The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Chung King Law - One of the best experts on this subject based on the ideXlab platform.
-
laminar Flame propagation in supercritical hydrogen air and methane air mixtures
Proceedings of the Combustion Institute, 2019Co-Authors: Wenkai Liang, Chung King LawAbstract:Abstract The propagation of laminar hydrogen/air and methane/air Flames in supercritical conditions was computationally simulated for the planar Flame configurations, incorporating descriptions of supercritical thermodynamics and transport as well as high-pressure chemical kinetics. The inaccuracies associated with the use of ideal gas assumptions for various components of the supercritical description were systematically assessed with progressively more complete formulation. Results show that, for hydrogen/air Flames, the laminar Flame speeds at high pressures increase due to the non-ideal equation of state (EoS), and is mainly due to the density modification of the initial mixture. Including the thermodynamic properties of heat capacity reduces the Flame speed because of the correspondingly reduced adiabatic Flame Temperature. Transport properties were found to have small effect because of the inherent insensitivity of the laminar burning rate to variations in the transport properties. For methane/air Flames, the use of recently reported high-pressure chemical kinetics considerably affects the laminar Flame speed, even for the same Flame Temperature.
-
on the off stoichiometric peaking of adiabatic Flame Temperature
Combustion and Flame, 2006Co-Authors: Chung King Law, Atsushi MakinoAbstract:The characteristic rich shifting of the maximum adiabatic Flame Temperature from the stoichiometric value for mixtures of hydrocarbon and air is demonstrated to be caused by product dissociation and hence reduced amount of heat release. Since the extent of dissociation is greater on the lean side as a result of the stoichiometry of dissociated products, the peaking occurs on the rich side. The specific heat per unit mass of the mixture is shown to increase monotonically with increasing fuel concentration, and as such tends to shift the peak toward the lean side. It is further shown that this is the cause for the lean shifting of the adiabatic Flame Temperature of oxidizer-enriched mixtures of N{sub m}H{sub n} and F{sub 2} and of NH{sub 3} and O{sub 2}, with various amounts of inert dilution, even though their maximum heat release still peaks on the rich side. (author)
-
detailed oxidation kinetics and Flame inhibition effects of chloromethane
Combustion and Flame, 1996Co-Authors: Hai Wang, T O Hahn, Chihjen Sung, Chung King LawAbstract:A comprehensive experimental and numerical study has been performed on the detailed oxidation kinetics and the Flame inhibition effects of chloromethane, with an emphasis on the isolation of the Temperature and chemical effects caused by substitution of methane in the fuel by chloromethane. The experimental efforts involved the determination of laminar burning velocities for a series of fuel mixtures of different ratios of chloromethane to methane, but with a fixed ratio of total fuel to oxygen (and air). The thermal and chemical effects were isolated by comparing the laminar burning velocities obtained with the adiabatic Flame Temperature uncompensated with the substitution of methane by chloromethane, versus those obtained with fixed adiabatic Flame Temperature achieved by replacing nitrogen in air with an equal amount of argon. The experimental results indicate that Temperature reduction due to increased chloromethane substitution is a significant factor for the reduction in the laminar burning velocity. Furthermore, when the results at a fixed Flame Temperature were examined on the basis of the mass burning rate, which is the eigenvalue for laminar Flame propagation, the response was found to be insensitive to the chloromethane concentration in the mixture. This implies the possibility of a corresponding insensitivity to the chlorine Flame chemistry. Concurrently, a detailed reaction mechanism of chloromethane/methane oxidation was compiled and validated against literature data from shock tube to flow reactor studies. Numerical simulation of the present experimental situation was then performed. The numerical results were found to be in close agreement with the current experimental findings.
Hasan Kayhan Kayadelen - One of the best experts on this subject based on the ideXlab platform.
-
a multi featured model for estimation of thermodynamic properties adiabatic Flame Temperature and equilibrium combustion products of fuels fuel blends surrogates and fuel additives
Energy, 2018Co-Authors: Hasan Kayhan KayadelenAbstract:Abstract This study introduces a new multi-featured equilibrium combustion model for fuels, fuel blends and surrogates which estimates mole fractions, adiabatic Flame Temperature and thermodynamic properties of the equilibrium combustion products. The model enables simultaneous consideration of unlimited number of CαHβOγNδ type fuels of different ratios and also enables any CαHβOγNδ type fuel additive, Argon, H2O, CO, CO2, N2, and O2 to be considered among the reactants. Equilibrium mole fractions and adiabatic Flame Temperature are not only necessary for estimating thermodynamic properties of exhaust gases but also provide key data to obtain the non-equilibrium concentrations. As for thermodynamic properties, precise calculation is necessary for accurate performance estimations of internal combustion engines. Meeting these fundamental needs and providing combustion analysis of numerous fuel blends of various mixing ratios, this new model can be a recourse tool for researchers working on fuels, surrogates, emissions and internal combustion engine modelling. Simulations of any combustion process including existence of exhaust gas recirculation, supplementary firing, steam injection, argon dilution, water injection, fuel emulsification and reheat process in gas turbines can easily be conducted by integrating this validated model into thermodynamic cycle models.
