共查询到20条相似文献,搜索用时 15 毫秒
1.
The effects of bluff-body lip thickness on the several physical parameters like flame length, radiant fraction, gas temperature and NOx emissions in liquefied petroleum gas (LPG)–H2 jet diffusion flame are investigated experimentally. Results indicate that the flame length reduces with the addition of hydrogen in the bluff-body stabilized flame, which can be attributed to the enhanced reactivity and residence time of the mixture gases. Moreover, with increasing lip thickness of the bluff body, the flame length also gets reduced. The soot free length fraction (SFLF) is observed to be enhanced with H2 addition to the fuel stream. In contrast, the SFLF gets reduced with increasing lip thickness repetition, which is due to the reduced induction period of soot formation. The emission index of NOx (EINOx) is found to be attenuated in coaxial burner with hydrogen addition. In contrast it is observed to be enhanced in bluff-body stabilized flame. The former is due to the reduction in residence time of gas mixture, whereas the latter can be explained on the basis of increased flame temperature. Besides this, NOx emission level is also found to be enhanced with increasing lip thickness due to enhanced residence time. 相似文献
2.
The effects of hydrogen fraction on laminar burning velocity, flame stability (Markstein number) and flame temperature of methane–hydrogen–air flame at global equivalence ratios of 0.7, 1.0 and 1.2 have been investigated numerically based on the full chemistry and the detailed molecular species transport. The effect of stretch rate on combustion characteristics is examined using an opposed-flow planar flame model, while the effect of flame curvature is identified by comparing a tubular flame to the opposed-flow planar flame. The difference in response on hydrogen fraction between the planar and curved flames has been observed. The results show when hydrogen fraction increases, the flame temperature and laminar burning velocity increases, and this effect is more significant at a large stretch rate; while Markstein length decreases. At a fixed stretch rate of 400 s−1, under which the flame approaches extinction limit, the flame temperature of the tubular flame is considerably higher than that of the planar opposed flow flame, which results most likely from the contribution of the positive flame curvature to the first Damkohler number. 相似文献
3.
Jinhua Wang Zuohua Huang Hideaki Kobayashi Yasuhiro Ogami 《International Journal of Hydrogen Energy》2012
Laminar burning velocities of CO–H2–CO2–O2 flames were measured by using the outwardly spherical propagating flame method. The effect of large fraction of hydrogen and CO2 on flame radiation, chemical reaction, and intrinsic flame instability were investigated. Results show that the laminar burning velocities of CO–H2–CO2–O2 mixtures increase with the increase of hydrogen fraction and decrease with the increase of CO2 fraction. The effect of hydrogen fraction on laminar burning velocity is weakened with the increase of CO2 fraction. The Davis et al. syngas mechanism can be used to calculate the syngas oxyfuel combustion at low hydrogen and CO2 fraction but needs to be revised and validated by additional experimental data for the high hydrogen and CO2 fraction. The radiation of syngas oxyfuel flame is much stronger than that of syngas–air and hydrocarbons–air flame due to the existence of large amount of CO2 in the flame. The CO2 acts as an inhibitor in the reaction process of syngas oxyfuel combustion due to the competition of the reactions of H + O2 = O + OH, CO + OH = CO2 + H and H + O2(+M) = HO2(+M) on H radical. Flame cellular structure is promoted with the increase of hydrogen fraction and is suppressed with the increase of CO2 fraction due to the combination effect of hydrodynamic and thermal-diffusive instability. 相似文献
4.
Experiments were performed to add hydrogen to liquefied petroleum gas (LPG) and methane (CH4) to compare the emission and impingement heat transfer behaviors of the resultant LPG–H2–air and CH4–H2–air flames. Results show that as the mole fraction of hydrogen in the fuel mixture was increased from 0% to 50% at equivalence ratio of 1 and Reynolds number of 1500 for both flames, there is an increase in the laminar burning speed, flame temperature and NOx emission as well as a decrease in the CO emission. Also, as a result of the hydrogen addition and increased flame temperature, impingement heat transfer is enhanced. Comparison shows a more significant change in the laminar burning speed, temperature and CO/NOx emissions in the CH4 flames, indicating a stronger effect of hydrogen addition on a lighter hydrocarbon fuel. Comparison also shows that the CH4 flame at α = 0% has even better heat transfer than the LPG flame at α = 50%, because the longer CH4 flame configures a wider wall jet layer, which significantly increases the integrated heat transfer rate. 相似文献
5.
