Effects of wall cooling with microchannels on swirl combustor performance

Microchannel cooling provides a potential idea for high-temperature rise combustor cooling design. The performance of the swirl combustor with a rectangular microchannel embedded inside its walls are experimentally investigated for the coolant Reynolds numbers ranging from 0 to 600. Furthermore, an analytical model of the interactions between microchannel cooling heat transfer and the combustion is established. The corresponding Reynolds average numerical simulation is performed and the realisable k-epsilon turbulence mode where the eddy-dissipation concept is adopted for the turbulence chemistry interactions with a 14-species 19-step methane/air reaction mechanism. The results show that the heat exchange capacity of the microchannel coolant, flame temperature, and NOx distributions are all piecewise functions of the coolant Reynolds number that flows through the microchannels. The wall temperature can quickly decrease by 55% at low Reynolds numbers while the outlet flame temperature decreases gently. The combustion reaction regions determined by the CH* chemiluminescence images and gained from the simulation maintain a V-shape under the same equivalent ratio regardless of the inlet Reynolds number, indicating the microchannel cooling has little effect on the main combustion zone. The experiments show the NOx emissions have fallen by more than 35% while the combustion efficiencies are maintained above 98%. Those results indicate the microchannel wall cooling can greatly reduce the wall temperature at low coolant Reynolds numbers to protect the combustor components and effectively reduce the NOx emissions, as the same time have a negligible impact on the main combustion zone. The simulation results match well with experiment for the structure of the swirling flame and the effects of microchannel cooling on the flame temperature, and the temperature distribution tendency is consistent with theoretical analysis. (C) 2020 Elsevier Masson SAS. All rights reserved.