Monitoring and control of a pulse detonation engine using a diode-laser fuel concentration and temperature sensor

Fuel measurements are needed to accurately tailor fuel charges in pulse detonation engines (PDEs) to improve engine performance and to validate PDE models and computations. Here, we report simultaneous concentration and temperature measurements of C2H4 fuel in a PDE using a newly developed diode-laser absorption sensor. These measurements enable characterization of the fuel loading and ignition timing of the engine. Based on these characterizations, a real-time control system that optimizes fuel consumption and maximizes specific impulse in the engine has been realized. Similar measurements Of C2H4 concentration and temperature were used to characterize pulse-to-pulse interference resulting from loading fresh fuel/oxygen reactants into hot combustion products. The sensor was used in a simple control scheme to minimize such interference, illustrating its potential role in control systems to maximize the engine's operation rate. During these studies, the sensor demonstrated two valuable improvements over traditional absorption spectroscopic techniques: (1) increased robustness and accuracy and (2) simultaneous measurements of concentration and temperature. These improvements are enabled by broad wavelength scanning of the Q-branch spectra Of C2H4 near 1.62 mum. The success achieved in these small-scale tests provides strong support for expanded use of diode-laser sensors in propulsion applications.