共查询到20条相似文献,搜索用时 46 毫秒
1.
Experimental investigations of H2 and H2-enriched syngas flame radiation properties have been conducted through spectroscopic and DFCD (Digital Flame Colour Discrimination) techniques. A spectrograph was employed to quantify the emission profile of H2-based flames in the UV–visible spectral domain. The OH* emission was found to be the strongest in reactants with highest amount of H2. Further addition of CO and/or CO2 resulted in the reduction of OH* intensity with the addition of CO2 causing greater radical intensity-loss than that of CO. The decrease in OH* intensity is accompanied by a corresponding increase in the CO–O* broadband continuum in the short-wavelength domain of the visible spectrum. Such reduction of OH* along with increase in CO–O* intensity can be related to the endothermic reaction mechanism of CO + OH => CO2 + H, which describes the role of CO/CO2 addition in H2-enriched syngas flames. Comparison with direct imaging results provided additional credence to the effect of temperature reduction as flames with CO and/or CO2 additions resembled colourations closer to typical bluish premixed hydrocarbon flame. The employment of DFCD processing effectively characterised different syngas combustion conditions by combining aspects of digital flame colour intensities with spatial combustion distributions. This colour signal quantification method was shown to yield useful characterisation of H2-based flames, similar to the use of OH* chemiluminescence intensity variation from spectrometry. Also, DCFD analysis was able to depict the variances between the burning of different syngas gaseous constituents. Thus, useful image-based parameters related to the H2-based combustion can be derived and potentially applied as a practical monitoring and characterisation mean for syngas combustion. 相似文献
2.
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
3.
This paper reports a numerical study on the combustion and extinction characteristics of opposed-jet syngas diffusion flames. A model of one-dimensional counterflow syngas diffusion flames was constructed with constant strain rate formulations, which used detailed chemical kinetics and thermal and transport properties with flame radiation calculated by statistic narrowband radiation model. Detailed flame structures, species production rates and net reaction rates of key chemical reaction steps were analyzed. The effects of syngas compositions, dilution gases and pressures on the flame structures and extinction limits of H2/CO synthetic mixture flames were discussed. Results indicate the flame structures and flame extinction are impacted by the compositions of syngas mixture significantly. From H2-enriched syngas to CO-enriched syngas fuels, the dominant chain reactions are shifting from OH + H2→H + H2O for H2O production to OH + CO→H + CO2 for CO2 production through the key chain-branching reaction of H + O2→O + OH. Flame temperature increases with increasing hydrogen content and pressure, but the flame thickness is decreased with pressure. Besides, the study of the dilution effects from CO2, N2, and H2O, showed the maximum flame temperature is decreased the most with CO2 as the dilution gas, while CO-enriched syngas flames with H2O dilution has highest maximum flame temperature when extinction occurs due to the competitions of chemical effect and radiation effect. Finally, extinction limits were obtained with minimum hydrogen percentage as the index at different pressures, which provides a fundamental understanding of syngas combustion and applications. 相似文献
4.
Tananop Piemsinlapakunchon Manosh C. Paul 《International Journal of Hydrogen Energy》2021,46(10):7573-7588
The paper presents a numerical investigation of the critical roles played by the chemical compositions of syngas on laminar diffusion flame instabilities. Three different flame phenomena – stable, flickering and tip-cutting – are formulated by varying the syngas fuel rate from 0.2 to 1.4 SLPM. Following the satisfactory validation of numerical results with Darabkhani et al. [1], the study explored the consequence of each species (H2, CO, CH4, CO2, N2) in the syngas composition. It is found that low H2:CO has a higher level of instability, which however does not rise any further when the ratio is less than 1. Interestingly, CO encourages the heat generation with less fluctuation while H2 plays another significant role in the increase of flame temperature and its fluctuation. Diluting CH4 into syngas further increases the instability level as well as the fluctuation of heat generation significantly. However, an opposite effect is found from the same action with either CO2 or N2. Finally, considering the heat generation and flame stability, the highest performance is obtained from 25%H2+75%CO (81 W), followed by EQ+20%CO2, and EQ+20%N2 (78 W). 相似文献
5.
