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81.
The flame quenching process in combustors was observed by high speed camera and Schlieren system, at the inflow conditions of Ma = 2.64, T 0 = 1 483 K, P 0 = 1.65 MPa, T = 724 K and P = 76.3 kPa. Changing process of the flame and shock structure in the combustor was clearly observed. The results revealed that the precombustion shock disappeared accompanied with the process in which the flame was blown out and withdrawed from the mainflow into the cavity and vanished after a short while. The time of quenching process was extended by the cavity flame holder, and the ability of flame holding was enhanced by arranging more cavities in the downstream as well. The flame was blown from the upstream to the downstream, so the flame in the downstream of the cavity was quenched out later than that in the upstream. 相似文献
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83.
Combustion characteristics of a dual-mode scramjet combustor with cavity flameholder 总被引:7,自引:0,他引:7
Combustion characteristics of a laboratory dual-mode ramjet/scramjet combustor were studied experimentally. The combustor consists of a sonic fuel jet injected into a supersonic crossflow upstream of a wall cavity pilot flame. These fundamental components are contained in many dual-mode combustor designs. Experiments were performed with an isolator entrance Mach number of 2.2. Air stagnation temperatures were varied from 1040 to 1490 K, which correspond to flight Mach numbers of 4.3–5.4. Both pure hydrogen and a mixture of hydrogen and ethylene fuels were used. High speed imaging of the flame luminosity was performed along with measurements of the isolator and combustor wall pressures. For ramjet mode operation, two distinct combustion stabilization locations were found for fuel injection a sufficient distance upstream of the cavity. At low T0, the combustion was anchored at the leading edge of the cavity by heat release in the cavity shear layer. At high T0, the combustion was stabilized a short distance downstream of the fuel injection jet in the jet-wake. For an intermediate range of T0, the reaction zone oscillated between the jet-wake and cavity stabilization locations. Wall pressure measurements showed that cavity stabilized combustion was the steadiest, followed by jet-wake stabilized, and the oscillatory case. For fuel injection close to the cavity, a hybrid stabilization mode was found in which the reaction zone locations for the two stabilization modes overlapped. For this hybrid stabilization, cavity fueling rate was an important factor in the steadiness of the flow field. Scramjet mode combustion was found to only exist in the cavity stabilized location for the conditions studied. 相似文献
84.
Oscillatory behaviour of state variables is desirable in pulse combustors, as properly designed pulsations lead to improved performances, such as higher thermal efficiency and lower emissions compared to steady combustors. In the present work, we perform a systematic investigation of the stability of steady states and limit cycles of a pulse combustor model through numerical continuation. Different bifurcation parameters such as tailpipe friction factor, wall temperature, convective heat transfer coefficient, inlet temperature and inlet fuel mass fraction are varied to identify the complete ranges of those parameters at which limit cycles can be expected. This analysis identifies alternative stable periodic regimes in parameter space (e.g. friction factor). In addition, a few performance indicators such as amplitude of oscillations, cycle-averaged heat transfer and cycle-averaged specific thrust are compared between different ranges of friction factor yielding limit cycle oscillations. The comparison clearly shows that, depending upon the application, friction factor can be chosen from different regimes. The time-integration of the model is also performed to support the bifurcation results obtained from numerical continuation, wherever appropriate. The complete stability margin of limit cycle oscillations for those bifurcation parameters can be useful for improved design of the combustor and for determining the optimal operating conditions of pulse combustors. 相似文献
85.
In this paper, we establish a constant‐type growth estimate in the Lipschitz norm of solutions to the 2D Navier–Stokes equations with fractional diffusion and a polynomial‐type growth estimate of solutions to the 3D axisymmetric Navier–Stokes equations. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
86.
Baolu Shi Qing Cao Dingjiang Xie Weikang Peng Ningfei Wang 《Proceedings of the Combustion Institute》2019,37(4):4329-4336
To utilize sustainable biofuel, the current study proposes a novel combustion technique that directly burns liquid ethanol without a spray system. Two swirling air flows are induced by tangentially injected the gas from two concentric tubes at different stages. The liquid ethanol is fed by a liquid tank at the center. At the beginning methane flame assists in preheating the system to vaporize liquid ethanol and ignite the vapor. Thereafter methane is switched off, and liquid ethanol can be continuously vaporized through self-burning released heat. The heat and mass transfer processes are examined to illustrate such self-sustained burning–heating–evaporating system. The ethanol flow rate is gradually increased to provide different heat output. The flame structures, temperature distributions and pollutant emissions are carefully examined. The results show that the ethanol can be steadily burned to provide heat output between 0.7 and 2.5?kW. Generally a blue flame is obtained, and the NOx and CO concentrations are ultralow. By increasing ethanol flow rate to exceed 8?mL/min, an unsteady, sooting flame is observed owing to incomplete evaporation and poor mixing. A parametric study is conducted to evaluate the influences of liquid tank position, flow rate and tip structure on the combustion characteristics. Additionally, an optimal operation condition is proposed. The current study provides a promising method to burn low-boiling liquid fuel in a clean, efficient and compact way. 相似文献
87.
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89.
An asymptotic solution of the momentum equation is given that describes the decay of swirling flow passing along the annulus formed between two concentric, straight, circular-section pipes having a common starting point. The flow is considered turbulent and approximations are made consistent with the notion of fully developed flow conditions. Applications of this approach are reviewed and shortcomings highlighted. A series of calculations are presented and compared with experimental and theoretical data previously obtained by the authors. It is shown that acceptable predictions of the overall flow behavior can be obtained over a wide range of initial conditions provided the calculations procedure is applied in regions of validity, which has not been the case in some published work. Substantial errors are found if, for example, the procedure is allowed to commence at inlet to the annulus owing to the inconsistency of the assumptions in the initially developing-flow region, which for this work extends at least five outer-pipe diameters downstream from inlet. The authors' previous numerical integration scheme may be used to predict flows satisfactorily in the developing-flow region and the present asymptotic solution used subsequently to reduce computation time and cost. 相似文献
90.
进气温度对微燃机燃烧室燃烧特性的影响分析 总被引:1,自引:0,他引:1
本文通过实验研究了在保持微型燃气轮机燃烧室出口排气温度不变的情况下,改变进口空气温度对燃烧室燃烧特性的影响.结果表明,随着燃烧室进气温度的增大,燃烧效率提高,燃烧室出口温度不均匀性系数减小,热阻增大,总压恢复系数有所降低.同时,实验结果还表明,随着燃烧室进口空气温度的增大,燃烧室出口处CO及未燃烬碳(UHC)排放浓度显著降低,但NO排放浓度则增大.根据实验结果,本文还分析了进气温度的改变对燃烧室燃烧特性的影响规律,为今后微型燃气轮机燃烧室的研制及改进提供了参考依据. 相似文献