Laser ignition and flameholding characteristics in supersonic airstreams

CFD simulations on effects of a focused laser pulse for combustion enhancement characteristics were conducted for supersonic airstreams with a transverse hydrogen-fuel injection. In order to estimate behaviors of a laser-induced plasma, temporal variations of its emission, and laser absorption processes were measured with photodiodes. From these measurements, characteristic time scales of the absorption process of an incident laser pulse and a plasma formation process were estimated. Numerical simulations using a time-dependent Navier-Stokes equation with finite-rate chemistry were also conducted to elucidate laser-induced ignition and mixing enhancement characteristics in supersonic airstreams with a transverse hydrogen injection. From the results, it was confirmed that, depending on the laser energy density and focal points, radicals, a shock wave, and shock-induced local turbulences were being formed through the laser irradiaton. Then recirculation zones with flamelets were induced. Moreover it was shown that these flamelets were growing in moving upstream and downstream from the focal point up to 1 msec. Consequently, it was shown that laser-induced plasmas could be effective in both combustion reaction and mixing enhancements for the supersonic combustion.