Fuels and Combustion
A sample of natural gas containing 80% methane (CH₄) and rest nitrogen (N₂) is burnt with 20% excess air. With 80% of the combustibles producing CO₂ and the reminder going to CO, the Orsat analysis in volume percent is

CO₂ : 6.26, CO : 1.56, O₂ : 3.91, H₂O :15.66, N₂ : 72.60
CO₂ : 7.42, CO : 1.86, O₂ : 4.64, N₂:86.02
CO₂ : 6.39, CO : 1.60, O₂ : 3.99, H₂O:25.96, N₂:72.06
CO₂ : 7.60, CO : 1.90, O₂ : 4.75, N₂ : 85.74

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Fuels and Combustion
The main drawback of supplying more excess air in the combustion of fuel is the

Intermittant and uncontrolled combustion of the fuel
Enhanced sensible heat loss in the flue gas
High exit flue gas temperature from the furnace
Excessive power requirement of air blower

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