共查询到20条相似文献,搜索用时 11 毫秒
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通过拓展层流火焰消耗速度的概念,将其定义与反应进程变量(progress variable)的定义相结合,给出了一个积分层流燃烧速度的广义定义。在准一维稳态系统中,分析了积分层流燃烧速度,以及其与未燃气体的位移速度和已燃气体的位移速度之间的关系。对甲烷-空气和丙烷-空气拉伸层流预混火焰在常温常压下进行了数值计算,研究了在不同当量比下,火焰拉伸对层流燃烧速度的影响,并得出了马克斯坦长度。对基于通过火焰前锋放热率的积分层流燃烧速度和基于燃料消耗率的积分层流燃烧速度进行了比较。结论表明低拉伸火焰的马克斯坦数与渐进分析一致,也与球形火焰获得的实验数据吻合。 相似文献
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《International Journal of Hydrogen Energy》2020,45(56):32508-32520
Laminar burning velocity, Markstein length, and critical flame radius of an H2/O2 flame with different diluents, He, Ar, N2 and CO2, were measured under elevated pressure with different diluent concentrations. The effects of pressures, diluents, and dilution and equivalence ratios were studied by comparing calculated and experimental results. The laminar burning velocity showed non-monotonic behavior with pressure when the dilution ratio was low. The reason is the radical pool reduced with increasing pressure and leads to the decrease of overall reaction order from larger than 2 to smaller than 2, and further leads to this non-monotonic phenomenon. A modified empirical equation was presented to capture the relationship between active radicals and laminar burning velocity. Critical radii and Markstein lengths both decrease with initial pressure and increase with equivalence ratio and dilution ratio. The calculated critical radii indicate that the Peclet number and flame thickness control the change of Rcr. It can be found that Leeff has a significant influence on Peclet number and leads to the decrease of critical flame radii of Ar, N2, and CO2 diluted mixture. Interestingly, the CO2 diluted mixture has the lowest Markstein length under stoichiometric conditions and a high value under fuel-rich conditions, consistent as the flame instability observed on the flame images. The reason is that the Leeff of CO2 diluted mixture increased rapidly with the equivalence ratio. 相似文献
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《能源学会志》2020,93(4):1278-1287
The freely-propagating laminar premixed flames of CH4–N2/CO2/H2O/Ar-O2 mixtures were conducted with the PREMIX code. The effects of the equivalence ratio and various oxidant atmospheres on the basic combustion characteristics were analyzed with the initial pressure and temperature of 1 atm and 398 K, respectively, O2 content in the oxidant of 21%. The chemical reaction mechanism GRI-Mech 3.0 was chosen to determine the effects of the oxidant atmospheres of N2/O2, CO2/O2, H2O/O2, and Ar/O2 on the adiabatic flame temperature, laminar burning velocity, flame structure, free radicals, intermediate species, net heat release rate and specific heat of the fuel/oxidant mixtures. The numerical results show that the maximum adiabatic flame temperatures and laminar burning velocities are at Ar/O2 atmosphere. The mole fractions of CO and H2 increased fastest at CO2/O2 atmosphere and H2O/O2, respectively. The mole fractions of CH3 and H follow the order Ar/O2> N2/O2>H2O/O2>CO2/O2. In addition, for 4 oxidant atmospheres, the peak mole fraction of C2H2 is following the order H2O/O2>Ar/O2>N2/O2>CO2/O2 and the net heat release rate is following the order Ar/O2>N2/O2>H2O/O2>CO2/O2 for all equivalence ratios. 相似文献
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Zhiyuan Zhang Xiangang Wang Jun Xiang Xibin Wang Haiyan Miao 《Combustion and Flame》2008,155(3):358-368
The laminar burning velocities and Markstein lengths for the methanol-air mixtures were measured at different equivalence ratios, elevated initial pressures and temperatures, and dilution ratios by using a constant volume combustion chamber and high-speed schlieren photography system. The influences of these parameters on the laminar burning velocity and Markstein length were analyzed. The results show that the laminar burning velocity of the methanol-air mixture decreases with an increase in initial pressure and increases with an increase in initial temperature. The Markstein length decreases with an increase in initial pressure and initial temperature, and increases with an increase in the dilution ratio. A cellular flame structure is observed at an early stage of flame propagation. The transition point is identified on the curve of flame propagation speed against stretch rate. The reasons for the cellular structure development are also analyzed. 相似文献
