The Experimental Study of the Autoignition Kernel Formation in a Jet

The non-premixed autoignition characteristic of a hot turbulent jet ejecting into the quiescent air was studied experimentally. The jet was the combustion product of fuel rich natural gas/air mixture burn in a thermally isolated combustion chamber. The combustion products discharge through a nozzle (13 and 20 mm in diameter) into the ambient air. The pre-chamber equivalence ratio, jet Reynolds number, and temperature are the governing parameters which are controlled by mass flow controller and thermocouples. The results of these experiments provide insight into the temporal and spatial non-premixed autoignition of the high-temperature combustible jet. Observations of ignition-flame formation –extinction behaviors of these jets are categorized into 1-no ignition 2- anchored diffusion flame 3- lifted diffusion flame 4- unstable diffusion flame 5- random autoignition kernel. The high-speed imaging helps to measure the location, lifetime and frequency of autoignition kernel using the in-house image processing developed code. Furthermore, the CH chemiluminescence imaging via an optical band-pass filter ensures that the jet composition is chemically quenched at the nozzle tip. The autoignition kernel can occur in radial and axial domain determined by the jet temperature and Reynolds number. The high-speed imaging shows that the most probable zone for autoignition kernel formation is on the jet axis and the jet Reynolds number has the major effect on axial distance. The jet temperature development merely extends this domain in the axial direction. Moreover, the temperature directly affects the lifetime and frequency of autoignition kernel.
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