Abstract
The behaviour of methane jet flames autoigniting in a turbulent cross-flow at MILD combustion conditions was examined experimentally. The methane jet was injected orthogonally into a turbulent, low oxygen (XO2x<8%) cross-flow at high temperatures in a cylindrical quartz tube. Regardless of cross-flow conditions, the methane jet autoignited and a flame was stabilized in a wide region clearly separated from the injection nozzle. OH∗ chemiluminescence images show that OH∗ intensity was not significantly diminished by changing XO2x, but the size of the reacting region, as well as its location, was noticeably sensitive to XO2x. Cross-flows enriched with additional air sustained methane jet flames with larger reactive regions than those diluted with N2 or composed of pure hot products. Additional cross-flow dilution with N2 shifted the reaction further downstream, an observation supported by the imaging of individual autoignition kernels. Mean OH-PLIF shows OH radical presence in areas devoid of heat release, as indicated by the time-averaged OH∗ chemiluminescence images. In all cases, OH-PLIF instantaneous images show regions with wide OH distributions, but sharp gradients, similar to those evident in traditional combustion regimes. The data interpretation is supported by laminar non-premixed flame calculations that demonstrate some differences and similarities between MILD and conventional flames.
Published Version
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