The synergistic effect of equivalence ratio and initial temperature on laminar flame speed of syngas
《International Journal of Hydrogen Energy》2022,47(55):23106-23117
The laminar flame speed of syngas (CO:H2 = 1:1)/air premixed gas in a wide equivalence ratio range (0.6–5) and initial temperature (298–423 K) was studied by Bunsen burner. The results show that the laminar flame speed first increases and then decreases as the equivalence ratio increasing, which is a maximum laminar flame speed at n = 2. The laminar flame speed increases exponentially with the increase of initial temperature. For different equivalent ratios, the initial temperature effects on the laminar flame speed is different. The initial temperature effects for n = 2 (the most violent point of the reaction) is lower than others. It is found that H, O and OH are affected more and more when the equivalence ratio increase. When the equivalence ratio is far from 2, the reaction path changes, and the influence of initial temperature on syngas combustion also changes. The laminar flame speed of syngas is more severely affected by H + O2 = O + OH and CO + OH = CO2 + H than others, which sensitivity coefficient is larger and change more greatly than others when the initial temperature and equivalence ratio change. Therefore, the laminar flame speed of syngas/air premixed gas is affected by the initial temperature and equivalence ratio. A new correlation is proposed to predict the laminar flame speed of syngas (CO:H2 = 1:1)/air premixed gas under the synergistic effect of equivalence ratio and initial temperature (for equivalence ratios of 0.6–5, the initial temperature is 298–423 K). 相似文献
6.
Peter G. LoutzenhiserAldo Steinfeld 《International Journal of Hydrogen Energy》2011,36(19):12141-12147
Solar syngas production from CO2 and H2O is considered in a two-step thermochemical cycle via Zn/ZnO redox reactions, encompassing: 1) the ZnO thermolysis to Zn and O2 using concentrated solar radiation as the source of process heat, and 2) Zn reacting with mixtures of H2O and CO2 yielding high-quality syngas (mainly H2 and CO) and ZnO; the ZnO is recycled to the first, solar step, resulting in net reaction βCO2 + (1 − β)H2O → βCO + (1 − β)H2. Syngas is further processed to liquid hydrocarbon fuels via Fischer-Tropsch or other catalytic processes. Second-law thermodynamic analysis is applied to determine the cycle efficiencies attainable with and without heat recuperation for varying molar fractions of CO2:H2O and solar reactor temperatures in the range 1900-2300 K. Considered is the energy penalty of using Ar dilution in the solar step below 2235 K for shifting the equilibrium to favor Zn production. 相似文献
7.
Nan DingRajat Arora Michael NorconkSeong-Young Lee 《International Journal of Hydrogen Energy》2011,36(4):3222-3231
In recent years, research efforts have been channeled to explore the use of environmentally-friendly clean fuel in lean-premixed combustion so that it is vital to understand fundamental knowledge of combustion and emissions characteristics for an advanced gas turbine combustor design. The current study investigates the extinction limits and emission formations of dry syngas (50% H2-50% CO), moist syngas (40% H2-40% CO-20% H2O), and impure syngas containing 5% CH4. A counterflow flame configuration was numerically investigated to understand extinction and emission characteristics at the lean-premixed combustion condition by varying dilution levels (N2, CO2 and H2O) at different pressures and syngas compositions. By increasing dilution and varying syngas composition and maintaining a constant strain rate in the flame, numerical simulation showed among diluents considered: CO2 diluted flame has the same extinction limit in moist syngas as in dry syngas but a higher extinction temperature; H2O presence in the fuel mixture decreases the extinction limit of N2 diluted flame but still increases the flame extinction temperature; impure syngas with CH4 extends the flame extinction limit but has no effect on flame temperature in CO2 diluted flame; for diluted moist syngas, extinction limit is increased at higher pressure with the larger extinction temperature; for different compositions of syngas, higher CO concentration leads to higher NO emission. This study enables to provide insight into reaction mechanisms involved in flame extinction and emission through the addition of diluents at ambient and high pressure. 相似文献
8.
