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Air injection 415

Table 13.2 Gross and net heating (calorific) values of simple fuels
(North America Mfg. Co. 1986).
Fuel Gross (kJ/g) Net (kJ/g)
Acetylene 50.014 48.309
Butane 49.593 49.771
Carbon 32.78 32.78
Carbon monoxide 10.11 10.11
Ethane 51.923 47.492
Hydrogen 142.11 120.08
Hydrogen sulfide 16.51 15.21
Methane 55.533 49.997
Octane 48.371 44.871
Propane 50.402 46.373
Sulfur 9.257 9.257

Table 13.2 lists the heating values of some simple fuels. When a perfect
mixture of fuel and air, originally at 60 F (15.6 C) is ignited and then cooled

to 60 F (15.6 C), the total heat release is called the gross heating value of the

fuel. The gross heating value minus the heat released by the condensation of
the water vapor in the combustion products is called net heating value.
Burger and Sahuquet (1972) defined a general combustion reaction
(combined reactions 1 and 2 in Table 13.1):
2 þ b x 1 b x

O 2 / CO þ H 2 O (13.8)
CH x þ þ CO 2 þ
4 1 þ b 1 þ b 2
2ð1 þ bÞ
In the above reaction, x is the atomic H/C ratio of the fuel and b is CO/
CO 2 ratio in the exhaust gases. They also derived the gross calorific value of
a unit mass of burned fuel (H 2 O being condensed):
265;700 þ 19;850b 31;175x 171;700
cal=g (13.9)
Q ¼ þ
12 þ x
ð1 þ bÞð12 þ xÞ
or
478;260 þ 356;130b 56;115x 309;060
BTU=lb (13.10)
0
12 þ x
Q ¼ þ
ð1 þ bÞð12 þ xÞ
The heat of reaction in terms of the oxidizer is:
* 265:7 þ 197:85b
Q ¼
b x
1 þ þ ð1 þ bÞ
2 4
31:175x 171:7 3
kcal=mol O 2 or BTU ft air (13.11)
2 þ b x
þ
þ
4
2ð1 þ bÞ