Laser-Based Sensor for High-Speed Heat Release Rate Measurements

Physical Sciences Inc. (PSI) proposes an optical sensor to infer local heat release rates in a gas turbine engine augmentor via measurement of the major reactant concentrations (fuel and O2) and temperature. The sensor is based on recent advances in high-speed tunable diode laser spectroscopy techniques developed by PSI for automobile engine applications. The sensor uses a short-path fiber-coupled probe to resolve fuel and temperature fluctuations at ~1cm spatial scale and up to 7.5kHz continuous output bandwidth for all three parameters. The goal is to resolve heat release fluctuations at scales that can be correlated to problematic acoustic modes that are often generated via combustion instabilities. Phase I of the program will include an experimental investigation of jet fuel absorption characteristics in a vitiated air stream at afterburner temperatures and will demonstrate the ability to measure effective fuel vapor concentration and vapor temperature. The Phase I effort will also include the empirical and analytical construction of an algorithm to yield heat release rate from the measured parameters, as well as the designs of the probe and overall sensor architecture. Phase II will focus on the development and construction of the sensor system, concluding with its delivery to the Air Force.