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《International Journal of Hydrogen Energy》2022,47(37):16686-16697
The present work reports experimental investigations on laminar burning velocity variation of CH4+H2+air mixtures at elevated temperatures (300–650 K) using an externally heated diverging-channel method. The effect of mixture equivalence ratio (? = 0.7–1.3) and H2 fraction (0–50% by volume) on burning velocity have been reported at elevated temperatures. The experimental measurements are compared with numerical simulations using GRI Mech 3.0 and FFCM-1 kinetic models. The obtained results exhibit an increase in the laminar burning velocity with H2 fraction due to the formation of H-atom as an intermediate. The temperature dependency is established through a power-law correlation. The temperature-exponent shows a parabolic variation with a minimum value at ? = 1.1. Reaction pathway diagram interprets the major oxidation paths followed by reactants for higher carbon-consumption with varying H2 fraction. The P2 pathway involving ethane breakdown plays a major role in enhancing the burning velocity at rich mixture conditions. 相似文献
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Denis Lapalme Romain Lemaire Patrice Seers 《International Journal of Hydrogen Energy》2017,42(12):8314-8328
This paper investigates the various techniques used in the literature to calculate the effective Lewis number of two-component (H2/CO and H2/CH4) and three-component fuels (H2/CO/CH4 and H2/CO/CO2) over a wide range of equivalence ratios (0.6 ≤ φ ≤ 1.4) under laminar flame conditions. The most appropriate effective Lewis number formulation is identified through comparison with experimentally extracted Lewis numbers (Le). The paper first identifies the proper methodology to extract the experimental Le from the burned Markstein length of an outwardly propagating flame. Second, the different methodologies for the calculation of the effective Le are presented and compared to experimental results for H2/CH4 and H2/CO mixtures. Based on the experimental results, it is shown that the calculation of the effective Le of mixtures can be divided into a three-step procedure depending on the equivalence ratio: (1) calculation of the Le for each fuel and the oxidizer; (2) use of the Le mixing rule; and (3) assessment of the necessity or not of combining the fuel's and oxidizer's Lewis numbers. The paper shows that, in rich mixtures, the oxidizer Le needs to be taken into account. Lastly, the methodology is validated for H2/CO/CH4 and H2/CO/CO2 fuels. 相似文献
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《International Journal of Hydrogen Energy》2019,44(2):1192-1212
The effect of the addition of hydrogen to various multicomponent natural gas (NG) blends is experimentally and numerically investigated. All the experiments are performed at a pressure of 0.1 MPa, a temperature of 300 ± 3 K, and a range of equivalence ratios (Φ = 0.6 to 1.4), using a constant pressure freely propagating spherical flame method. Numerical simulations are performed using the CHEMKIN-PRO® simulation software, with three different chemical kinetic mechanisms. Laminar burning velocity (LBV) and burned gas Markstein length (Lb) of the various NG-H2 blends at three different levels of hydrogen in the fuel, viz., 25%, 50%, and 75%, are experimentally evaluated to assess the effect of the simultaneous presence of H2 and higher hydrocarbons (HC) in various NG blends. The addition of H2 enhances the combustion chemistry of all the NG blends, and hence, increases the LBV. However, the effect is more prominent for the NG6-H2 blend, which has a higher mole fraction of CH4. The NG5-H2 blend, which has a higher mole fraction of C3H8 maintains a positive Lb for a wider range of equivalence ratios (0.7–1.4). The LBV prediction using the GRI-MECH 3.0 mechanism is within the range of experimental uncertainty, for the blends with up to 50% H2 in the fuel. The prediction of LBV using GRI-MECH 3.0 is the closest to the experimental results for the blends with 75% H2 in the fuel when compared with those using San Diego and USC-MECH 2.0 mechanisms. 相似文献
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《International Journal of Hydrogen Energy》2020,45(39):20391-20399