Santosh K. Paidi Amrutha Bhavaraju Mohammad Akram Sudarshan Kumar 《International Journal of Hydrogen Energy》2013
The laminar burning velocities of H2–air mixtures diluted with N2 or CO2 gas at high temperatures were obtained from planar flames observed in externally heated diverging channels. Experiments were conducted for an equivalence ratio range of 0.8–1.3 and temperature range of 350–600 K with various dilution rates. In addition, computational predictions for burning velocities and their comparison with experimental results and detailed flame structures have been presented. Sensitivity analysis was carried out to identify important reactions and their contribution to the laminar burning velocity. The computational predictions are in reasonably good agreement with the present experimental data (especially for N2 dilution case). The burning velocity maxima was observed for slightly rich mixtures and this maxima was found to shift to higher equivalence ratios (Ф) with a decrease in the dilution. The effect of CO2 dilution was more profound than N2 dilution in reducing the burning velocity of mixtures at higher temperatures. 相似文献
6.
Andrea Gruber Prashant S. Salimath Jacqueline H. Chen 《International Journal of Hydrogen Energy》2014
Direct numerical simulations are performed to investigate the transient processes of laminar flame–wall interaction and quenching near a porous, permeable wall and compared against a reference case of a non-porous impermeable wall. A boundary condition formulation that models species (hydrogen in this case) transport through a permeable wall, driven by the fuel species partial pressure difference between the feed and the permeate side of a selective membrane, has been implemented in a high-order finite difference direct numerical simulation code for reactive flows (S3D) by Chen et al. (2009) [1]. The present results are obtained for lean, stoichiometric and rich initial mixture conditions on the permeate side of the permeable wall and indicate that the characteristic parameters of the flame–wall interaction (wall heat flux, quenching distance) are affected to a large extent by the presence of the membrane hydrogen flux. Concurrently, the hydrogen flux through the membrane is also strongly affected by the presence of the flame during the transient flame–wall interaction process, finally resulting in a strong feedback mechanism between the membrane hydrogen flux and the flame that greatly increases boundary layer flashback speeds at fuel lean conditions. 相似文献
7.
Xudong Jiang Pengfei Li Junjun Guo Fan Hu Feifei Wang Jianchun Mi Zhaohui Liu 《International Journal of Hydrogen Energy》2018,43(17):8534-8557
This study systematically investigates the detailed mechanism of nitrogen oxides (NOx) in CH4 and CH4/H2 jet flames with O2/CO2 hot coflow. After comprehensive validation of the modeling by experiments of Dally et al. [Proc. Combust. Inst. 29 (2002) 1147–1154]; the effects of CO2 replacement of N2, mass fraction of oxygen in the coflow (YO2), and mass fraction of hydrogen in the fuel jet (YH2) on NO formation and destruction are investigated in detail. For methane oxy-fuel combustion, the NNH route is found to control the NO formation at YO2 ≤ 3%, while both NNH and N2O-intermediate routes dominate the NO production at 3% < YO2 < 10%. When YO2 ≥ 10%, NO is obtained mainly from thermal mechanism. Moreover, in the oxy-combustion of methane and hydrogen fuel blends with YO2 = 3%, with hydrogen addition the contribution of the NNH and prompt routes increases, while that of the N2O-intermediate route decreases. Furthermore, the chemical effect of CO2 is significant in reducing NO in both oxy-combustion of methane with YO2 ≤ 3% and combustion of methane and hydrogen fuel blends with YH2 ≤ 10%. 相似文献
8.
Cylindrical compacts of magnetite were isothermally reduced at 773–1273 K with pure H2 or H2–H2O mixtures. The initial reduction rates increased with temperature and partial pressures of H2 in the H2–H2O mixtures. However, with progressing reduction, a dense iron layer formed around the wüstite grains and the rate significantly reduced. In this regime, solid state oxygen diffusion through the dense iron layer was rate limiting. This retardation of reduction occurred at degrees of reduction of 51–89%, depending on the temperature and H2 partial pressure, which has a linear relationship with the dimensionless kinetic parameter, k1mixed/k2mixed, (k1mixed, k2mixed: contribution of gaseous mass transport (GMT) and interfacial chemical reaction (ICR) to the reduction rate, respectively) in the reaction-regime controlled by a combination of both mechanisms. However, under certain conditions (H2, H2–10%H2O, 773 K//H2–10, 20%H2O, 873 K//H2–20%H2O, 973 K) the retardation was absent because of the formation of a microporous iron layer product. 相似文献
9.
