A small, uncooled plasma torch was developed and used in combination with a novel injector design to study ignition and flameholding in hydrogen-fueled supersonic flows. The plasma torch was operated with mixtures of hydrogen and argon at total flows of 4.7 x 10 3 to 3.30 x 10 4 seem. The fuel injector design consisted of five small upstream pilot fuel injectors, a rearward-facing step for recirculation, and three main fuel injectors downstream of the step. The plasma torch was located in the recirculation region and aU injection was perpendicular to the Mach 2 stream. The combustion tests were conducted in a direct-connect mode at simulated scramjet combustor conditions of Mach 2, total temperatures of 780-1560 K, and a static pressure of 101 kPa. Both semifreejet and ducted tests were conducted. The experimental results indicate that a low-power plasma torch operating on a 1:1 volumetric mixture of hydrogen and argon and located in the recirculation zone fueled by the upstream pilot fuel injectors is a good igniter for the flow conditions simulating a flight Mach number of 3.7 (T t , total temperature of the air = 780 K). The total temperature required to autoignite the hydrogen fuel for this injector geometry was 1470 K. The new injector configuration was shown to be a good flameholder over a wide range of total temperatures. Spectroscopic measurements were used to verify the presence of hydrogen atoms in the torch exhaust. Hydrogen atoms appear to be responsible for ignition at air total temperatures below 890 K. This observation is based on the results of the spectroscopic tests and the fact that a 100% argon plasma with the same power input did not ignite the flow at these temperatures.
A computational study of a scramjet combustor with swept ramp fuel injectors was conducted with the SPARK Navier -Stokes computer code. Turbulence was modeled with a two-zone algebraic turbulence model, while combustion was modeled with two nite rate H 2 -air chemistry models. The calculated reacting ow eld was mixing-limited. However, the extent of mixing was affected by the chemical reactions. Heat release from the chemical reactions signi cantly reduced the mixing between the fuel and airstreams. Comparisons between the calculations and experimental measurements of the wall pressure, surface heat ux, in-stream pitot pressure, as well as Mie scattering ow visualization were made and good overall agreement was observed. Nomenclature b j A T j = Arrhenius pre-exponential factor for the jth reaction c m T = eddy viscosity constant D = Damkohler number F = force G = gap, equals twice the duct height, 7.62 cm k f j = reaction rate coef cient for the jth reaction M = Mach number p = pressure T = temperature T a j = activation temperature for the jth reaction u = velocity component in the x direction V i = diffusion velocity of species i in the x direction w Ç i = chemical production rate of species i x, y, z = Cartesian coordinates P Y H O 2 = mass fraction of water caused by combustion I Z H = mass fraction of elemental hydrogen originating in the fuel jet Dt = time step ri = density of species i
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