Hydrogen (H2) is an effective additive to improve the issue of low laminar burning velocity of some biofuels. In order to better understand the laminar burning characteristics of ethyl acetate (EA) with or without H2 addition, experimental investigations of laminar burning characteristics were carried out by using the high-speed Schlieren photography technique in a constant volume combustion chamber. Tests were conducted under various equivalence ratios ranging from 0.5 to 1.4 with an initial temperature of 358 K, an initial pressure of 0.1 MPa and a H2/air proportion of 0%, 4%, 8% and 12% by volume. Laminar burning velocities, together with other parameters such as laminar burning flux, flame thickness, Markstein length and Markstein number, were calculated and discussed. In addition, the experimental data were compared with numerical simulations based on the Dayma model. Results showed that the laminar burning velocity of EA was enhanced with the increase of H2 addition, and the maximum value reached 95.09 cm/s at φ = 0.6 with 12% H2, a value more than twice as fast as that of pure EA (39.3 cm/s). Moreover, H2 was found to extend the lower flammability limit of EA. The laminar burning velocities simulated with the Dayma model agreed well with the experimental results of EA at various H2 additions. 相似文献
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Experimental and numerical study on the laminar burning velocity of hydrogen enriched biogas mixture
《International Journal of Hydrogen Energy》2019,44(39):22240-22249
The laminar burning velocities of biogas-hydrogen-air mixture at different fuel compositions and equivalence ratios were determined and studied using the spherical flame method. The combined effects of H2 and CO2 on the laminar burning velocity were investigated quantitatively based on the kinetic effects and the thermal effects. The results show that the laminar burning velocities of the BG40, BG50 and BG60 are increased almost linearly with the H2 addition owing to the improved fuel kinetics and the increased adiabatic flame temperature. The dropping trend of laminar burning velocity from the BG60-hydrogen to the BG40-hydrogen is primarily attributed to the decreased adiabatic flame temperature (thermal effects). The GRI 3.0 mechanism can predict the laminar burning velocity of biogas-hydrogen mixture better than the San Diego mechanism in this study. Whereas, the GRI mechanism still needs to be modified properly for the hydrogen-enriched biogas as the CO2 proportion exceeds 50% in the biogas at the fuel-rich condition. The increased CO2 exerts the stronger suppression on the net reaction rate of H + O2=OH + O than that of H + CH3(+M) = CH4(+M), which contributes to that the rich-shift of peak laminar burning velocity of biogas-hydrogen mixture requires higher H2 addition as the CO2 content is enhanced. For the biogas-hydrogen fuel, the H2 addition decreases the flame stability of biogas fuel effectively due to the increased diffusive-thermal instability and hydrodynamic instability. The improved flame stability of biogas-hydrogen fuel with the increased CO2 content is resulted from the combined effects of diffusive-thermal instability and hydrodynamic instability. 相似文献
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《International Journal of Hydrogen Energy》2020,45(33):16838-16850
An experimental and numerical study on the combined effect of N2/CO2 dilution and hydrogen addition on the laminar burning velocity (LBV) of methane-oxygen mixtures was conducted. The experiments were performed at atmospheric conditions using the heat flux method for effective equivalence ratios (ϕF) varying from 0.7 to 1.3. The results show that the hydrogen addition causes an increase in LBV for all the mixture conditions. The variation in LBV based on hydrogen addition parameter (RH) for all N2 dilution conditions were following a linearly increasing trend. The strong effect of hydrogen addition on LBV is observed at lean and rich mixtures compared to that at near stoichiometric mixture conditions. The experimental results show that the percentage variation in LBV with RH at rich mixture is more substantial at 75% N2 dilution compared to that at 65% N2 dilution. 相似文献
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Flame front evolution and laminar flame parameter evaluation of buoyancy-affected ammonia/air flames
