Measurement of OH density and gas temperature in incipient spark-ignited hydrogen–air flame

To investigate the electrostatic ignition of hydrogen–air mixtures, the density of OH radicals and the gas temperature are measured in an incipient spark-ignited hydrogen–air flame using laser-induced predissociation fluorescence (LIPF). The assessment of the electrostatic hazard of hydrogen is necessary for developing hydrogen-based energy systems in which hydrogen is used in fuel cells. The spark discharge occurs across a 2-mm gap with pulse duration approximately 10 ns. First, a hydrogen (50%)–air mixture is ignited by spark discharge with E=1.35EminE=1.35Emin, where E   is the spark energy and EminEmin is the minimum ignition energy. In this mixture, OH density decreases after spark discharge. It is 3×1016 cm−33×1016 cm−3 at t=0 μst=0 μs and 4×1015 cm−34×1015 cm−3 at t=100 μst=100 μs, where t   is the postdischarge time. On the other hand, the gas temperature increases after spark discharge. It is 900 K at t=30 μst=30 μs and 1400 K at t=200 μst=200 μs. Next, a stoichiometric (hydrogen (30%)–air) mixture is ignited by spark discharge with E=1.25EminE=1.25Emin. In this mixture, OH density is approximately constant at 4×1016 cm−34×1016 cm−3 for 150 μs after spark discharge, and the gas temperature increases from 1000 K (t=0 μst=0 μs) to 1800 K (t=150 μst=150 μs).