Shigeo Kondo

The rotational spectra, molecular structure, dipole moment, and hyperfine constants of HOBr and DOBr

Abstract Pure rotational spectra of the 79Br and 81Br isotopic species of gaseous hypobromous acid, HOBr and DOBr, as well the v3 = 1 excited state of HOBr have been observed and analyzed. Structural parameters have been derived from the ground state rotational constants. The permanent molecular dipole moment of DOBr and the bromine nuclear quadrupole coupling and spin rotation constants of all the species have been determined.

Flammability assessment of CH2CFCF3: Comparison with fluoroalkenes and fluoroalkanes

The burning velocity, flammability limits, and heat of combustion of CH(2)CF=CF(3) (1234yf) have been studied to elucidate the fundamental flammability properties of this new alternative refrigerant with low global-warming potential. The burning velocity of 1234yf was measured independently by schlieren photography and the spherical vessel method. In the spherical vessel method, the burning velocities of 1234yf and its analogues CH(2)=CFCHF(2) (1243yf) and CH(2)=CHCF(3) (1243zf) as well as those of typical fluoroalkanes CH(2)F(2) (HFC-32) and CH(3)=CHF(2) (HFC-152a) were measured in mixtures of air at various O(2)/(N(2)+O(2)) ratios. The maximum burning velocity of 1234yf was found to be 1.2+/-0.3 cm s(-1), which was approximately one-fifth that of HFC-32 (6.7 cm s(-1)) and one order of magnitude less than those of 1243yf (19.8 cm s(-1)) and 1243zf (14.1 cm s(-1)). The flame propagation of 1234yf was highly sensitive to flame temperature compared to that of the other compounds. The measured flammability limits and calculated heat of combustion of 1234yf were also determined.

A study on flammability limits of fuel mixtures

Flammability limit measurements were made for various binary and ternary mixtures prepared from nine different compounds. The compounds treated are methane, propane, ethylene, propylene, methyl ether, methyl formate, 1,1-difluoroethane, ammonia, and carbon monoxide. The observed values of lower flammability limits of mixtures were found to be in good agreement to the calculated values by Le Chateliers formula. As for the upper limits, however, some are close to the calculated values but some are not. It has been found that the deviations of the observed values of upper flammability limits from the calculated ones are mostly to lower concentrations. Modification of Le Chateliers formula was made to better fit to the observed values of upper flammability limits. This procedure reduced the average difference between the observed and calculated values of upper flammability limits to one-third of the initial value.

Rate constants for the reactions of OH radicals with CF3OCF=CF2 and CF3CF=CF2

Abstract The rate constants for the reactions of OH radicals with trifluoromethyl trifluorovinyl ether (CF 3 OCF=CF 2 ) and hexafluoropropene (CF 3 CF=CF 2 ) have been measured over the temperature range 250–430 K. Kinetic measurements have been carried out using the flash photolysis and laser photolysis methods combined, respectively, with the laser-induced fluorescence technique. The Arrhenius rate constants have been determined as k (CF 3 OCF=CF 2 )=1.01 −0.04 +0.04 ×10 −12 exp [(320±10)/T] , and k (CF 3 CF=CF 2 )=8.74 −0.33 +0.34 ×10 −13 exp [(260±10)/T] cm 3 molecule −1 s −1 .

Burning velocity measurements of nitrogen-containing compounds

Burning velocity measurements of nitrogen-containing compounds, i.e., ammonia (NH3), methylamine (CH3NH2), ethylamine (C2H5NH2), and propylamine (C3H7NH2), were carried out to assess the flammability of potential natural refrigerants. The spherical-vessel (SV) method was used to measure the burning velocity over a wide range of sample and air concentrations. In addition, flame propagation was directly observed by the schlieren photography method, which showed that the spherical flame model was applicable to flames with a burning velocity higher than approximately 5 cm s(-1). For CH3NH2, the nozzle burner method was also used to confirm the validity of the results obtained by closed vessel methods. We obtained maximum burning velocities (Su0,max) of 7.2, 24.7, 26.9, and 28.3 cm s(-1) for NH3, CH3NH2, C2H5NH2, and C3H7NH2, respectively. It was noted that the burning velocities of NH3 and CH3NH2 were as high as those of the typical hydrofluorocarbon refrigerants difluoromethane (HFC-32, Su0,max=6.7 cm s(-1)) and 1,1-difluoroethane (HFC-152a, Su0,max=23.6 cm s(-1)), respectively. The burning velocities were compared with those of the parent alkanes, and it was found that introducing an NH2 group into hydrocarbon molecules decreases their burning velocity.

