Mixture Preparation Effects on Distributed Combustion for Gas Turbine Application - Novel Combustion Concepts for Sustainable Energy Development - page 283

(a) PR (b) CA (c) NP0 (d) NP1 T (K)

Fig. 7 Temperature distribution at the air/fuel injection plane for the different cases

the mixture is essentially different. Temperature distribution for the air/fuel injec-
tion plane is shown in Fig. 7 . It can be seen that in case CA (see Fig. 7 b), there is a
rapid temperature increase at the center of the air/fuel jet. The temperature at the
center of the jet approaches 1,700 K which is relatively high as compared to the
surrounding jet

flow with a temperature of about 1,300 K. This rapid temperature
increase indicates that ignition occurs at this point, where the igniting mixture
consists of air and fuel with minimal amounts of hot and reactive gases. One should
note that, according to temperature plots, recirculated gases having a temperature of
about 2,000 K are separated from the ignition zone with cooler air jet (of about
1,300 K). Such oxygen-rich combustion, which fosters thermal NO production,
indicates lack of adequate mixing under this scenario. Consequently distributed
reaction requirements are not satis

fl

behavior that
should be avoided in combustors for near-zero emissions. A similar behavior can be
seen in case

ed leading to a “ diffusion fl ame ”

“ ”

but to a smaller extent (see Fig. 7 c), where combustion occurs
only between air and fuel without recirculated hot products. On the other hand,
temperature distribution for cases PR and NP1 (see Fig. 7 a, d) indicates that such
early ignition of only air and fuel does not exist.
Figure 8 shows the fuel jet decay for each of the cases discussed here. By
comparing methane decay plots with temperature plots, one can interpret the mixing
and ignition process. For case CA, the area at the jet center with high temperature
rise as shown in Fig. 7 b corresponds with methane depletion shown in Fig. 8 b. It is
to be noted that for premixed combustion, the plotted results are for fuel mixture
fraction relative to the inlet fuel mixture fraction.

NP0

(a) PR (b) CA (c) NP0 (d) NP1

Fig. 8 Methane mass fraction distribution at the air/fuel injection plane for the different cases