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排序方式: 共有220条查询结果,搜索用时 812 毫秒
81.
82.
83.
Benzyl is a resonantly stabilized radical that commonly occurs as an intermediate in the combustion of aromatic compounds. The bimolecular reaction of benzyl with HO2 is important in the oxidation of toluene, especially at low to moderate temperatures, where unimolecular decomposition of the benzyl radical is slow. We show that the addition of HO2 to the methylene site in benzyl produces a vibrationally excited benzylhydroperoxide adduct, with over 60 kcal mol−1 (251 kJ mol−1) of excess energy above the ground state. RRKM simulations are performed on the benzyl + HO2 reaction, using thermochemical and kinetic parameters obtained from ab initio calculations, with variational transition state theory (VTST) for treatment of barrierless radical + radical reaction kinetics. Our results reveal that the benzyl + HO2 reaction proceeds predominantly to the benzoxyl radical + OH at temperatures of around 800 K and above, with the production of stabilized benzylhydroperoxide molecules dominating at lower temperatures. The heat of formation of the benzyl radical is calculated as 52.5 kcal mol−1 (219.7 kJ mol−1) at the G3B3 level of theory, in relative agreement with other recent determinations of this value. 相似文献
84.
Gerald Mairinger Alessio Frassoldati Alberto Cuoci Matteo Pelucchi Ernst Pucher Kalyanasundaram Seshadri 《Proceedings of the Combustion Institute》2019,37(2):1605-1614
Experimental and computational investigations are carried out to elucidate the fundamental mechanisms of autoignition of surrogates of jet-fuels at elevated pressures up to 6 bar. The jet-fuels tested are JP-8, Jet-A, and JP-5, and the surrogates tested are the Aachen Surrogate made up of 80 % n-decane and 20 % 1,3,5-trimethylbenzene by mass, Surrogate C made up of 60 % n-dodecane, 20 % methylcyclohexane and 20 % o-xylene by volume, and the 2nd generation Princeton Surrogate made up of 40.4 % n-dodecane, 29.5 % 2,2,4-trimethylpentane, 7.3 % 1,3,5-trimethylbenzene and 22.8 % n-propylbenzene by mole. Using the counterflow configuration, an axisymmetric flow of a gaseous oxidizer stream, made up of a mixture of oxygen and nitrogen, is directed over the surface of an evaporating pool of a liquid fuel. The experiments are conducted at a fixed value of mass fraction of oxygen in the oxidizer stream and at a fixed value of the strain rate. The temperature of the oxidizer stream at autoignition, Tig, is measured as a function of pressure, p. Experimental results show that the critical conditions, of autoignition of the surrogates are close to that of the jet-fuels. Overall the critical conditions of autoignition of Surrogate C agree best with those of the jet-fuels. Computations were performed using skeletal mechanisms constructed from a detailed mechanism. Predictions of the critical conditions of autoignition of the surrogates are found to agree well with measurements. Computations show that low-temperature chemistry plays a significant role in promoting autoignition for all surrogates. The low-temperature chemistry, of the component of the surrogate with the greatest volatility, was found to have the most influence on the critical conditions of autoignition. 相似文献
85.
Liquid-spray flames are encountered in many practical combustion devices such as gasoline direct injection and diesel engines, gas turbine combustors as well as industrial furnaces. As opposed to gaseous fuels, additional phase-change steps present in liquid sprays not only complicate the overall combustion process, but also make in-situ, laser-based combustion diagnostics challenging. In particular, the formation of carbon monoxide (CO) due to incomplete fuel-air mixing and partial oxidation becomes a major challenge. In this study, we apply femtosecond, two-photon laser-induced fluorescence (fs-TPLIF) to measure CO concentration in piloted liquid-spray flames, taking into account possible signal interferences in the 230.1-nm, B1Σ+←X1Σ+ excitation scheme. A modified, flat-flame McKenna burner fitted with a direct-injection high-efficiency nebulizer (DIHEN) was used to produce piloted liquid-methanol spray flames. Although single-laser-shot OH-PLIF images show the presence of strong turbulent interactions in the core region, shot-averaged OH-PLIF images indicate that near the nozzle-exit region, the primary reaction takes place in an annular region around the droplet cloud, in general. A detailed spectroscopic study reveals that the signal interference at 460?nm originating from the second-order scattering of the excitation laser, which becomes approximately an order of magnitude stronger than CO fluorescence spectral lines near the nozzle exit region. The specific spectral filtering scheme introduced in our recent work is proved to be capable of suppressing interferences primarily originating from C2 Swan-band emissions. Two-dimensional CO maps along with OH-PLIF flame structure data provide key insights into the CO formation in piloted liquid-spray flames, while providing critical validation datasets for advanced computational models. 相似文献
86.
