Showing papers by "Walter F. O'Brien published in 1989"

Plasma torch igniter for scramjets

Abstract: A small, uncooled plasma torch was developed and used in combination with an injector designed to study ignition and flameholding in hydrogen-fueled supersonic flows. The plasma torch was operated on mixtures of hydrogen and argon with total flows of 10 to 70 scfh. 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 all injection was perpendicular to the Mach 2 stream. Both semi-freejet 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 flow conditions simulating a flight Mach number of 3.7. The total temperature required to autoignite the hydrogen fuel for this injector geometry was 2640 R. The injector configuration was shown to be a good flameholder over a wide range of total temperature. Spectroscopic measurements were used to verify the presence of air total temperatures below 1610 R.

Operating characteristics of a hydrogen-argon plasma torch for supersonic combustion applications

Abstract: The residence time of the combustible mixture in the combustion chamber of a scramjet engine is much less than the time normally required for complete combustion. Hydrogen and hydrocarbon fuels require an ignition source under conditions typically found in a scramjet combustor. Analytical studies indicate that the presence of hydrogen atoms should greatly reduce the ignition delay in this environment. Because hydrogen plasmas are prolific sources of hydrogen atoms, a low-power, uncooled hydrogen plasma torch has been built and tested to evaluate its potential as a possible flame holder for supersonic combustion. The torch was found to be unstable when operated on pure hydrogen; however, stable operation could be obtained by using argon as a body gas and mixing in the desired amount of hydrogen. The stability limits of the torch are delineated and its electrical and thermal behavior documented. An average torch thermal efficiency of around 88 percent is demonstrated.

Sensitivity Analysis and Optimum Design Method for Reduced Rotor–Stator–Strut Flow Interaction

Abstract: A potential flow model based on the Douglas–Neumann formulation that can handle interaction problems has been used to analyze the pressure distribution produced by a stator-strut system at the rotor trailing edge. A pressure disturbance sensitivity analysis of some stator and strut parameters was performed and results are discussed in both space and frequency domains. A method for pressure distribution optimization is presented and the outcome analyzed. The optimum stator-strut configuration brings about reduced potential flow disturbances. The pressure wave amplitude produced by the strut is lowered to the same order of magnitude as that induced by the stator alone.

Dynamic turbine blade temperature measurements

Abstract: Turbine blade surface temperatures were studied during transient operation in a turbofan engine test rig. A single fiber radiation pyrometer was used to view the suction side of the blades from approximately 60% axial chord to the trailing edge at an average radial location of 70% blade height. A single ceramic-coated blade produced a once-per-revolution signal that allowed for the tracking of individual blades during the transients. The investigation concentrated on the light-off starting transient and the transients obtained during accelerating and decelerating between power settings. During starting and acceleration transients, the blade surface temperature gradient was observed to reverse. This phenomenon was most apparent during starting when the trailing edge was initially much hotter than the 60% chord location, resulting in large temperature gradients. In steady operation, the trailing-edge temperature was lower than the 60% chord location, and the gradients were less severe. During deceleration transients, the trailing edge cooled more rapidly than the 60% chord location. This resulted in larger temperature gradients than were seen in steady operation, but no profile inversion was observed. These temperature gradients and profile inversions represent a cycling of thermally induced stresses which may contribute to low-cycle fatigue damage. A simple one-dimensional heat transfer model is presented as a means of explaining the different heating rates observed during the transients.