CO2 Mass Fraction Research Articles

Formation of anthropogenic secondary organic aerosol (SOA) and its influence on biogenic SOA properties

Abstract. Secondary organic aerosol (SOA) formation from mixed anthropogenic and biogenic precursors has been studied exposing reaction mixtures to natural sunlight in the SAPHIR chamber in Jülich, Germany. In this study aromatic compounds served as examples of anthropogenic volatile organic compound (VOC) and a mixture of α-pinene and limonene as an example for biogenic VOC. Several experiments with exclusively aromatic precursors were performed to establish a relationship between yield and organic aerosol mass loading for the atmospheric relevant range of aerosol loads of 0.01 to 10 μg m−3. The yields (0.5 to 9%) were comparable to previous data and further used for the detailed evaluation of the mixed biogenic and anthropogenic experiments. For the mixed experiments a number of different oxidation schemes were addressed. The reactivity, the sequence of addition, and the amount of the precursors influenced the SOA properties. Monoterpene oxidation products, including carboxylic acids and dimer esters were identified in the aged aerosol at levels comparable to ambient air. OH radicals were measured by Laser Induced Fluorescence, which allowed for establishing relations of aerosol properties and composition to the experimental OH dose. Furthermore, the OH measurements in combination with the derived yields for aromatic SOA enabled application of a simplified model to calculate the chemical turnover of the aromatic precursor and corresponding anthropogenic contribution to the mixed aerosol. The estimated anthropogenic contributions were ranging from small (≈8%) up to significant fraction (>50%) providing a suitable range to study the effect of aerosol composition on the aerosol volatility (volume fraction remaining (VFR) at 343 K: 0.86–0.94). The aromatic aerosol had higher oxygen to carbon ratio O/C and was less volatile than the biogenic fraction. However, in order to produce significant amount of aromatic SOA the reaction mixtures needed a higher OH dose that also increased O/C and provided a less volatile aerosol. The SOA yields, O/C, and f44 (the mass fraction of CO2+ ions in the mass spectra which can be considered as a measure of carboxylic groups) in the mixed photo-chemical experiments could be described as linear combinations of the corresponding properties of the pure systems. For VFR there was in addition an enhancement effect, making the mixed aerosol significantly less volatile than what could be predicted from the pure systems. A strong positive correlation was found between changes in volatility and O/C with the exception during dark hours where the SOA volatility decreased while O/C did not change significantly. Thus, this change in volatility under dark conditions as well as the anthropogenic enhancement is due to chemical or morphological changes not affecting O/C.

Numerical simulations of non-premixed turbulent combustion of CH4–H2 mixtures using the PDF approach

The present work is devoted to the study of non-premixed turbulent combustion with the PDF approach using three turbulence models: k-ɛ model, modified k-ɛ model and RSM model. A detailed kinetic mechanism is used in the numerical simulations. The three turbulence models are compared and evaluated with the experimental data and the numerical results of the literature. The evaluation concludes that the modified k-ɛ is the most appropriate for simulating this kind of flame. A study of the effect of hydrogen addition on methane combustion is performed. Hydrogen addition causes the elevation of combustion temperature, the decreasing of CO and CO2 mass fractions but leads to the increase of NO mass fraction.

Prediction of the seismic time-lapse signal of CO2/CH4injection into a depleted gas reservoir - Otway Project

Stage I of the Otway project conducted by the Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) in 2007-2010 included injection of 66000 tons of CO2-rich gas into a depleted gas reservoir at Naylor field, Otway Basin, Victoria. In this paper we present a seismic modelling study that estimates the time lapse response of CO2/CH4 injection into the Waarre C reservoir. Based on the static geological model, acoustic impedance inversion of the seismic baseline data as well as log data, two models with different levels of detail in the reservoir properties are built. The distribution of the injected CO2/CH4 mixture in the reservoir and the gas properties are obtained from flow simulations. In order to predict the change in acoustic impedance after injection, we employed the Gassmann fluid substitution workflow. The modelled total differences in acoustic impedance for different amounts of CO2/CH4 injected are of the same order of magnitude for both models and reflect the CO2 mass fractions predicted by flow simulations. Finally zero incidence synthetic data are computed for these cases using a statistical wavelet of the baseline data. The computed synthetics are compared to surface seismic and VSP monitoring data. The repeatability of the surface seismic data is too low to detect the predicted signal. For the 3D VSP data, the time-lapse signal/noise has a similar order of magnitude as the predicted signal. It may have the level required to detect the signal.

