Page 151 - Mechanical Engineer's Data Handbook

140 MECHANICAL ENGINEER’S DATA HANDBOOK

Rs
Mixture strength M,=-x 100% Approximate
R
molecular
Weak mixture M,< 100% Element Formula weight
Rich mixture M,> 100%
Benzene C6H6 78
Butane C4H10 58
Carbon C 12
Carbon monoxide co 28
3.16.2 Combustion equations Carbon dioxide CO, 44
Ethane CZH, 30
The following are the basic equations normally used Ethanol C,HsOH 46
for combustion processes. A table of elements and Ethene 28
compounds is given. Hydrogen C2H4 2
H
Carbon: C + 0, + CO,; 2C + 0, + 2CO Methane CH4 16
Hydrogen: 2H, +O, + 2H,O Met h a n o 1 CH,OH 32
Sulphur: S + 0, + SO, Nitrogen N, 28
Octane C8H,* 114
Typical hydrocarbon fuels : Oxygen 0, 32
C4H8+6O2 + 4C0,+4H20 Pentane CSHl, 72
C,H60 + 30, + 2C0, +3H,O
Propane C3H8 44
Carbon with air (assuming that air is composed of Propene C3H6 42
79% nitrogen and 21% oxygen by volume): Sulphur S 32
Sulphur monoxide SO 48
79 79
C+O,+-N, + CO,+-N, (by volume) Sulphur dioxide SO, 64
21 21 Water (steam) H,O 18
28 x 79 28 x 79
12C+ 32 0, +- 21 N, +44COz+~ N,
Engine exhaust and frue gas analysis
(by mass)
If the analysis includes the H,O (as steam) produced
since the molecular weights of C, 0,, CO, and N, are by the combustion of hydrogen, it is known as a ‘wet
12,32,44 and 28. analysis’. Usually the steam condenses out and a ‘dry
analysis’ is made.
3.16.3 Molecular weights of elements
and compounds 3.16.4 Solid and liquid fuels

The molecular weights of elements and compounds Let: c=%C, h=%H,, o=%O,, n=%N,, s=%S,
used in combustion processes are listed in the table. all by mass.

(2.67~ + 8h +s-0)
Stoichiometric air/fuel ratio R, =
23.3
If x = 0.84~ + 0.3 135s + 0.357n +0.0728ERS + 27.4R
y = x + 5h (using E = 0 for a stoichiometric air/fuel
ratio)