Fuels and Combustion
A carbonaceous fuel (containing no H₂ or hydrocarbons) is burnt and the resulting flue gas contains 21% CO₂. It means that

Complete combustion of fuel has taken place
21% excess air has been used for combustion
21% excess oxygen has been used for combustion
No excess air has been used for combustion

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

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Fuels and Combustion
Which of the following would require least amount of secondary air for combustion?

Bituminous coal containing 20% ash and 25% volatile matter
Coke breeze containing 25% ash and 2% volatile matter
Anthracite containing 10% volatile matter and 8% ash
Semi-bituminous coal containing 25% ash and 20% volatile matter

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