Measurement Science and Technology | 2021
Localized characteristic velocity (c*) for rocket combustion analysis based on gas temperature and composition via laser absorption spectroscopy
Abstract
In this work, a method for experimentally determining a local characteristic velocity, c∗ , is presented for purposes of analyzing rocket combustion progress based on in-situ laser absorption spectroscopy measurements of temperature and gas composition. Measuring c∗ from spatially-varying thermochemical properties provides an alternative to the classical c∗ evaluation, which uses global chamber pressure and mass flow rate measurements. Accordingly, the novel method provides more detailed insight to the underlying mechanisms (multi-phase thermochemistry, diffusive mixing, turbulence, etc) governing combustion performance in the spatial domain. The method is demonstrated on an RP-2/O2 liquid-propellant rocket engine (LRE) and a PMMA/O2 hybrid rocket combustion experiment. Localized c∗ results for the LRE are obtained via in-chamber measurements of temperature, CO, and CO2 and are presented over a range of pressures ( P= 28–83 bar) and mixture ratios (MR = 2.5–5). For the hybrid rocket combustion experiment, one-dimensional tomographic reconstruction techniques are used to spatially-resolve the flow-field thermochemistry and obtain spatially-resolved measurements of temperature, CO, CO2, and H2O. These measurements are compiled to obtain spatially-resolved c∗ images of the combustion zone. The c∗ results from both experiments are compared to the theoretical c∗ expected from chemical equilibrium, providing for a method to assess combustion performance or progress locally within the combustion zone.