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METI/ECCJ/AOTS Training Program Vietnam

The "air ratio" is calculated from the O2% of the exhaust gas.
  • The simplified equation for obtaining the air ratio is: Air ratio = 21/(21 - O2% value) where O2 is the oxygen content obtained by analysis (dray base value).
  • Normally, the air ratio may be calculated by this equation. The criteria of the Law Concerning Rational Use of Energy specify this equation.
  • As the air ratio becomes large, the difference between the result obtained by the simplified equation and the real value becomes large. (See the graph.)
  • The air ratio is defined as "real air value/theoretical air volume."
  • The air ratio of 1 (one) represents an ideal state in which no more than required air is used for combustion (theoretical combustion).
  • The air in excess of air ratio at 1 (one) is called "excess air" which causes heat loss by carrying out air from the stack at heated state.
  • The air ratio short of 1 (one) causes incomplete combustion, associated with the incomplete combustion heat loss.
Larger air ratio leads to larger heat loss with the exhaust gas.
Fuel saving by air ratio improvement - with graph
  • Reduction of the air ratio (reduction of O2% in the exhaust gas) reduces heat loss with the exhaust gas.
  • This in turn leads to fuel saving.
  • The graph illustrates result of air ratio reduction.
  • In fuel saving rate, 13A gas and fuel oil A differ only very little.
  • At lower exhaust gas temperatures, the effect is small.
  • (Example)
    If air ratio can be reduced from the present 1.6 (O2 = 8.4%) to 1.2 (O2 = 3%), a fuel saving of 2.8% is realizable.
Effect of air ratio reduction
The graphs are developed on the assumption that a change in air ratio does not affect the exhaust gas temperature.
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