A simple algorithm is proposed for step-by-step time integration of stiff ODEs in Chemical Kinetics. No predictor-corrector technique is used within each step of the algorithm. It is assumed that species concentration...A simple algorithm is proposed for step-by-step time integration of stiff ODEs in Chemical Kinetics. No predictor-corrector technique is used within each step of the algorithm. It is assumed that species concentrations less than 10-6 mol·L-1 do not activate any chemical reaction. So, within each step, the time steplength Δt of the algorithm is determined from the fastest reaction rate maxR by the formula Δt = 10-6mol·L-1/max R. All the reversible elementary reactions occur simultaneously;however, by a simple book-keeping technique, the updating of species concentrations, within each step of the algorithm, is performed within each elementary reaction separately. The above proposed simple algorithm for Chemical Kinetics is applied to a simple model for hydrogen combustion with only five reversible elementary reactions (Initiation, Propagation, First and Second Branching, Termination by wall destruction) with six species (H2, O2, H, O, HO, H2O). These five reversible reactions are recommended in the literature as the most significant elementary reactions of hydrogen combustion [1] [2]. Based on the proposed here simple algorithm for Chemical Kinetics, applied to the global mechanism of proposed five reversible elementary reactions for hydrogen combustion, a simple and short computer program has been developed with only about 120 Fortran instructions. By this proposed program, the following are obtained: 1) The total species concentration of hydrogen combustion, starting from the sum of initial reactants concentrations [H2] + [O2], gradually diminishes, due to termination reaction by wall destruction, and tends to the final concentration of the product [H2O], that is to the 2/3 of its initial value, in accordance to the established overall stoichiometric reaction of hydrogen combustion 2H2 + O2 → 2H2O. 2) Time-histories for concentrations of main species H2, O2, H, H2O of hydrogen combustion, in explosion and equilibrium regions, obtained by the proposed program, are compared to corresponding ones obtained by accurate computational studies of [3]. 3) In the first step of the algorithm, the only nonzero species concentrations are those of reactants [H2], [O2]. So, the maximum reaction rate is that of the forward initiation reaction max R = Rif = kif[H2] [O2], where the rate constant kif is very slow. Thus, the first time steplength Δt1 = 10-6mol·L-1/max R results long in sec. After the first step, the sequences of all the following Δt’s are very short, in μsec. So, the first time steplength Δt1 can be considered as ignition delay time. 4) It is assumed that explosion corresponds to ignition delay time Δt1 t1 = 10 sec., can be considered as explosion limit curve. This curve is compared to the corresponding one obtained by the accurate computational studies of [2].展开更多
Biomass is a kind of renewable energy which is used increasingly in different types of combustion systems or in the production of fuels like bio-oil. Lycopodium is a cellulosic particle, with good combustion propertie...Biomass is a kind of renewable energy which is used increasingly in different types of combustion systems or in the production of fuels like bio-oil. Lycopodium is a cellulosic particle, with good combustion properties, of which microscopic images show that these particles have spherical shapes with identical diameters of 31 μm. The measured density of these particles is 1.0779 g/cm2. Lycopodium particles contain 64.06% carbon, 25.56% oxygen, 8.55% hydrogen and 1.83% nitrogen, and no sulfur. Thermogravimetric analysis in the nitrogen environment indicates that the maximum of particle mass reduction occurs in the temperature range of 250-550 ℃ where the maximum mass reduction in the DTG diagrams also occurs in. In the oxygen environment, an additional peak can also be observed in the temperature range of 500-600 ℃, which points to solid phase combustion and ignition temperature of lycopodium particles. The kinetics of reactions is determined by curve fitting and minimization of error.展开更多
