Toshio Mogi

Catalytic Combustion of Pre-Vaporized Liquid Fuel

Fundamental characteristics of the catalytic combustion of vaporized kerosene spray were experimentally investigated. This study is a part of the development of a ceramic gas turbine engine for automobiles. Kerosene was used as a test fuel and its spray was injected from a swirl atomizer into a hot air stream. The inlet air temperature was elevated up to 900 K to vaporize the kerosene spray. Premixed gas of air and kerosene vapor was introduced into the catalyst. The total equivalence ratio was controlled from Φ=0.18-0.32. The palladium catalyst was supported on a cordierite honeycomb monolith. Catalytic combustion phenomena were categorized in three typical states: (a) state of partial reaction in the catalytic monolith, (b) state of homogeneous reaction in the monolith, (c) state of homogeneous reaction with a blue flame supposed on the monolith. A parabolic shape blue flame in the state of (c) appeared downstream of the monolith. This flame was very stable and its temperature was relatively low compared with conventional premixed flames of hydrocarbon fuel because the equivalence ratio was much lower than those of premixed flames. The distance from the monolith to the ignition point of this flame became short with a rise of the inlet air temperature, even if the volumetric airflow rate increased with the air temperature. Spontaneous emission spectra of radiation from the blue flame were measured. Strong spectral peaks of OH, CH, and CO + radicals were observed in the spectra. This spectral structure was quite different from that of a blue flame of premixed propane.

Toward Risk Assessment of Explosion Hazard: Experimental Determination of Flame Fractal Dimension

Quantitative risk analysis is a method to evaluate risk and to identify areas for risk reduction. The final goal of our study is to propose an effective method for risk assessment of explosion hazard. To achieve the goal, a phenomenon that influences the consequences of explosion is first identified: self-turbulization and resulting acceleration of expanding flame during explosion. The fractal dimension is then identified as the key parameter that characterizes the phenomenon. Since the previous method to determine fractal dimension relies on large-scale explosion experiment, it has not been easy to determine fractal dimension. This paper demonstrates the possibility of determining fractal dimension by analyzing flame images of small-scale experiment, which might significantly reduce the cost of risk assessment of explosion hazard.

Wrinkling of Large-Scale Flame in Lean Propane–Air Mixture Due to Cellular Instabilities

ABSTRACT In accidental gas explosions, flame acceleration owing to cellular instabilities such as diffusional–thermal instability and Darrieus–Landau instability can cause considerable damages, for example, the formation of a strong blast wave. In particular, as the flame scale increases, Darrieus–Landau instability, caused by a density jump, progressively dominates in the flame acceleration. In this study, we experimentally investigated the growth and wrinkling owing to Darrieus–Landau instability of a spherically expanding flame in a large-scale experiment, in which a propane-air mixture of the equivalence ratio ϕ = 0.8 was filled and ignited in a plastic tent of 27 m3. Experimental images of large-scale flames of the lean propane–air mixture, for which the flame is diffusional–thermally stable, were analyzed. The edge of flame was detected and rearranged in polar coordinates. The results show that small-scale cells merge and form a bigger cell. The generated bigger cell grows by the instability mechanism and eventually forms a large single cusp. In addition, the peak-to-peak amplitude of the wrinkled flame was evaluated. The value of peak-to-peak amplitude increased as time progressed. Such a cellular flame gives rise to a fractal-like structure and acceleration of its propagation speed. The fractal dimension of the wrinkled flame surface was evaluated by logarithmically plotting the flame speed versus its radius and also by a box-counting method. The results demonstrated that the wrinkled structure of a large-scale flame can be characterized by its fractal dimension and that a transition period into a well-developed self-similar regime exists.

Analysis on a Fuel Spray Mixture Suffered by Partial Oxidation through a Catalytic Honeycomb.

A fuel spray mixture suffered by partial oxidation through a catalytic honeycomb was studied experimentally. The palladium catalyst supported on the cordierite honeycomb monolith was used. Kerosene vapor was introduced into the ca talytic honeycomb. The parabolic shape blue flame that was supported on the catalytic honeycomb was formed even if the equivalence ratio of the mixture was less than stoi-chiometry. To clarify a reaction process in an combustible gas between the honeycomb and the blue flame, CO, HC (C1-C7) and NO were analyzed. When blue flame appeared, CO and HC concentration were increased between the honeycomb and flame. Further, high molecular species (C8-C15) in the combustible gas were trapped by the water-cooled condenser system and they were analyzed by the gas chromatograph and mass spectroscopy. Spontaneous emission spectra from the blue flame were measured. Strong spectral peaks of OH, CH and H2O radicals were observed in it. To compare with the spectra, spontaneous emission spectra from the pre-vaporized flame of kerosene mixture were measured.

Structure of Spray Flames in a Hot Air Stream.

Behavior of a spray combustion in a hot air was studied experimentally. A kerosene spray was injected from swirl atomizer into a hot air stream. The air temperature was controlled from room temperature to 1 100 K which was higher than the self-ignition temperature of a kerosene spray. Flame shape and temperature distribution were measured to characterize the spray combustion appeared in the hot air stream. Flow state around the spray was visualized by a Schlieren method to analyze the behavior of the air entrainment into the flame. Furthermore, Mie scattering from the spray droplets by irradiation of the laser beam was observed to visualize the spray concentration in a flame. As the result, ignition point was shifted to the upstream side with an increase of air temperature. When the air temperature became higher than 800 K, the blue flame appeared at the bottom portion of the flame. Penetration of the spray became shorter with an increase of air temperature. Spatial distribution of the spray which were not vaporized in a flame was strongly affected by the air temperature.