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Performance of self-sustaining methanol auto-thermal reforming (ATR) was investigated experimentally in order to elucidate a reforming reaction mechanism and a condition required for high purity H2 production for compact reformer. The reformer consists of vaporizing and reforming sections in a single unit. The exothermic oxidation and endothermic steam reforming (STR) take place simultaneously in the reforming section. The reforming section is surrounded by the vaporizing section and then the heat for vaporization is supplied from the reforming section. Two types of exothermic oxidation reaction were investigated as the heat source for STR; one is a partial oxidation (POX) and the other is a total oxidation (TOX). CuO/ZnO/Al2O3 catalyst and Pt/Al2O3 catalyst were used for STR and POX, respectively. While, only CuO/ZnO/Al2O3 catalyst was needed for TOX because TOX took place when fuel and oxygen were supplied to the CuO/ZnO/Al2O3 catalyst. Experiments were investigated in the range of oxygen/carbon ratio (O/C ratio) 0.1-1.5, steam/carbon ratio (S/C ratio) 1.0-3.0 and N2 mole ratio 79-50 % in oxidizer. The results showed that the H2 formation reached maximum at around O/C=0.4 in both STR/POX and STR/TOX cases in the present study. When O/C ratio is decreased from 0.4, heat formation by the oxidation reactions decreases and is insufficient to reform residual CH3OH by STR. As a result, H2 formation and the methanol conversion ratio decrease. When O/C ratio is increased from 0.4, the H2 formation decreases, because methanol is consumed with the excess O2 by TOX and CH3OH for STR decreases. After all, O/C=0.4 gives an appropriate balance of heat supply and methanol for H2 production. These results elucidate that the reaction rate of oxidation reactions, POX and TOX, is much faster than that of STR. In other words, methanol is first consumed by the oxidation reaction and the residual methanol is used for STR. For S/C ratio, H2 formation is decreased in the higher S/C ratio. N2 mole ratio in oxidizer has few influence over the reforming gas. The chemical equilibrium calculations support the experimental results.

The performance of high purity hydrogen production from methanol for a compact steam reformer with a hydrogen purification membrane was investigated experimentally. A 77 wt.% Pd/23 wt.% Ag membrane with 25µm thickness and CuO/ZnO/ Al2 O3 catalyst were used. Heating was performed by a Bunsen type burner using City Gas 13A. The methanol reforming and purification of H2 were investigated at different reference catalyst zone temperatures (589-689K), pressures at the retentate side (0.2-0.5MPa), steam to methanol(S/C) ratios (0.8-1.6) and reactant flow rates (1.7×10-4 to 4.4×10-4 mol/s). The results show that at high reference temperature, high pressure and certain points of the reactant flow rate, the maximum hydrogen permeation rate is obtained when the S/C ratio is around 1. The modified Sieverts’ equation which considers the decrease in H2 concentration at the membrane surface, was proposed. The experimental result was lower than the permeation rate estimated by the modified Sieverts’ equation, which is probably caused by the adsorption of non-H2 species during permeation. It is further demonstrated that the modified Sieverts’ equation is able to estimate a more reasonable hydrogen permeation rate in comparison to the estimation by the ordinary Sieverts’ equation. In addition, it is shown that the compact methanol steam reformer with a Pd/Ag membrane is able to produce high purity hydrogen with very low CO concentration, which fulfills the Polymer Electrolyte Fuel Cell (PEFC) requirement (

Responses of the premixed methane/air mixture flames under equivalence ratio oscillations were numerically investigated assuming axi-symmetric stagnation flow fields. The flame motion was numerically investigated at three different oscillation frequencies (10, 20 and 50 Hz) and with three oscillation cases namely: lean case, rich case and lean rich crossover case. Methane/air mixture with equivalence ratio oscillation was issued from the burner exit with 1.0 m/s uniform velocity profile. The effects of frequency and amplitude of the equivalence ratio oscillation were discussed. The amplitude of the equivalence ratio oscillation is attenuated between the burner exit and the upstream edge of the preheat zone. The attenuation is much significant for higher frequency. The amplitude of the flame temperature oscillation attenuates following the attenuation of the equivalence ratio oscillation. The flame location makes the closed cycle around the flame location of correspond equivalence ratio in the steady state condition. The formation of the cycle can be explained by the back support effect. It was further demonstrated that, the back support effect influences the dynamic response of the flame location, in that, the direction of the cycles of the dynamic response in the lean case and the rich case are different. Furthermore, the time variation of the flame location plays a significant effect to the flame displacement speed.

Stabilizing mechanism of a methane-air edge flame that is a partially premixed flame, is investigated experimentally using the axisymmetric wall jet burner. Measurements of stability limits, flame locations and velocity fields with PIV, and visualization of themal boundary layer around of the edge flame have been performed. As a result, it is found that Peclet number Pe, which is expressed as Pe= Ut× pe/D, where Ut is tangential velocity toward the edge flame, Pe is curvature radius of thermal boundary layer of the edge flame and D is mass diffusivity, shows constant value at stability limits. The Pe physically means the ratio between partially premixing time to form flammable mixing layer and residential time of a fluid element in partially premixing region. Therefore, the result obviously indicates that the edge flame's stability is determined due to the balance between the partially premixing time and the residential time in partially premixed region. Thus, it is clear that a partially premixing, which is absent in a pure premixed flame, is important for stabilizing mechanism of the edge flame in the wall jet.