An experimental study was conducted to investigate the influence of hydrogen addition on the heat transfer characteristics of a biogas (60%CH4–40%CO2) flame. Results show improved flame stability and higher flame temperature in the premixed flame upon hydrogen addition. Both temperature and burning speed are increased in 1.0 ≤ Ф ≤ 1.5. Comparison of the premixed and diffusion flames reveals that the former yields higher heat transfer than the latter, due to higher flame temperature and larger volume of hot gas in the premixed flame. The total heat transfer rates of the two flames show opposite trends with increasing level of hydrogen addition, which is explained by the different structures. In the premixed flame, the contact of large cool core with target plate configures the high-temperature flame zone to a radial location with larger distance from the stagnation point than that of the diffusion flame, contributing to its higher heat transfer rate. 相似文献
10.
Ignition delay times of H2/O2 mixtures highly diluted with Ar and doped with various amounts of N2O (100, 400, 1600, 3200 ppm) were measured in a shock tube behind reflected shock waves over a wide range of temperatures (940–1675 K). The pressure range investigated during this work (around 1.6, 13 and 32 atm) allows studying the effect of N2O on hydrogen ignition at pressure conditions that have never been heretofore investigated. Ignition delay times were decreased when N2O was added to the mixture only for the higher nitrous oxide concentrations, and some changes in the activation energy were also observed at 1.5 and 32 atm. When it occurred, the decrease in the ignition delay time was proportional to the amount of N2O added and depended on pressure and temperature conditions. A detailed chemical kinetics model was developed using kinetic mechanisms from the literature. This model predicts well the experimental data obtained during this study and from the literature. The chemical analysis using this model showed that the decrease in the ignition delay time was mainly due to the reaction N2O + M ? N2 + O + M which provides O atoms to strengthen the channel O + H2 ? OH + H. 相似文献
11.
Tae Hyung Kim Won Sik Song Jeong Park Oh Boong Kwon Jong Ho Park 《International Journal of Hydrogen Energy》2012
Effects of strain rate and preferential diffusion of H2 on flame extinction are numerically explored in interacting premixed syngas–air flames with the fuel compositions of 50% H2 + 50% CO and 30% H2 + 70% CO. Flame stability diagrams mapping lower and upper limit fuel concentrations at flame extinction as a function of strain rate are examined. Increasing strain rate reduces the boundaries of both flammable lean and rich fuel concentrations and produces a flammable island and subsequently even a point, implying that there exists a limit strain rate over which interacting flame cannot be sustained anymore. Even if effective Lewis numbers are slightly larger than unity on the lean extinction boundaries, the shape of the lean extinction boundary is slanted even at low strain rate, i.e. ag = 30 s−1 and is more slanted in further increase of strain rate, implying that flame interaction on lean extinction boundary is strong and thus hydrogen (as a deficient reactant) Lewis number much less than unity plays an important role of flame interaction. It is also shown that effects of preferential diffusion of H2 cause flame interaction to be stronger on lean extinction boundaries and weaker on rich extinction boundaries. Detailed analyses are made through the comparison between flame structures with and without the restriction of the diffusivities of H2 and H in symmetric and asymmetric fuel compositions. The reduction of flammable fuel compositions in increase of strain rate suggests that the mechanism of flame extinction is significant conductive heat loss from the stronger flame to ambience. 相似文献
12.
In this paper, a numerical study of coupled heat and mass transfer during the desorption process of metal–hydrogen reactor (Mg2Ni–H2), is presented. Analytical expressions describing, the reaction kinetic and the equilibrium pressure of the Mg2Ni-H2 system have been determined and integrated into a theoretical model that describes the dynamic behavior of the reactor. This model, which takes into account radiative heat transfer, is solved by the control volume finite element method (CVFEM). The numerical simulation is used to present the time–space evolutions of the temperature and the hydride density within the reactor and to evaluate the effect of radiative heat transfer and the governing operating parameters (outlet pressure, temperature of heating fluid, heat exchange coefficient) on the dynamic behavior of the reactor. In addition, a new geometric configuration of the reactor is proposed and simulated. 相似文献
13.
