Optical diagnostics for cryogenic liquid propellants combustion

Detailed experimental studies of cryogenic propellant combustion are needed to improve design and optimization of high performance liquid rocket engines. A test facility called MASCOTTE has been built up by ONERA to study elementary processes (atomization, droplet vaporization. turbulent combustion...) that are involved in the combustion of liquid oxygen (LOX) and gaseous hydrogen (GH2). This article reports results from experiments carried-out on MASCOTTE under a consortium of laboratories and manufacturers associating ONERA, CNRS, CNES and SEP. on the jet flame issued from a single coaxial injector. This device fed with liquid oxygen and gaseous hydrogen is placed in a chamber equipped with quartz windows. The spray and the flame are observed with a set of optical methods : high speed cinematography. light emission from OH radicals, laser induced fluorescence of OH and O 2 , elastic scattering from the LOX jet. These techniques are used to obtain images of the spray and of the flame zone. It is then possible to deduce the flame location with respect to the liquid jet from simultaneous elastic scattering of the LOX jet and LIF of OH measurements or from average emission images treated with Abel's transform. The images obtained by exciting the fluorescence of O 2 provide complementary information on the flame shape and they may be used to estimate the local reaction rate. Quantitative temperature measurements based on Coherent Anti-Stokes Raman Scattering from H2 and LOX droplets size and velocity measurements by means of a Phase Doppler Particle Analyzer give additional clues on the spray and the combustion zone.