9.8.2 Fuel Heating Value (HV: HHV and LHV)
With the enthalpy of formation values compiled, the heating values of a reaction
can be calculated (see Table 9.4). For instance, take the following reaction:
C 8 H 18 l
ð Þ þ 17:5 O 2 þ 3:76N 2
ð
Þ!8CO 2 þ 9H 2 O l
ð Þ þ 5O 2 þ 65:8 N 2
Table 9.4 Properties of some common fuels and hydrocarbons
Fuel
(phase)
Formula
Molar
mass
(kg/kmol)
Density
a
(kg/L)
Enthalpy of
vaporization
b
(kJ/kg)
Specific
heat
a c p
(kJ/kg K)
Higher
heating
value
c
(kJ/kg)
Lower
heating
value
c
(kJ/kg)
Carbon (s) C
12.011
2
–
0.708
32,800
32,800
Hydrogen
(g)
H 2
2.016
–
–
14.4
141,800
120,000
Carbon
monoxide
(g)
CO
28.013
–
–
1.05
10,100
10,100
Methane
(g)
CH 4
16.043
–
509
2.20
55,530
50,050
Methanol
(l)
CH 4 O
32.042
0.790
1168
2.53
22,660
19,920
Acetylene
(g)
C 2 H 2
26.038
–
–
1.69
49,970
48,280
Ethane (g) C 2 H 6
30.070
–
172
1.75
51,900
47,520
Ethanol (l) C 2 H 6 O
46.069
0.790
919
2.44
29,670
26,810
Propane (l) C 3 H 8
44 097
0.500
335
2.77
50,330
46,340
Butane (l) C 4 H 10
58.123
0.579
362
2.42
49,150
45,370
1-Pentene
(l)
C 5 H 10
70.134
0.641
363
2.20
47,760
44,630
Isopentane
(l)
C 5 H 12
72.150
0.626
–
2.32
48,570
44,910
Benzene (l) C 6 H 6
78.114
0.877
433
1.72
41,800
40,100
Hexene (l) C 6 H 12
84.161
0.673
392
1.84
47,500
44,400
Hexane (l) C 6 H 14
86.177
0.660
366
2.27
48,310
44,740
Toluene (l) C 7 H 8
92.141
0.867
412
1.71
42,400
40,500
Heptane (l) C 7 H 16
100.204 0 684
365
2.24
48,100
44,600
Octane (l) C 8 H 18
114.231 0.703
363
2.23
47,890
44,430
Decane (l) C 10 H 22
142.285 0.730
361
2.21
47,640
44,240
Gasoline
(l)
C n H 1.87n
100–110 0.72–
0.78
350
2.4
47,300
44,000
Light
diesel (l)
C n H 1.8n
170
0.78–
0.84
270
2.2
46,100
43,200
Heavy
diesel (l)
C n H 1.7n
200
0.82–
0.88
230
1.9
45,500
42,800
Natural gas
(g)
C n H 3.8n N 0.1n 18
–
–
2
50,000
45,000
a
At 1 atm and 20 °C
b At 25 °C for liquid fuels, and 1 atm normal boiling temperature for gaseous fuels
c
At 25 °C. Multiply by molar mass to obtain heating values in kJ/kmol
9.8 Combustion Chemical Reactions and Enthalpy Balance
265
With the enthalpy of formation values compiled, the heating values of a reaction
can be calculated (see Table 9.4). For instance, take the following reaction:
C 8 H 18 l
ð Þ þ 17:5 O 2 þ 3:76N 2
ð
Þ!8CO 2 þ 9H 2 O l
ð Þ þ 5O 2 þ 65:8 N 2
Table 9.4 Properties of some common fuels and hydrocarbons
Fuel
(phase)
Formula
Molar
mass
(kg/kmol)
Density
a
(kg/L)
Enthalpy of
vaporization
b
(kJ/kg)
Specific
heat
a c p
(kJ/kg K)
Higher
heating
value
c
(kJ/kg)
Lower
heating
value
c
(kJ/kg)
Carbon (s) C
12.011
2
–
0.708
32,800
32,800
Hydrogen
(g)
H 2
2.016
–
–
14.4
141,800
120,000
Carbon
monoxide
(g)
CO
28.013
–
–
1.05
10,100
10,100
Methane
(g)
CH 4
16.043
–
509
2.20
55,530
50,050
Methanol
(l)
CH 4 O
32.042
0.790
1168
2.53
22,660
19,920
Acetylene
(g)
C 2 H 2
26.038
–
–
1.69
49,970
48,280
Ethane (g) C 2 H 6
30.070
–
172
1.75
51,900
47,520
Ethanol (l) C 2 H 6 O
46.069
0.790
919
2.44
29,670
26,810
Propane (l) C 3 H 8
44 097
0.500
335
2.77
50,330
46,340
Butane (l) C 4 H 10
58.123
0.579
362
2.42
49,150
45,370
1-Pentene
(l)
C 5 H 10
70.134
0.641
363
2.20
47,760
44,630
Isopentane
(l)
C 5 H 12
72.150
0.626
–
2.32
48,570
44,910
Benzene (l) C 6 H 6
78.114
0.877
433
1.72
41,800
40,100
Hexene (l) C 6 H 12
84.161
0.673
392
1.84
47,500
44,400
Hexane (l) C 6 H 14
86.177
0.660
366
2.27
48,310
44,740
Toluene (l) C 7 H 8
92.141
0.867
412
1.71
42,400
40,500
Heptane (l) C 7 H 16
100.204 0 684
365
2.24
48,100
44,600
Octane (l) C 8 H 18
114.231 0.703
363
2.23
47,890
44,430
Decane (l) C 10 H 22
142.285 0.730
361
2.21
47,640
44,240
Gasoline
(l)
C n H 1.87n
100–110 0.72–
0.78
350
2.4
47,300
44,000
Light
diesel (l)
C n H 1.8n
170
0.78–
0.84
270
2.2
46,100
43,200
Heavy
diesel (l)
C n H 1.7n
200
0.82–
0.88
230
1.9
45,500
42,800
Natural gas
(g)
C n H 3.8n N 0.1n 18
–
–
2
50,000
45,000
a
At 1 atm and 20 °C
b At 25 °C for liquid fuels, and 1 atm normal boiling temperature for gaseous fuels
c
At 25 °C. Multiply by molar mass to obtain heating values in kJ/kmol
9.8 Combustion Chemical Reactions and Enthalpy Balance
265