The combustion researches on safety mattes have been important since the early times of combustion research. In this paper, the application of combustion researches on the combustion control techniques for prevention and mitigation of combustion-induced disasters. The factor analyses of fire and explosion disasters, which are typical combustion-induced disasters, are performed to make clear how the combustion researches could contribute. Also the risk assessment of fire and explosion disasters is explained. As an example of such combustion research, the research of dust explosion is presented. Dust explosion is much more complicated than gas explosion. The knowledge of flame structure, flame propagating mechanism and dust particle behavior is necessary to understand dust explosion phenomena. Such knowledge is indispensable to establish the combustion control techniques for preventing and mitigating the dust explosion disasters.
Science Council of Japan pointed out the importance of scientific investigation of industrial disasters in 1965. A large number of researches have been carried out to understand the basic cause of disasters. In this report, several fire related disasters, which occurred in development phase of new technology, are shown from the viewpoint of combustion science and technology.
One of the objectives of this paper about recent trends in fires in boreal and tropical forests is to raise reader's awareness of wilderness fires as a type of disaster mainly caused by human activity. Firstly, three global scale biomass fires occurring in savanna, tropical forest, and boreal forest areas were mainly described. Biomass fires in the three major areas were compared with using data for total vegetation area, fire area, primary production, biomass density, and fraction of biomass consumed by the fires. This comparison clearly showed several important characteristics of the three kinds of biomass fires. Then, characteristics of the three fire types of biomass were briefly described to explain the values for the fraction of biomass consumed by various biomass fires. Secondly, the effect of peat fires in Indonesia on the world environment were discussed from the global warming point of view. Finally, the starting mechanism of lightning-caused fires occurring in boreal forests was discussed by considering characteristics of dry thunderstorms.
The utilization of hydrogen for energy use is attractive since the exhaust gas is H2O alone and will spread widely, when renewable energies and CO2 reduction technologies are combined with the hydrogen-oxygen energy chain. In order to promote the widespread use of fuel cell vehicles, supply stations of high pressure hydrogen should be constructed in a city area, based on the safety regulations such as maximum storage amount, layout, material, safety distance, or protection wall. For the purpose, fundamental data for the open-jet hydrogen flame of high-pressurized hydrogen up to 80MPa have been accumulated. In this report, the scale of diffusion flame, flame stabilization, and radiation from flame are discussed. Furthermore, when the blown-down cloud of high pressure hydrogen was ignited at several tens milliseconds delay, the flame propagated at a high speed over 400m/s through the hydrogen-air mixture with a strong turbulence. Moreover, the outline of risk assessment and safety countermeasures for hydrogen supply station is introduced.
As for industrial combustion apparatuses, turbulent nonpremixed combustion systems are widely used due to the facility for stabilization; i.e., the safety. However, the systems produce easily unexpected gases such as NOx and soot. The information in advance based on numerical simulation is crucial for the design of combustion apparatus to optimize the system. In the present review paper, regimes of nonpremixed combustion are given and the modeling is explained. The eddy dissipation model is empirical or intuitive, but robust. The flamelet model is widely used in industrial and academic levels, but in controversy for assumptions. The conditional moment closure method is an improvement of the flamelet model. The PDF method can deal with reaction exactly, but costly. The presumed multivariate PDF method may be a solution of the turbulent combustion modeling. This method is between the flamelet model and the PDF method, with the ability of exact evaluation of reaction.
An experimental study about effects of unsteadiness on extinction behavior of counterflow non-premixed edge flame was conducted. The counterflow non-premixed edge flame was established in the flow field with non-uniform stretch rate distribution between inclined counterflow slot-jet burners. Changes in the flow velocity, fuel volume ratio and fuel mass flux at the burner exit resulted in propagation of the edge flame. The propagation velocity of the flame edge was measured and the local stretch rate at the flame edge of the non-stationary edge flame was compared to that of the stationary edge flame. Experimental results showed the propagation velocity of the edge flame was in proportion to the rate of change in flow conditions. There was no difference between ignition mode in which the edge flame propagated toward a high stretch side and extinction mode in which the edge flame propagated toward a low stretch side. The local stretch rate at the flame edge of the non-stationary edge flame was the same as that of the stationary edge flame in all experimental conditions. It was noted that these results were obtained in the flow field with a relatively small rate of change in the flow condition.
Although heat release rate is one of the important combustion characteristics, its direct measurement is impossible. Recently, Najm et al. have reported that the heat release rate is well correlated with the product of OH and HCHO fluorescence signals in PLIF measurement. So far, it is well confirmed that this approach can be applied to premixed combustion. In this study, we tried to evaluate the heat release rate in diffusion flame in the same manner. Before that, we numerically investigated the correlation between heat release rate and the product of OH and HCHO concentrations in counter-flow diffusion flame. It is found that the profile of large heat release rate is well correlated with the product of OH and HCHO concentrations, because the heat release rate largely depends on HCO production rate, described by OH and HCHO concentrations through HCHO + OH → HCO + H2O. However, in the region where the heat release rate is relatively small, the same correlation is not observed. In PLIF measurement, since the profiles of OH and HCHO fluorescence signals match those concentrations predicted by simulation, these radial concentrations are well determined by experiments. The product of OH and HCHO fluorescence signals shows the similar profile to that of the simulated heat release rate. However, different from the premixed flame, the disagreement was found especially in the region of small heat release rate. Thus, it is concluded that the region of large heat release rate in diffusion flame is well correlated with OH and HCHO PLIF measurement.