Turbulent non-premixed combustion of gaseous fuels is of importance for many technical applications, especially for the steel and refractory industry. Accurate turbulent flow and temperature fields are of major import...Turbulent non-premixed combustion of gaseous fuels is of importance for many technical applications, especially for the steel and refractory industry. Accurate turbulent flow and temperature fields are of major importance in order to predict details on the concentration fields. The performances of the GRI-Mech 3.0 and the Jones and Lindstedt mechanisms are compared. Detailed chemistry is included with the GRI-Mech 3.0 and J-L kinetic mechanisms in combination with the laminar flamelet combustion model. The combustion system selected for this comparison is a confined non-premixed methane flame surrounded by co-flowing air The simulation results are compared with experimental data of Lewis and Smoot （2001）.展开更多
The combustion processes of homogeneous charge compression ignition （HCCI） engines whose piston surfaces have been coated with catalyst （rhodium or platinum） were numerically investigated. A singlezone model and a...The combustion processes of homogeneous charge compression ignition （HCCI） engines whose piston surfaces have been coated with catalyst （rhodium or platinum） were numerically investigated. A singlezone model and a multi-zone model were developed. The effects of catalytic combustion on the ignition timing of the HCCI engine were analyzed through the single-zone model. The results showed that the ignition timing of the HCCI engine was advanced by the catalysis. The effects of catalytic combustion on HC, CO and NOx emissions of the HCCI engine were analyzed through the multi-zone model. The results showed that the emissions of HC and CO （using platinum （Pt） as catalyst） were decreased, while the emissions of NOx were elevated by catalytic combustion. Compared with catalyst Pt, the HC emissions were lower with catalyst rhodium （Rh） on the piston surface, but the emissions of NOx and CO were higher.展开更多
The NO formation experiments simulating moderate and intense low-oxygen dilution(MILD)oxy-coal combustion conditions were conducted on a laminar diffusion flame burner with the coflow temperatures of 1473-1873 K and t...The NO formation experiments simulating moderate and intense low-oxygen dilution(MILD)oxy-coal combustion conditions were conducted on a laminar diffusion flame burner with the coflow temperatures of 1473-1873 K and the oxygen volume fractions of 5%-20%in O_(2)/CO_(2),O_(2)/Ar and O_(2)/N_(2)atmospheres.The flame images of pulverized coal combustion were captured to obtain the ignition delay distances,and the axial species concentrations were measured to obtain the variation of NO formation and reduction.The NO yield in O_(2)/Ar atmosphere decreased by nearly 0.2 when the oxygen volume fraction decreased from 20%to 5%and by about 0.05 when the coflow temperature decreased from 1873 K to 1473 K.The NO yield in O_(2)/CO_(2)atmosphere was 0.1-0.15 lower than that in O_(2)/Ar atmosphere.The optimal kinetic parameters of thermal NO and fuel NO formation rate were obtained by a nonlinear fit of nth-order Arrhenius expression.Finally,the relative contribution rates of thermal NO to total NO(Rth)and NO reduction to fuel NO(Rre)were quantitatively separated.Rth decreases with the increase of oxygen volume fraction,below 6%at 1800 K,25%at 2000 K.Rre is almost unaffected by the coflow temperature and affected by the oxygen volume fraction,reaching 30%at 5%O_(2).展开更多
Chemical looping combustion is a promising technology for energy conversion due to its low-carbon, high-efficiency, and environmental-friendly feature. A vital issue for CLC process is the development of oxygen carrie...Chemical looping combustion is a promising technology for energy conversion due to its low-carbon, high-efficiency, and environmental-friendly feature. A vital issue for CLC process is the development of oxygen carrier, since it must have sufficient reactivity. The mechanism and kinetics of CO reduction on iron-based oxygen carriers namely pure Fe2O3 and Fe2O3 supported by alumina （Fe2O3/Al2O3） were investigated using thermo-gravimetric analysis. Fe2O3/Al2O3 showed better reactivity over bare Fe2O3 toward CO reduction. This was well supported by the observed higher rate constant for FezO3/Al2O3 over pure Fe2O3 with respective activation energy of 41.1±2.0 and 33.3±0.8 kJ. mol^-1. The proposed models were compared via statistical approach comprising Akaike information criterion with correction coupled with F-test. The phase-boundary reaction and diffusion control models approximated to 95% confidence level along with scanning electron microscopy results; revealed the promis- ing reduction reactions of pure Fe203 and Fe2O3/Al2O3. The boosting recital of iron-based oxygen carrier support toward efficient chemical looping combustion could be explained accurately through the present study.展开更多
