Etude de la combustion de gaz de synthèse issus d'un processus de ...

Chapter 6
H 2 O, (3) N 2 , (4) O 2 , (5) CO, (6) H 2 , (7) H, (8) O, (9) OH, (10) NO, and (11) N, which are
considered to be in chemical equilibrium. The calculation of their concentrations and,
subsequently, each zone’s thermodynamic properties is based on the values of
pressure, temperature and fuel–air equivalence ratio. For this reason, the atom balance
equations of the C–H–O–N system are considered along with the following eight
equilibrium reactions (Ferguson, 1986):
H + O ⇔ H O
1
2 2 2 2
CO + O ⇔CO
1
2
2 2
CH + 2O ⇔ CO + 2H O
4 2 2 2
H + O ⇔OH
1 1
2 2 2 2
O + N ⇔ NO
1 1
2 2 2 2
(6.12)
tel-00623090, version 1 - 13 Sep 2011
1
2
1
2
1
2
H
O
N
2
2
2
⇔ H
⇔ O
⇔ N
The various thermodynamic properties (specific enthalpy, specific internal energy,
specific volume, specific heat capacity at constant pressure) and thermodynamic
derivatives (derivative of logarithmic specific volume with respect to logarithmic
temperature and pressure) of the unburned and burned mixtures, needed for the
calculations, are computed according to the mole fraction of each species and the gas
mixture rule. For this purpose, the well established coefficients (Heywood, 1988) of the
polynomial curves that have been fitted to the various species thermodynamic data
from JANAF tables are used. For the evaluation of specific internal energy of species i,
the following relation can be applied according to JANAF Table thermodynamic data
(Gordon and McBride, 1971; Heywood, 1988):
5
⎡⎛
ain
n ⎞ ⎤
ui( T)
= Rsi ⎢⎜
∑ T ⎟+ ai6
−T⎥
⎣⎝
n=
1 n ⎠ ⎦
(6.13)
where constants a in for the above polynomial relation can be found, for example, in
(Ferguson, 1986; Heywood, 1988). Two sets of data are available for constants a in , one
for temperatures up to 1000 K and another for temperatures from 1000 to 5000 K. The
reference temperature is 298 K. Also,
h( T) = u ( T)
+ R T
(6.14)
i i si
171