1
ME 525
Homework #3
Due Thursday, February 17, 2011
Prof. Lucht (E-mail address:
[email protected])
1.
The CHEMKIN code was used to perform a calculation for constant-volume combustion of a
mixture of 20% H
2
, 8%O
2
, and 72% N
2
(on a molar basis) at an initial temperature of 900 K
and pressure of 0.8 atm.
A time step of 5.0e-06 sec (0.001 msec) was used and the total
calculation time was 4.0e-03 sec (4 msec).
The results of the calculation are contained in an
Excel file on the class website (CHEMKINDataHW3P1StudentVersion.xlsx).
(a) Using the results of the CHEMKIN calculation and the data from the H-O-N kinetic
mechanism from Example 6.3 on pp. 195-196 in the text, evaluate the applicability of
the partial equilibrium assumption for the following two reactions at times of 1.90 and
1.98 msec:
2
2
2
1
2
(1)
(2)
k
H
O
O
OH
k
OH
H
H
H O
The following curve fit expressions for Gibbs free energies of formation may be useful:
2
0
2
,
0
2
,
0
2
,
0
2
,
221,290
55.172
0.0010263
251,230
63.254
0.0007315
38,742
15.636
0.00042668
245,370
52.615
0.0010741
f H
f O
f OH
f H O
J
g
T
T
T
gmol
J
g
T
T
T
gmol
J
g
T
T
T
gmol
J
g
T
T
T
gmol
(b)
Use the three-step extended Zeldovich mechanism (Eqns. 21-23, from the H-O-N kinetic
mechanism from Example 6.3, p. 196, Turns) to calculate d[NO]/dt for times of 1.98 and
3.0 msec.
Neglect reverse reactions and assume that the N-atom is in steady state, but
use actual computed values for [O], [O
2
], [N
2
], and [OH].
Comment on the relative
effects of T and [O].
Note:
If you wish, you can obtain the CHEMKIN code from me via email or by stopping by
my office, ME 87.
However, the results that you need for this problem are already
contained in the Excel file.
Solution
Time (ms)
T (K)
P (atm)
x
H
x
O2
x
O
1.90
9.35120E+02
8.29840E-01
1.37480E-03
7.76180E-02
1.17620E-04
1.98
1.8187E+03
1.54070E+00
3.7519E-02
6.8938E-03
5.0354E-03
3.00
2.33790E+03
1.91580E+00
2.28270E-03
9.15980E-05
5.48660E-05

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