The current PDE facility has the capability of producing detonative environments, which are studied using sensors developed at Stanford's HTGL. Optical based diagnostic methods for measurement of gas temperature, velocity, and species, are being employed to investigate details of the combustion process.
As shown in the above figure, the engine consists of a 1.6 m tube which is closed at one end and open to the atmosphere at the other. The engine operates by injecting premixed fuel (ethylene) and oxygen near the closed end, and igniting it once the entire engine is filled. A detonation wave forms within the first 30 cm of the tube, which propagates at approximately 2400 m/s towards the open end. The high pressure formed at the closed end creates thrust, which would be used to propel a vehicle.
Measurement ports are located along the tube, spaced 10 cm apart. Each measurement port can accommodate an optical absorption probe (to measure temperature, burned gas velocity, or species concentration), a pressure transducer (to measure thrust), an ionization probe (used to measure detonation wave speed), or an ignition electrode. The open end can be replaced with various nozzles in order to investigate their impact on engine thrust, as well as chemical rates.
Optical based diagnostic methods are being employed to measure pertinant PDE performance parameters including temperature, pressure, species concentrations, burned gas velocity, and fuel concentration. These diagnostics provide important data for both PDE simulation validation and performance evaluation. These measurements present new challenges for diagnostic system designers. These diagnostics must resolve detonation events with microsecond time resolution and overcome challenging measurement environments which include strong flowfield emission, large pressure gradients inducing beam stearing, and mechanical vibration.
Stanford PDE facility shown above.