《International Journal of Hydrogen Energy》2021,46(77):38504-38518
For flames with very low burning speed, the flame propagation is affected by buoyancy. Flame front evolution and laminar flame parameter evaluation methods of buoyancy-affected flame have been proposed. The evolution and propagation process of a center ignited expanding ammonia/air flame has been analyzed by using the methods. The laminar flame parameters of ammonia/air mixture under different equivalence ratio (ER) and initial pressure have been studied. At barometric pressure, with the increase of ER, the laminar burning velocity (LBV) of ammonia/air mixture undergoes a first increase and then decrease process and reaches its maximum value of 7.17 cm/s at the ER of 1.1, while the Markstein length increases monotonously. For ammonia/air flames with ER less than unity, the flame velocity shows a decreasing trend with stretch rate, resulting in the propensity to flame instability, but no cellular structure was observed in the process of flame propagation. As the initial pressure increases, the LBV decreases monotonously as well as the Markstein length. The flame thicknesses of ammonia/air mixtures decrease with initial pressure and are much thicker than those of hydrogen flames, which makes a stronger stabilizing effect of curvature on the flame front. The most enhancement of LBV is contributed by the dehydrogenation reaction of NH3 with OH. The NO concentration decreases significantly with the increase of ER. 相似文献
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T.S. Cheng Y.-C. ChangY.-C. Chao G.-B. ChenY.-H. Li C.-Y. Wu 《International Journal of Hydrogen Energy》2011,36(20):13207-13217
The effects of variations in the fuel composition on the characteristics of H2/CO/CH4/air flames of gasified biomass are investigated experimentally and numerically. Experimental measurements and numerical simulations of the flame front position and temperature are performed in the premixed stoichiometric H2/CO/CH4/air opposed-jet flames with various H2 and CO contents in the fuel. The adiabatic flame temperatures and laminar burning velocities are calculated using the EQUIL and PREMIX codes of Chemkin collection 3.5, respectively. Whereas the flame structures of the laminar premixed stoichiometric H2/CO/CH4/air opposed-jet flames are simulated using the OPPDIF package with the GRI-Mech 3.0 chemical kinetic mechanisms and detailed transport properties. The measured flame front position and temperature of the stoichiometric H2/CO/CH4/air opposed-jet flames are closely predicted by the numerical calculations. Detailed analysis of the calculated chemical kinetic structures reveals that the reaction rate of reactions (R38), (R46), and (R84) increase with increasing H2 content in the fuel mixture. It is also found that the increase in the laminar flame speed with H2 addition is most likely due to an increase in active radicals during combustion (chemical effect), rather than from changes in the adiabatic flame temperature (thermal effect). Chemical kinetic structure and sensitivity analyses indicate that for the stoichiometric H2/CO/CH4/air flames with fixed H2 concentration in the fuel mixture, the reactions (R99) and (R46) play a dominant role in affecting the laminar burning velocity as the CO content in the fuel is increased. 相似文献
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《International Journal of Hydrogen Energy》2023,48(62):24101-24112
Global reaction mechanisms (GRMs) are widely used in combustion engineering. However, it is difficult to find GRMs commonly available for various mixtures of H2, CO, and CH4 (with air), which are likely to be the primary fuels in the future. In this study, a series of GRMs were optimized to follow the results of the five detailed reaction mechanisms (GRI 3.0, USC II, San Diego, FFCM-1, CRECK) for the essential fuels (H2, CO, CH4) and their mixtures (at 300 K and 1 bar). At first, a 1-step GRM of H2+air (R1) and another of CO + air (R2), were optimized to reproduce their respective laminar burning velocities (LBVs). After that, an additional water-gas shift reaction (R3) was suggested to improve the prediction for the H2+CO + air mixture. Similarly, a 1-step GRM (M1) was developed for the fuel-lean mixtures of CH4+air, and