Multiply conditioned analyses of stratification in highly swirling methane/air flames

The effects of stratification on a series of highly swirling turbulent flames under globally lean conditions (ϕg=0.75) are investigated using a new high-spatial resolution multi-scalar dataset. This dataset features two key properties: high spatial resolution which approaches the 60 micron optical limit of the measurement system, and a wavelet oversampling methodology which significantly reduces the influence of noise. Furthermore, the very large number of realizations (30,000) acquired in the stratified cases permits statistically significant results to be obtained even after aggressive conditioning is applied. Data are doubly conditioned on equivalence ratio and the degree of stratification across the flame in each instantaneous realization. The influence of stoichiometry is limited by conditioning on the equivalence ratio at the location of peak CO mass fraction, which is shown to be a good surrogate for the location of peak heat release rate, while the stratification is quantified using a linear gradient in equivalence ratio across the instantaneous flame front. This advanced conditioning enables robust comparisons with the baseline lean premixed flame. Species mass fractions of both carbon monoxide and hydrogen are increased in temperature space under stratified conditions. Stratification is also shown to significantly increase thermal gradients, yet the derived three-dimensional flame surface density is shown to be relatively insensitive to stratification. Whilst the presence of instantaneous stratification broadens the curvature distribution relative to the premixed case, the degree of broadening is not significantly influenced by the range of global stratification ratios examined in this study.

Large Eddy Simulations and experimental studies of turbulent premixed combustion near extinction

In this paper, lean premixed flames featuring local extinction are simulated numerically by Large Eddy Simulations (LES) and investigated experimentally by one-dimensional, spatially resolved Raman scattering. Two unconfined piloted lean premixed natural gas/air flames with equivalence ratios ϕ=0.71 and 0.65 are studied. The Reaction–Diffusion Manifold (REDIM) technique is employed together with the presumed joint Filtered Density Function (FDF) to carry out the LES. In the present work, two reduced coordinates, the CO2 and N2 mass fractions, are considered in the REDIM look-up table, and the joint FDF of them is modelled in terms of two statistically independent FDFs. Good overall agreement between the experimental data and the LES results is obtained. Scatter plots from measurements and instantaneous data from LES show states with local extinction, mainly in the leaner flame. The results demonstrate the capability of the proposed REDIM-presumed joint FDF method to deal with the phenomenon of local extinction in lean premixed flames.

Phase equilibrium of the system supercritical carbon dioxide–lemon essential oil: New experimental data and thermodynamic modelling

New experimental phase equilibrium data on the system supercritical CO2–lemon oil are provided at 50°C and 70°C, for pressures in the range 8.6–10.1MPa and 9.7–13.5MPa, respectively. Additional phase equilibrium data on the binary sub-system CO2–limonene are also provided. The measurements were carried out in a double-chamber isothermal apparatus of 340cm3. Both the mass fraction of CO2 in the two phases and in the overall system was measured. The composition of the two phases on CO2-free basis was also measured. A thermodynamic model based on the Peng–Robinson equation of state was developed in order to represent the behaviour of the system supercritical CO2–lemon oil. The model uses only regression parameters calculated from binary sub-systems, thus being predictive with respect to the multicomponent mixture. A good representation of the phase equilibrium data is obtained with the proposed thermodynamic model.

Subgrid-scale mixing of mixture fraction, temperature, and species mass fractions in turbulent partially premixed flames

The subgrid-scale (SGS) mixing of mixture fraction, temperature, and species mass fraction in turbulent partially premixed (Sandia) flames is studied. We focus on the effects of the SGS mixing regimes and the spatial relationships among the scalars on the SGS mixing of the species mass fractions. High-resolution lines images are used to obtain the scalar filtered mass density function and the conditionally filtered diffusion. The results show that for small SGS variance the scalar fields have a relatively simple structure. For large SGS variance the structure is more complex. The spatial relationships among the scalars result in different SGS scalar structures and SGS mixing characteristics, with the mass fraction of CO2 being the simplest and that of CO being the most complex. The results in this study present a challenging test for SGS mixing models.

