Experimental and numerical study of cap-like lean limit flames in H 2 -CH 4 -air mixtures
Hernandez Perez, Francisco
van Oijen, Jeroen A.
de Goey, Laurentius P.H.
KAUST DepartmentClean Combustion Research Center
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AbstractLean limit flames of H2-CH4-air mixtures stabilized inside a tube with an inner diameter of 30 mm in a downward flow are studied experimentally and numerically. A transition from bubble-like flames, with a long decaying skirt, to cap-like flames with a sharp visible flame edge at the bottom is observed as the lean flammability limit is approached. This transition is accompanied by formation of a secondary weak flame front inside the cap-like flame. The CH* chemiluminescence distribution of the studied flames is recorded and the velocity field of the lean limit flames is measured using Particle Image Velocimetry (PIV). The flame temperature field is measured utilizing the Rayleigh scattering method. Numerical prediction with a mixture-averaged transport model and skeletal mechanism for CH4 qualitatively reproduces the above experimentally observed phenomena. The presence of negative flame displacement speed for the entire leading edge of the cap-like flames is numerically predicted and experimentally demonstrated. The secondary weak flame front is located in a region with reverse upward flow of the recirculation zone, which is found to support the propagation of the leading edge with a negative flame displacement speed. Furthermore, radiative heat loss has a significant influence on the lean flammability limit of the cap-like flames.
CitationZhou Z, Shoshin Y, Hernández-Pérez FE, van Oijen JA, de Goey LPH (2018) Experimental and numerical study of cap-like lean limit flames in H 2 -CH 4 -air mixtures. Combustion and Flame 189: 212–224. Available: http://dx.doi.org/10.1016/j.combustflame.2017.10.031.
SponsorsThe financial support of the Dutch Technology Foundation (STW), Project 13549, is gratefully acknowledged. The authors thank Prof. Clinton Groth for providing access to the CFFC (Computational Framework for Fluids and Combustion) code.
JournalCombustion and Flame