The radiation effect on flame temperature and NO emission of H2-lean (0.2H2 + 0.8CO) and H2-rich (0.8H2 + 0.2CO) syngas/air counterflow diffusion flames was numerically investigated using OPPDIF code incorporated with the optical thin model, statistical narrow band model and adiabatic condition. Firstly, the coupled effect of strain rate and radiation was studied. Disparate tendencies of NO emission with an increasing strain rate between H2-lean and H2-rich syngas flames were found at very small strain rate, and the effect of radiation reabsorption on NO formation can be neglected when the strain rate was greater than 100 s?1 for both H2-lean and H2-rich syngas flames. Because the radiation effect is vital to flames with small strain rate, its impact on flame temperature and NO emission was investigated in detail at a strain rate of 10 s?1. The results indicated that NO formation is more sensitive to radiation reabsorption than flame temperature, especially for the H2-rich syngas flame. The underlying mechanism was discovered by using reaction pathway analysis. Furthermore, the radiation effect under CO2 dilution of the syngas fuel was examined. It was demonstrated that the radiation effect on flame temperature became more prominent with the increase of CO2 concentration for both H2-lean and H2-rich syngas. The radiation effect on NO emission increased first and then decreased with an increasing CO2 content for H2-lean syngas, whereas for H2-rich syngas the radiation effect is monotonic. 相似文献
9.
Extinction studies of weakly-stretched near-limit lean premixed syngas/air flames were conducted in a twin-flame counterflow configuration. Experiments showed that buoyancy-induced natural convection at normal gravity strongly disturbed these flames. In order to validate the simulation, accurate extinction data was obtained at micro-gravity. Experimental data obtained from the 3.6 s micro-gravity drop tower showed that the extinction equivalence ratio increased with the increasing global stretch rate and decreased with the increasing H2 mole fraction in the fuel. Numerical simulation was conducted with CHEMKIN software using GRI 3.0 and USC-Mech II mechanisms. The predicted extinction limit trend was in agreement with the micro-gravity experimental data. Sensitivity analyses showed that the competition between the main branching reaction H + O2 ⇔ O + OH and the main termination reaction H + O2 + M ⇔ HO2 + M in the H2/O2 chemistry determined the extinction limits of the flames. The dominant species for syngas/air flame extinction was the H radical. The key exothermal reaction changed from OH + CO ⇔ H + CO2 to OH + H2 ⇔ H + H2O with the increasing H2 mole fraction in the fuel. Also, the mass diffusion played a more important role than chemical kinetics in the flame extinction. When the H2 mass diffusion was suppressed, the reaction zone was pushed to the stagnation plane and the flame became weaker; while H mass diffusion is suppressed, the reaction zone slightly shifted towards the upstream and the flame was slightly strengthened. 相似文献
10.
Extensive computations were made to determine the flammability limits of opposed-jet H2/CO syngas diffusion flames from high stretched blowoff to low stretched quenching. Results from the U-shape extinction boundaries indicate the minimum hydrogen concentrations for H2/CO syngas to be combustible are larger towards both ends of high strain and low strain rates. The most flammable strain rate is near one s−1 where syngas diffusion flames exist with minimum 0.002% hydrogen content. The critical oxygen percentage (or limiting oxygen index) below which no diffusion flames could exist for any strain rate was found to be 4.7% for the equal-molar syngas fuels (H2/CO = 1), and the critical oxygen percentage is lower for syngas mixture with higher hydrogen content. The flammability maps were also constructed with strain rates and pressures or dilution gases percentages as the coordinates. By adding dilution gases such as CO2, H2O, and N2 to make the syngas non-flammable, besides the inert effect from the diluents, the chemical effect of H2O contributes to higher flame temperature, while the radiation effect of H2O and CO2 plays an important role in the flame extinction at low strain rates. 相似文献
11.
ZrO2-supported tungsten oxides were used for cyclic production of syngas and hydrogen by methane reforming (reduction) and water splitting (re-oxidation). The reduction characteristics of WO3 to WO2 and WO2 to W were examined at various temperatures (1073–1273 K) and reaction times. Significant portions of the tungsten oxides were also reduced by the produced H2 and CO. The extent of reduction by H2 varied greatly depending on temperature and WO3 content and also on the reduction of either WO3 or WO2, while that by CO was consistently low. When the overall degree of reduction became sufficiently high, methane decomposition started to proceed rapidly, resulting in considerable carbon deposition and H2 production. Consequently, the H2/(CO + CO2) ratio varied from around 1 to higher than 2. During the repeated cyclic operations with a proper reduction time at a given temperature, the syngas and hydrogen yields decreased gradually while the H2/(CO + CO2) ratio remained nearly constant and the carbon deposition was negligible. 相似文献
12.
