditions of a SI engine. This chamber simulates the engine combustion chamber conditions except turbulence of air–fuel mixture. It has four optical windows at diametrically opposite locations, which are used for laser ignition and optical diagnostics simultaneously. All experiments were conducted at 10 bar chamber pressure and 373 K chamber temperature. Initial stage of combustion phenomena was visualized by employing Shadowgraphy technique using a high speed CMOS camera. Flame kernel development of the combustible fuel–air mixture was investigated under different relative air–fuel ratios (λ=1.2−1.7) and the images were interrogated for temporal propagation of flame front. Pressure-time history inside the combustion chamber was recorded and analyzed. This data is useful in characterizing the laser ignition of natural gas–air mixture and can be used in developing an appropriate laser ignition system for commercial use in SI engines.

► Laser-induced ignition was investigated for compressed natural gas–air mixtures.
► Q-switched Nd: YAG laser was used for the ignition of CNG–air mixture at the fundamental wavelength (1064 nm).
► Combustion was visualized by employing Shadowgraphy technique using a high speed CMOS camera.