Daisuke Shimokuri

Development of a small-scale power system with meso-scale vortex combustor and thermo-electric device

A small-scale vortex combustion power system has been developed using a thermo-electric device (TED). The system consisted of a heat medium, TED, and cooling plates. A vortex combustion chamber (7 mm inner diameter and 27 mm long) was fabricated inside the heat medium (40 × 40 × 20 mm and 52 g of duralumin). It was found that a stable propane/air flame could be established in the narrow 7 mm channel even for the large heat input conditions of 213 ~ 355 W. With a couple of TEDs, the maximum of 8.1 W (9.8 V × 0.83 A) could be successfully obtained for 355 W heat input, which corresponded to the energy conversion rate of 2.4%. The results of the gas and the combustor wall temperature measurements showed that the heat transfer from the burned gas to combustor wall was significantly enhanced by the vortex flow, which contributed to the relatively high efficiency energy conversion on the vortex combustion power system.

An Experimental Study on Methane/Oxygen-Air Combustion With a Rapidly Mixed Type Tubular Flame Burner

Methane/oxygen-air combustion has been attempted by using a rapidly mixed type tubular flame burner with four slits, from two of which a fuel is injected and from another two an oxidizer is injected. The oxygen concentration (molar) in the oxygen-air oxidizer has been varied from 21% (air) to 100% (pure oxygen). Results show that uniform tubular flame combustion can be obtained for a wide range of equivalence ratios, if the oxygen molar concentration in the oxygen-air oxidizer is less than about 50%. Above 50%, however, very intense turbulent combustion occurs frequently and the circular-shaped tubular flame is deformed as oval-shaped for most equivalence ratios. The uniform tubular flame range is reduced and quite limited in the vicinity of lean condition. Detailed observations show that for pure (or near pure) oxygen oxidizer, two diffusion flames are established between the fuel and oxidizer streams at the exits of the fuel slits, which prevents fuel from mixing with oxygen, resulting in a violent turbulent combustion downstream the slits. With use of a burner with smaller slit width, however, formation of the diffusion flame is inhibited and a uniform tubular flame can be established, although still limited close to the lean extinction limit. To fully understand the flame characteristics above, the burning velocities are calculated for various equivalence ratios as well as for various oxygen concentrations in the oxygen-air oxidizer using the CHEMKIN PREMIX code with the GRI kinetic mechanism.Copyright

Development of a portable power system with meso-scale vortex combustor and thermo-electric device

In this study, a small scale power generation system with a meso-scale vortex combustor has been developed. The system was consisted of a couple of thermo-electric device and a heat medium. The medium was made of duralumin, 40 × 40 × 20 mm and 52 g weight, and the vortex combustion chamber of 7 mm inner diameter was embedded in it. It was found that a stable flame could be established in the narrow 7 mm channel even the mean axial velocity reached 1.2 m/s. And furthermore, the vortex flow significantly enhanced the heat transfer from the burned gas to combustion chamber, and as a result, the medium was heated to 300°C quickly (within 5 minutes) by the combustion of propane / air mixture for 145W input energy. The system could successfully generate 1.98 W (4.3 V and 0.46 A), which corresponded to the energy conversion rate of 0.7 % per unit thermo-electric device.

Effects of the Air-Fuel Ejection Velocity Ratio on the Combustion Characteristics and the Unburned Gas Compositions of the Propane–Air Rapidly Mixed Tubular Flame Combustion

In this paper, effects of the difference between the air injection velocity and the fuel injection velocity on the rapidly mixed tubular flame have been investigated. A parameter of αst which is the ratio of the air injection velocity to the fuel injection velocity at stoichiometric condition has been introduced, and five tubular flame burners with different αst , 0.6, 1.2, 2.4, 6.0 and 11.9 were examined. Stability limits of the propane-air flame and the local fuel concentrations of unburned mixture have been determined. Results show that, with αst = 0.6 and αst = 1.2, in burner a stable tubular flame can be established in the range of Φ = 0.45 to 2.1 and Φ = 0.48 to 2.15. When αst is increased to 2.4, in which the air injection velocity is almost two times higher than that of the fuel at stoichiometric condition, the stable combustion range shifts to the relatively fuel rich side of Φ = 0.55 to 2.35. With further increase in the αst to 6.0 and 11.9, stable combustion range shifts to richer side of Φ = 0.6 to 2.45, and Φ = 0.7 to 2.9, respectively. Results of gas analysis have revealed that, for αst = 0.6 and αst = 1.2, although the total equivalence ratio of supplied air and fuel were stoichiometric, a fuel rich mixture gas of Φ = 1.13 and Φ = 1.17 was formed locally at the center of the burner. Increasing in the αst leads to a decrease in the local equivalence ratio, such as Φ = 0.95, 0.42, and 0.19 for αst = 2.4, 6.0 and 11.9, respectively. These results indicate that the mixing process of air and fuel in the rapidly mixed tubular flame is greatly affected by the injection velocity ratio, suggesting the possibility of the flame front structure control by the injection velocity ratio.Copyright