The stabilization characteristics and local extinction structures of partially premixed methane/air flames were studied using simultaneous OH-PLIF/PIV techniques, and large eddy simulations employing a two-scalar flamelet model. Partial premixing was made in a mixing chamber comprised of two concentric tubes, where the degree of partial premixing of fuel and air was controlled by varying the mixing length of the chamber. At the exit of the mixing chamber a cone was mounted to stabilize the flames at high turbulence intensities. The stability regime of flames was determined for different degree of partial premixing and Reynolds numbers. It was found that in general partially premixed flames at low Reynolds numbers become more stable when the level of partial premixing of air to the fuel stream decreases. At high Reynolds numbers, for the presently studied burner configuration there is an optimal partial premixing level of air to the fuel stream at which the flame is most stable. OH-PLIF images revealed that for the stable flames not very close to the blowout regime, significant local extinction holes appear already. By increasing premixing air to fuel stream successively, local extinction holes grow in size leading to eventual flame blowout. Local flame extinction was found to frequently attain to locations where locally high velocity flows impinging to the flame. The local flame extinction poses a future challenge for model simulations and the present flames provide a possible test case for such study.
Bibliographical noteFunding Information:
Acknowledgements This work was partly sponsored by the Swedish Research Council VR, SSF and STEM through CeCOST and the Swedish International Development Agency (SIDA) fund for the MENA countries through the joint project between Egypt and Sweden, and partly sponsored by China Natural Science Foundation (grant no. 50428605) and CSC (China Scholarship Council).
- Flame holes
- Flame stabilization
- Local quenching
- Partially premixed flames
ASJC Scopus subject areas
- General Chemical Engineering
- General Physics and Astronomy
- Physical and Theoretical Chemistry