Scale of vortex zones of the hydrogen flame in a supersonic air flow

Vortex formation during diffusion combustion of a fuel in a supersonic high-temperature air flow is considered. Results of experimental and numerical activities on studying the vortex scale, changes in the vortex size, and relations with the wave structure of the flow and combustion intensity are analyzed.     

Liftoff height behavior in a non-premixed turbulent hydrogen jet with coaxial air

To understand hydrogen lifted flames, the experimental approximation of liftoff height in non-premixed turbulent conditions was studied. The objectives were to analyze liftoff height behavior and to derive the normalized expression for lifted jet with the effective diameter (d_F,eff). Hydrogen flow velocity varied from 100 m/s to 300 m/s. Coaxial air velocity was regulated from 12 m/s to 20 m/s. For the simultaneous measurement of velocity field and reaction zone, particle image velocimetry using hydroxyl radicals (PIV/OH) planar laser-induced fluorescence (PLIF) techniques with neodymium-droped yttrium–aluminum-gamet (Nd:YAG) lasers and charge-coupled device/intensified charge-coupled device (CCD/ICCD) cameras were used. Liftoff height decreased with increased fuel velocity. The flame stabilized in a lower velocity region next to the faster fuel jet due to the mixing effects of the coaxial air flow. The stabilization point was defined as the point where local flow velocity is balanced with turbulent flame propagation velocity. On the basis of the far field concept, we could derive the experimental approximation of the liftoff height divided by the effective diameter.     

Effects of combustion on the interaction of an underexpanded wall hydrogen jet with a supersonic flow in a planar channel

Zhukovskii. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 6, pp. 11–17, November–December, 1992.     

Efficiency of hydrogen combustion in a high-temperature supersonic air flow for different methods of injection

The efficiency of hydrogen burnup in a supersonic air flow is studied for different methods of fuel injection. The combustion rate and combustion efficiency were determined by detecting the emission intensity of the OH radical over the length of the flare. The distinctive features and heat release characteristics of each of the delivery methods are established, so that a desired heat release behavior can be obtained by choosing suitable injectors. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 2, pp. 3–8, Mach–April 1999.     

Flame length scaling in a non-premixed turbulent diluted hydrogen jet with coaxial air

The effect of fuel composition on flame length was studied in a non-premixed turbulent diluted hydrogen jet with coaxial air. Because coaxial air entrained in a fuel stream enhances the mixing rate of fuel and air, it substantially reduces flame length. The observed flame length was expressed as a function of the ratio of coaxial air to fuel jet velocity and compared with a theoretical prediction based on the velocity ratio. Four cases of fuel mixed by volume were determined: 100% H₂, 80% H₂/20% N₂, 80% H₂/20% CO₂, and 80% H₂/20% CH₄. In addition, fuel jet air velocity and coaxial air velocity were varied in an attached flame region as u_F = 86-309 m/s and u_A = 7-14 m/s. In this study, we derived a scaling correlation for predicting the flame length in a simple jet with coaxial air using the effective jet diameter in a near-field concept. The experimental results showed that the visible flame length was in good relation to the theoretical prediction. The scaling analysis is also valid for diluted hydrogen jet flames with varied fuel composition, which affects flame length by varying the density of the fuel.     

Investigation of mass transport in gas diffusion layer at the air cathode of a PEMFC

In a polymer electrolyte membrane fuel cell (PEMFC), slow diffusion in the gas diffusion electrode may induce oxygen depletion when using air at the cathode. This work focuses on the behavior of a single PEMFC built with a Nafion^® based MEA and an E-TEK gas diffusion layer and fed at the cathode with nitrogen containing 5, 10 and 20% of oxygen and working at different cell temperatures and relative humidities. The purpose is to apply the experimental impedance technique to cells wherein transport limitations at the cathode are significant. In parallel, a model is proposed to interpret the polarization curves and the impedance diagrams of a single PEMFC. The model accounts for mass transport through the gas diffusion electrode. It allows us to qualitatively analyze the experimental polarization curves and the corresponding impedance spectra and highlights the intra-electrode processes and the influence of the gas diffusion layer.     

Effect of an H2O2 additive on hydrogen ignition and combustion in a supersonic air flow

The effect of small amounts of inert and reacting additives (such as hydrogen peroxide, its decomposition products,CO ₂, etc.) on the ignition and combustion of hydrogen in a high-temperature supersonic air flow was studied experimentally. It is shown that direct doping of the fuel has little effect on the combustion ofH ₂, whereas injection of hydrogen peroxide or small amounts of pure hydrogen ahead of the nozzle decreases suddenly the ignition delay, indicating the profound effect of the reaction products. Comparative experiments with inert additives showed that these additives only lead to a decrease in the air-flow temperature. Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 3, pp. 70–75, May–June, 1997.