Transport characteristic study of methane steam reforming coupling methane catalytic combustion for hydrogen production

Methane steam reforming coupling methane catalytic combustion for hydrogen production is an effective method of process intensification for this reaction with strong heat effect. In this paper, simulation of this coupling process was carried out. Effects of inlet parameters of methane steam reforming and methane catalytic combustion on reactor performance were investigated. Results showed that, methane conversion at steam reforming channel outlet nearly approached 100%, however, methane conversion was greatly influenced by inlet velocity in catalytic combustion channel; H2 and CO mass fraction was influenced by coupling of heat generation and consumption in the reactor. The temperature distribution in both steam reforming and combustion channels presented a T-shaped profile indicating a catalytic combustion controlling mechanism of the reactor. The maximum hot spot temperature difference variations in both channels expressed a half saddle-shaped. Local imbalance of strong heat effect of steam reforming and catalytic combustion led to a sharp hot spot near the reactor inlet. Simulation results of methane steam reforming and catalytic combustion coupling process indicate that the catalyst activity at reactor inlet needs to be redesigned and optimized.

Combustion simulation technique for reducing chemical mechanisms using look-up table of chemical equilibrium calculations: Application to CO–H2–air turbulent non-premixed flame

This paper presents a dimension reduction technique for turbulent non-premixed flames based on a chemical equilibrium method combined with a reaction calculation. An advantage of the proposed technique is that it simplifies the process of building a reduced chemical mechanism according to the accuracy requirement for the chemical species. The proposed technique reduces the computational time for the combustion simulation. In this technique, chemical species are roughly divided into two groups: The first includes fuels and intermediate species; the intermediate species include only those necessary for high accuracy. The second group comprises the rest of the species, and their mass fractions are obtained from a look-up table prepared using chemical equilibrium calculations conducted prior to the combustion simulation. The obtained results were compared with the experimental data of a CO–H2–air turbulent non-premixed flame and computational data obtained using the eddy dissipation concept (EDC) model. The major mass fractions of CO, H2, and H2O, as well as the temperature and mixture fraction obtained using the proposed technique, were in good agreement with these reference data. Furthermore, compared with the EDC model, the minor mass fractions of OH, O, and NO obtained using the proposed technique were close and the computational time was 75% lower.

Transported scalar PDF calculations of a swirling bluff body flame (‘SM1’) with a reaction diffusion manifold

The modeling of a reacting swirling flow behind a bluff-body burner (SM1) in the framework of RANS and transported scalar PDF is presented. The EMST mixing model is applied and the composition space is reduced to mixture fraction (Z) and a progress variable (CO2 mass fraction, YCO2) by means of a Reaction Diffusion Manifold (REDIM). With an ad hoc adjustment of the turbulent Schmidt number, the mean flow and mixing fields obtained are comparable to LES results from the literature. The REDIM reduction of the composition space to (Z,YCO2) is discussed and its validity for the present swirling flame is first considered by an a priori comparison with experimental data. The (Z,YCO2) – scatter plots from the transported PDF calculation show the capacity to reproduce the mixing between fresh air and hot products in the recirculation zone above the bluff-body. However, too little scatter is observed. The study of tracer trajectories helps to better understand the capacities and limitations of the modeling approach. Zones where mixing competes with reaction can be identified, and coincide with the highly rotating collar region where local extinction is expected to take place. However, in our modeling, the competition between mixing and reaction is not enough to lead to local extinction. An important modeling deficiency is claimed to be the use of a mean time scale in the EMST mixing model, which limits the possibilities to model high scalar dissipation rate events.

Flow of CO2–ethanol and of CO2–methanol in a non-adiabatic microfluidic T-junction at high pressures

In this work, an experimental investigation of the single- and multiphase flows of two sets of fluids, CO2–ethanol and CO2–methanol, in a non-adiabatic microfluidic T-junction is presented. The operating conditions ranged from 7 to 18 MPa, and from 294 to 474 K. The feed mass fraction of CO2 in the mixtures was 0.95 and 0.87, respectively. Under these operating conditions, CO2 was either in liquid, gas or supercritical state; and the mixtures experienced a miscible single phase or a vapour–liquid equilibrium (VLE), with two separated phases. Taylor, annular and wavy were the two-phase flow regimes obtained in the VLE region. In the single phase region, the observed flows were classified into standard single-phase flows, “pseudo” two-phase flows and local phenomena in the T-junction. Flow regime maps were generated, based on temperature and pressure conditions. Two-phase flow void fractions and several parameters of Taylor flow were analysed. They showed a clear dependency on temperature, but were mostly insensitive to pressure. A continuous accumulation of liquid, either in the CO2 channel or at the CO2-side wall after the T-junction, disturbed most of the experiments in VLE conditions by randomly generating liquid plugs. This phenomenon is analysed, and capillary and wetting effects due to local Marangoni stresses are suggested as possible causes.

