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形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2020-06-24, 資料番号: PA2110026000

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2017-07-06, 資料番号: PA1810059000

The reactions of NO2 with cis-/trans-CH3NHNH, CH3NNH2 and CH2NHNH2 have been studied theoretically by quantum chemical calculations and steady-state unimolecular master equation analysis based on RRKM theory. The barrier heights for the roaming transition states between nitro (RNO2) and nitrite (RONO) isomerization reactions and those for the concerted HONO and HNO2 elimination reactions from RNO2 and RONO, affect the pressure dependences of the product-specific rate coefficients. At ambient temperature and pressure, the dominant product of the reactions of NO2 with cis-/trans-CH3NHNH and CH2NHNH2 would be expected to be HONO with trans-CH3NNH and CH2NNH2, respectively, whereas it is CH3N(NH2)NO2 for CH3NNH2 + NO2. The product-specific rate coefficients for the titled and related reactions on the same potential energy surfaces were proposed for kinetics modeling., 形態: カラー図版あり, Physical characteristics: Original contains color illustrations, 資料番号: PA1610065000

Direct numerical simulation (DNS) of a cryogenic nitrogen/nitrogen gas temporally developing mixing layer in transcritical conditions was conducted to explore the influence of the pseudo vaporization at the pseudo-critical temperature. For comparison, a cryogenic nitrogen/nitrogen gas mixing layer in ideal-gas conditions was also simulated with the same initial profiles of density and velocity. Flow visualization and statistical analysis revealed that dominant eddies in development of turbulence were not directly affected by the pseudo vaporization, and were formed in the upper stream region of the mixing layer in the same manner as in the ideal-gas condition. Thus, the Reynolds stress and turbulent heat flux were similar between the two conditions. Accordingly, the mean and fluctuation profiles of streamwise velocity and specific enthalpy were also similar between the two conditions. Therefore, it is noted that the turbulent transport mechanisms of momentum and heat are little affected by the pseudo vaporization. In contrast, the density profiles were influenced by the pseudo vaporization. The cryogenic dense nitrogen was entrained deeply into the middle part of the mixing layer under the transcritical condition. This is because the nitrogen maintains a relatively high density until heated up to the pseudo-critical temperature. As a result, the mean profile of density in the transcritical condition was much higher than that in the ideal-gas condition through the mixing layers. Consequently, the transport mechanism of mass under the transcritical condition is considered to be influenced by the pseudo vaporization.

5th European Conference for Aeronautics and Space Sciences, EUCASS 2013 (July 1-5, 2013.), Munich, Germany, "Many of liquid rocket engines used in first stage of launch vehicles operate at a pressure above the critical pressure of oxygen, 5.04 MPa. The cryogenic oxygen injected into a combustion chamber is heated up to several thousand kelvin, therefore the high-density cryogenic oxygen necessarily experiences sudden expansion called “pseudo-boiling”1 at the pseudo-critical temperature. The pseudo-boiling has large impact on the mixing characteristics, hence a jet injected from a temperature below the pseudo-critical temperature must be distinguished from that injected from a temperature above the pseudo-critical temperature. The former is referred to as “transcritical jet” while the latter is simply called supercritical jet. Quantitative measurement data of transcritical jets are indispensable both for the better understanding of mixing phenomena and for the validation of numerical methods, but there are only few quantitative experimental data made public.2 In this report, axial and radial temperature profiles of a single phase cryogenic nitrogen jet under supercritical pressure are measured, and the influence of pseudo-boiling upon the jet mixing will be discussed.", 資料番号: PA1510093000

Cryogenic single round and coaxial jets were observed under subcritical and transcritical conditions using a high-speed camera to explore the effects of the single-phase-like and two-phase-like properties of transcritical fluids on the unsteady behavior and flow structures of the jets. Cryogenic nitrogen and gaseous nitrogen were used as injectants. Cryogenic nitrogen was clearly visualized in all cases as the dark core. In the cases of single round jets, the large-scale characteristics of the jet behavior observed, such as the width of the dark core and the length scale of wave development in the mixing layers, were similar to those observed under subcritical conditions. Furthermore, dense nitrogen in the mixing layer entrained into the ambient environment and stretched in a manner similar to that observed under subcritical conditions. However, in contrast to the droplet formation observed under subcritical conditions, the entrained dense nitrogen diffused in a manner similar to turbulent mixing in a variable-density single-phase mixing layer. This means that the microscale behaviors that occur under transcritical conditions, which are comparable to turbulent eddies, are similar to those that occur in variable-density single-phase jets. In the cases of coaxial jets, the turbulent-eddy-scale phenomena observed were also similar to those observed for variable-density single-phase jets. However, in contrast to the phenomena observed for single round jets, the larger-scale behavior of the dark core was different from that observed under subcritical conditions. Two significant features were observed only under transcritical conditions. The first feature was the formation of shear-layer instability waves near the injector exit. The second feature was the shedding of dense nitrogen lumps from the end of the dark core at nearly uniform intervals. Because similar behavior was not observed under subcritical conditions, the single-phase-like properties of transcritical fluids are considered to have induced these features. The present correlation between the dark core length and the outer-to-inner jet momentum flux ratio was found to be in good agreement with the empirical correlation for variable-density single-phase coaxial jets., 形態: カラー図版あり, Physical characteristics: Original contains color illustrations, 資料番号: PA1610078000