Chemical-looping combustion(CLC)is considered to be a vital method for utilizing hydrocarbon fuel with low carbon emissions.A honeycomb fixed-bed reactor is a new kind of reactor for CLC.However,the further applicatio...Chemical-looping combustion(CLC)is considered to be a vital method for utilizing hydrocarbon fuel with low carbon emissions.A honeycomb fixed-bed reactor is a new kind of reactor for CLC.However,the further application of the reactor is limited by the inadequacy of the kinetic equations for CLC.In this paper,the experimental studies on the kinetic of Fe-based oxygen carriers were carried out by the CLC experiments using syngas which was obtained from one typical type of coal gasification products.The experimental results show that there were two individual stages for the kinetic characteristics during the fuel reaction process.Therefore,the CLC fuel reaction process could be described by a two-stage unreacted-core shrinking model and the reaction rate equations for each of the two phases were provided.In both stages,the dominant resistances were analyzed.The activation energy and the reaction order in both stages were calculated respectively as well.Comparing the experimental results of reaction rate with the calculated results of the obtained rate equations,it could be clearly seen that the reaction kinetics model was appropriate for the CLC in the honeycomb reactor.This work is expected to provide a guideline for the future development and industrial design of the honeycomb CLC reactors from the perspective of kinetics.展开更多
The detailed surface reaction mechanism of methane on rhodium catalyst was analyzed. Comparisons between numerical simulation and experiments showed a basic agreement. The combustion process of homogeneous charge comp...The detailed surface reaction mechanism of methane on rhodium catalyst was analyzed. Comparisons between numerical simulation and experiments showed a basic agreement. The combustion process of homogeneous charge compression ignition （HCCI） engine whose piston surface has been coated with catalyst （rhodium and platinum） was numerically investigated. A multi-dimensional model with detailed chemical kinetics was built. The effects of catalytic combustion on the ignition timing, the temperature and CO concentration fields, and HC, CO and NOx emissions of the HCCI engine were discussed. The results showed the ignition timing of the HCCI engine was advanced and the emissions of HC and CO were decreased by the catalysis.展开更多
The greenhouse problem has a significant effect on our communities such as,health and climate.Carbon dioxide is one of the main gases that cause global warming.Therefore,CO2 capture techniques have been the focus of a...The greenhouse problem has a significant effect on our communities such as,health and climate.Carbon dioxide is one of the main gases that cause global warming.Therefore,CO2 capture techniques have been the focus of attention these days.The chemical looping combustion technique adopted the air reactor and fuel reactor to recycle heat energy.This study presents a numerical and experimental investigation on a fuel reactor in chemical looping combustor(CLC)system.The present numerical model is introduced by the kinetic theory of granular flow and coupled with gas–solid flow with chemical reactions to simulate the combustion of solids in the CLC.The k–εturbulent model was used to model the gas phase and the particle phase.The developed model simplify the prediction of flow patterns,particle velocities,gas velocities,and composition profiles of gas products and the distribution of heterogeneous reaction rates under the same operating conditions.The predicted and experimental results were compared according to the basis of determination coefficient(R2).In addition the results showed that there is a good agreement between the predicted and experimental data.The value of(R2)for CO,CO2 and CH4 was 0.959,0.925 and 0.969 respectively.This shows that the present model is a promising simulation for solid particle combustion and gives the power direction for the design and optimization of the CLC systems.展开更多