Carbon dioxide sorption and diffusion in coals: Experimental investigation and modeling

CO2 sorption and diffusion in coal are closely related to the occurrence of coal and gas outburst, geological sequestration of CO2 in coalbeds, and enhancing coalbed methane recovery by injecting CO2. Hence, it is significant to investigate the sorption properties and diffusion models of CO2 in coal. Here we used a newly designed experimental apparatus at Peking University to investigate the sorption and diffusion properties of CO2 in natural coal samples from Dashucun Mine and Wutongzhuang Mine in Handan city, Hebei province, and Jinhuagong Mine in Datong city, Shanxi province, and obtained CO2 sorption isotherms and diffusivity models. The results indicate that, in a certain pressure range, CO2 sorption isotherms for the coal samples are consistent with the Langmuir model, which assumes that monolayer sorption occurs at the interface between coal matrix and CO2 molecules, and the sorption isotherms feature nonstandard hyperbolas in mathematics. At the same pressure and temperature, as the vitrinite content increases, coal adsorbs more CO2 molecules. The relation between the sorption capacity and the coal rank may be described as a “U-type” trend, and medium rank coal has the least sorption capacity. The bulk diffusivity of CO2 in coal is not constant; in the range of CO2 mass fraction greater than 1%, it increases roughly linearly with increasing mass fraction of CO2 adsorbed (or CO2 partial pressure) in coal. CO2 diffusivity in coal is approximately 10−4 to 10−2 mm2/s in magnitudes, and the diffusivity ranges in coal samples are 3×10−4 to 8×10−3 mm2/s from Dashucun Mine, 2×10−4 to 4×10−3 mm2/s from Wutongzhuang Mine, and 2×10−4 to 4×10−3 mm2/s from Jinhuagong Mine. The results of the CO2 sorption and diffusion study can be applied to help predict and prevent coal and gas outburst as well as to evaluate the feasibility in geological sequestration of CO2 and to enhance coalbed methane recovery.

Large Eddy Simulations of a piloted lean premix jet flame using finite-rate chemistry

A Large Eddy Simulation (LES) model capable of accurately representing finite-rate chemistry effects in turbulent premixed combustion is presented. The LES computations use finite-rate chemistry and implicit LES combustion modelling to simulate an experimentally well-documented lean-premixed jet flame stabilized by a stoichiometric pilot. The validity of the implicit LES assumption is discussed and criteria are expressed in terms of subgrid scale Damköhler and Karlovitz numbers. Simulation results are compared to experimental data for velocity, temperature and species mass fractions of CH4, CO and OH. The simulation results highlight the validity and capability of the present approach for the flame and in general the combustion regime examined. A sensitivity analysis to the choice of the finite-rate chemistry mechanism is reported, this analysis indicates that the one and two-step global reaction mechanisms evaluated fail to capture the reaction layer with sufficient accuracy, while a 20-species skeletal mechanism reproduces the experimental observations accurately including the key finite-rate chemistry indicators CO and OH. The LES results are shown to be grid insensitive and that the grid resolution within the bounds examined is far less important compared to the sensitivity of the finite-rate chemistry representation. The results are analyzed in terms of the flame dynamics and it is shown that intense small scale mixing (high Karlovitz number) between the pilot and the jet is an important mechanism for the stabilization of the flame.

