Combustion and Flame, Vol.199, 352-364, 2019
The effects of cross-flow fuel injection on the reacting jet in vitiated cross-flow
The effects of cross-flow fuel injection on a slotted jet flame consisting of an ethylene-air premixture are investigated experimentally. Cross-flow conditions of 9001< and 100m/s were chosen to closely simulate the environment of a secondary combustor in a staged combustion system. It was found that increasing the cross-flow equivalence ratio (Phi(infinity)) requires a consequent reduction in the jet equivalence ratio (Phi(j)) for jet flame stabilization in order to avoid the formation of locally rich mixtures beyond the flammability limits of the flame. Stable flames were achieved for a low cross-flow equivalence ratio of Phi(infinity) = 0.4 across a range of jet equivalence ratio values and momentum flux ratios, demonstrating the ability of the transverse jet to extend the flammability limits of the cross-flow mixture. Significantly, as Phi(infinity) is increased beyond a certain point, no ethylene is required to be present in the jet mixture, and a jet consisting only of air is able to stabilize the flame. Due to the fluidic nature of the flame stabilization mechanism of these flames, they are dubbed fluidically stabilized flames (FSF). OH* chemiluminescence and high-speed particle image velocimetry were utilized to gain deeper understanding of the flame behavior and flow field features of the FSF. In contrast to bluff-body stabilized flames, it was found that the FSF provides increased control of the flame shape, with increasing flame width and penetration for higher jet momentum flux ratios (J). The FSF was also demonstrated to be a highly dynamical phenomenon, characterized by a dominant peak frequency that is dependent on both Phi(j) and Phi(infinity). Proper orthogonal decomposition of the time-resolved velocity fields shows that heat release affects the dynamics of the FSF in a similar manner to the reacting jet in cross-flow (RjICF), as demonstrated in a previous study. Finally, the flame behavior was found to be highly dependent on the cross-flow fueling mechanism, with coherent flame oscillations present when the fuel injection point is closely-coupled to the flame stabilization location. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.