《International Journal of Hydrogen Energy》2023,48(18):6705-6721
The proton-conducting solid oxide electrolysis cell (H-SOEC) is a clean technology for syngas production from H2O and CO2 through electrochemical and chemical reactions. However, it provides a low CO2 conversion and produces a syngas product with a high H2O content. To improve the H-SOEC for syngas production, H-SOEC coupled with a dry methane reforming process (H-SOEC/DMR) was proposed in this work. The process flowsheet of the H-SOEC/DMR was developed and further used to evaluate the performance of the H-SOEC/DMR process. From the performance analysis of the H-SOEC/DMR process, it was found that the CO2 and CH4 conversions were higher than 90% and 80%, respectively, when the process was operated in the temperature range of 1073–1273 K. In addition, the result showed that a syngas product with a low H2O content could be obtained. Energy efficiency was then considered and the results indicated that the highest energy efficiency of 72.80% could be achieved when the H-SOEC/DMR process was operated at a temperature of 1123 K, pressure of 1 atm, and current density of 2500 A m?2. Based on a pinch analysis, a heat exchanger network was applied to the H-SOEC/DMR process that improved the energy efficiency to 81.46%. Finally, an exergy analysis was performed and showed that the H-SOEC/DMR unit had the lowest exergy efficiency as a high-temperature exhaust gas was released. 相似文献
13.
José Antonio Delgado Dobladez Vicente Ismael Águeda Maté Silvia Álvarez Torrellas Marcos Larriba Pablo Brea 《International Journal of Hydrogen Energy》2021,46(33):17522-17533
In recent years, there has been growing interest in the dry reforming of methane (using CO2 instead of H2O) to obtain syngas, due to its economic and environmental advantages. In this reaction, to achieve conversions close to 100%, it is necessary to work at temperatures higher than 1000 °C. However, to attenuate the catalyst deactivation by sintering is convenient to work at lower temperatures, so that normally the syngas (mixture CO + H2) is obtained mixed with unreacted CO2 and CH4. In this work a process has been simulated to recover the syngas from the product of a dry reforming reaction of methane at 700 °C by means of a Dual PSA (Dual Pressure Swing Adsorption) process with heavy reflux using BPL activated carbon as an adsorbent, operating at 25 °C. The process can recover syngas with purity and recovery higher than 99%. Unreacted CO2 and CH4 can be recycled to the reactor, leading to effective CO2 and CH4 conversions close to 100%. The process specific energy input (SEI) is 4.7 thermal kJ per L (STP) of syngas. The process can also be used to recover the syngas contained in the tail gas of a H2 purification PSA from SMR-off gas. 相似文献
14.
《International Journal of Hydrogen Energy》2020,45(32):16210-16218
A highly CO2-selective high-silica SSZ-13 zeolite membrane was used for H2 production by separating CO2 from syngas (CO2/H2 mixture). High-silica SSZ-13 zeolite membranes were fabricated using outside asymmetric alumina tubes by secondary growth of ball-milled SSZ-13 seeds. The composition of membrane gel and synthesis time were modified. The Si/Al ratio in framework of the membrane was as high as 42 when SiO2/Al2O3 ratio of the gel increased to 140. The effects of test parameters such as pressure drop, temperature, feed flow rate and concentration on membrane performance were investigated. The test pressure drop was up to 2 MPa. The ultra-high CO2/H2 selectivity of 161 with excellent CO2 permeances of ~6.3 × 10−7 mol/(m2 s Pa) (=3760 GPU) were observed for the best membrane at 243 K and pressure drop of 0.2 MPa. Carbon dioxide permeance through high-silica SSZ-13 zeolite membrane was 4.2 × 10−7 mol/(m2 s Pa) (=2500 GPU) at 298 K and pressure drop of 2.0 MPa, and the CO2/H2 selectivity was 17.4. The current high-silica SSZ-13 zeolite membranes exceeded the upper bound of polymeric membranes and other inorganic membranes in CO2/H2 plots and owned great potentials for H2 production from syngas. 相似文献
15.
