Numerical Study on the Stabilization of a Self-Sustaining Steady-State Premixed Cool Flame

Abstract

The unexpected finding of the quasi-steady state cool flame onboard the International Space Station motivated increasing interests to study the dynamic behaviors of cool flames. One key scientific question is how to form and stabilize a self-sustaining steady-state cool flame in a burner with well-defined boundary conditions. This paper numerically studied the stabilization of a self-sustaining steady-state premixed dimethyl ether/O2/N2 cool flame. The dual S-curve response in the perfectly-stirred reactor was first analyzed and the results indicated three ways to form a self-sustaining premixed cool flame: 1) igniting the unburned fresh mixture by decreasing the residence time, 2) igniting the unburned mixture by increasing the temperature of the unburned fresh mixture, and 3) extinguishing an extremely lean or an extremely rich hot flame by decreasing the residence time. Using the counterflow configuration, the proposed three ways were successfully demonstrated by tuning the flow temperature and stretch rate. Moreover, double structured flames, i.e., a leading premixed cool flame front followed by a premixed warm flame, were numerically reported in the counterflow flame configuration. The thermal and species structures of the double flames were also discussed.