A new blowdown nonequilibrium plasma magnetohydrodynamic (MHD) supersonic wind tunnel operated at complete steady state has been developed and tested at Ohio State. The wind tunnel can be operated at Mach numbers up to M = 3-4 and mass flow rates of up to 45 g/s at a stagnation pressure of 1 atm. Pitot tube and schlieren measurements in a M = 3 test section showed reasonably good flow quality, up to 80% inviscid core across the larger dimension and up to 50% inviscid core across the smaller dimension of the flow. Stable and diffuse transverse rf discharges (rf power up to 1 kW) have been sustained in M = 3 nitrogen flows, at magnetic fields of up to B = 1.5 T. Operation at higher magnetic fields produced a more uniform rf plasma in the MHD test section. Hall parameter and electric conductivity of the flow have been inferred from the dc (MHD) current and voltage measurements at different values of the magnetic field. At B = 1.5 T and rf power of 500 W, the Hall parameter is β ∼ = 3 and the conductivity is σ ∼ = 0.05 mho/m. At the rf power of 1 kW, the extrapolated conductivity is ∼0.1 mho/m. The results of the present work demonstrate the Lorentz force effect on the supersonic boundary layer in M = 3 flows of nitrogen ionized by a high-power transverse rf discharge in the presence of the magnetic field. Boundary-layer density fluctuation spectra are measured using the laser-differential-interferometry diagnostics. In particular, decelerating Lorentz force applied to the flow produces a well-reproduced increase of the density fluctuation intensity by up to 10-20% (1-2 dB), compared to the accelerating force of the same magnitude applied to the same flow. The effect is produced for two possible combinations of the magnetic field and MHD current directions producing the same Lorentz force direction (both for accelerating and decelerating force). The effect is observed to increase with the flow conductivity. On the other hand, the effect of Joule heating on the density fluctuation spectra appears insignificant.
Results are presented of nonequilibrium rf plasma assisted combustion experiments in premixed air-fuel flows. The experiments have been conducted in methane-air, ethylene-air, and CO-air mixtures. The results show that large volume ignition by the uniform and diffuse rf plasma can be achieved at significantly higher flow velocities (up to u = 25 m/s) and lower pressures (P = 60-130 torr) compared to both a spark discharge and a dc arc discharge. The experiments also demonstrated flame stabilization by the rf plasma, without the use of any physical obstacle flameholders. Fourier transform infrared (FTIR) absorption spectra of combustion products show that a significant fraction of the fuel (up to 80%) burns in the test section. Temperature measurements in the diffuse rf discharge using FTIR emission spectra show that the flow temperature in the plasma before ignition (T = 250-550 • C at P = 60-120 torr) is considerably lower than the autoignition temperatures for ethylene-air mixtures at these pressures (T = 600-700 • C). Visible emission spectroscopy measurements in C 2 H 4-air flows in the rf discharge detected presence of radical species such as CH, C 2 , and OH, as well as O atoms. In CO-air flows, O and H atoms have been detected in the rf plasma region and CO 2 emission (carbon monoxide flame bands) in the flame downstream of the rf plasma.
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