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191.
基于带化学反应的二维轴对称Euler方程,利用带有Superbee限制函数的波传播算法,对共振腔中的氢气-空气预混气的聚心燃烧进行了数值模拟,讨论了共振腔不同抛物面对起爆的影响。数值结果表明,在开始阶段,燃烧诱导的激波在轴心、火焰和固壁的反射,使火焰失稳,随后共振腔中的抛物壁面上产生一定频率和强度的反射激波,不断穿越火焰,使火焰进一步失稳,加剧了燃烧速度,最终导致爆轰的形成。同时,火焰在与激波的作用过程中,形状扭曲变形,呈封闭端小敞口端大的扁平头部蘑菇云。共振腔抛物面的不同形状引起激波聚焦位置的变化,会影响激波和火焰的相互作用,使起爆提前或推迟,甚至不起爆。 相似文献
192.
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195.
Acrylic acid modified magnesium hydroxide nano-needles (AA–Mg(OH)2) had been synthesized by alkaline injected into magnesium chloride solution at about 0°C in the presence of acrylic acid
(AA). Then the polystyrene/magnesium hydroxide nano-needles composite (PS/Mg(OH)2) had been prepared by the radical copolymerization with styrene in toluene system using AA–Mg(OH)2 as a macro-monomer. The elemental analysis (EA) and Fourier transform infrared (FTIR) analyses show that the polystyrene
had been grafted onto the surfaces of the nano-needles (AA–Mg(OH)2). The nano-needles (AA–Mg(OH)2) had better dispersibility in polystyrene matrix as observed by transmission electron microscope (TEM) analysis. The thermal
behavior analysis results from the differential scanning calorimetry (DSC) indicated that the magnesium hydroxide nano-needles
had lower thermal decomposition temperature than that of the polymer matrix and it is expected that the nano-needles prepared
by the proposed method could be used as an environmental-friendly flame retardant. 相似文献
196.
The high pressure phase transition and elastic behavior of rare earth monoselenides (CeSe, EuSe and LaSe) which crystallize
in a NaCl-structure have been investigated using the three body interaction potential (TBIP) approach. These interactions
arise due to the electronshell deformation of the overlapping ions in crystals. The TBP model consists of a long range Coulomb,
three body interactions and the short range overlap repulsive forces operative up to the second neighboring ions. The authors
of this paper estimated the values of the phase transition pressure and the associated volume collapse to be closer than other
calculations. Thus, the TBIP approach also promises to predict the phase transition pressure and pressure variations of elastic
constants of lanthanide compounds.
相似文献
197.
Rotational Coherent anti-Stokes Raman spectroscopy (CARS) has the last decades been developed into a useful tool for thermometry and concentration measurements in combustion. In this paper, we present a novel polarization approach of the technique, which will enhance its potential and widen the range of conditions at which it can be utilized. The theory of the polarization approach is described in detail. It is shown that by specific arrangement of the polarizations of the laser beams, total suppression of the non-resonant background signal can be obtained, and thus by probing only the resonant CARS signal the diagnostic utility of the technique increases. The main benefit of the approach is in situations where the non-resonant background signal is relatively high in comparison with the resonant signal. The high potential of polarization rotational CARS for thermometry is demonstrated in some illustrative examples, for example, nitrogen thermometry on the fuel side of diffusion flames, and carbon monoxide thermometry in the product gas of ethylene/oxygen/argon-flames. 相似文献
198.
A linear stability analysis is conducted to study the onset of near-limit flame oscillation with radiative heat loss in 1-D chambered planar flames using multi-scale activation-energy asymptotics. The oscillatory instability near the radiation-induced extinction limit at large Damköhler numbers is identified, in additional to the one near the kinetic limit at small Damköhler numbers. It is shown that radiative loss assumes a similar role as varying the thermal diffusivity of the reactants. Thus, flame oscillation near the radiative limit is still thermal-diffusive in nature although it may develop under unity Lewis numbers. The unstable range of Damköhler numbers near the radiative limit shows quite similar parametric dependence on the Lewis numbers of reactants, LeF and LeO, the stoichiometry, ?, and the radiative loss as that near the kinetic limit. They both increase monotonically with LeO and ? and increase then decrease with LeF. Increasing radiative loss extends the parameter range under which flame oscillations may develop. However, they show different dependence on the temperature difference between the supplying reactants. Unless radiative loss approaches its maximum value the system can sustain, flame oscillation near the radiative limit is only possible within a limited range of ΔT, whereas it is promoted monotonically with decreasing ΔT near the kinetic limit. Furthermore, while radiative loss shows small effect on the nondimensional oscillation frequency, the dimensional frequency of flame oscillations near the radiative limit can be substantially smaller than that near the kinetic limit. 相似文献
199.
Hongyan Sun S.I. Yang G. Jomaas C.K. Law 《Proceedings of the Combustion Institute》2007,31(1):439-446
Laminar flame speeds were accurately measured for CO/H2/air and CO/H2/O2/helium mixtures at different equivalence ratios and mixing ratios by the constant-pressure spherical flame technique for pressures up to 40 atmospheres. A kinetic mechanism based on recently published reaction rate constants is presented to model these measured laminar flame speeds as well as a limited set of other experimental data. The reaction rate constant of CO + HO2 → CO2 + OH was determined to be k = 1.15 × 105T2.278 exp(−17.55 kcal/RT) cm3 mol−1 s−1 at 300-2500 K by ab initio calculations. The kinetic model accurately predicts our measured flame speeds and the non-premixed counterflow ignition temperatures determined in our previous study, as well as homogeneous system data from literature, such as concentration profiles from flow reactor and ignition delay time from shock tube experiments. 相似文献
200.
The sooting behaviour of binary fuel mixtures was evaluated both experimentally and through computer simulations. The soot volume fraction in laminar diffusion flames of mixtures of ethylene/propane, methane/ethylene, methane/propane, methane/ethane, methane/butane, ethane/propane and ethane/ethylene fuels was measured using 2-dimensional line of sight attenuation. A synergistic effect was observed for the ethylene/propane, methane/ethylene, methane/ethane and ethane/ethylene mixtures. The synergistic effect translated into a higher soot concentration for a mixture fraction than could be yielded by the added contribution of both pure fuels. Such an effect was not observed for the methane/propane, methane/butane and ethane/propane mixtures. Through experiments in which the flame temperature was kept constant, it was determined that the synergistic effect in the methane/ethylene mixture is very temperature dependent whereas, that in the ethylene/propane mixture is not. This phenomenon was further studied through the modeling of the ethylene/propane mixture. Numerical simulations were carried out using two different soot models. The simulations confirmed the presence of a synergistic effect. It was found that the effect could be directly correlated to a synergistic effect in the concentration of n-C4H5 and n-C4H3, which could be traced back to an interaction between ethylene and methyl radical species. These results yield further insight into the pathways to soot formation and highlight the importance of further analyzing binary fuel mixtures as a means of understanding soot formation in practical devices using industrial fuels. 相似文献