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Ignition enhancement by addition of NO and NO2 from a N2/O2 plasma torch in a supersonic flow 总被引:1,自引:0,他引:1
Kenichi Takita Naoyuki Abe Goro Masuya Yiguang Ju 《Proceedings of the Combustion Institute》2007,31(2):2489-2496
The effects of NO and NO2 produced by using a plasma jet (PJ) of a N2/O2 mixture on ignition of hydrogen, methane, and ethylene in a supersonic airflow were experimentally and numerically investigated. Numerical analysis of ignition delay time showed that the addition of a small amount of NO or NO2 drastically reduced ignition delay times of hydrogen and hydrocarbon fuels at a relatively low initial temperature. In particular, NO and NO2 were more effective than O radicals for ignition of a CH4/air mixture at 1200 K or lower. These ignition enhancement effects were examined by including the low temperature chemistry. Ignition tests by a N2/O2 PJ in a supersonic flow (M = 1.7) for using hydrogen, methane, and ethylene injected downstream of the PJ were conducted. The results showed that the ignitability of the N2/O2 PJ is affected by the composition of the feedstock and that pure O2 is not the optimum condition for downstream fuel injection. This result of ignition tests with downstream fuel injection demonstrated a significant difference in ignition characteristics of the PJ from the ignition tests with upstream fuel injection. 相似文献
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Dunxi Yu Minghou Xu Hong Yao Jiancai Sui Xiaowei Liu Yun Yu Qian Cao 《Proceedings of the Combustion Institute》2007,31(2):1921-1928
The chemical composition of particles generated during pulverized coal combustion is the consequence of their formation processes. This work aims to use the size resolved elemental composition of coal-derived particles to identify their formation modes. A size-classified bituminous coal is burnt in a laboratory drop tube furnace at 1150, 1250, and 1350 °C, respectively. The elemental composition of the size-segregated particles from coal combustion is analyzed and the total mass fraction size distributions of Si and Al are obtained. Three particle formation modes are observed in these distribution profiles. The coarse mode has the highest value of the total mass fraction of Si and Al while the ultrafine mode has the lowest one. The total mass fraction of Si and Al in these two modes is nearly independent of particle size. It is believed that the coarse mode is formed by the mineral coalescence mechanism and the ultrafine mode by the vaporization–condensation mechanism. The difference in the total mass fraction of Si and Al between the central mode and the other two indicates that the central mode is formed by different mechanisms. Based on the observation that the total mass fraction of Si and Al in this mode increases with increasing particle size, heterogeneous condensation of vaporized species on existing fine residual ash particles is proposed to account for the formation of these particles. The study of the elemental composition of the three modes represented in five categories verifies the proposed formation mechanisms for them to some extent. 相似文献
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Effects of fine fuel droplets on a laminar flame stabilized in a partially prevaporized spray stream
Hiroshi Nomura Masashi Hayasaki Yasushige Ujiie 《Proceedings of the Combustion Institute》2007,31(2):2265-2272
A partially prevaporized spray burner was developed to investigate the interaction between fuel droplets and a flame. Monodispersed partially prevaporized ethanol sprays with narrow diameter distribution were generated by the condensation method using rapid pressure reduction of a saturated ethanol vapor–air mixture. A tilted flat flame was stabilized at the nozzle exit using a hot wire. Particle tracking velocimetry (PTV) was applied to measurements of the droplet velocity; the laminar burning velocity was obtained from gas velocity derived from the droplet velocity. Observations were made of flames in partially prevaporized spray streams with mean droplet diameters of 7 μm and the liquid equivalence ratios of 0.2; the total equivalence ratio was varied. In all cases, a sharp vaporization plane was observed in front of the blue flame. Flame oscillation was observed on the fuel-rich side. At strain rates under 50 s−1, the change in the burning velocity with the strain rate is small in fuel-lean spray streams. In spray streams of 0.7 and 0.8 in the total equivalence ratio, burning velocity increases with strain rates of greater than 50 s−1. However, in spray streams with 0.9 and 1.0 in the total equivalence ratio, burning velocity decreases as the strain rate increases. At strain rates greater than 80 s−1, burning velocity decreases with an increased gas equivalence ratio. The effect of mean droplet diameter, and the entry length of droplets into a flame on the laminar burning velocity, were also investigated to interpret the effect of the strain rate on the laminar burning velocity of partially prevaporized sprays. 相似文献
996.
Chadwick C. Rasmussen Sulabh K. Dhanuka James F. Driscoll 《Proceedings of the Combustion Institute》2007,31(2):2505-2512
Laser-induced fluorescence of OH and CH2O was imaged to investigate the flame stabilization mechanism in a flameholder with a Mach 2.4 free stream. Ethylene was burned in a rectangular cavity with two points of injection: the aft wall and the cavity floor. When injected from the aft wall, the fuel came into immediate contact with hot combustion products from the reaction zone under the shear layer. Primary combustion occurred under the shear layer and in the aft region of the cavity volume. In contrast, when fuel was injected from the floor, a jet-driven recirculation zone of hot products near the upstream wall of the cavity served as a flameholder. The reaction then occurred on the underside of the shear layer. In conditions near lean blowout, significant changes in the flameholding mechanisms were observed. Improved CH2O fluorescence signal was obtained by taking advantage of the long fluorescence lifetime at low pressures and delaying the camera gate to reduce the background signal. 相似文献
997.
Ying Huang Grant A. Risha Vigor Yang Richard A. Yetter 《Proceedings of the Combustion Institute》2007,31(2):2001-2009
The combustion of bimodal nano/micron-sized aluminum particles with air is studied both analytically and experimentally in a well-characterized laminar particle-laden flow. Experimentally, an apparatus capable of producing Bunsen-type premixed flames was constructed to investigate the flame characteristics of bimodal-particle/air mixtures. The flame speed is positively affected by increasing the mass fraction of nano particles in the fuel formulation despite the lower flame luminosity and thicker flame zone. Theoretically, the flames are assumed to consist of several different regimes for fuel-lean mixture, including the preheat, flame, and post flame zones. The flame speed and temperature distribution are derived by solving the energy equation in each regime and matching the temperature and heat flux at the interfacial boundaries. The analysis allows for the investigation of the effects of particle composition and equivalence ratio on the burning characteristics of aluminum-particle/air mixtures. Reasonable agreement between theoretical results and experimental data was obtained in terms of flame speed. The flame structure of a bimodal particle dust cloud may display either an overlapping or a separated configuration, depending on the combustion properties of aluminum particles at different scales. At low percentages of nano particles in the fuel formulation, the flame exhibits a separated spatial structure with a wider flame regime. At higher nano-particle loadings, overlapping flame configurations are observed. 相似文献
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