The relation between blowoff characteristics of the edge flame in a methane-air diffusion flame and its flame structure has been investigated by using our original burner. The burner can form an edge flame without premixed flame, as a hole, in the stagnation region of an axisymmetric impinging jet. Varying the hole diameter, blowoff limits and maximum flame temperature were measured for an edge flame's blowoff character, and also, for an edge flame's structure, temperature profile and flame location were measured and a thermal boundary layer around the edge flame was visualized with laser tomographic technique. It is found that all the edge flames in the stagnation flow have a critical stagnation velocity gradient, beyond which the flame can never be existed. The critical stagnation velocity gradient that represents the overall reaction rate in the edge flame zone decreases as the hole diameter is increased. The increase in a hole diameter leads to change of the edge flame's structure and to addition of two heat loss factors to the edge flame. One heat loss factor is the edge flame-wall interaction, which occurs due to decrease in the edge flame's location. Another is penetration of cold flow into a hole in the flame, which occurs due to decrease in the overlapping range of thermal boundary layer of the edge flame in the hole. These additional heat losses occur at lower stagnation velocity gradient and have stronger influence on the edge flame as a hole diameter becomes larger. Consequently the overall reaction rate in the edge flame zone is reduced by the increase in a hole diameter. Finally it is clarified that the edge flame shows qualitatively same extinction as a pure diffusion flame, when the flame zone of the edge flame lies spatially as the boundary that divides between oxidizer side and fuel side in spite of existence of a partially premixture of fuel and oxidizer ahead of the reaction zone in the edge flame region.

Transition processes from the edge flame without premixed flame to the edge flame with premixed flame, the triple flame, of methane-air edge flame are experimentally investigated by using the novel burner system. The burner system forms a diffusion flame in an axisymmetric wall jet. The measurements of the stability limits and the flame locations, and the observation of the flame shapes have been performed. The burner can make three types of the stable edge flame. First one is the edge flame without premixed flame, whose location is determined by the wall interaction with the edge flame, that is, the thermal factor. Second one is the edge flame with premixed flame, whose location is still determined by the thermal factor. Third one is the edge flame with premixed flame, and the location is determined by a balance between the propagation rate of the edge flame and the local velocity of unburnt mixture, that is, the fluid dynamical factor. The change of the dominant factor for flame location is due to the increase in the partially premixing region ahead of the edge flame. The increase in the partially premixing region makes it possible to form premixed flame and the first edge flame changes into the second one. Further increase in the partially premixing region lead to an increase in a total amount of the heat release around the edge flame region and the flow field ahead of the edge flame diverges. Finally, the edge flame is lifted up by the flow divergence and the dominant factor to determine the edge flame location changes from the thermal factor to the fluid dynamical factor.

The flow field of the turbulent counterflowing stream with and without nonpremixed flames, and the behavior of diffusion region of turbulent nonpremixed flames have been investigated experimentally. The turbulent characteristics of each side flow in a counterflowing stream would be regarded as keeping their initial turbulent characteristics from one burner exit to near the stagnation region. And the mutual interferences of turbulence of both flows are slight in the present nonreactive turbulent counterflow field. The trends of velocity fields at every turbulent condition agree well with the flow field of nonreactive turbulent counterflowing stream and it is considered that the mutual interferences of both air side stream turbulence and fuel side stream turbulence seem to be slight in a turbulent counterflowing stream with nonpremixed flames. The behavior of diffusion region including the nonpremixed flame is mostly affected by the turbulence of the air stream. And it indicate that the presence of a certain close relation between the macroscopic behavior of diffusion region caused by the turbulent effect and extinction phenomena of turbulent nonpremixed flames formed in a counterflowing stream.

The velocity variation induced by the sinusoidal wall oscillation is measured along the stagnating streamline and its amplitude is estimated. The mechanisms of the flow velocity oscillation are discussed in terms of the amplitude of the flow velocity oscillation when the angular frequency of the wall oscillation ω, the average distance between the nozzle and the wall y^-ω, and the flow velocity at the nozzle exit U0 are varied. The characteristics of the flow velocity oscillation are classified into three regions by a Strouhal number S=ωy^-ω/U0. When S 6, it is dominated by the change of the wall velocity. In between, 2

A stability limit of the diffusion flame with fuel injection from a porous wall in a laminar flat plate boundary layer is measured as functions of fuel (CH4) concentration of CH4/N2 injectant mixture (x) and its injection velocity (v). The free stream velocity (U∞) is set as 0.6 m/s. The thermal condition at the wall is controlled by setting temperature at the upstream end of the porous wall as a reference temperature. When v>20 mm/s, the flame becomes unstable with the separation of leading flame edge with decreasing x. The value of x at the stability limit is constant without regard to v as long as the wall temperatrure is kept constant. As the wall temperature is decreased the value of x increases. The separation is supposed to take place as a result of the limit of the reaction rate. When v

