Anchoring of premixed jet flames in vitiated crossflow with pulsed nanosecond spark discharge

Abstract

This paper deals with the effect of non-equilibrium plasma on the anchoring of a premixed jet flame in hot vitiated crossflow at atmospheric pressure. The turbulent vitiated crossflow was generated by an array of 4 ×4 premixed turbulent jet flames burning a lean mixture of air and natural gas at an equivalence ratio of 0.7 and a thermal power of 50 kW. The rich jet, with equivalence ratio jet varied between 1 and 3, was injected perpendicularly to the vitiated crossflow in a rectangular duct, with jet-to-crossflow momentum flux ratios ranging from 1 to 26. A nanosecond repetitively pulsed discharge was initiated in the vicinity of the windward side of the jet root. The effect of discharge power and repetition rate on the lift-off height of the flame is systematically analyzed for different combinations of jet equivalence ratio and momentum ratio. High speed chemiluminescence imaging of the flame and of the discharge shows that the initiation of the discharge on the windward side of the jet enhances the combustion chemistry, reducing the ignition time and the lift-off height of the flame. It is shown that the nanosecond repetitively pulsed discharges are able to maintain a robust anchoring of the flame for a wide range of operating conditions at relatively low electric power cost. Emission spectroscopy and OH-PLIF measurements were carried out to show that the plasma has both thermal and kinetic effects on flame anchoring respectively via intense localized heating of the mixture at temperatures exceeding 3000 K and via an intense production of OH radicals.