Ignition delays were measured in a shock tube for syngas mixtures with argon as diluent at equivalence ratios of 0.3, 1.0 and 1.5, pressures of 0.2, 1.0 and 2.0 MPa and temperatures from 870 to 1350 K. Results show that the influences of equivalence ratio on the ignition of syngas mixtures exhibit different tendency at different temperatures and pressures. At low pressure, the ignition delay increases with an increase in equivalence ratio at tested temperature. At high pressures, however, an opposite behavior is presented, that is, increasing equivalence ratio inhibits the ignition at high temperature and vice versa at intermediate temperature. The affecting degree of equivalence ratio on ignition delay is different for each mixture at given condition, especially for the syngas with high CO concentration. Sensitivity analyses demonstrate that reaction H + O2 = O + OH (R1) dominates the syngas oxidation under all conditions. With the increase of CO mole fraction, reactions CO + OH = CO2 + H (R27) and CO + HO2 = CO2 + OH (R29) become more important in the syngas ignition kinetics. With the increase of pressure, the reactions related to HO2 and H2O2 play the dominate role. The opposite influence of equivalence ratio on ignition delay at high- and intermediate-temperatures is chemically interpreted through kinetic analyses. 相似文献
16.
《International Journal of Hydrogen Energy》2019,44(51):27741-27748
Biomass-derived syngas (CO2 + CO + H2) has emerged as a potential non-fossil fuel source to yield transportation fuel via Fischer Tropsch Synthesis (FTS) reaction. Thus, the present study demonstrates the conversion of CO2 containing syngas into fuel range hydrocarbon via Fischer Tropsch Synthesis over Fe–Co bimetallic catalyst. The experimental tests were carried out in a fixed bed continuous reactor to investigate the effect of CO2 on CO/CO2 conversion. Accordingly, obtained data were validated by FTS kinetic model for a plug flow reactor. It was found that the unique combination of Fe and Co bimetallic catalyst facilitates both FTS and water gas shift (WGS) reaction simultaneously that helps to convert CO2 along with CO. It was also observed that the presence of iron in the catalyst helps in conversion of CO2 into hydrocarbons, only when a particular concentration of CO2 in syngas is reached, i.e., critical ratio RC (CO2/CO + CO2) due to the occurrence of reverse water gas reaction (RWGS) which varies with the temperature and the feed gas composition (H2/CO/CO2 molar ratio). At 240 °C and hydrogen deficient condition, the critical ratio was measured to be 0.74 whereas for hydrogen balanced condition, it was measured 0.6. The kinetic model developed in the present study predicted trends for % CO conversion, % carbon conversion, and % CO2 conversion which is applicable for a wide range of critical ratio RC (CO2/(CO + CO2) = 0 to 1). The model also predicted that a positive conversion of CO2 could be achieved at lower CO2 concentration by increasing the reaction temperature. At 260 °C and 280 °C, the value of Rc were 0.31 and 0.18 were measured. 相似文献
17.
Changsong Cui Yue Wang Yongcheng Tong Shiwei Wang Chusheng Chen Zhongliang Zhan 《International Journal of Hydrogen Energy》2021,46(39):20305-20312
High temperature co-electrolysis of H2O/CO2 allows for clean production of syngas using renewable energy, and the novel fuel-assisted electrolysis can effectively reduce consumption of electricity. Here, we report on symmetric cells YSZ-LSCrF | YSZ | YSZ-LSCrF, impregnated with Ni-SDC catalysts, for CH4-assisted co-electrolysis of H2O/CO2. The required voltages to achieve an electrolysis current density of ?400 mA·cm?2 at 850 °C are 1.0 V for the conventional co-electrolysis and 0.3 V for the CH4-assisted co-electrolysis, indicative of a 70% reduction in the electricity consumption. For an inlet of H2O/CO2 (50/50 vol), syngas with a H2:CO ratio of ≈2 can be always produced from the cathode under different current densities. In contrast, the anode effluent strongly depends upon the electrolysis current density and the operating temperature, with syngas favorably produced under moderate current densities at higher temperatures. It is demonstrated that syngas with a H2:CO ratio of ≈2 can be produced from the anode at a formation rate of 6.5·mL min?1·cm?2 when operated at 850 °C with an electrolysis current density of ?450 mA·cm?2. 相似文献
18.