Fluctuating temperature has been measured using a laser Rayleigh scattering technique along a centerline of turbulent stagnating opposed jets (cold jet velocity : 2m/s) with different temperatures up to about 400°C. The temperature signals show that the temperature fluctuation is characterized by spike type fluctuations with a sharp increase or decrease in temperature between hot and cold jets. This indicates that the temperature fluctuation is mainly attributed to the large-scale fluctuations of the boundary between the hot and cold jets. Profiles of mean temperature and rms value of fluctuating temperature can be normalized using a similarity parameter based on the bulk strain rate, characteristic intensity and scale of the turbulence when the temperature difference is less than 200°C.

The hydrogen concentration of a hydrogen/nitrogen mixture at a stability limit of a diffusion flame formed in a downstream region of a backward-facing step is experimentally measured as functions of the step height, the distance from the step to the fuel injection point, the freestream velocity and the fuel injection velocity. The stabilization conditions can be divided into three types depending on the fuel injection point. When the fuel injection point is located near the reattachment point, the hydrogen concentration at the stability limit increases more significantly than that in other regions due to shear turbulence. Furthermore, in this region, the stabilization conditions can be divided into two types as a function of l* and lr. where l* is the distance from the step to the center of the reattachment region and lr is the distance from the step to the reattachment point : the flame as l*/lr>1 is more stable than that as l*/lr

Measurements of mean values and turbulent intensities of velocity and temperature fluctuations of grid turbulence have been done in a developing region just after an electrically heated screen. The air velocity is set as 1m/s. The electric current to the screen is adjusted to be the downstream temperature (Ta) 32°C, 100°C or 150°C. A hot wire anemometry with compensation of temperature variation is used to measure velocity with temperature variation. In a developing region, both velocity and temperature distributions become non-uniform at just downstream of the heated screen. The distributions recover gradually to the uniform condition in a downstream region. A turbulent energy dissipates with the distance from the heated screen. The dissipation rate is decreased with increasing air temperature.

Effects of heat loss and flame stretch on the lean-limit extinction of laminar premixed flames in a stagnation point flow have been studied experimentally. The bulk stretch rate was varied from 40s-1 to 420s-1, while the Lewis number (Le) was varied from 0.85 to 1.8. The extinction of the lean propane/air flame (Le>1) is mainly caused by the flame stretch. On the other hand, the extinction of lean methane/air and lean methane/CO2-O2 flames (Le

Mie scattering technique with silicon oil droplets (MSOD) has been applied in a laminar premixed flame in a stagnation point flow. A 1.2W laser beam of 514.5nm wavelength has been used as a light source, and fine silicon oil droplets (diameter

The burning intensity of inverted flame base has been studied by using Infrared Rays Emission Computed Tomography. The results substantiate the general concept of the influence of flame stretch and preferential diffusion on the burning intensity. Specifically it was found that the burning intensity increases (decreases) towards the inverted flame base for mixtures whose effective Lewis number is smaller (greater) than unity: this behavior is qualitatively opposite to that observed for regular Bunsen flame tip because of the reversed flame curvature. It is further demonstrated that a heat loss to the stabilizing rod and a flow acceleration toward the flame base appear to have very small influences on the flame behavior, while flame curvature exerts strong influence on these phenomena.

The temperature has been measured in a field in which laminar hydrogen (6.0 m/s at the center of a burner exit) was injected into a co-flowing air stream (6.0 m/s) with some kinds of grid turbulence. It is shown that the ratio of a laminar flame length to the turbulent one is proportional to the turbulent Reynolds number, Reι, (integral scale is considered a characteristic length) in the measured extent (Reι≤1000), and therefore that the integral scale of a reactant flow is an important parameter for the flames in this paper. The width of a flame displacement is estimated from the temperature profiles when the flame is assumed to be a wrinkled laminar flamelet. The width is also measured directly by a flow visualization method. Both the widths obtained by the two different methods agree well with each other. This fact indicates that the turbulent flame in this paper can be treated as a wrinkled laminar flamelet.

Experimental investigations on an aerodynamic structure of a laminar boundary layer diffusion flame over a horizontal flat plate have been performed. Effects of gravitational force and velocity gradient of free stream velocity have been discussed. When a fuel (methane) is injected upward, the velocity around a flame zone is locally accelerated, and the velocity gradient at the wall is increased as compared with that of isothermal flow. On the other hand, when a fuel is injected downward, the velocity is retarded, and the velocity gradient at the wall is decreased in not only a downstream region of the leading flame edge but also the upstream region. This reveals that the gravitational force varies the local pressure distribution not only in a downstream region of the leading flame edge but also in the upstream region. It is also elucidated that the velocity gradient of free steam velocity varies the velocity profiles in a boundary layer.