GRI-MECH

Bowman, G., Frenklach, M., Gardiner, B., Smith, G., Serauskas, B. GRI-Mech, Gas Research Institute, Chicago, Ilinois. http //www.me.berkeley.edu/gri-mech/ index.html... 

GRI-Mech 2.11, available through the World Wide Web, http //www.me.berkeley. 

Many detailed reaction mechanisms are available from the Internet. GRI-Mech (www.me.berkeley.edu/gri-mech/) is an optimized detailed chemical reaction mechanism developed for describing methane and natural gas flames and ignition. The last release is GRI-Mech 3.0, which was preceded by versions 1.2 and 2.11. The conditions for which GRI-Mech was optimized are roughly 1000-2500K, lOTorr to lOatm, and equivalence ratios from 0.1 to 5 for premixed systems. 

Notably, the Gas Research Institute s mechanism (GRI-MECH) for methane combustion is well-established, drawing on research from several groups over several decades to define and calibrate kinetic and thermodynamic data for each elementary reaction step. Additional mechanisms" for methane oxidation are also available and updated periodically to include the most recent data. 

Smith GP, Golden DM, Frenklach M, Moriarty NW, Eiteneer B, Goldenberg M, et al. [Online. Internet. Accessed 1 June 2007]. 

There has been a great deal of research on the combustion of small hydrocarbons, including nitrogen-cycle chemistry leading to nitric-oxide formation and abatement [138]. There are a number of methane-air reaction mechanisms that have been developed and validated [274,276,278], the most popular one being GRI-Mech [366]. There is also active research on the kinetics of large hydrocarbon combustion [81,88,171,246,328-330,426]. 

Even comprehensive mechanisms, however, must be utilized with caution. The GRI-Mech fails, for instance, under pyrolysis or very fuel-rich conditions, because it does not include formation of higher hydrocarbons or aromatic species. Its predictive capabilities are also limited under conditions where the presence of nitrogen oxides enhances the fuel oxidation rate (NO f sensitized oxidation), a reaction that may affect unbumed hydrocarbon emissions from some gas-fired systems, for example, internal combustion engines. 

The objective of this exercise is to evaluate the potential of oxidation of unbumed hydrocarbons in the exhaust channel of lean-bum natural gas engines. Use GRI-Mech 3.0 (GRIM30. mec [366]) as starting mechanism and assume plug-flow conditions in the exhaust channel. 

Evaluate the ability of GRI-Mech 3.0 to describe this process. 

Figure 16.8 shows model predictions for a freely propagating, atmospheric-pressure, stoichiometric, methane-air flame in which the air contains water vapor at 100% relative humidity. The reaction mechanism for the simulation is GRI-mech 3.0, which contains some 35 species and 217 reactions [366]. From the solution shown in Fig. 16.8 it is apparent that the flame structure can be complex, involving the interactions among many chemical species. 

Assume that the combustion process occurs under well-mixed conditions. Use perfectly stirred reactor software together with the GRI-Mech mechanism (GRIM30. mec) to estimate the formation of NO in adiabatic combustion of CH4 with an excess-air ratio of 1.1... 

Use laminar premixed free-flame calculations with a detailed reaction mechanism for hydrocarbon oxidation (e.g., GRI-Mech (GRIM30. mec)) to estimate the lean flammability limit for this gas composition in air, assuming that the mixture is flammable if the predicted flame speed is equal to or above 5 cm/s. For comparison, the lean flammability limits for methane and ethane are fuel-air equivalence ratios of 0.46 and 0.50, respectively. 

Use GRI-Mech (GRIM30. mec) and a laminar premixed flame code to calculate the flame speed of a methane-air mixture at selected pressures between 0.1 and 10 atm. Evaluate whether the empirical correlation [412] for methane-air flames,... 

The purpose of this exercise is to investigate the effect of an inert (CO2) and a chemically active agent (iron pentacarbonyl, Fe(CO)s) on the flame speed of an atmospheric, stoichiometric methane-air flame. Employ a laminar premixed flame code to determine the flame speed, using GRI-Mech extended with a subset for iron pentacarbonyl chemistry [344] (GRIMFe.mec). 

Using GRI-Mech (GRIM30. mec), determine the temperature and species distributions for a freely propagating, stoichiometric, methane-air, mixture at a pressure of 10 Torr. From the solution determine the volumetric heat-release-rate profile through the thickness of the flame. 

Using the hydrogen-oxygen subset of GRI-Mech, assemble a suitable reaction mechanism. 

Assuming an appropriate ignition source and using GRI-Mech for the reaction mechanism, compute the structure of the steady-state strained diffusion flame. 

Based on a hydrogen-oxygen reaction mechanism that is extracted from GRI-Mech, compute the flow field and species profiles for the nominal flow conditions. For the purposes of evaluating the gas-phase flow, assume that surface chemistry can be neglected. 

G.P. Smith, DM. Golden, M. Frenklach, N.W. Moriarty, B. Eiteneer, M. Golden-berg, C.T. Bowman, R.K. Hanson, S. Song, W.C. Gardiner, V. Lissianski, and Z. Qin. GRI-Mech—An Optimized Detailed Chemical Reaction Mechanism for Methane Combustion. Technical Report http //www.me.berkeley.edu/gri-mech, Gas Research Institute, 1999. 

The flame structure is modeled by solving the conservation equations for a laminar premixed burner-stabilized flame with the experimental temperature profile determined in previous work using OH-LIF. Three different detailed chemical kinetic reaction mechanisms are compared in the present work. The first one, denoted in the following as Lindstedt mechanism, is identical to the one reported in Ref. 67 where it was applied to model NO formation and destruction in counterffow diffusion flames. This mechanism is based on earlier work of Lindstedt and coworkers and it has subsequently been updated to include more recent kinetic data. In addition, the GRI-Mech. 2.11 (Ref. 59) and the reaction mechanism of Warnatz are applied to model the present flame. 

The major differences in the HCN/CN chemistry have been outlined above and the peak HCN concentrations computed by GRI-Mech 2.11 and the Warnatz mechanism are higher than those of the Lindstedt mechanism by factors of 1.5 and 1.7 respectively. The CN radical is primarily formed from HCN through the hydrogen abstraction reactions and subsequently consumed by the reactions with O2 and the O and OH radicals. Therefore, predictions of CN radical concentrations are sensitive to the predictions of the CH and CH2 radicals. The measured CN CH ratio of 1 34 can be compared with the computed values using the Lindstedt mechanism (1 17), GRI-Mech 2.11 (1 12) and the Warnatz mechanism (1 2.7) respectively. The significant over-prediction of CN concentrations obtained with the mechanism of Warnatz is predominantly due to uncertainties in the C atom chemistry and the branching of the CH -f NO reaction. 

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