Katsuyuki Konishi

Radiative emission fraction of pool fires burning silicone fluids

The steady-state mass burning flux and the radiative flux profiles to the surroundings were measured for a series of burning silicone fluids and organic fuels in 0.1-m, 0.3-m, 0.6-m and 1-m pool burners. Short-chain silicone oligomers and aliphatic/aromatic hydrocarbons exhibited a strong dependence of the mass flux and the radiative fraction on pool size. The longer chain length silicone fluids and alcohols exhibited both markedly lower mass fluxes and radiative components of heat release and these parameters were virtually independent of pool size. Silica, a gas-phase combustion product of the silicone fluids, was observed to deposit into the vaporizing liquid pool, the yield increasing with silicone chain length. This necessitated correcting the measured apparent mass flux for the liquid volume displaced by the silica. The measured radiative power emitted from flames burning silicone oligomers and hydrocarbons was substantially larger than the power radiated by flames burning long-chain silicone fluids or alcohols. The mass gasification flux and the radiative fraction of the silicones fluids and the organic fuels were well correlated by the ratio of the heat of combustion to the heat of gasification of the fluids.

Ignition process of fuel spray injected into high pressure high temperature atmosphere

The ignition process of fuel sprays injected into high pressure high temperature atmosphere has been studied experimentally and theoretically, and a new concept for the ignition process has been proposed. Experiments were conducted using a large high pressure combustion chamber and a high pressure fuel injection system. Ignition and fuel spray behavior were observed with high speed photography. From these experiments, it may be inferred that the ignition of fuel spray occurs at the stagnation region of the fuel spray tip. The color of the first flame observed was blue. The stagnation velocity gradient at the fuel spray tip, proportional to the fuel spray tip speed and inversely proportional to the fuel spray tip width, decreases rapidly with time from the start of fuel injection or with distance from the fuel nozzle tip. Based on experimental results, a new concept for fuel spray ignition, derived from the knowledge of ignition in a stagnation flow field, has been proposed. By using the equations governing ignition phenomena in the stagnation flow field solved by the asymptotic method, the ignitable limit and ignition time in the stagnation region at the fuel spray tip have been analyzed. These studies show that the ignition behavior of the fuel spray can be well explained by considering the effects of the stagnation velocity gradient at the fuel spray tip on the ignition time of the fuel-air system. The ignition delay of a fuel spray is divided into two parts: one is the time spent for reducing the velocity gradient at the spray tip below the critical velocity gradient for ignition; the other part is the time for an ignition reaction at the given velocity gradient. Since the latter is much smaller than the former, most of the ignition delay is time for reducing the velocity gradient at the fuel spray tip below the critical velocity gradient for ignition. Experimentally obtained ignition delay data can be predicted fairly well by using the above concept.

Global properties of gaseous pool fires

Global flame properties were measured as a function of fuel mass flux in a series of experiments conducted on gaseous pool fires burning in a quiescent environment. The measurements included radiative heat loss, heat transfer to the burner, and sensible enthalpy transfer to the surroundings by convection. A large number of fires was studied encompassing a wide range of pool fire parameters. Measurements were conducted using methane, propane, natural gas, and acetylene in burners varying from 0.1 to 1 m in diameter, producing flames from 0.1 to 2 m in height with total heat release rates from 0.4 to 200 kW. From these measurements. the combustion efficiency was calculated for smoky fires. The measurements were used to test flame height correlations available in the literature for smoky fires. The correlations work well for nonsmoky fires but have not been proven for smoky fires. The measured flame heights conformed to the literature correlations for the nonsmoky flames burning methane, propane, and natural gas. When applied to high mass flux acetylene flames, however, the flame height measurements deviated from the literature flame height correlations. The correlations performed only slightly better when they were based on Q o the sensible enthalpy heat loss. Caution is suggested when applying the standard literature flame-height correlations to smoky firestthat may occur in realistic fire scenarios.

Measurement of the burning surface temperature in ammonium perchlorate

There are a number of inconsistencies in the measured values reported for the burning surface temperatures of ammonium perchlorate (AP). Therefore, the temperature profile near the burning surface of pure AP was measured using microthermocouples. A pressed AP specimen was burned using a propane/air diffusion flame or by increasing initial temperature below the pressure deflagration limit of AP. Since a small cavity may exist around the thermocouple, a large AP crystal was grown around the thermocouple head, and it was also used in the temperature measurement of the burning surface. A video recording of the AP surface was also male using a charge-coupled device (CCD) camera during the combustion process. The time on videotape was synchronized with that on the record of the thermocouple measurements using a flash lamp. As a result, the time at which the thermocouple bead appeared on the burning surface was precisely identified on a temperature-time diagram, and the burning surface temperature was obtained. It was found that the surface temperature of pure AP is in the range of 450–480 ° C, and it was ascertained that the burning surface temperature is independent of the regression rate and the heating rate of the AP specimen. On the other hand, the surface temperature does depend on pressure. The slope of the logarithmic pressure versus reciprocal surface temperature was 130–160 kJ/mol. This value is slightly higher than one-half of the heat of dissociation for AP. Our results were similar to results obtained by Powling et al. with an infrared-radiation technique. However, these results are different from those measured by thermocouples in several other studies. These differences may actually reflect differences in the methods used to identify the burning surface in the measured temperature data.

Effect of pressure on the burning surface temperature of a polymeric fuel for a solid propellant

The relationship between the burning surface temperature and the regression rate of a polymeric fuel used in a solid rocket has been studied. The values of the surface activation energies derived from the Arrhenius pyrolysis equation for a polymeric fuel are not consistent and, from past studies, have been in the range 20 to 400 kJ/mol. Furthermore, the pressure dependence on the burning surface temperature has previously not been discussed in any detail. Hydroxyl-terminated polyester (HTPE) was chosen in this study as a typical polymeric fuel, along withprepolymer HTPE and glycerin. The burning surface temperature was determined using a thermocouple embedded in the specimen. The burning surface was simultaneously observed using a video camera to detect when the thermocouple emerged from the burning surface. Furthermore, the boiling phenomena of HTPE and glycerin were also examined, and thermogravimetric analysis (TGA) of the samples was also employed. As a result, the regression rate was found not to affect the burning surface temperature in the range of 0.04–0.12 mm/s, and the curing agent did not influence the burning surface temperature. On the other hand, the burning surface temperature was dependent on pressure, even in the polymeric fuel. For HTPE and glycerin, the pressure dependency obtained by the combustion experiment agreed well with those obtained by the boiling experiment and by the thermochemical method, TGA.

Tip Opening and Burning Intensity of Bunsen Flames Diluted with Nitrogen.

Tip opening and burning intensity of Bunsen flames diluted with nitrogen have been experimentally investigated. Methane/air and propane/air flames were used in the experiment. The tip opening limit was mapped as a function of the equivalence ratio φ and added nitrogen ratio X, and the tip temperature was measured. Results show that the burning at the tip was intensified in rich flame for methane and lean flame for propane. The maximum allowable dilution by nitrogen also occurs in rich flame (φ=1.05) for methane and lean flame (φ=0.94) for propane. The tip temperature steeply decreases with increasing X on the lean side for methane and the rich side for propane, while it gradually decreases on the rich side for methane and the lean side for propane. These results at the tip were due to the preferential diffusion and nonunity Lewis number through negative stretch induced by flame curvature. The present flame responses to preferential diffusion and Lewis number are ompletely reversed for those of positively stretched stagnation flames.