Related Resources: power transmission

### 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 %

Source:

Marks Standard Handbook for Mechanical Engineers

Related