-
effect of natural gas components on its Flame Temperature equilibrium combustion products and thermodynamic properties
Journal of Natural Gas Science and Engineering, 2017Co-Authors: Hasan Kayhan KayadelenAbstract:Abstract It is a known fact that the composition of natural gas varies widely from source to source and from time to time even in the same source. Such variations in gas composition cause variations in Flame Temperature, its combustion products and thermodynamic properties which can affect gas-fueled engine performance and its emissions. The purpose of this study is to investigate effects of varying amounts of natural gas diluent components such as ethane (C 2 H 6 ), isobutane (C 4 H 10 ), propane (C 3 H 8 ), carbon dioxide (CO 2 ) and nitrogen (N 2 ) on methane–air combustion under different pressures, unburned mixture Temperatures and equivalence ratios. Results show that adiabatic Flame Temperature is mostly increased by isobutane followed by propane and ethane however it is mostly influenced by CO 2 content in the gas which decreases Flame Temperature 80 K in %70 CH 4 - %30 CO 2 mixture at stoichiometric conditions. As for specific heat, the highest increase is again for isobutane followed by propane and ethane content but it is decreased mostly by N 2 . Effect of increasing secondary fuel content on product species is greatest at equivalence ratio near unity except for CO and H 2 . Analysis results including equilibrium compositions are validated and expected to be a reference guide for scientists, engineers and NG consumers to evaluate and compare natural gas samples of different compositions.
Jun Li - One of the best experts on this subject based on the ideXlab platform.
-
physical and chemical effects of co2 and h2o additives on counterflow diffusion Flame burning methane
Energy & Fuels, 2013Co-Authors: Lin Wang, Sheng Chen, Chuguang Zheng, Jun LiAbstract:A numerical study is conducted to understand better the Flame structure in a CH4–O2/N2/CO2/H2O counterflow diffusion Flame with various mole fractions of CO2 and H2O. Special interest is focused on the thermal, chemical, and diffusion effects of these species on the Flame Temperature and emission index of CO (EICO). A key result of the study is that the Flame Temperature is significantly reduced because of the chemical and thermal effects of CO2. However, H2O has a minor effect on the Flame Temperature, because its chemical effect almost cancels out its thermal effect. Meanwhile, the chemical effect of CO2 induces the EICO to increase noticeably, although other effects of H2O and CO2 slightly decrease it. The diffusion effect of CO2 only affects the distributions of the Flame Temperature and major species. Moreover, the pathways of fuel oxidation reactions are also investigated, and it is found that the low-Temperature hydrocarbon reaction pathway (C1 branch) becomes more active under oxy-fuel combustion ...
-
a numerical study on premixed micro combustion of ch4 air mixture effects of combustor size geometry and boundary conditions on Flame Temperature
Chemical Engineering Journal, 2009Co-Authors: Jun Li, S K Chou, Wenming Yang, Z W LiAbstract:Abstract A numerical study on CH 4 –air premixed combustion in micro-combustors was undertaken by solving the 2D governing equations. The effects of combustor size and geometry, inlet velocity profile and slip-wall boundary condition on the Flame Temperature were investigated. The simulation results showed that a larger combustor ( d = 2 mm) gives higher Flame Temperature only when the flow velocity is below a certain level. With regard to the combustor geometry, a 2D planar channel ( H = 1 mm) represents higher Flame Temperature than a cylindrical tube with d = 2 mm (equal hydrodynamic diameter), over the velocity range covered by the present study. In addition, it was noted that the Flame Temperatures in the cylindrical tube and 2D planar channel are quite close when H = 0.65 d is satisfied. The fully developed velocity profile applied at the inlet plane was found to have the Flames anchored further from the entrance than the uniform profile, but no remarkable difference in terms of Flame Temperature (≤3 K) was observed. A simple analysis of the competing time scales (axial convection and radial diffusion) was presented to address the difference of Flame structure between the methane–air and hydrogen–air mixtures. Finally, it was shown that in a combustor with d = 1 mm the effects of slip-wall boundary are negligible, compared to the bulk velocity and gases Temperature.
Iskender Gokalp - One of the best experts on this subject based on the ideXlab platform.
