Fuel and Combustion MCQs

382. A liquid/gaseous fuel containing hydrocarbons and high amount of sulphur is burnt with 40% excess air. The flue gas still contains large amount of carbon monoxide. This may be due to the

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Presence of large quantity of hydrogen in the fuel
Low calorific value of the fuel
High sulphur content in the fuel
Lack of thorough mixing of fuel with air
✅ The correct answer is option D.

383. Which of the following would require least amount of secondary air for combustion?

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Coke breeze containing 25% ash and 2% volatile matter
Anthracite containing 10% volatile matter and 8% ash
Bituminous coal containing 20% ash and 25% volatile matter
Semi-bituminous coal containing 25% ash and 20% volatile matter
✅ The correct answer is option A.

386. 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

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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
✅ The correct answer is option B.