Combustion initiation in non-premixed high-speed flow by long-spark discharge

Summary form only given. A subject of consideration is the dynamic of filamentary pulse discharge generated along contact zone of two co-flown gases. Experimental facility consists of blow-down wind tunnel PWT-50, system of the high-voltage pulse-repetitive feeding, and diagnostic equipment (schlieren device; pressure, voltage, current, radiation sensors; spectroscopic system; etc.) Typical parameters: p=0.2-1 bar, velocity M=0-2, pulse duration t=0.1-1 mus, power release W=20-100 MW. Recently the effect of enormously fast turbulent expansion of the post-discharge channel was observed experimentally. In this paper a result of parametrical study of the mixing efficiency due to instability development are discussed. The next announced item is that the discharge position and dynamics depend on the test parameters and physical properties of gases involved. The next problem encountered, particularly, in modeling plasma of inflammable gases is the necessity to combine approaches of high non-thermal plasma kinetics and of classic thermal combustion. Such unification was made by the authors who showed numerically that for plasma ignition of ethylene-air mixture within a reasonable length of a supersonic flow rather high energy input per mass of gas flow is required (about 210 J/g). We anticipate that usage of non-uniform (filamentary) plasma may accelerate essentially ignition of premixed fuel-air flows. To examine this assumption the model was developed for burning initiation by a series of periodically positioned transverse streamer-like discharges in approximation of distributed mixing of excited and non-excited gas streams. The model includes simulations of the discharge of a small radius in supersonic flow of ethylene-dry air mixture with followed gradual mixing of excited gas with main flow. At mixing time t(mix)=100 and t(mix) =500 mus the required reduced energy input is about 40 J/g, that is remarkably lower than for uniform discharge.