Viscosity and rheological behaviour of carbon dioxide-expanded fish oil triglycerides: Measurement and modeling

Viscosity and rheological behaviour of carbon dioxide-expanded (CX) fish oil (FO) triglycerides (CXFO) were determined at 40, 55, and 70 °C at pressures of up to 12 MPa using a rotational rheometer equipped with a high pressure cell at shear rates of 100–500 s −1. The mass fraction of CO 2 ( w CO 2 ) in CXFO was determined at 40 and 55 °C at pressures of up to 25 MPa. The viscosity of CXFO determined at a shear rate of 300 s −1 decreased substantially with pressure due to dissolution of CO 2 in FO. Decrease in viscosity with pressure and hence w CO 2 was temperature dependent. The viscosity of CXFO decreased with a pressure increase from 0.1 to 12.2 MPa by about 90% (25 to 2.65 mPa s) and 70% (11.6 to 3.38 mPa s) at 40 °C and 70 °C, respectively. A new empirical model correlating the viscosity of CXFO to temperature and pressure was developed. The viscosity decreased up to w CO 2 levels of about 30% (w/w) then approaching a constant level. CXFO viscosity data were successfully correlated to w CO 2 and pure component viscosities using the empirical Grunberg and Nissan model. Rheological measurements showed dilatant flow behaviour for CXFO at elevated pressures, with the flow behaviour index approaching 1.5 at 12.4 MPa. Novel process development and design of equipment will benefit from a better understanding of such rheological behaviour.

Viscosity measurement and modeling of canola oil and its blend with canola stearin in equilibrium with high pressure carbon dioxide

During enzymatic reactions carried out in supercritical CO 2 (SCCO 2) media, CO 2 can expand the liquid reactant mixture, especially lipid-type substances, due to pressure increase and dissolution of CO 2, causing viscosity reduction, and improvement of the diffusion of reactants and products. For better understanding of the transesterification reaction of canola oil and canola stearin in SCCO 2 media, the viscosity of canola oil at 40, 50, 65, and 75 °C and its blend with canola stearin (30 wt%) at 65 °C in equilibrium with high pressure CO 2 was measured up to 12.4 MPa using a rotational rheometer equipped with a high pressure cell. The solubility of CO 2 in canola oil at 40 and 65 °C and its blend with canola stearin at 65 °C was also determined at pressures of up to 20 MPa using a high pressure view cell. The viscosity of canola oil at 40, 50, 65, and 75 °C and its blend with canola stearin at 65 °C decreased exponentially to 87.2, 84.7, 74.8, 66.2, and 74.2% of its value at atmospheric pressure, respectively, with pressure increase up to 12.4 MPa. The viscosity of the samples decreased with an increase in temperature, but the effect of temperature diminished above 10 MPa. The viscosities of CO 2-expanded canola oil and its blend with canola stearin at 65 °C were similar up to 12.4 MPa. The samples exhibited shear-thickening behavior as the flow behavior index reached almost 1.2 at elevated pressures. The mass fraction of CO 2 in canola oil at 40 and 65 °C and its blend with canola stearin at 65 °C reached 24 and 21% at 20 MPa, respectively. The Grunberg and Nissan model was used to correlate the viscosity of CO 2-expanded lipid samples.

Dispersion of Twin Inclined Fume Jets of a Variable Height within a CrossFlow

Twin elliptic inclined tandem jets are emitted within an oncoming cooler crossflow. The jets contain a non reactive fume whose dispersion is tracked all over the surrounding domain. Such a configuration may be found in chimney stacks, ships’ chimneys, etc. We propose to evaluate in the present paper the impact of the jets’ height on the resulting dispersion process. To reach this goal, a numerical simulation of a double jet model of variable height is carried out by means of the finite volume method together with a non uniform grid system. The model, validated by previous experimental data, allowed the tracking of the emitted fume by studying the evolution of a single particle contained within this fume, the Carbone dioxide (CO2) mass fraction. This is possible thanks to the assumption of handling a non reactive fume, which is adopted only to simplify the calculations. The CO2 mass fraction was mainly tracked between the emitting nozzles, in a try to find out the changes brought by the extension of the emitting jet nozzles on the flow trapped between them.

Density of Carbon Dioxide + Brine Solution from Tianjin Reservoir under Sequestration Conditions

Density data of carbon dioxide (CO2) + brine solution from Tianjin reservoir were determined using magnetic suspension balance (MSB). Measurements were performed in the pressure range (10 to 18) MPa and at the temperatures (313 to 353) K. CO2 mass fraction in solution was selected up to 0.040. The experimental results revealed that the density of CO2 + brine solution decreases with increasing temperature and increase with increasing pressure. The density of CO2 + brine solution increases almost linearly with increasing mass fraction of CO2 in solution. The slope of the density vs CO2 mass fraction curves decreased from 0.222 to 0.185 as temperature increased from 313 to 353 K and is independent of pressure. Two regression functions were developed to describe the density data of CO2-free brine and CO2 + brine solution from Tianjin reservoir under sequestration conditions, and the errors between experimental results and prediction were within 0.004% and 0.03%, respectively.