为了理解甲醇/柴油双燃料机的自燃特性并为燃烧计算所需骨架机理提供理论依据,以正庚烷作为柴油替代物,应用快速压缩机对宽广实验条件下甲醇/正庚烷混合燃料的自燃特性进行了研究。实验条件覆盖了甲醇/柴油双燃料机的典型工况。实验研...为了理解甲醇/柴油双燃料机的自燃特性并为燃烧计算所需骨架机理提供理论依据,以正庚烷作为柴油替代物,应用快速压缩机对宽广实验条件下甲醇/正庚烷混合燃料的自燃特性进行了研究。实验条件覆盖了甲醇/柴油双燃料机的典型工况。实验研究结果显示,随着压力升高、甲醇比例减少或当量比增大,混合燃料滞燃期变短。根据实验数据验证了爱尔兰国立大学(National University of Ireland,NUI)的正庚烷详细机理对甲醇/正庚烷的适用性,并利用该机理在CHEMKIN PRO软件中进行了化学动力学分析。结果表明,甲醇与正庚烷竞争羟基(hydroxyl,OH)从而抑制系统氧化过程。敏感性分析结果显示,超氧化氢(HO_(2))反应生成过氧化氢(H_(2)O_(2))是燃烧过程中最敏感的反应,抑制系统氧化过程的进行。本研究可为获得适用于甲醇/柴油双燃料机燃烧计算的骨架机理提供理论依据。展开更多
文摘A simple algorithm is proposed for step-by-step time integration of stiff ODEs in Chemical Kinetics. No predictor-corrector technique is used within each step of the algorithm. It is assumed that species concentrations less than 10-6 mol·L-1 do not activate any chemical reaction. So, within each step, the time steplength Δt of the algorithm is determined from the fastest reaction rate maxR by the formula Δt = 10-6mol·L-1/max R. All the reversible elementary reactions occur simultaneously;however, by a simple book-keeping technique, the updating of species concentrations, within each step of the algorithm, is performed within each elementary reaction separately. The above proposed simple algorithm for Chemical Kinetics is applied to a simple model for hydrogen combustion with only five reversible elementary reactions (Initiation, Propagation, First and Second Branching, Termination by wall destruction) with six species (H2, O2, H, O, HO, H2O). These five reversible reactions are recommended in the literature as the most significant elementary reactions of hydrogen combustion [1] [2]. Based on the proposed here simple algorithm for Chemical Kinetics, applied to the global mechanism of proposed five reversible elementary reactions for hydrogen combustion, a simple and short computer program has been developed with only about 120 Fortran instructions. By this proposed program, the following are obtained: 1) The total species concentration of hydrogen combustion, starting from the sum of initial reactants concentrations [H2] + [O2], gradually diminishes, due to termination reaction by wall destruction, and tends to the final concentration of the product [H2O], that is to the 2/3 of its initial value, in accordance to the established overall stoichiometric reaction of hydrogen combustion 2H2 + O2 → 2H2O. 2) Time-histories for concentrations of main species H2, O2, H, H2O of hydrogen combustion, in explosion and equilibrium regions, obtained by the proposed program, are compared to corresponding ones obtained by accurate computational studies of [3]. 3) In the first step of the algorithm, the only nonzero species concentrations are those of reactants [H2], [O2]. So, the maximum reaction rate is that of the forward initiation reaction max R = Rif = kif[H2] [O2], where the rate constant kif is very slow. Thus, the first time steplength Δt1 = 10-6mol·L-1/max R results long in sec. After the first step, the sequences of all the following Δt’s are very short, in μsec. So, the first time steplength Δt1 can be considered as ignition delay time. 4) It is assumed that explosion corresponds to ignition delay time Δt1 t1 = 10 sec., can be considered as explosion limit curve. This curve is compared to the corresponding one obtained by the accurate computational studies of [2].
基金supported by the Ministry of Science, Research & Technology of Iran
文摘Biomass is a kind of renewable energy which is used increasingly in different types of combustion systems or in the production of fuels like bio-oil. Lycopodium is a cellulosic particle, with good combustion properties, of which microscopic images show that these particles have spherical shapes with identical diameters of 31 μm. The measured density of these particles is 1.0779 g/cm2. Lycopodium particles contain 64.06% carbon, 25.56% oxygen, 8.55% hydrogen and 1.83% nitrogen, and no sulfur. Thermogravimetric analysis in the nitrogen environment indicates that the maximum of particle mass reduction occurs in the temperature range of 250-550 ℃ where the maximum mass reduction in the DTG diagrams also occurs in. In the oxygen environment, an additional peak can also be observed in the temperature range of 500-600 ℃, which points to solid phase combustion and ignition temperature of lycopodium particles. The kinetics of reactions is determined by curve fitting and minimization of error.
