The use of a plasma jet for flame stabilization and promotion of combustion in supersonic air flows

Abstract The feasibility of the use of a plasma jet was investigated for the improvement of flame stabilization and the promotion of combustion of a fuel jet injected into supersonic air streams. Fuel gas (hydrogen) was injected transversely into supersonic air streams of M = 2.1 or 2.7 ( P s = 1.0 atm), with the pressure ratio P t,i P s = 16 , and the plasma (hydrogen, nitrogen, or argon) produced by a plasma jet was injected at 25 mm downstream from the fuel injector in most cases. The onset and spread of combustion and its influence on the flow field were investigated by the schlieren method and direct photography, and also by measurements of temperature and pressure in the reacting gas stream. It was shown that the injection of plasma, which is produced with relatively small electrical power, is very effective for flame stabilization and promotion of combustion, when the position of injection is adequate. For example, in the supersonic air stream of M = 2.1 with very low static temperature ( T s = 154°K), the progress of combustion of more than 68% was observed with the aid of hydrogen plasma jet operated by 4.7-kW electrical-power expenditure (∼2% of chemical energy throughput), at the cross section 10 cm downstream from the injection port of the plasma jet. It was also shown that the effectiveness of nitrogen plasma on the promotion of combustion is nearly equal to that of hydrogen plasma, although, in the valuation based on input electrical power, the nitrogen plasma jet is superior to the hydrogen plasma jet.