The stabilization characteristics of turbulent lifted diffusion flames of CH4/CO blended fuels

Abstract

The outstanding stabilization characteristics of lifted turbulent jet diffusion flames of CH4/CO blended fuels in still air were investigated experimentally by igniting the flame from downstream in the initial condition of a nonreacting fuel jet. In this study, we concentrated on the effects of the shift of outstanding reaction paths on the stabilization characteristics as the composition of the blended CH4/CO is varied. Systematic experiments were conducted using the nonintrusive diagnostics of shuttered laser particle image velocimetry (PIV), OH∗ chemiluminescence, and digital image processing to study the flame stabilization characteristics in terms of the key parameters such as the instantaneous flame-base location, lift-off height, and streamline velocity distribution in the vicinity of the edge flame leading point by varying the exit velocity and blended-fuel concentration. A conditional leading point from shutter PIV measurement is defined to calculate the instantaneous streamline velocity profile at the flame base. For the CO concentration in fuel blends lower than 80%, the stabilization is similar in characteristics to that proposed by the triple flame model. As the CO concentration is increased to 90%, the flame stabilizes on the fuel-rich side and the stabilization characteristics may be related to the maximum burning velocity at the rich equivalence ratio. This is confirmed by the location of the instantaneous flame stabilization point defined by the instantaneous leading point of the lifted flame with respect to the fuel concentration profiles.