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Products of Combustion , Emissions and Reactions

Products of Combustion, Emissions and Reactions

The products arising from the complete combustion of a fuel are CO₂, H₂O, and if sulfur is present, SO₂. Accompanying these are the nitrogen brought in with the air and the oxygen in the excess of air. Hence the products of complete combustion are principally CO₂, H₂O, N₂, and O₂. The presence of CO indicates incomplete combustion. In simple calculations the reaction of nitrogen with oxygen to form noxious oxides, often termed NOx, such as nitric oxide (NO), nitrogen peroxide (NO₂), etc., is neglected. In practice, an automobile engine is run at a lower compression ratio to reduce NOx formation. The reduced pollution is bought at the expense of reduced operating efficiency. The composition of the products of combustion is readily calculated from the combustion equations, as shown by the following illustrative example.

Coefficients in reaction equations			Coefficients multiplied by V
O2	CO2	H2O	O2	CO2	H2O
0.5	0	1	0.04	0	0.08
0.5	1	0	0.11	0.22	0
2	1	2	0.048	0.024	0.048
0	1	0	0	0.066	0
0	0	0	0	0	0
			0.198	0.31	0.128

For 1 ft³ of the producer gas, 0.198 ft³ of O² is required for complete combustion. The minimum volume of air required is 0.198/0.21 = 0.943 ft³ and with 20 percent excess the air supplied is 0.943 x 1.2 = 1.132 ft³. Of this, 0.238 ft³ is oxygen and 0.894 ft³ is N₂. Consequently, for 1 ft³ of the fuel gas, the exhaust gas contains

CO2	0.31 ft3
H2O	0.128 ft3
N2	0.61 + 0.894 = 1.504 ft3
O2 (excess)	0.238 - 0.198 = 0.040 ft3
= 1.982 ft3

or

CO2	15.7 %
H2O	6.5 %
N2	75.8 %
O2 (excess)	2.0 %
= 100.0 %

${\displaystyle }$Source:

Marks Standard Handbook for Mechanical Engineers

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