University of California at Berkeley Berkeley, CA 94720-1740, USA Telephone: (510) 643-1676 Internet: email@example.com
Two sets of elementary reactions reduced from
reported here. They were developed by truncation of the original
GRI-Mech with the objective of developing a
smallest set of reactions (i.e.,
still a detailed mechanism but with the smallest numder of variables)
to reproduce closely the
main combustion characteristics predicted by the full mechanism,
The two sets are:
load to diskoption in your Mosaic application) you can download files with the reduced mechanisms. These are ASCII files in the
CHEMKIN IIformat. For the thermodynamics data you must use thermo12.dat, the thermodynamics data of
GRI-Mech. The thermo12.dat file can be downloaded from the GRI-Mech Home Page. If you experience difficulties with downloading any of these files, please contact the authors.
GRI-Mechin the present case). The following criteria are applied to identify the non-contributing reactions:
| R(i) | < e(r) | R(ref) | and
| R(i) delta-H(i) | < e(q) Q
where R(i) is the rate of reaction i, R(ref) is the rate of a reference reaction (e.g., the maximum rate), delta-H(i) is the enthalpy change of reaction i, Q is the maximum value among all the terms |R(i) delta-H(i)|, and e(R) and e(Q) are the chosen parameters considerably smaller than unity. The first criterion tests the contribution a given reaction makes to the main chain branching while the second criterion tests the contribution to the heat release.
Reactions whose rates, both forward and reverse, satisfy the above inequalities at all grid points of the calculation are removed from the mechanism. This procedure eliminates a specific species when all reactions of such a species happen to be removed.
The present reduction was performed using e(r) = e(q) = 0.02, under the following
test conditions: shock-tube ignition of methane-air mixtures at wide ranges of
initial conditions (equivalence ratio PHI = 0.2 - 2.0, initial pressure Po = 0.1
- 50 atm, and initial temperature To = 1300-2500 K); and methane-air adiabatic
flames at 1 and 20 atm. This procedure generated a 22-species, 104 reactions
set, which is referred to as
Additional analysis of
reaction fluxes and sensitivities to removal of selected species was performed on
DRM19. Those chemical species which were showed near-zero
sensitivity were removed. This resulted in a smaller set, 19-species and 84
reactions, which is referred to as
DRM22, were tested against
GRI-Mechusing a series of ignition delay and laminar flame speed simulations.
DRM22works well for all the initial conditions tested: the deviations from
GRI-Mechdo not exceed 4 % and are below 2 % for most cases.
DRM19also performs well and the deviations are typically within 6-8 % with respect to
GRI-Mech. The accuracy of
DRM19drops at lower temperatures and higher pressures. For example, at To = 1100 K, Po = 10 atm and PHI = 0.2, the ignition delay calculated with
DRM19has 37 % relative error. The deviations increase further at even higher initial pressures, e.g., 89 % for stoichiometric methane-air mixture at Po = 100 atm and To = 1050 K (for comparison,
DRM22has 3.5 % error at these conditions). However, no extensive tests were carried out for these conditions since
GRI-Mechitself was not validated at these conditions either.
Figure 1. Relative deviations of ignition delays calculated with the reduced mechanisms in comparison to
for methane-air mixtures: solid lines -
dashed lines -
DRM22was also tested on laminar adiabatic premixed methane-air flames at 1 and 20 atm, the conditions against which
GRI-Mechwas optimized and validated. Four parameters were used for comparison: adiabatic flame velocity and maximum mole fractions of major radicals, H, OH and CH3. (The adiabatic flame temperature computed with the reduced mechanisms was found to be practically indistinguishable from that predicted by
DRM19begins to deviate significantly as PHI increases (see the top panel of Figure 2). The maximum mole fraction of OH is predicted well by both reduced schemes for lean to stoichiometric mixtures (less than 1 % for PHI = 1.0). As PHI increases, the accuracy of
DRM19drops (84 % for PHI = 1.5) while that of
DRM22still remains reasonable (7.5 % for PHI = 1.5). The maximum CH3 mole fraction is predicted within 20 % by
DRM19(10 % for PHI = 1.0) and within 10 % by
DRM22(8 % for PHI = 1.0 ).
Figure 2. Relative deviations of adiabatic flame velocities and peak concentrations of selected species calculated with the reduced mechanisms in comparison to
GRI-Mech for atmospheric,
adiabatic, laminar, premixed methane-air flames: solid lines -
DRM22, dashed lines -
DRM19is better for the lean to stoichiometric mixtures.
Figure 3. Relative deviations of adiabatic flame velocities and peak concentrations of selected species calculated with the reduced mechanisms in comparison to
GRI-Mech for 20-atm
adiabatic, laminar, premixed
methane-air flames: solid lines -
DRM22, dashed lines -