-
simulation of a syngas counter flow diffusion Flame structure and no emissions in the pressure range 1 10 atm
Fuel Processing Technology, 2014Co-Authors: Khadidja Safer, Fouzi Tabet, Ahmed Ouadha, Meriem Safer, Iskender GokalpAbstract:Abstract This paper reports a numerical investigation of syngas Flame structure and NO reaction pathways over a wide range of operating conditions (H 2 /CO ratio between 0.4 and 2.4, scalar dissipation rate from equilibrium to extinction and ambient pressure from 1 to 10 atm) in mixture fraction space. An analysis of optimal operation conditions for syngas combustion in regard to NO index emissions is also provided. Flame structure is characterized by solving Flamelet equations with the consideration of radiation. The chemical reaction mechanism adopted is GRI-Mech 3.0. The computational predictions showed that Flame Temperature exhibits a peak at an intermediate scalar dissipation rate for a given value of H 2 /CO ratio. From hydrogen-lean syngas to hydrogen-rich syngas fuels, maximum Flame Temperature increases for scalar dissipation rate values lower than the intermediate value whereas decreases at higher values. Zeldovich route is found to be the main NO formation route and its contribution to the NO production continually increases with the increase of hydrogen content and pressure. Hydrogen-rich syngas Flames produce more NO at lower scalar dissipation rates while NO levels increase towards hydrogen-lean syngas Flames at higher scalar dissipation rates.
-
combustion characteristics of hydrogen rich alternative fuels in counter flow diffusion Flame configuration
Energy Conversion and Management, 2013Co-Authors: Khadidja Safer, Fouzi Tabet, Ahmed Ouadha, Meriem Safer, Iskender GokalpAbstract:Abstract Fuels containing large amounts of hydrogen have combustion properties highly depending on composition, in particular hydrogen concentration, and operating conditions such as pressure. A thorough understanding of strained laminar Flames is a prerequisite to achieve improved knowledge of more complex system involving hydrogen-rich alternative fuels. This paper reports a numerical investigation of syngas counter-flow diffusion Flame structure and emissions over a wide range of operating conditions (H2/CO ratio between 0.4 and 2.4 and ambient pressure from 1 to 10 atm). Special attention is focused on optimal operating conditions in regard to NOx emissions and NOx reactions pathways. Flame structure is characterized by solving Flamelet equations with the consideration of radiation. The chemical reaction mechanism adopted is GRI-Mech 3.0. Computational results showed that Flame structure and emissions are impacted by syngas composition and ambient pressure. The maximum Flame Temperature exhibits a peak at an intermediate scalar dissipation rate for a given value of H2/CO ratio. For values of strain rate lower than the intermediate value, Flame structure is influenced by combined effects of adiabatic Temperature and radiation heat loss, whereas only adiabatic Temperature effect prevails at higher values of strain rate. The Flame Temperature increases more the syngas is H2-rich for strain rates values below the intermediate value. The opposite behavior is noticed at strain rate values higher than the intermediate value. NOx formation is closely related to Flame Temperature. Hydrogen-rich syngas Flames produce more NOx at lower strain rates while NOx levels increase towards hydrogen-lean syngas Flames at higher strain rates. Zeldovich route is found to be the main NOx formation route and its contribution to the NOx production continually increases with H2 content and pressure.
Alexander A Konnov - One of the best experts on this subject based on the ideXlab platform.
-
the Temperature dependence of the laminar burning velocity and superadiabatic Flame Temperature phenomenon for nh3 air Flames
Combustion and Flame, 2020Co-Authors: Zhihua Wang, Yong He, Alexander A KonnovAbstract:Abstract Combustion of ammonia (NH3) as a carbon-free alternative fuel has been recently widely studied, with vast majority of the burning velocity data obtained at room Temperature. In the present study, the laminar burning velocity SL of NH3/air mixtures has been measured at unburnt gas Temperature Tu from 298 K to 448 K, covering equivalence ratios from 0.85 to 1.25 and at 1 atm using the heat flux method. Kinetic simulations were made with five literature mechanisms developed for NH3 combustion, i.e., Nakamura et al., Otomo et al., San Diego, Okafor et al., and Mei et al. mechanisms, and the influence of radiation heat losses was considered. Using the obtained burning velocity data at different Temperatures, the Temperature dependence coefficients α in S L S L 0 = ( T u T u 0 ) α were derived, and compared with different models’ predictions. Further analyses of the Temperature dependence of SL were carried out through examination of the overall activation energy, Temperature and species profiles as well as the reaction paths, and a unique Flame structure at the rich side of adiabatic NH3/air Flames was found, which resembles ‘over-rich’ phenomena in hydrocarbon Flames. At equivalence ratio larger than 1.1 ± 0.05, the NH3/air Flames become so rich that (1) the NH2 radical overwhelms the H and OH radicals in maximum mole fraction; (2) after the Flame front, H2O converts back to H2 with NO formed at the same time, causing the superadiabatic Flame Temperature phenomena, i.e. adiabatic Flame Temperature being lower than the maximum achieved in the Flame. Moreover, local minimum NO concentration is found right after the over-rich NH3/air Flame front, which may be helpful in reducing NO emissions from NH3 Flames in practical applications.