For applications of the high-temperature air combustion technology (HiCOT) to waste incinerators, diffusion flame of blended fuel gases and high-temperature air in the stretch flow field were investigated. In this study, extinction limits of the counterflow diffusion flame for CH4-C3H8 blended fuel gases were obtained experimentally and numerically, varying the mixture fraction, fuel concentration and air temperature. Since the flame is unable to stabilize at small stretch rates due to the natural convection caused by buoyancy under normal gravity condition, the experiments were performed under microgravity condition. As increasing C3H8 percent of blended fuel gases and air temperature, extinction limits were extended. As increasing air temperature, the extinction limits at low stretch rates were not extended as much as that at high stretch rates. This reason is that, with increase of air temperature, the effect of radiation heat loss also becomes large at low stretch rates.
CF3I is a potential replacement of HALON fire extinguishing agents. However, it emits very toxic gases when applied against fire. So all possible schemes to reduce its amount should be evaluated for it to come into practical use. CF3Br, which has close chemical characteristics with CF3I, is known to have an enhanced combustion inhibition effect when it is mixed with some inert gas. It is easily anticipated that CF3I also has such effect, but it has not been studied yet. This paper reports an experimental study on reduction of explosion limit concentration of methane/air mixture when CF3I is added solely or together with some inert gas. When CF3I was added solely to a stoichiometric mixture of methane and air, explosion pressure observed in an explosion vessel decreased as concentration of CF3I increased. However, the profile of explosion pressure curve with concentration was quite different with the case of CF3Br. In the case of CF3Br, the explosion pressure decreased monotonically as the concentration increased, and no explosion occurred after the concentration exceeded the limit value. On the other hand, in the case of CF3I, the explosion pressure decreased as the concentration increased just as in the case of CF3Br, while the concentration was smaller than about 8%. Then the explosion pressure increased as the concentration increased. It reached a peak pressure, and decreased again until the concentration reached the limit value (51.5%). The enhanced inhibition effect was also observed when CF3I was combined with nitrogen or carbon dioxide.
The prediction performance of a scalar probability density function (PDF) method is assessed in turbulent jet diffusion flames to seek an improvement of the method. The present PDF method is based on the conserved scalar approach, dealing with the mixture fraction as a scalar. This discards the most advantageous property of PDF modeling, which is capable of treating a reaction exactly, but allows evaluation of the prediction performance of PDFs in a simple manner. The effects of the number of Monte Carlo particles, molecular mixing model and fuel are especially discussed. The modified Curl model and the interaction by exchange with mean (IEM) model are evaluated as molecular mixing models. Two methane/hydrogen and hydrogen/nitrogen flames are dealt to assess the effect of fuel on the performance of the PDF method, together with of the conventional flamelet model calculations. It is found that every physical process like the convection, molecular mixing and turbulent diffusion requires sure participation of particles in each numerical process to get a calculation accuracy. Both the molecular mixing models guarantee to the second moment of scalar fluctuation, but more improved models are required for higher moments. The present PDF method can predict at higher accuracy regardless of fuel than the flamelet model calculations. However, downstream from the maximum temperature position on the centerline of jet flame the performance of PDF method is weakened.