Injection of liquid fuels in supersonic airstreams

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Virginia Polytechnic Institute and State University

An experimental study of the ignition of liquid fuels injected transverse to a hot supersonic (M=1.65) air stream was conducted. The liquids considered were kerosene, CS₂ and water as an inert control. The major variables were: air stagnation temperature in the range 1500 to 2300ºF, injectant flow rate and injection angles from 90º to 45º upstream. The experimental observations were: temperature measurements on the wall near the injector and in the flow downstream of injection self-luminosity photographs and infrared photographs taken with a Thermographic camera. Special attention was directed at the behavior of the liquid layer that had previously been found to form near the injector. No unequivocal evidence of ignition of either fuel was found for normal injection at these conditions. However, clear evidence of ignition of CS₂ was found for the upstream injection angle for To ≥ 2030°F and 80 ≤ Pj ≤ 135 psi. Higher injection pressures and thus high flow rates failed to produce ignition at any temperature tested. Evidence of CS₂ ignition was found in the infrared photographs and wall and in-stream temperature measurements simultaneously. The infrared photograph indicated possible ignition of the kerosene for upstream injection, but this could not be corroborated with the temperature measurements.