Current Issue : July - September Volume : 2018 Issue Number : 3 Articles : 5 Articles
A robust fiber Bragg grating (FBG) hydrogen gas sensor for reliable multipoint-leakage monitoring has been developed. The\nsensing mechanism is based on shifts of center wavelength of the reflection spectra due to temperature change caused by\ncatalytic combustion heat. The sensitive film which consists of platinum-supported silica (Pt/SiO2) catalyst film was obtained\nusing sol-gel method. The precursor solution was composed of hexachloroplatinic acid and commercially available silica\nprecursor solution. The atom ratio of Si : Pt was fixed at 13 : 1. A small amount of this solution was dropped on the substrate\nand dried at room temperature. After that, the film was calcined at 500�°C in air. These procedures were repeated and therefore\nthick hydrogen-sensitive films were obtained. The catalytic film obtained by 20-time coating on quartz glass substrate showed a\ntemperature change 75 K upon exposure to 3 vol.% H2. For realizing robust sensor device, this catalytic film was deposited and\nFBG portion was directly fixed on titanium substrate. The sensor device showed good performances enough to detect hydrogen\ngas in the concentration range below lower explosion limit at room temperature. The enhancement of the sensitivity was\nattributed to not only catalytic combustion heat but also related thermal strain....
As a kind of high explosives, aluminized explosive cannot release the energy maximumly, which is a key problem. Using DTA-TG\nequipment, the ignition performance of three kinds of aluminized explosives (RDX, HMX, and CL-20) with different mass\npercentages of aluminum powder (0%, 10 wt.%, 20 wt.%, and 30 wt.%) was investigated. The results showed that the energy release\nof the HMX/Al composite explosive with 10 wt.%, 20 wt.%, and 30 wt.% aluminum powder was only equivalent to 80%, 65%, and\n36% of pure HMX, respectively. It was similar to RDX/Al and CL-20/Al composite explosives, except the CL-20/Al mixture with\n10% aluminum powder. Rather than participating in the ignition and combustion, the aluminum powder does effect the complete\nreaction of RDX, HMX, and CL-20 in the initial stage of ignition or in the lower temperature area of the boundary....
To evaluate the effects of inlet pressure on the ignition process of spray combustion, the images of the ignition process were\nrecorded and the outlet temperatures were measured under inlet pressure of 0.04ââ?¬â??0.16 MPa. The initial flame formation and\nflame propagation and the effects of the inlet pressure on the initial flame formation were observed. A variation of outlet\ntemperature, flame propagation, initial time of outlet temperature rise, time of maximum temperature rise, and temperature rise\nrate was investigated. With increasing inlet pressure, the time of initial flame formation and time of maximum area growth rate\nof flame decrease and the centroid location move radially. The radial distances of the initial flame centroid gradually increased\nby about 13%, 5%, 6%, 12%, 57%, and 24%. The trace of flame centroid is determined from the distribution of fuel and is related\nto the initial SMD of the atomizer. The maximum temperature rise and temperature rise rate are determined by the rate of\nflame chemical reaction, rate of large drop evaporation, and fuel/air ratio. With increasing inlet pressure, the maximum\ntemperature rise increased by 50%, 58%, 12%, 11%, and âË?â??9%, respectively. Meanwhile, the rate of the temperature rise increased\nby about 47%, 54%, 11%, 11%, and âË?â??7%, respectively....
The effect of the preparation method on the properties of LaMnO3 and\nLa0.8Sr0.2MnO3 perovskite was studied. Materials were prepared by four methods:\nsol-gel, chemical combustion, solvothermal and spray pyrolysis and\ncharacterized. The effect of the synthesis method on the texture, acid-base\ncharacter of the surface, reducibility with hydrogen, oxygen desorption, surface\ncomposition and catalytic activity for combustion of lean methane was\nstudied. It was found that synthesis method affects physicochemical properties\nof obtained materials-solvothermally produced materials exhibit\nwell-developed surface area, presence of reactive oxygen species on surface\nand high catalytic activity for CH4 combustion. Generally, LaMnO3 and\nLa0.8Sr0.2MnO3 perovskites show catalytic activity for lean CH4 combustion\ncomparable or higher than the activity of 0.5 wt.% Pt/Al2O3 but lower than 1\nwt.% Pd/Al2O3....
Theoretical investigations are performed on mechanism and kinetics of the reactions of ethyl radical C2H5 with NCO radical.The\nelectronic structure information of the PES is obtained at the B3LYP/6-311++G(d,p) level of theory, and the single-point energies\nare refined by the CCSD(T)/6-311+G(3df,2p) level of theory.The rate constants for various product channels of the reaction in the\ntemperature range of 200ââ?¬â??2000K are predicted by performing VTST and RRKMcalculations.Thecalculated results show that both\nthe N and O atoms of the NCO radical can attack the C atom of C2H5 via a barrierless addition mechanism to form two energyrich\nintermediates IM1 C2H5NCO(89.1 kcal/mol) and IM2C2H5OCN(64.7 kcal/mol) on the singlet PES.Then they both dissociate\nto produce bimolecular products P1 C2H4 + HOCN and P2 C2H4 + HNCO. At high temperatures or low pressures, the reaction\nchannel leading to bimolecular product P2 is dominant and the channel leading to P1 is the secondary, while, at low temperatures\nand high pressures, the collisional stabilization of the intermediate plays an important role and as a result IM2 becomes the primary\nproduct.The present results will enrich our understanding of the chemistry of the NCO radical in combustion processes....
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