2017 Volume 59 Issue 190 Pages 312-326
In this study the possibility of ultra-lean combustion of methane-air tubular flames was investigated by numerical calculation with detailed chemistry, and the results were compared with counterflow twin flames. As a result, it was found that tubular flames can realize ultra-lean combustion since the radiative heat loss is much smaller than planar 1-D flames because of the smallness of the residence time of the burned gas, but the equivalence ratios of the leanest limits of tubular flames are larger than those of the counterflow twin flames of the similar stretch rates due to an intrinsic tendency of extinction based on the configuration of tubular flames. In addition, the possibility of ultra-dilute combustion of tubular flames of CO2 diluted methane and air was also investigated numerically. The obtained result showed that tubular flames can also realize ultra-dilution combustion, and the extent of dilutions at the largest dilution limits for tubular flames are smaller than those of counterflow twin flames of the similar stretch rate, due to the same reasons as the ultra-lean combustion case.