文摘Turbulent non-premixed combustion of gaseous fuels is of importance for many technical applications, especially for the steel and refractory industry. Accurate turbulent flow and temperature fields are of major importance in order to predict details on the concentration fields. The performances of the GRI-Mech 3.0 and the Jones and Lindstedt mechanisms are compared. Detailed chemistry is included with the GRI-Mech 3.0 and J-L kinetic mechanisms in combination with the laminar flamelet combustion model. The combustion system selected for this comparison is a confined non-premixed methane flame surrounded by co-flowing air The simulation results are compared with experimental data of Lewis and Smoot （2001）.
基金the National Key Basic Research Development Project of China (2001CB209201)
文摘The combustion processes of homogeneous charge compression ignition （HCCI） engines whose piston surfaces have been coated with catalyst （rhodium or platinum） were numerically investigated. A singlezone model and a multi-zone model were developed. The effects of catalytic combustion on the ignition timing of the HCCI engine were analyzed through the single-zone model. The results showed that the ignition timing of the HCCI engine was advanced by the catalysis. The effects of catalytic combustion on HC, CO and NOx emissions of the HCCI engine were analyzed through the multi-zone model. The results showed that the emissions of HC and CO （using platinum （Pt） as catalyst） were decreased, while the emissions of NOx were elevated by catalytic combustion. Compared with catalyst Pt, the HC emissions were lower with catalyst rhodium （Rh） on the piston surface, but the emissions of NOx and CO were higher.
基金supported by the National Natural Science Foundation of China(grant number:51976120).
文摘The NO formation experiments simulating moderate and intense low-oxygen dilution(MILD)oxy-coal combustion conditions were conducted on a laminar diffusion flame burner with the coflow temperatures of 1473-1873 K and the oxygen volume fractions of 5%-20%in O_(2)/CO_(2),O_(2)/Ar and O_(2)/N_(2)atmospheres.The flame images of pulverized coal combustion were captured to obtain the ignition delay distances,and the axial species concentrations were measured to obtain the variation of NO formation and reduction.The NO yield in O_(2)/Ar atmosphere decreased by nearly 0.2 when the oxygen volume fraction decreased from 20%to 5%and by about 0.05 when the coflow temperature decreased from 1873 K to 1473 K.The NO yield in O_(2)/CO_(2)atmosphere was 0.1-0.15 lower than that in O_(2)/Ar atmosphere.The optimal kinetic parameters of thermal NO and fuel NO formation rate were obtained by a nonlinear fit of nth-order Arrhenius expression.Finally,the relative contribution rates of thermal NO to total NO(Rth)and NO reduction to fuel NO(Rre)were quantitatively separated.Rth decreases with the increase of oxygen volume fraction,below 6%at 1800 K,25%at 2000 K.Rre is almost unaffected by the coflow temperature and affected by the oxygen volume fraction,reaching 30%at 5%O_(2).
文摘Chemical looping combustion is a promising technology for energy conversion due to its low-carbon, high-efficiency, and environmental-friendly feature. A vital issue for CLC process is the development of oxygen carrier, since it must have sufficient reactivity. The mechanism and kinetics of CO reduction on iron-based oxygen carriers namely pure Fe2O3 and Fe2O3 supported by alumina （Fe2O3/Al2O3） were investigated using thermo-gravimetric analysis. Fe2O3/Al2O3 showed better reactivity over bare Fe2O3 toward CO reduction. This was well supported by the observed higher rate constant for FezO3/Al2O3 over pure Fe2O3 with respective activation energy of 41.1±2.0 and 33.3±0.8 kJ. mol^-1. The proposed models were compared via statistical approach comprising Akaike information criterion with correction coupled with F-test. The phase-boundary reaction and diffusion control models approximated to 95% confidence level along with scanning electron microscopy results; revealed the promis- ing reduction reactions of pure Fe203 and Fe2O3/Al2O3. The boosting recital of iron-based oxygen carrier support toward efficient chemical looping combustion could be explained accurately through the present study.