Prediction of flammability of gases by using F-number analysis.

A novel method of predicting flammability limits has been proposed. This method utilizes a new flammability index called F-number. For this purpose, an empirical expression of F-number has been derived to account for the flammability characteristics of various organic substances. The analysis has been done by fitting to the observed values of F-number for a wide variety of organic gases and vapors. As a result, it has been found that F-number is an excellent tool to analyze the flammability characteristics of various substances. It has also been shown that the values of upper and lower flammability limits can be derived from F-number together with the stoichiometric concentration corrected for the effect of selective diffusion.

Spontaneous ignition limits of silane and phosphine

Abstract Spontaneous ignition limits of silane and phosphine have been investigated at relatively low concentrations. For silane, the spontaneous ignition occurs if the mixture concentrations is such that the silane/oxygen ratio is higher than a certain threshold limit value. In other words, the mixture is not stable if the ratio is higher than a certain value. On the other hand, in the case of phosphine the threshold limit line has been found to be a little curved, though the reason for the fact is not clear. At any rate, it is concluded that the spontaneous ignition of both silane and phosphine occurs as a result of a competition of chain branching and chain breaking reactions, in a way that is qualitatively similar to that in hydrogen oxidation.

Premixed silaneoxygennitrogen flames

Abstract The burning velocities of lean premixed silaneoxygennitrogen flames were measured in the silane and oxygen concentration ranges from 1.6% to 2.9% and from 4% to 24%, respectively. Combustion product analyses and flame temperature measurements were also carried out. The burning velocity of a silaneair flame is around 55 cm/s at a silane concentration of 2%. For lean mixtures, when the oxygen concentration is reduced, dependence of burning velocity upon silane concentration decreases but does not significantly affect the flame temperature. For extremely lean flames, the degree of hydrogen production increases with decreasing silane, although silane is consumed almost completely. On the other hand, if the silane concentration exceeds stoichiometric, the burning velocity increases gradually with increasing silane concentration. In that case, silane as well as oxygen are consumed completely and, at the same time, hydrogen rather than water production becomes dominant. The mechanism of silane combustion is discussed, based on numerical calculations, where the mechanism used in the calculation is assembled by analogy of silane to methane combustion.

A Numerical Study of Low Temperature Silane Combustion

Abstract A mechanism of low temperature silane combustion has been proposed in the present work based on the assumption that a trace amount of water vapor helps the occurrence of spontaneous ignition at room temperature. This assumption has been made based upon the fact that the combustion product of silane influences positively the occurrence of spontaneous ignition. Energetic calculation of the reaction path way for low temperature silane combustion also supports this assumption [Kondo et al., 1999]. A numerical model has been constructed which can interpret the spontaneous ignition limit at room temperature, the ignition delay times, and the second explosion limit of silane mixtures simultaneously.

Calculation of minimum ignition energy of premixed gases.

The minimum ignition energy of premixed gases has been calculated by using two theoretical expressions and compared with the experimental data. One expression considers the amount of energy that the minimal flame should have, and the other the heat loss from the surface of the minimal flamelet. The former is a cubic function of the quenching distance while the latter is a quadratic function of quenching distance. It has been found that the latter expression gives a better fit to the experimental data than the former, though the discrepancy is considerable even for the latter expression. The calculated widths of the fronts of the minimal flame for various fuels were about one-order of magnitude smaller than the corresponding experimentally determined quenching distances, although no clear correlation relationship between the two quantities was found.