The species concentrations of non-premixed hydrogen and syngas flames were examined using results obtained from direct numerical simulation technique with flamelet generated manifold chemistry. Flames with pure H2 and H2/CO mixtures are discussed for an impinging jet flame configuration. Single-point data analyses are presented illustrating the effects of fuel composition on species concentrations. In general, scatterplots of all species show the effects of fuel variability on the flame compositional structures. The behaviours of major combustion products and key radicals species indicate the effects of CO concentration on the 2/CO syngas combustion. In particular, high concentration of CO tends to induce local extinction in the 2/CO flames in which critical chemical reactions of the fuel mixture such as CO + OH become important. The unsteady fluctuations of species profiles in the wall jet region characterise the complexity of the distributions of compositional structures in the near-wall region with respect to the effects of CO concentration on the combustion of hydrogen-enriched fuels. 相似文献
19.
《International Journal of Hydrogen Energy》2022,47(37):16649-16664
The NO mechanism under the moderate or intense low-oxygen dilution (MILD) combustion of syngas has not been systematically examined. This paper investigates the NO mechanism in the syngas MILD regime under the dilution of N2, CO2, and H2O through counterflow combustion simulation. The syngas reaction mechanism and the counterflow combustion simulation are comprehensively validated under different CO/H2 ratios and strain rates. The effects of oxygen volume fraction, CO/H2 ratio, pressure, strain rate, and dilution atmosphere are systematically investigated. For all the MILD cases, the contribution of the prompt and NO-reburning routes to the overall NO emission is less than 0.1% due to the lack of CH4 in fuel. At atmospheric pressure, the thermal route only accounts for less than 20% of the total NO emission because of the low reaction temperature. Moreover, at atmospheric pressure, the contribution of the NNH route to NO emission is always larger than 55% in the N2 atmosphere. The N2O-intermediate route is enhanced in CO2 and H2O atmospheres due to the increased third-body effects of CO2 and H2O through the reaction N2 + O (+M) ? N2O (+M). Especially in the H2O atmosphere, the N2O-intermediate route contributes to 60% NO at most. NO production is reduced with increasing CO/H2 ratio or pressure, mainly due to decreased NO formation from the NNH route. Importantly, a high reaction temperature and low NO emission are simultaneously achieved at high pressure. To minimize NO emission, the reactions should be operated at high values of CO/H2 ratios (i.e., >4) and pressures (e.g., P > 10 atm), low oxygen volume fractions (e.g., XO2 < 15%), and using H2O as a diluent. This study provides a new fundamental understanding of the NO mechanism of syngas MILD combustion in N2, CO2, and H2O atmospheres. 相似文献
20.
Chemical effects of added CO2 on the extinction characteristics of H2/CO/CO2 syngas diffusion flames
Jeong Park Jeong Soo Kim Jin Oh Chung Jin Han Yun Sang In Keel 《International Journal of Hydrogen Energy》2009
Chemical effects of added CO2 on flame extinction characteristics are numerically studied in H2/CO syngas diffusion flames diluted with CO2. The two representative syngas flames of 80% H2 + 20% CO and 20% H2 + 80% CO are inspected according to the composition of fuel mixture diluted with CO2 and global strain rate. Particular concerns are focused on impact of chemical effects of added CO2 on flame extinction characteristics through the comparison of the flame characteristics between well-burning flames far from extinction limit and flames at extinction. It is seen that chemical effects of added CO2 reduce critical CO2 mole fraction at flame extinction and thus extinguish the flame at higher flame temperature irrespective of global strain rate. This is attributed by the suppression of the reaction rate of the principal chain branching reaction through the augmented consumption of H-atom from the reaction CO2 + H→CO + OH. As a result the overall reaction rate decreases. These chemical effects of added CO2 are similar in both well-burning flames far from extinction limit and flames at extinction. There is a mismatching in the behaviors between critical CO2 mole fraction and maximum flame temperature at extinction. This anomalous phenomenon is also discussed in detail. 相似文献