Localized characteristic velocity (c*) for rocket combustion analysis based on gas temperature and composition via laser absorption spectroscopy
Fabio A. Bendana, Isabelle C. Sanders, Nora Stacy, R. Mitchell Spearrin
Abstract
Abstract In this work, a method for experimentally determining a local characteristic velocity, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mi>c</mml:mi> <mml:mo>∗</mml:mo> </mml:msup> </mml:math> , is presented for purposes of analyzing rocket combustion progress based on in-situ laser absorption spectroscopy measurements of temperature and gas composition. Measuring <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mi>c</mml:mi> <mml:mo>∗</mml:mo> </mml:msup> </mml:math> from spatially-varying thermochemical properties provides an alternative to the classical <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mi>c</mml:mi> <mml:mo>∗</mml:mo> </mml:msup> </mml:math> 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/O 2 liquid-propellant rocket engine (LRE) and a PMMA/O 2 hybrid rocket combustion experiment. Localized <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mi>c</mml:mi> <mml:mo>∗</mml:mo> </mml:msup> </mml:math> results for the LRE are obtained via in-chamber measurements of temperature, CO, and CO 2 and are presented over a range of pressures ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>P</mml:mi> <mml:mo>=</mml:mo> </mml:math> 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, CO 2 , and H 2 O. These measurements are compiled to obtain spatially-resolved <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mi>c</mml:mi> <mml:mo>∗</mml:mo> </mml:msup> </mml:math> images of the combustion zone. The <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mi>c</mml:mi> <mml:mo>∗</mml:mo> </mml:msup> </mml:math> results from both experiments are compared to the theoretical <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mi>c</mml:mi> <mml:mo>∗</mml:mo> </mml:msup> </mml:math> expected from chemical equilibrium, providing for a method to assess combustion performance or progress locally within the combustion zone.