V. Ratna Kishore Ringkhang MuchaharyAnjan Ray M.R. Ravi 《International Journal of Hydrogen Energy》2009
Global warming due to CO2 emissions has led to the projection of hydrogen as an important fuel for future. A lot of research has been going on to design combustion appliances for hydrogen as fuel. This has necessitated fundamental research on combustion characteristics of hydrogen fuel. In this work, a combination of experiments and computational simulations was employed to study the effects of diluents (CO2, N2, and Ar) on the laminar burning velocity of premixed hydrogen/oxygen flames using the heat flux method. The experiments were conducted to measure laminar burning velocity for a range of equivalence ratios at atmospheric pressure and temperature (300 K) with reactant mixtures containing varying concentrations of CO2, N2, and Ar as diluents. Measured burning velocities were compared with computed results obtained from one-dimensional laminar premixed flame code PREMIX with detailed chemical kinetics and good agreement was obtained. The effectiveness of diluents in reduction of laminar burning velocity for a given diluent concentration is in the increasing order of argon, nitrogen, carbon dioxide. This may be due to increased capabilities either to quench the reaction zone by increased specific heat or due to reduced transport rates. The lean and stoichiometric H2/O2/CO2 flames with 65% CO2 dilution exhibited cellular flame structures. Detailed three-dimensional simulation was performed to understand lean H2/O2/CO2 cellular flame structure and cell count from computed flame matched well with the experimental cellular flame. 相似文献
14.
B. Larousse P. Lovera J.M. Borgard G. Roehrich N. Mokrani C. Maillault D. Doizi V. Dauvois J.L. Roujou V. Lorin P. Fauvet P. Carles J.M. Hartmann 《International Journal of Hydrogen Energy》2009
In order to assess the choice of the sulphur–iodine thermochemical cycle for massive hydrogen production, a precise knowledge of the concentrations of the gaseous species (HI, I2, and H2O) in thermodynamic equilibrium with the liquid phase of the HI–I2–H2O ternary mixture is required, in a wide range of concentrations and for temperatures and pressures up to 300 °C and 50 bar. 相似文献
15.
This study has been implemented in two sections. At first, the turbulent jet flame of DLR-B is simulated by combining the k–ε turbulence model and a steady flamelet approach. The DLR-B flame under consideration has been experimentally investigated by Meier et al. who obtained velocity and scalar statistics. The fuel jet composition is 33.2% H2, 22.1% CH4 and 44.7% N2 by volume. The jet exit velocity is 63.2 m/s resulting in a Reynolds number of 22,800. Our focus in the first part is to validate the developed numerical code. Comparison with experiments showed good agreement for temperature and species distribution. At the second part, we exchanged methane with propane in the fuel composition whilst maintaining all other operating conditions unchanged. We investigated the effect of hydrogen concentration on C3H8–H2–N2 mixtures so that propane mole fraction extent is fixed. The hydrogen volume concentration rose from 33.2% up to 73.2%. The achieved consequences revealed that hydrogen addition produces elongated flame with increased levels of radiative heat flux and CO pollutant emission. The latter behavior might be due to quenching of CO oxidation process in the light of excessive cold air downstream of reaction zone. 相似文献
16.
Jonathan Mbah Sesha Srinivasan Burton Krakow John Wolan Yogi Goswami Elias Stefanakos Narayana Appathurai 《International Journal of Hydrogen Energy》2010
An innovative, nanostructured composite, anode electrocatalyst, material has been developed for the electrolytic splitting of (100%) H2S feed content gas operating at 135 kPa and 150 °C. A new class of anode electrocatalyst with general composition, RuO2–CoS2 has shown great stability and desired properties at typical operating conditions. This configuration showed stable electrochemical operation over the period of 24 h and also exhibited a maximum current density of (0.019 A/cm2). The kinetic behaviors of various anode-based electrocatalysts demonstrated that, exchange current density, which is a direct measure of the electrochemical reaction, increased with RuO2–CoS2-based anodes. Moreover, high levels of feed utilization were possible using these materials. Electrochemical performance, current density, and sulfur tolerance were enhanced compared to the other tested anode configurations. The structural, microstructural and surface behavior of RuO2–CoS2 anode electrocatalyst was investigated in detail. 相似文献
17.