a 2-step GRM (R1+M1) was proposed for the fuel-lean mixtures of H2+CH4+air. In the case of the mixture of H2+CO + CH4+air, an additional methane oxidation reaction (M1L) producing H2 and CO was suggested, and a 4-step GRM (R1+R2+R3+M1L) showed reliable results in the fuel-lean conditions. However, to get reliable LBVs over all equivalence ratios, two additional reactions (M2+M3) were proposed to reflect the endothermic reaction. Furthermore, the pre-exponential factor of the methane oxidation reaction (M1R) varied as a function of the hydrogen concentration in the fuel. Conclusively, acceptable LBVs could be obtained for the H2+CO + CH4+air mixtures in a moderate temperature range (300 K–600 K). 相似文献
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在定容燃烧弹内研究了初始压力为0.5 MPa时,不同初始温度和燃空当量比下二甲醚-空气混合气预混层流火焰的层流燃烧速率和马克斯坦长度,分析了火焰拉伸对火焰传播速率的影响.基于容弹燃烧的双区模型计算了预混层流燃烧的燃烧特性参数.结果表明:随着初始温度的增加,二甲醚-空气预混合气的无拉伸火焰传播速率和无拉伸层流燃烧率增加;对于给定的初始温度,在化学当量比偏浓混合气一侧存在一个层流燃烧速度的峰值;随初始温度和当最比增加,马克斯坦长度值减小,火焰前锋面的不稳定性增加;最大燃烧压力随初始温度的增加而下降,压力升高率随初始温度的增加而降低. 相似文献
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《International Journal of Hydrogen Energy》2022,47(14):9030-9044
Fundamental combustion characteristics of H2/air flames with the addition of actual H2/air combustion residuals (a mixture of 65% N2 + 35% H2O by mole) are examined experimentally and numerically at 1–2 bar, 373–473 K, equivalence ratio of 0.7, and dilution ratios of 0–40%. Spherically expanding flame measurements at constant pressure show that flame speed and adiabatic flame temperature drop almost linearly with increasing diluent level. Detailed numerical simulations and analyses of sensitivity coefficients reveal that this is because of the low chemical reactivity of the dilution mixture. On the other hand, the change in burned gas Markstein length with the dilution mixture addition is found more complex and cannot be represented with a linear trend. Experimental flame speed data are compared with results of chemical kinetic analyses obtained by several chemical mechanisms in order to assess the accuracy of these models. 相似文献
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《International Journal of Hydrogen Energy》2022,47(85):36073-36083
Unstretched laminar burning velocity (LBV) and intrinsic instabilities of Refined producer gas (H2:CO:CH4)-Air mixtures were systematically investigated at 300 K, 1–4 bar and ? = 0.8–1.2 using freely expanding spherical flame method. In H2/CO/CH4 rich mixtures, LBV increased with increase in CO (and reduction in CH4)/H2 (and reduction in CH4)/H2 (and reduction in CO) at any given equivalence ratio, while peak LBV occurred at ? = (1.2 and remained at 1.2)/(1.2 and shifted to 1.1)/(1.1 and remained at 1.1). Computed unstretched LBV using GRI Mech 3.0 and FFCM mechanisms deviated from measurements with initial pressure. From the comprehensive susceptibility analysis (to instabilities), the composition H2:CO:CH4 = 0:1:1 had the highest resilience towards thermo-diffusive and hydrodynamic instabilities. Refined producer gas with higher mole fractions of H2 were vulnerable to intrinsic instabilities, while increment in CH4 suppressed the susceptibility to hydrodynamic instability and increment in CO suppressed the thermo-diffusive instability. 相似文献
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Geyuan YIN Chaojun WANG Meng ZHOU Yajie ZHOU Erjiang HU Zuohua HUANG 《Frontiers in Energy》2022,16(2):263
The laminar flame speeds of ammonia mixed with syngas at a high pressure, temperature, and different syngas ratios were measured. The data obtained were fitted at different pressures, temperatures, syngas ratios, and equivalence ratios. Four kinetic models (the Glarborg model, Shrestha model, Mei model, and Han model) were compared and validated with experimental data. Pathway, sensitivity and radical pool analysis are conducted to find out the deep kinetic insight on ammonia oxidation and NO formation. The pathway analysis shows that H abstraction reactions and NHi combination reactions play important roles in ammonia oxidation. NO formation is closely related to H, OH, the O radical produced, and formation reactions. NO is mainly formed from reaction, HNO+ H= NO+ H2. Furthermore, both ammonia oxidation and NO formation are sensitive to small radical reactions and ammonia related reactions. 相似文献