Exploring combustion characteristics of a novel micro combustor with a fan swirler for thermophotovoltaic system

초록

The combustion and thermal characteristics of non-premixed methane (CH4)-air flames in a swirl micro combustor are numerically investigated for potential use in a thermophotovoltaic (TPV) system. Swirling flows associated with methane-air combustion are simulated using a Reynolds stress model and detailed chemistry of GRI-Mech 3.0. The optimal condition for improved emission and combustion performance is established by taking into account six blade angles and three fuel-lean equivalence ratios, to consider among other geometric features of the fan swirler and operating conditions. The reactive swirling flows in a micro combustor with a fan swirler are modified by altering the blade angle (theta(b)). For theta(b) = 5 degrees, 10 degrees, and 15 degrees, the swirl micro combustor with a two-vortex structure exhibits a significant enhancement of the fuel-air mixing and thermal performance compared to no-swirl combustor. As theta(b) increases, inner vortices close to the fuel stream and outer vortices near the combustor wall behind the fan blades are developed according to the interaction of swirling flows and recirculating flows due to the blockage effect of the fan blades. For theta(b) = 15 degrees, the strong interaction between two vortex regions maximizes combustion efficiency. The combustion efficiency is highest at theta(b) = 15 degrees and lowest at theta(b) = 75 degrees. For three fuel-lean conditions of theta(b) = 15 degrees, the flame zone is enlarged towards the combustion chamber wall, resulting in a high and uniform wall temperature. The resulting radiant emitter efficiencies for a TPV system are increased by 28.3 %-35.1 % compared to that of the no-swirling micro combustor. The results indicate that the fan swirler has recirculation flows for the best emitter and combustion efficiency unlike vane-type swirlers.

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