Difference between revisions of "Premix CH 4/Air flame with scheme GRI12"

Revision as of 14:55, 5 July 2017

Objectives

The Stochastic_GRI12 test case describes a reduction of the GRI1.2 scheme for a 1D premixed flame. Starting with 32 species and 177 reactions, we reduce to 14 species and 26 reactions.

Key parameters

The target species considered for this test case are O2, CO and CO2. The characteristics of the premixed flame are displayed below :

listFlames.push_back(new PremixedFlames(/*T_fuel*/ 300, 
                                        /*T_ox*/ 300,
                                        /*Pressure*/ 1E+05,
                                        /*Ratio*/ 0.75,
                                        /*Y_fuel*/ "CH4:1.0",
                                        /*X_fuel*/ "",
                                        /*Y_ox*/ "O2:0.21, N2:0.79",
                                        /*X_ox*/ "",
                                        /*reference_flame_path*/ "flames/flame__Phi_0_75__P_100000__T_300.cantera",
                                        /*flame_path*/ "flames/flame"));

Results

DRGEP step

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

scheme : GRI12 
number of species : 32 
number of reaction : 177 
reference flame : flames/flame__Phi_0_75__P_100000__T_300.cantera
Pressure : 1 bar 
equivalence ration : 0.75 
Composition :		<O2:0.202024>  
                       <CH4:0.0379821> 
                       <N2:0.759994> 

followed by the the species associated with their rank :

4.17578965277519e-189  AR 
1.81320667696424e-06  HCCOH 
3.33272520534669e-05  C2H 
0.000136594690602079  CH2CO 
0.000228724937160335  C 
0.00039194258246205  C2H2 
0.000909271897890726  HCCO 
0.00324304055657054  CH 
0.00391278892730799  C2H3 
0.00395833642581853  CH3OH 
0.00517918655958378  CH2OH 
0.0158390004661296  C2H4 
0.0158390004661296  C2H5 
0.0160151369051444  CH2(S)
0.0209164664682532  C2H6
0.0317122146887158  CH2 
0.0395596174129288  H2O2
0.0796917798682698  H2 
0.0949180222420726  CH3 
0.108929211050051  HCO 
0.123697044495215  CH2O 
0.154156160901222  H2O 
0.165970760424094  CH3O 
0.222439341655666  O 
0.292243743837601  HO2 
0.501413374426018  OH 
0.501449580770414  H 
1  O2 
1  CH4
1  CO 
1  CO2 
1  N2

From a detailed 32 species scheme, we obtain reduced schemes (31 to 14 species). and we choose the one with 14 species for the next step.

Fig1 : Comparison between the reference trajectories of the target species, the temperature and the flame speed (in black), and the trajectories computed with the reduced mechanism with 14 transported species and 42 reactions, after a DRGEP species reduction (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 :

--
--

After this step, by comparing the reference trajectories with the new ones, we choose to delete 16 reactions, so the next step is performed with 14 species and 26 reactions.

Fig2 : Comparison between the trajectories of the target species, the temperature and the flame speed computed with the reduced 14-species 42-reaction mechanism (in black) , and the trajectories computed with the reduced mechanism with 14 transported species and 26 reactions after a DRGEP reaction reduction (in red).

QSS step

The QSS step provides the QSS criteria of each species and the different links with the others species :

Species H  0.0581710482364302
Species O  0.0160759870785582
Species O2  0.277560360139677
Species OH  0.0144373005142915
Species H2O  0.314791474636433
Species HO2  0.010252726793236
Species CH3  0.100336627880574
Species CH4  0.79524736833312
Species CO  0.694064507028327
Species CO2  0.692897407440143
Species HCO  0.00243878401227475
Species CH2O  0.0772557856780877
Species CH3O  0.0207969879289909
Species N2  0

Interactions with species H  with QSS Criteria 0.0581710482364302
HO2:2  CH3:1  CH2O:2  CH3O:1  N2:1  

Interactions with species O  with QSS Criteria 0.0160759870785582
OH:1  HO2:1  CH3:1  CH2O:1  CH3O:1  

Interactions with species OH  with QSS Criteria 0.0144373005142915
O:1  OH:2  HO2:1  CH3:2  HCO:2  CH2O:1  CH3O:1  

Interactions with species HO2  with QSS Criteria 0.010252726793236
H:2  O:1  OH:1  CH3:1  CH2O:1  N2:1  

Interactions with species CH3  with QSS Criteria 0.100336627880574
H:1  O:1  OH:2  HO2:1  

Interactions with species HCO  with QSS Criteria 0.00243878401227475
OH:2  

Interactions with species CH2O  with QSS Criteria 0.0772557856780877
H:2  O:1  OH:1  HO2:1  

Interactions with species CH3O  with QSS Criteria 0.0207969879289909
H:1  O:1  OH:1  

Interactions with species N2  with QSS Criteria 0
H:1  HO2:1 

We choose to put the species CH3O and HCO in QSS hypothesis due to their low QSS coefficient. The species HO2 could have been a good candidate too but it is linked to himself (non linearity).

In order to obtain the trajectories of the 14-species 26-reaction reduced scheme with these 2 species in QSS hypothesis, we run the getQSSfile step and we obtain the following graphs.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, the temperature and the flame speed (in black), and the trajectories computed with the reduced mechanism with 12 transported species and 26 reactions after a DRGEp reaction reduction (in red).

Optimisation

Bibliography