Difference between revisions of "Multi-inlet CH 4/Air flame with scheme GRI12"

Revision as of 17:20, 25 July 2017

Objectives

The Stochastic_GRI12 test case describes a reduction of the GRI1.2 scheme for a 0D 2-inlet configuration. Starting with 32 species and 177 reactions, we reduce to 12 transported species, 2 species in quasi steady assumption and 29 reactions.

Key parameters

The target species considered for this test case are O2, CO and CO2. We are at atmospheric pressure, and the fuel is injected in its gaseous form (no evaporation model). The inputs of the 3 inlets (oxidiser, fuel and burned gases) are displayed below :

Characteristics of the air inlet :

  listInlets.push_back(new MultipleInlet(
               /*Temperature*/ 700,
               /*Pressure*/ 1E+05,
               /*Mass flow rate*/ 0.500,
               /*Xk*/ "O2:0.21, N2:0.79",
               /*Yk*/ "",
               /*Evaporation model*/ false,
               /*Droplet diameter*/ 0.0,
               /*Evaporation time*/ 0.0,
               /*Liquid density*/ 0.0,
               /*Evaporation latent heat*/ 0.0));

Characteristics of the fuel inlet :

  listInlets.push_back(new MultipleInlet(
               /*Temperature*/ 450,
               /*Pressure*/ 1E+05,
               /*Mass flow rate*/ 0.02,
               /*Xk*/ "CH4:1.0",
               /*Yk*/ "",
               /*Evaporation model*/ false,
               /*Droplet diameter*/ 0.0,
               /*Evaporation time*/ 0.0,
               /*Liquid density*/ 0.0,
               /*Evaporation latent heat*/ 0.0));

Characteristics of the burned gases inlet :

  listInlets.push_back(new Characteristics_MultipleInlet(
               /*Temperature*/ 2500,
               /*Pressure*/ 1E+05,
               /*Mass flow rate*/ 0.200,
               /*Xk*/ "N2:0.76308, O2:0.093573, H2O:0.072355, CO2:0.070468",
               /*Yk*/ "",
               /*Evaporation model*/ false,
               /*Droplet diameter*/ 0.0,
               /*Evaporation time*/ 0.0,
               /*Liquid density*/ 0.0,
               /*Evaporation latent heat*/ 0.0));
               /*tau_t*/ 2e-04,
               /*delta_t*/ 1e-05,
               /*nbIterations*/ 200,
               /*BurnedGases*/ true));

Results

DRGEP Step

While running the DRGEP species step, your terminal should display the following information :

Reading initial mechanism "mechanisms/gri12.xml" with description "gri12" ----------> OK
Number of species: 32
Number of reactions: 177
Set the mole fraction of inlet 0
Set the mole fraction of inlet 1
Set the mole fraction of inlet 2

Composition to enter  For the equilibrium computation to get the Burned gases 
Compo_H_mixed 334274
X_O2: 0.16931
X_H2O: 0.019848
X_CH4: 0.0418227
X_CO2: 0.0193304
X_N2: 0.749689
T_mixed 1063.63
Nb particles  0  500
Nb particles  1  17
Nb particles  2  200
Nmix 35
Set the mole fraction of inlet 0
Set the mole fraction of inlet 1
Set the mole fraction of inlet 2

followed by the the species associated with their rank :

0  AR
2.3181e-16  C
2.44619e-09  CH
2.59722e-09  HCCOH
5.68614e-09  C2H
1.49031e-08  CH2CO
1.27776e-07  C2H2
2.68843e-07  HCCO
3.69712e-05  C2H3
7.25527e-05  CH2OH
0.00365571  H2O2
0.00537274  C2H4
0.00537274  C2H5
0.00543792  CH2(S)
0.00598963  CH2
0.0100589  CH3OH
0.0179344  H2
0.0199904  HCO
0.0576166  O
0.145908  CH3O
0.342307  H
0.373973  C2H6
0.460535  OH
0.483807  CH2O
0.999998  HO2
0.999999  CH3
1  O2
1  H2O
1  CH4
1  CO
1  CO2
1  N2

From a detailed 32 species scheme, we obtain reduced schemes (31 to 11 species). and we choose the one with 14 species for the next step. With 13 species and less, the trajectories of the targets and the temperature are too different from the detailed ones to be easily optimised.

Fig1 : Comparison between the reference trajectories of the target species and the temperature (in black), and the trajectories computed with the reduced mechanism with 14 transported species and 42 reactions (in red).

