This paper describes an experimental investigation using an array of high-frequency pressure transducers located in the isolator/combustor region of a direct-connect hydrocarbon-fueled, scramjet combustor. Isolator/combustor entrance conditions were fixed and representative of a Mach-5.5 flight condition. Mean, standard deviation, and spectral content of measured pressures were similar to those measured in previous studies. A simple model relating the sum of measured pressures and the fuel flow rate delivered to the primary injectors was developed. Pressure measurements were post-processed and evaluated for use in a shock-position-control sensor to detect engine unstart. Four methods of post-processing the pressure data and corresponding detection criteria were evaluated: a) 150% pressure rise, b) 150% increase in standard deviation, c) 150% increase in power spectral density (PSD), and d) summation of pressures. Pressure summation typically provided 1-2 s more lead time in detecting unstart then any other method.

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