Numerical investigation of a novel micro combustor with double-cavity for micro-thermophotovoltaic system

Highlights: • Double-cavity micro combustor is presented and numerically investigated. • Outer wall temperature of double-cavity combustor is more uniform and higher than that of single-cavity combustor. • Usable radiation energy and radiation efficiency of double-cavity combustor are relatively higher in all studied cases. • The optimum cavity gap length is determined by inlet velocity. - Abstract: The micro combustor is a key component of a micro-thermophotovoltaic (TPV) system. In this study, a novel double-cavity micro combustor is proposed for a micro-TPV system. The thermal performance of the double-cavity micro combustor is numerically investigated. We found that the new combustor can obtain higher and more uniform temperature distribution along the wall because of the second high temperature zone formed in the downstream cavity at relatively high inlet velocity, which is desirable for the micro-TPV system. When the inlet velocity is 12 m/s and the H₂/air equivalence ratio is 0.3, the usable radiation energy is increased from 2.13 W for the single-cavity combustor to 2.59 W for the double-cavity combustor. The corresponding radiation efficiency increases from 1.25% to 1.53%. Meanwhile, the combustion characteristics of the two micro combustors are studied under different H₂/air equivalence ratios at a fixed inlet velocity. The usable radiation energy and radiation efficiency of the double-cavity combustor are higher than that of the single-cavity combustor, and both values increased by increasing equivalence ratio. Furthermore, the influence of cavity gap length between the two cavities is examined at different inlet velocities. Results show that the optimum cavity gap length is determined by inlet velocity.