Real-Time Plume Velocity Measurement of Solid Propellant Rocket Motors Using TDLAS Technique

Accurate measurement of plume velocity plays an important role in investigation of rocket motors, and the plume velocity is an indicator of energy level of solid propellants. A method based on laser Doppler effect using tunable diode laser absorption spectroscopy (TDLAS) is employed in this study. The absorption spectrum of water vapor feature at 1391.7 nm is utilized to measure the plume velocity. Three solid propellants, double-base (DB), composite modified double-base (CMDB), and nitrate ester plasticized polyether (NEPE) i. e., are burned in a motor with an internal diameter of 50 mm and their plume velocities are measured with scanned-WMS-2f technique. Afterburning reactions in the plume are numerically simulated. The simulations can provide insight into the nuances in measured TDLAS results and give confidence in the result. The results show that TDLAS is a good method to measure plume velocity. The relative standard deviation of the measurements is less than 4 %. The difference between the measured velocity and the simulated one is less than 8.25 %. Additionally, it is found that NEPE has the largest plume velocity, and the velocity of DB is the lowest. Uncertainties of velocity measurement using TDLAS are analyzed. Measurement uncertainty comes from velocity non-uniformity in the direction perpendicular to the plume direction. Furthermore, it can be found that it is better to put the measurement position close to the nozzle exit to reduce measurement errors.