The effect of the degree of premixing between fuel and oxidizer mixture on combustion efficiency over a range of equivalence ratio (0.7, 0.8, 0.9 and 1.0) and combustor pressure (3.04, 4.05 and 6.08 bar) is investigated for highly (70% by volume) diluted CO 2 oxy-fuel (CH 4 /CO 2 /O 2 ) flames and CH 4 /Air flames. A micromixer combustor where the degree of premixing can be varied by changing fuel injection location in the micromixer is used. For both CH 4 /CO 2 /O 2 and CH 4 /Air flames, the combustion efficiency in general increases as the equivalence ratio or combustor pressure increases when other flow parameters are fixed. However, for fixed operating conditions, the combustion efficiency for CH 4 /Air flames is consistently higher than for CH 4 /CO 2 /O 2 flames. The degree of premixing between fuel and CO 2 /O 2 mixture is found to be a key parameter in determining combustion efficiency for highly CO 2 -diluted CH 4 /CO 2 /O 2 flames while for CH 4 /Air flames the degree of premixing does not affect the combustion efficiency as much. The combustion efficiency gain for CH 4 /CO 2 /O 2 flames decreases as the non-uniformity factor increases, indicating enhanced premixing between fuel and oxidizer promotes more efficient combustion process. The combustion efficiency generally increases with combustor pressure when other operating parameters are fixed for both CH 4 /CO 2 /O 2 and CH 4 /Air flames. However, the CH 4 /CO 2 /O 2 flames exhibit higher efficiency gain with respect to the increase of combustor pressure than the CH 4 /Air flames.
Jeon et al. (Thu,) studied this question.