Stabilization Heights in Lifted Methane-Air Jet Diffusion Flames Diluted with Nitrogen

Measurements of stabilization heights in lifted turbulent methane-air jet diffusion flames are performed in order to test a theory on local quenching of diffusion flamelets. The global residence time d/u(0), (d the nozzle diameter, u(0) the nozzle exit velocity) is scaled with chi(q) the instantaneous scalar dissipation rate at quenching. This quantity had been identified before to be characteristic for the extinction of diffusion flamelets. Values for chi(q) are deduced from measurements of laminar diffusion flames in a counter flow geometry. The scaling is performed for constant values of Z(gt), the conserved scalar variable at stoichiometric conditions. Both the fuel and the air stream are diluted to obtain constant values of Z(qt). Scaling with chi(q) makes the curves for different residence times collapse into one curve with. however. considerable experimental scatter. From this is concluded that Z(q) is the essential kinetic parameter describing quenching effects in turbulent diffusion flames.