H. Xue

Microscale combustion research for application to micro thermophotovoltaic systems

Abstract A novel power MEMS concept, a micro thermophotovoltaic (TPV) system, is first described in this work, which would use hydrogen as fuel and would be capable of delivering 3–10 W electrical power in a package less than 1 cubic centimeter in volume. A microcombustor is one of the most important components of a micro TPV system. A high and uniform temperature distribution along the wall of the microcombustor is required to get a high electrical power output. However, sustaining combustion in a MEMS size combustor will be largely affected by the increased heat losses due to the high surface to volume ratio, which tends to suppress ignition and quench the reaction. In order to test the feasibility of combustion in microdevices and determine the relevant factors affecting microcombustion, numerical and experimental work was performed. The results indicated that a high and uniform temperature could be achieved along the wall of the flame tube.

A prototype microthermophotovoltaic power generator

A prototype microthermophotovoltaic (micro-TPV) power generator is described in this letter. The system is made of a SiC (silicon carbide) emitter, a simple nine-layer dielectric filter, and a GaSb (gallium antimony) photovoltaic cell array. In a microcombustor of 0.113 cm3 in volume, when the flow rate of hydrogen is 4.20 g/h, the micro-TPV system is able to deliver an electrical power output of 1.02 W, corresponding to an open-circuit electrical voltage of 2.28 V and a short-circuit current of 0.59 A. The prototype of the micro-TPV system will make it possible for us to substitute batteries with micropower generators in micromechanical devices in the near future.

Development of a prototype micro-thermophotovoltaic power generator

A prototype micro-thermophotovoltaic (micro-TPV) power generator is described in this paper. The system comprises a SiC emitter, a simple nine-layer dielectric filter and a GaSb PV cell array. When the flow rate of hydrogen is 4.20 g h−1 and the H2/air ratio is 0.9, the micro-TPV system is able to deliver an electrical power output of 0.92 W in a micro-combustor of 0.113 cm3 in volume. The open-circuit electrical voltage and short-circuit current are 2.32 V and 0.52 A, respectively. If we replace the GaSb PV cells with GaInAsSb PV cells, then an electrical power output of 1.45 W can be expected.

Micro combustion in sub-millimeter channels for novel modular thermophotovoltaic power generators

The performance of micro combustion-driven power systems is strongly influenced by the combustor structure. A novel modular thermophotovoltaic (TPV) power generator is presented, which is based on the sub-millimeter parallel plate combustor. It has the potential to achieve a high power density because of the high radiation energy per unit volume due to the high surface-to-volume ratio of the micro-combustor. The work experimentally investigated the ignition limitation for two micro-combustors. It also studied the effects of three major parameters on a sub-millimeter combustor, namely hydrogen to oxygen mixing ratio, hydrogen volumetric flow rate and nozzle geometry. The results show that the combustion efficiency decreases with the increase of the hydrogen flow rate, which is caused by reduced residence time. The average wall temperature with the rectangular nozzle is 25 K higher than that with the circle nozzle. The output electrical power and power density of the modular TPV power generator are projected to be 0.175 W and 0.0722 W cm−3 respectively. We experimentally achieve 0.166 W of electrical power, which is in good agreement with the model prediction.

Predicting the temperature of a premixed flame in a microcombustor

We apply the scale analysis and the simulation to relate the flame temperature in a microcombustor to the external wall surface temperature. In deriving the equation for predicting the flame temperature, we account for the detailed reaction mechanisms in the combustion process and we assume that the flow in the combustor tube is laminar. Experimental investigations have been conducted to validate the equation. We employ hydrogen as a fuel and obtain a stable flame in microcombustors with internal radii of 3, 4 and 6mm. Good agreement between the measured and the predicted flame temperature has been achieved. In predicting the flame temperature, we use a Nusselt number Nu=3.650 and 4.363 for the tube diameters of 6mm and above and 4mm and below, respectively.

Study of catalytic combustion and its effect on microthermophotovoltaic power generators

The demand for compact power sources with high energy density is increasing. A microthermophotovoltaic (micro-TPV) power generator is a renewable energy source with high power density and without moving parts. A thin layer of platinum was successfully deposited on the inner surface of the microcombustor as catalyst by reducing platinum from H2PtCl6, which is able to improve the flame structure in the microcombustor and increase the output power density of the micro-TPV system. The output electrical power of the system with platinum as catalyst is increased by 11–23.8% compared with that without platinum.

Effects of different parameters on the flow field of peripheral ported rotary engines

The performance of rotary engines is significantly influenced by the flow field. In this study, a detailed mathematical model was integrated into the simulation software FLUENT to investigate the gas flow field in a peripheral ported rotary engine by including a dynamic mesh model and a turbulent flow model. The models were also validated by experimental data. The basic flow mechanism in the combustion chamber was numerically studied. Meanwhile, the effects of the three major parameters on the flow field inside the combustion chamber, namely, rotating speed, intake shape, and intake angle, were also investigated. Results showed that a constantly changing swirl was formed in the combustion chamber during the intake and compression strokes as a result of the combined effects of the pocket of the rotor and the swirls in the combustion chamber. The swirl eventually broke into a unidirectional flow near the top dead center because of the significant decrease in combustion chamber volume. Furthermore, with the change in rotating speed, intake shape, and intake angle, significant differences in flow speed, inertia, and distribution were observed when the fluid entered the combustion chamber, which, in turn, led to obvious differences in the flow field, volume coefficient, and average turbulence kinetic energy in the combustion chamber.

Design Conceits and Testing of a Prototype Micro Thermophotovoltaic System

The design and testing of micro thermophotovoltaic (micro-TPV) system is described in this paper. The system is made of a SiC emitter, a dielectric filter and a GaSb photovoltaic cell array. The open-circuit voltage and short-circuit current can be measured by a multimeter, and the output power can be calculated. The effect of mass flux and the distance between the PV cell and outer wall of the combustor on the output power is also analyzed. When the flow rate of hydrogen is 4.133 g/hr and the H2/O2 ratio is 1.8, the micro-TPV system is able to deliver an electrical power output of 1.355W in a micro combustor of 0.195 cm3 in volume. The open-circuit electrical voltage and short-circuit current are 1.85 V and 1.032 amp respectively. This work makes it possible for us to replace batteries with micro-TPV systems as the power of micro mechanical devices in near future

Micro Combustion Research for Micro Thermophotovoltaic Systems

A research program is currently underway with the purpose of developing a novel, MEMS-sized thermophotovoltaic (TPV) system, which would use hydrogen as fuel and would be capable of delivering power on the order of watts in a package less than one cubic centimeter in volume. High surface to volume ratio is very favorable to the output power density per unit volume, though it tends to suppress ignition and quench the reaction in micro devices. This is the most attractive feature of micro TPV system. As part of an effort to develop such a micro power system, numerical and experimental works are carried to test feasibility of combustion in micro devices and determine relevant factors affecting micro combustion. Results indicate micro flame tube combustor is favorable in keeping the uniform of temperature along the wall, and stable combustion could be achieved in a tube with a sudden step within wider flow rate and wider hydrogen/air ratio than in straight tube. High and uniform temperature has been achieved along the wall of flame tube, which is very important to the efficiency of micro TPV system.Copyright