Simple reaction mechanism

[b.pfeiffelmann]

Hello all,
I am trying to implement simple reaction mechanism in Cantera. To
verify this I have used the python free_h2_air demo and calculated the
flame speed of methane/air. The results with the GRI3.0 reaction
mechanism are good. But when I try to use the the 1-step reaction-
mechanism from Westbrook and Dryer (SIMPLIFIED REACTION MECHANISMS FOR
THE OXIDATION OF HYDROCARBON FUELS IN FLAMES, DOI:
0.1080/00102208108946970) I get wrong results.

This is my own written cti file.

units(length = "cm", time = "s", quantity = "mol", act_energy = "kcal/
mol")


ideal_gas(name = "methaneair",
elements = " O H C N ",
species = " gri30: O2 H2O CH4 CO2 N2 ",
reactions = "all",
transport = "Mix",
initial_state = state(temperature = 300.0,
pressure = OneAtm) )

#-------------------------------------------------------------------------------
# Reaction data
#-------------------------------------------------------------------------------

# Reaction 1
reaction(equation = "CH4 + 2 O2 => CO2 + 2 H2O", kf = [6.70000E+12, 0,
48.4], order = 'CH4:0.2 O2:1.3')

Could anybody find the mistake or is it not possible to implement such
a simple reaction mechanism?
Thanks.
B. Pfeiffelmann

[Clayton Fox]

I am currently having the very same issue. Any update on this? 

gri30.cti (with Full Mechanism) 

• Flame Speed: SL= 38.24 cm/s (Good !)
  
• [CO]/[CO2] = 0.11 (W&D have 0.14 for two step) (Good!)
  

1stepgri30.cti (1 step using W&D Set 3 equation)

• Flame Speed: SL= 22.3 cm/s (No good)
  
• [CO]/[CO2] =Not applicable  

Thank you,

I have attached my .cti and resulting CSV files. 

Any update on to this?  It would suggest the 1 step Westbrook and Dryer are missing something? Or the way its entered into cantera is incorrect?  

[Bryan W. Weber]

Clayton,

As I recall, that paper assumes constant specific heats (although I can't find it in the text). By default, GRI-3.0 assumes varying specific heats (and when you import species from GRI, you're bringing their thermo with them), and this will have a big effect on the adiabatic flame temperature, and consequently, the flame speed.

Best,
Bryan

[Clayton Fox]

Bryan,

Thank you for that information.
 
Just to be clear, your talking about the NASA thermo properties (5 coefficients plus temperature ranges)?  How about the species transport properties, well depth etc?

If I need to calculate them by hand I will, or if there is a source for constant specific heat I would try those. 

Are these the properties you mean would change for constant specific heats?

Methane as an example:

species(name = "CH4",
    atoms = " C:1  H:4 ",
    thermo = (
       NASA( [  200.00,  1000.00], [  5.149876130E+00,  -1.367097880E-02,
                4.918005990E-05,  -4.847430260E-08,   1.666939560E-11,
               -1.024664760E+04,  -4.641303760E+00] ),
       NASA( [ 1000.00,  3500.00], [  7.485149500E-02,   1.339094670E-02,
               -5.732858090E-06,   1.222925350E-09,  -1.018152300E-13,
               -9.468344590E+03,   1.843731800E+01] )
             ),
    transport = gas_transport(
                     geom = "nonlinear",
                     diam =     3.75,
                     well_depth =   141.40,
                     polar =     2.60,
                     rot_relax =    13.00),
    note = "L 8/88"
       )
 


Thank you,

Clayton,