基金the support of the National Key Research and Development Program of China (No. 2016YFB0901401)the Chinese Academy of Sciences Frontier Science Key Research Project (QYZDY-SSW-JSC036)
文摘Chemical-looping combustion(CLC)is considered to be a vital method for utilizing hydrocarbon fuel with low carbon emissions.A honeycomb fixed-bed reactor is a new kind of reactor for CLC.However,the further application of the reactor is limited by the inadequacy of the kinetic equations for CLC.In this paper,the experimental studies on the kinetic of Fe-based oxygen carriers were carried out by the CLC experiments using syngas which was obtained from one typical type of coal gasification products.The experimental results show that there were two individual stages for the kinetic characteristics during the fuel reaction process.Therefore,the CLC fuel reaction process could be described by a two-stage unreacted-core shrinking model and the reaction rate equations for each of the two phases were provided.In both stages,the dominant resistances were analyzed.The activation energy and the reaction order in both stages were calculated respectively as well.Comparing the experimental results of reaction rate with the calculated results of the obtained rate equations,it could be clearly seen that the reaction kinetics model was appropriate for the CLC in the honeycomb reactor.This work is expected to provide a guideline for the future development and industrial design of the honeycomb CLC reactors from the perspective of kinetics.
文摘The detailed surface reaction mechanism of methane on rhodium catalyst was analyzed. Comparisons between numerical simulation and experiments showed a basic agreement. The combustion process of homogeneous charge compression ignition （HCCI） engine whose piston surface has been coated with catalyst （rhodium and platinum） was numerically investigated. A multi-dimensional model with detailed chemical kinetics was built. The effects of catalytic combustion on the ignition timing, the temperature and CO concentration fields, and HC, CO and NOx emissions of the HCCI engine were discussed. The results showed the ignition timing of the HCCI engine was advanced and the emissions of HC and CO were decreased by the catalysis.
文摘The greenhouse problem has a significant effect on our communities such as,health and climate.Carbon dioxide is one of the main gases that cause global warming.Therefore,CO2 capture techniques have been the focus of attention these days.The chemical looping combustion technique adopted the air reactor and fuel reactor to recycle heat energy.This study presents a numerical and experimental investigation on a fuel reactor in chemical looping combustor(CLC)system.The present numerical model is introduced by the kinetic theory of granular flow and coupled with gas–solid flow with chemical reactions to simulate the combustion of solids in the CLC.The k–εturbulent model was used to model the gas phase and the particle phase.The developed model simplify the prediction of flow patterns,particle velocities,gas velocities,and composition profiles of gas products and the distribution of heterogeneous reaction rates under the same operating conditions.The predicted and experimental results were compared according to the basis of determination coefficient(R2).In addition the results showed that there is a good agreement between the predicted and experimental data.The value of(R2)for CO,CO2 and CH4 was 0.959,0.925 and 0.969 respectively.This shows that the present model is a promising simulation for solid particle combustion and gives the power direction for the design and optimization of the CLC systems.
文摘为了理解甲醇/柴油双燃料机的自燃特性并为燃烧计算所需骨架机理提供理论依据,以正庚烷作为柴油替代物,应用快速压缩机对宽广实验条件下甲醇/正庚烷混合燃料的自燃特性进行了研究。实验条件覆盖了甲醇/柴油双燃料机的典型工况。实验研究结果显示,随着压力升高、甲醇比例减少或当量比增大,混合燃料滞燃期变短。根据实验数据验证了爱尔兰国立大学(National University of Ireland,NUI)的正庚烷详细机理对甲醇/正庚烷的适用性,并利用该机理在CHEMKIN PRO软件中进行了化学动力学分析。结果表明,甲醇与正庚烷竞争羟基(hydroxyl,OH)从而抑制系统氧化过程。敏感性分析结果显示,超氧化氢(HO_(2))反应生成过氧化氢(H_(2)O_(2))是燃烧过程中最敏感的反应,抑制系统氧化过程的进行。本研究可为获得适用于甲醇/柴油双燃料机燃烧计算的骨架机理提供理论依据。