Renan B. Kops Fernando M. Pereira Miriam Rabaçal Mário Costa 《Proceedings of the Combustion Institute》2019,37(3):2977-2985
This article investigates the effect of steam on the ignition of single particles of solid fuels in a drop tube furnace under air and simulated oxy-fuel conditions. Three solid fuels, all in the size range 125–150 µm, were used in this study; specifically, a low rank sub-bituminous Colombian coal, a low-rank/high-ash sub-bituminous Brazilian coal and a charcoal residue from black acacia. For each solid fuel, particles were burned at a constant drop tube furnace wall temperature of 1475?K, in six different mixtures of O2/N2/CO2/H2O, which allowed simulating dry and wet conventional and oxy-fuel combustion conditions. A high-speed camera was used to record the ignition process and the collected images were treated to characterize the ignition mode (either gas-phase or surface mode) and to calculate the ignition delay times. The Colombian coal particles ignite predominately in the gas-phase for all test conditions, but under simulated oxy-fuel conditions there is a decrease in the occurrence of this ignition mode; the charcoal particles experience surface ignition regardless of the test condition; and the Brazilian coal particles ignite predominately in the gas-phase when combustion occurs in mixtures of O2/N2/H2O, but under simulated oxy-fuel conditions the ignition occurs predominantly on the surface. The ignition delay times for particles that ignited in the gas-phase are smaller than those that ignited on the surface, and generally the simulated oxy-fuel conditions retard the onset of both gas-phase and surface ignition. The addition of steam decreases the gas-phase and surface ignition delay times of the particles of both coals under simulated oxy-fuel conditions, but has a small impact on the gas-phase ignition delay times when the combustion occurs in mixtures of O2/N2/H2O. The steam gasification reaction is likely to be responsible for the steam effect on the ignition delay times through the production of highly flammable species that promote the onset of ignition. 相似文献
87.
Laminar flame speeds of premixed jet fuel/air with the addition of hydrogen, methane and ethylene are measured in a constant-volume bomb at an initial temperature of 420 K, initial pressure of 3 atm, equivalence ratios of 0.6–1.5 and gas mass fractions of 0–50%. The experimental results show that the addition of hydrogen and ethylene can significantly improve the laminar flame speed of the liquid jet fuel, while the addition of methane shows a weak inhibitory effect, and these effects are relatively remarkable on the fuel-rich conditions. The laminar flame speed of the dual fuels/air is linearly dependent on the additional gas mass fraction. A kinetic analysis indicates that the gas addition causes both thermodynamic and chemical kinetic effects on the laminar flame speed of the dual fuels/air. The adiabatic temperature increases and decreases with the addition of hydrogen/ethylene and methane, respectively. A sensitivity analysis shows that the reactions concerning to the H, CH3 and C2H3 radicals become significant with the addition of hydrogen, methane and ethylene, respectively, and that the different values of the rate of product (ROP) of these species via the critical reactions lead to a different promotional or inhibitory effect on the fuel-rich and fuel-lean conditions. 相似文献
88.
89.
Mark T. Holtzapple Richard R. Davison M. Kyle Ross Salvador Aldrett-Lee Murlidhar Nagwani Chang-Ming Lee Champion Lee Seth Adelson William Kaar David Gaskin Hiroshi Shirage Nan-Sheng Chang Vincent S. Chang Mitchell E. Loescher 《Applied biochemistry and biotechnology》1999,79(1-3):609-631
The MixAlco process is a patented technology that converts any biodegradable material (e.g., sorted municipal solid waste,
sewage sludge, industrial biosludge, manure, agricultural residues, energy crops) into mixed alcohol fuels containing predominantly
2-propanol, but also higher alcohols up to 7-tridecanol. The feed stock is treated with lime to increase its digestibility.
then, it is fed to a fermentor in which a mixed culture of acid-forming microorganisms produces carboxylic acids. Calcium
carbonate is added to the fermentor to neutralize the acids to their corresponding carboxylate salt. The dilute (−3%) carboxylate
salts are concentrated to 19% using an amine solvent that selectively extracts water. Drying is completed using multi-effect
evaporators. Finally, the dry salts are thermally converted to ketones which subsequently are hydrogenated to alcohols. All
the steps in the MixAlco process have been proven at the laboratory scale. A techno-economic model of the process indicates
that with the tipping fees available in New York ($126/dry tonne), mixed alcohol fuels may be sold for $0.04/L ($0.16/gal)
with a 60% return on investment (ROI). With the average tipping fee in the United States rates ($63/dry tonne), mixed alcohol
fuels may be sold for $0.18/L ($0.69/gal) with a 15% ROI. In the case of sugarcane bagasse, which may be obtained for about
$26/dry ton, mixed alcohol fuels may be sold for $0.29/L ($1.09/gal) with a 15% ROI. 相似文献
90.
界面膜引发的乳化燃油燃烧中的振荡反应 总被引:1,自引:1,他引:0
有关小分子醇、H。和CO等易燃气体在铂催化下的高温燃烧的温度振荡及以表面活性剂为关键组分的液膜扩散振荡已有报道"-'-.但由界面膜作用而产生的乳化燃油燃烧中的振荡反应尚无其它可操作的原始研究文献,只是在前文['j中提及过出现该现象.为了解乳化燃油燃烧过程中界面变化及其对燃烧的作用,通过静态燃烧实验配方的调节及变换以改变燃烧界面的情况.实验发现,在乳化燃油中加入一般的食用豆油,并使之水解出长链竣酸盐,则富集在燃烧界面上的长链竣酸盐所形成的界面膜对燃烧的自阻抑作用便会产生明显的振荡反应,形成火焰温度与高… 相似文献