From the reduced scheme with 14 species, the DRGEP reaction step displays the associated 42 reactions (forward, reverse and global) with their rank. The global reactions are displayed below :

Reaction 11  6.97477e-05
Reaction 2  8.75759e-05
Reaction 1  8.98678e-05
Reaction 18  0.00213229
Reaction 31  0.00291462
Reaction 6  0.00363456
Reaction 10  0.00375711
Reaction 22  0.00511265
Reaction 12  0.00898034
Reaction 7  0.0106843
Reaction 8  0.0106849
Reaction 34  0.0173608
Reaction 19  0.0185876
Reaction 25  0.0221759
Reaction 29  0.0222202
Reaction 37  0.0372901
Reaction 24  0.0446721
Reaction 9  0.0449009
Reaction 40  0.0555031
Reaction 32  0.0696855
Reaction 39  0.0865175
Reaction 3  0.144344
Reaction 30  0.156095
Reaction 14  0.166212
Reaction 35  0.167587
Reaction 38  0.178616
Reaction 23  0.250862
Reaction 36  0.357038
Reaction 21  0.360875
Reaction 26  0.419329
Reaction 28  0.459053
Reaction 5  0.487659
Reaction 42  0.602514
Reaction 20  0.633343
Reaction 15  0.740476
Reaction 16  0.789885
Reaction 17  0.828505
Reaction 41  0.846392
Reaction 33  0.948112
Reaction 13  0.969275
Reaction 4  0.971434
Reaction 27  0.992353

After this step, by comparing the reference trajectories with the new ones, we choose to delete 13 reactions, so the next step is performed with 14 species and 29 reactions. Indeed, with 28 and less species, the final state of the trajectories is not well predicted and difficult to represent even with the optimisation step.

Fig2 : Comparison between the reference trajectories of the target species and the temperature (in black), and the trajectories computed with the reduced mechanism with 14 transported species and 29 reactions (in red).

QSS Step

While running the QSS step, your terminal should display the following information :

Species H  0.00707074
Species O  0.00347138
Species O2  1
Species OH  0.00238597
Species H2O  0.0394215
Species HO2  0.0120837
Species CH3  0.0951441
Species CH4  0.774634
Species CO  1
Species CO2  1
Species HCO  0.00480146
Species CH2O  0.178736
Species CH3O  0.00520346
Species N2  1

Interactions with species H  with QSS Criteria 0.00707074
H2O:2  HO2:1  CH3:1  CH2O:2  CH3O:1  

Interactions with species O  with QSS Criteria 0.00347138
OH:1  H2O:1  HO2:1  CH3:1  CH2O:1  CH3O:1  

Interactions with species OH  with QSS Criteria 0.00238597
O:1  OH:2  HO2:1  CH3:2  HCO:2  CH2O:2  CH3O:1  

Interactions with species H2O  with QSS Criteria 0.0394215
H:2  O:1  HO2:1  CH3:1  HCO:2  

Interactions with species HO2  with QSS Criteria 0.0120837
H:1  O:1  OH:1  H2O:1  CH3:2  CH2O:1  

Interactions with species CH3  with QSS Criteria 0.0951441
H:1  O:1  OH:2  H2O:1  HO2:2  HCO:1  CH2O:1  

Interactions with species HCO  with QSS Criteria 0.00480146
OH:2  H2O:2  CH3:1  

Interactions with species CH2O  with QSS Criteria 0.178736
H:2  O:1  OH:2  HO2:1  CH3:1  

Interactions with species CH3O  with QSS Criteria 0.00520346
H:1  O:1  OH:1

We choose to put the species CH3O and HCO in QSS hypothesis due to their low QSS coefficient.

In order to obtain the trajectories of the 12-transported species 29-reactions reduced scheme, we run the getQSSfile step and we observe that the final state and the shape of the trajectories are conserved. It is under these conditions that the optimisation step will be efficient.

Fig3 : Comparison between the reference trajectories of the target species and the temperature (in black), and the trajectories computed with the reduced mechanism with 12 transported species and 42 reactions (in red).

Optimisation Step

The final step of the ORCh method, the genetic algorithm, enables to recover the trajectories of the target species. Firstly, we allowed a 10 % variation on the pre exponential factor, the temperature exposant and the energy activation in order to find their optimal values.

A population of 40 elements was used during 38 generations.

Secondly, in order to obtain more precise trajectories, we allowed a 1 % variation on the pre exponential factor, the temperature exposant and the energy activation. 42 more generations were performed in that case.

The following trajectories of the temperature, the flame speed and the target species match perfectly the ones of the reference detailed scheme with only 12 transported species and 26 reactions.