A Two-Dimensional Numerical Simulation of Combustion and Heat Transfer in Radiant Porous Burners

Premixed combustion inside a porous medium is presently under investigation due to the characteristics of this technology, which provides controlled flames. The authors present numerical methods for the simulation of premixed methane/air flames in porous media using a 6-step reduced mechanism. The laminar 2-dimensional model is based on a macroscopic formulation of the heat and mass transport equations for laminar flow. The finite volume method is used for simulation with a boundary-fitted nonorthogonal coordinate system. The effects of the model on temperature and species are examined in 2 porous burners with different geometries and materials. The results are compared with the experiments available in the literature. In the first reactor analyzed, the CO mass fraction calculated is compared with the available experimental data. The good agreement with the experimental data suggests that the numerical model is an excellent tool to investigate pollutants formation. In the second reactor studied, the temperature field calculated is compared with experimental data. The effect of an injection plate at the entry of the burner is predicted, the 2D field of temperatures and mass fractions of species, giving an insight of the 3D profile of the flame. The strong advective effect caused by the acceleration of the flow due to the injection plate causes a conical flame shape. The numerical simulation of the conical flame predicted the temperature field and the flame position. A sensitivity study to the Rosseland mean attenuation coefficient, to the thermal conductivity of the solid and to the porosity is presented. It is shown that the properties of the preheating region do not significantly affect the CO emissions at the exit of the reactor, although the properties of the combustion region have a strong influence.

J056043 詳細化学反応式を簡略化するための平衡法を利用した燃焼計算方法によるメタン部分予混合火炎の数値解析([J05604]乱流における運動量,熱,物質の輸送現象(4))

This paper presents a dimension reduction technique for turbulent partial non-premixed flames based on a chemical equilibrium method combined with a reaction calculation. An advantage of the proposed technique is that it simplifies the process of building a reduced chemical mechanism according to the accuracy requirement for the chemical species. The proposed technique reduces the computational time for the combustion simulation. In this technique, chemical species are roughly divided into two groups: The first includes fuels and intermediate species; the intermediate species include only those necessary for high accuracy. The second group comprises the rest of the species, and their mass fractions are obtained from a look-up table prepared using chemical equilibrium calculations conducted prior to the combustion simulation. The obtained results were compared with the experimental data of a Sandia Flame D and computational data obtained using the eddy dissipation concept (EDC) model. The major mass fractions of CH_4, O_2, and CO_2, as well as the temperature obtained using the proposed technique, were in good agreement with these reference data. Furthermore, compared with the EDC model, the mass fractions of CO obtained using the proposed technique were close and the computational time was 67% lower.

Numerical simulation of laminar co-flow methane–oxygen diffusion flames: effect of chemical kinetic mechanisms

Laminar co-flow methane–oxygen flames issuing into the unconfined atmosphere have been studied. A numerical model, which employs different chemical kinetics sub-models, including a skeletal mechanism with 43 reaction steps and 18 species and four global reaction mechanisms (two 2-steps and two 4-steps mechanisms), and an optically thin radiation sub-model, has been employed in the simulations. Numerical model has been validated against the experimental results available in literature. The numerical predictions from the global kinetic mechanisms have been compared with the 43-steps mechanism predictions. At all oxygen flow rates, the predictions of the distributions of temperature, mass fractions of CH4, O2 and CO2 by the 2-steps mechanisms are closer to 43-steps mechanism. The overall distribution of H2O predicted by 2-steps mechanisms is close to that of 43-steps except for the maximum value. Especially at higher oxygen flow rates, the modified 2-steps mechanism predicts these quantities much closer to those predicted by the 43-steps mechanism. Further, the 2-steps mechanisms predict location of the reaction zone accurately. However, they can just give an idea of overall CO distribution in terms of the axial and radial locations within which CO will almost be consumed, but not its maximum value in the domain. The 4-steps mechanisms predict the trend of variation of these quantities quite reasonably. However, they under-predict the location of the reaction zone. At higher oxygen flow rates, the predictions by 4-steps mechanisms becomes better, especially in the prediction of maximum CO and H2O. Over all, the modified 2-steps mechanism can be recommended for reasonable and economical predictions of oxy-rich methane flames.