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It's interesting to see this paper continue to be interesting to
people. When I ran the cases with negative values of the fuel
exponents, I actually solved the singularity in two different ways.
1. Set an artifical floor to the concentration of methane.
This could be something like 10 x exp(-20). This had to be done
with in-line code, and many codes don't let you do this.
2. Add a reverse reaction with the same rate data, but with
an even more extreme negative power on the fuel concentration.
If the fuel power was -0.3 for the forward reaction, the power for the
reverse reaction would be -1.3. Then the A factor of the reverse
reaction could be set to give a low concentration at the equilibrium
that would then be calculated.
At the same time, most kinetics software prohibits these negative
values, and at one time, only our HCT code allowed fractional or
negative exponents in these rate coefficients.
Charlie Westbrook
At 9:18 AM -0700 11/20/08, Moffat, Harry K wrote:
Hi,
I've put in a feature request on sourceforge.net to add this capability in the near future.
I think it would be particular useful to add an additional flag also indicating that the user really means this, as the negative orders means there will be a singularity as the concentration goes to zero that must be addressed in some manner.
Best wishes,
Harry
Harry Moffat (w) (505) 844-6912
Nanoscale and Reactive Processes (f) (505) 844-8251
Sandia National Laboratories hkmoffa@...
P. O. Box 5800-0836
Albuquerque, NM 87185-0836
-----Original Message-----
From: cantera@yahoogroups.com [mailto:cantera@yahoogroups.com] On Behalf Of usenechal
Sent: Thursday, November 20, 2008 6:41 AM
To: cantera@yahoogroups.com
Subject: [cantera] negative reaction-order
Hi,
in a well known 1-step reaction-mechanism from Westbrook and Dryer
(SIMPLIFIED REACTION MECHANISMS FOR THE OXIDATION OF HYDROCARBON FUELS
IN FLAMES, DOI: 10.1080/00102208108946970) i found a negative
reaction order for methane. When I try with
reaction( "CH4 + 2 O2 => CO2 + 2 H2O", [8.30000E+012, 0, 30],
order = " CH4:-0.3 O2:1.3")
in the cti-file I get:
Error: reaction order must be non-negative
Is it possible to bring such a reaction with into cantera?
best regards
ulf
P.S. looking forward to cantera-2.0 :)
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