Combustion characteristics and flame-kernel development of a laser ignited hydrogen–air mixture in a constant volume combustion chamber

• Laser ignition of H2–air mixtures (λ = 2.0–5.0) was experimentally investigated.
• The flame kernel visualization was done by shadowgraphy.
• As λ increased, maximum chamber pressure and rate of pressure rise decreased.
• A number of wave fronts were seen in the toroidal surface of the laser ignited H2–air.
• Higher pulse energy led to higher flame speed but similar cylinder pressure.

Laser ignition of hydrogen–air mixture was carried out in a constant volume combustion chamber (CVCC) at 10 bar initial chamber filling pressure and 373 K chamber temperature. A Q-switched Nd:YAG laser at 1064 nm with a pulse duration of 6–9 ns was used for plasma generation and ignition of combustible hydrogen–air mixture. Pressure–time history of different hydrogen–air mixtures was measured in the CVCC and flammability limits of hydrogen–air mixture were measured. Flame kernel development was investigated for different air–fuel mixtures using Shawdowgraphy and flame propagation distances were calculated. Minimum ignition energy was measured for hydrogen–air mixtures of different air–fuel ratios and effect laser pulse energy on pressure–time history in the CVCC was experimentally measured. Upon increasing the laser pulse energy, time taken to attain peak cylinder pressure reduced which resulted in faster combustion in hydrogen–air mixtures however the peak cylinder pressure remained similar.