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The low thermal performance of conventional micro-combustor (CMC) is one of the major obstacles hindering the development of micro-thermophotovoltaic (MTPV) system. In the present research, micro-combustor with conical ring (MCCR) is proposed to enhance the overall performance. A comparative study of the temperature field, pressure field, velocity field and combustion efficiency of the CMC and MCCR is conducted. The numerical results show that when the inlet velocity is 8 m/s, compared with the CMC, the mean outer wall temperature, combustion efficiency and pressure loss of the MCCR-6 increased by 32.3 K (2.6%), 0.05% and 718.6 Pa (273.4%), respectively, while the standard deviation of outer wall temperature decreased by 31.4 K (49.5%). Additionally, the MC made using SiC provides a better overall performance, the conical ring (CR) is installed at 6 mm from the step with better overall performance. • A conical ring insert combustor with premixed hydrogen/air combustion is developed. • The effect of conical ring mounting position and structural parameters on performance is investigated. • The velocity field, temperature field and pressure field are compared for different operating conditions. • How to enhance heat transfer performance of the MTPV system is investigated. • Developed combustor is of better potentiality for applications in MTPV system. [ABSTRACT FROM AUTHOR]

• A backward facing step and unique inlet shape are used in a micro combustors. • The non-premixed hydrogen/air combustors with catalyst segment are compared. • Key parameters affecting the performance of a non-premixed hydrogen/air combustors are summarized. In this work, a type of non-premixed hydrogen/air micro combustor is designed for the application of micro-thermophotovoltaic (MTPV) systems. The micro combustor is presented with a backward-facing step and unique inlet shape to enhance the mixing performance and flame stabilization. The combustion, flow, and heat transfer characteristics of non-premixed hydrogen/air combustion in micro combustors with/without catalyst segment are numerically investigated. The results indicate that the homogeneous reaction is obviously weakened in the catalytic combustor, but a higher and more uniform outer wall temperature is obtained, and the outer wall temperature difference can be decreased by up to 28%. The flow characteristics of gaseous mixture in the catalytic combustor are better than those in the non-catalytic combustor. When the inlet velocity is 10 m/s, the average flow velocity and pressure loss of the catalytic combustor are decreased by up to 5.6% and 250 Pa, respectively. Furthermore, the heat of reaction and total heat flux at the gas–solid interface of the catalytic combustor are obviously higher and lower than those of the non-catalytic combustor, and the outer wall heat loss ratio is increased by up to 0.59% when the inlet velocity is 10 m/s. All in all, it can be concluded that adopting catalytic combustion to the micro combustor is extremely suitable for the application of MTPV systems. [ABSTRACT FROM AUTHOR]

In order to strengthen the internal flow and heat transfer and increase the stability of the flame, various methods to improve combustion efficiency were proposed. In terms of spatial structure, the optimization methods are divided into two categories: insertion geometry and internal molding. Both of them change the combustion efficiency by affecting the flow and heat transfer, but the degree is different; for catalytic combustion, heat and mass transfer, heterogeneous/homogeneous reaction and other derivative processes are the key to improve the combustion efficiency; as for fuels, changing the type and mixing mode are effective means to improve combustion efficiency. In addition, the research on improvement of the energy conversion and emission performance of micro thermophotovoltaic(MTPV) system, micro thermoelectric(MTE) system and micro engine(ME) was reviewed. Compared with the existing research, it is found that the single optimization method has limitations, it cannot guarantee the positive effect under all operating conditions, the future research direction is to combine the advantages of a variety of optimization methods, besides, with the development and maturity of technology, the number of studies on diffusion combustion is increasing, and its practicability has been improved. Meanwhile, the further research and development of micro-energy mechanical system(MEMS) technology can be effectively promoted by the application of field synergy principle and Molecular Dynamics in numerical simulation. Based on this work, the research status of flow, heat transfer and performance improvement in combustion-based MEMS can be presented to relevant researchers more clearly. • Process in heat transfer performance improvement are summarized. • Process in micro combustion performance improvement are summarized. • Process in energy conversion performance improvement are summarized. • Future works for the performance improvement are introduced. [ABSTRACT FROM AUTHOR]