Youngjoon Shin Jiwoon ChangTaehoon Lee Kiyoung LeeYongwan Kim 《International Journal of Hydrogen Energy》2014
The sulfur–iodine (SI) cycle to produce hydrogen from water requires a multistage distillation column to concentrate a sulfuric acid solution. To design a concentration process of a sulfuric acid solution that can be applied to the cycle, its static and dynamic simulation is essentially demanded. A 50 NL H2/h scale SI test facility to be operated under a pressurized environment has been constructed in Korea. This study focuses on the sulfuric acid multi-stage distillation column (SAMDC-50L) for the 50 NL H2/h SI test facility. The SAMDC-50L was designed and installed in 2012. Based on the design specifications and operation method, a start-up behavior of the SAMDC-50L has been analyzed using the simulation code “KAERI-DySCo”. As a result of the start-up dynamic simulation, it is confirmed that the SAMDC-50L will approach to the steady state value within 30,000 s to fulfill the hydrogen production rate of 50 NL H2/h. On the other hand, it is expected that the operation time approaching a steady state decreases with an increase in the set point of the condenser temperature until a dew point of the top vapor product and the time required for the transition to the complete steady state is increased with an increasing reflux ratio and reboiler hold-up. 相似文献
18.
Experiments were conducted to investigate the combustion and emission characteristics of a diesel engine with addition of hydrogen or methane for dual-fuel operation, and mixtures of hydrogen–methane for tri-fuel operation. The in-cylinder pressure and heat release rate change slightly at low to medium loads but increase dramatically at high load owing to the high combustion temperature and high quantity of pilot diesel fuel which contribute to better combustion of the gaseous fuels. The performance of the engine with tri-fuel operation at 30% load improves with the increase of hydrogen fraction in methane and is always higher than that with dual-fuel operations. Compared with ULSD–CH4 operation, hydrogen addition in methane contributes to a reduction of CO/CO2/HC emissions without penalty on NOx emission. Dual-fuel and tri-fuel operations suppress particle emission to the similar extent. All the gaseous fuels reduce the geometry mean diameter and total number concentration of diesel particulate. Tri-fuel operation with 30% hydrogen addition in methane is observed to be the best fuel in reducing particulate and NOx emissions at 70 and 90% loads. 相似文献
19.
Jérôme Andrieux Laetitia Laversenne Olesia KrolRodica Chiriac Zeinab BouajilaRichard Tenu Jean Jacques CouniouxChristelle Goutaudier 《International Journal of Hydrogen Energy》2012
The binary phase diagram NaBO2–H2O at ambient pressure, which defines the different phase equilibria that could be formed between borates, end-products of NaBH4 hydrolysis, has been reviewed. Five different solid borates phases have been identified: NaBO2·4H2O (Na[B(OH)4]·2H2O), NaBO2·2H2O (Na[B(OH)4]), NaBO2·2/3H2O (Na3[B3O4(OH)4]), NaBO2·1/3H2O (Na3[B3O5(OH)2]) and NaBO2 (Na3[B3O6]), and their thermal stabilities have been studied. The boundaries of the different Liquid + Solid equilibria for the temperature range from −10 to 80 °C have been determined, confirming literature data at low temperature (20–50 °C). Moreover the following eutectic transformation, Liq. → Ice + NaBO2·4H2O, occurring at −7 °C, has been determined by DSC. The Liquid–Vapour domain has been studied by ebullioscopy. The invariant transformation Liq. → Vap. + NaBO2·2/3H2O has been estimated at 131.6 °C. This knowledge is paramount in the field of hydrogen storage through NaBH4 hydrolysis, in which borate compounds were obtained as hydrolysis reaction products. As a consequence, the authors propose a comparison with previous NaBO2–H2O binary phase diagrams and its consequence related to hydrogen storage through NaBH4 hydrolysis. 相似文献
20.
R. Liberatore A. CeroliM. Lanchi A. SpadoniP. Tarquini 《International Journal of Hydrogen Energy》2008
The Sulphur–Iodine thermochemical cycle for hydrogen production has been investigated by ENEA in the framework of the Italian TEPSI Project whose main objective is the realization of an integrated loop plant at a laboratory scale. For the design of the separation–purification equipments, the study of vapour–liquid equilibrium characterization of the ternary HI–H2O–I2 system is considered a key factor. The aim of the present work is to provide new experimental isobaric vapour–liquid equilibrium data for this system by ebulliometry varying both temperature and solution composition. The temperature range has been extended up to about 144 °C, the iodine concentration range from 0.2%w/w to 90%w/w while HI weight fraction varies from 4%w/w to 67%w/w in the liquid phase. Most of the data obtained in this work are in good agreement with other experimental data retrieved from literature, which have been recorded in similar operative conditions but acquired by different procedures. 相似文献