Application of laser ignition to hydrogen-air mixtures at high pressures

To optimise combustion in a wide field of applications, lasers represent attractive future alternative ignition sources, especially for internal combustion engines. Experiments were carried out in a high pressure, constant volume chamber (up to 25MPa peak pressure and initial temperature of 473K). Laser induced ignition of different hydrogen-air mixtures (air/fuel equivalence ratio λ=1.8-8) was investigated, using different filling pressures (p=0.5-4.2MPa), different ignition energies (pulse energy PE=1-50mJ), different chamber temperatures (T=393-473K) and different focal length lenses (f=60, 120mm). A Q-switched Nd:YAG laser at 1064nm with a pulse duration of about 5ns was used for ignition. An InGaAs photodetector (800-1800nm) and a piezoelectric pressure transducer were used to characterise the combustion. Gas mixtures between λ=2.5 and 3.6 showed knocking combustions. With increasing initial pressures the minimum pulse energy was decreasing.