%0 Journal Article %A Singla, G. %A Souflaire, P. %A Rolon, Juan-Carlos %A Candel, Sebastien %D 2007 %I Begell House %K transcritical combustion, cryogenic flames, emission imaging, and spectroscopy %N 6 %P 733-748 %R 10.1615/IntJEnergeticMaterialsChemProp.v6.i6.50 %T FLAME STRUCTURE UNDER DOUBLY TRANSCRITICAL AND GASEOUS INJECTION CONDITIONS %U https://www.dl.begellhouse.com/journals/17bbb47e377ce023,46ae61aa3e0cddf4,14867a405e5d5131.html %V 6 %X Experiments on coaxial injection of transcritical reactants (liquid oxygen and methane injected at a temperature lower than the critical value, but at a pressure exceeding the critical pressure) indicate that the flame features a nonstandard structure with two light emission regions. The first is located close to the central oxidizer stream, while the second is established near the outer boundary of the fuel. To interpret this unusual result, experiments have been carried out in the same injection geometry, but with gaseous oxygen and methane at atmospheric pressure. This configuration is investigated using light emission and optical multi-channel spectroscopy. It is also found that emission originates from two layers. The inner layer close to the oxygen jet is due to OH* emission, while the outer layer corresponds to CH* and OH* radiation. It is concluded that the mechanisms leading to the double reactive layers in the transcritical and gaseous cases are of a different nature. In the former case, the inner layer corresponds to a flame formed by non-premixed reactants, while the outer layer is probably due to some initial mixing of the injected propellants. In the latter case, the flame is essentially controlled by staged combustion with an initial decomposition of the fuel followed by its oxidation. %8 2007-11-01