# Energy Engineering Questions and Answers – Combustion of Fuels

This set of Energy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Combustion of Fuels”.

1. The process of burning fuels in the presence of oxygen is called _________
a) Induction
b) Ignition
c) Condensation
d) Combustion

Explanation: The process of burning fuels in the presence of oxygen is called combustion. Due to the presence of combustible elements like carbon (C), hydrogen (H) and sulfur (S), fuels burn in presence of oxygen and generate heat from the fuels.

2. The minimum temperature at which a substance begins to burn is called ________
a) Fire point temperature
b) Auto ignition
c) Ignition temperature
d) Flash point temperature

Explanation: The minimum temperature at which a substance begins to burn is called ignition temperature. No substance can catch fire unless it is heated up to a certain minimum temperature. The ignition of every substance is definite. For example, the ignition temperature of white phosphorous is 35°C. It means, white phosphorous starts burning only if it is heated up to 35°C.

3. The substance which helps in combustion of fuels is called _________
a) Igniter
b) Flammables
c) Supporter
d) Inflammables

Explanation: The substance which helps in combustion of fuels is called supporter fuels/combustible elements. For example, oxygen is a supporter of combustion because in the absence of oxygen fuels cannot burn.

4. What is necessary for complete combustion of fuels?
a) There should be no water content in the fuel
b) Sufficient amount of air is required
c) High quantity of fuel
d) Open space to burn easily

Explanation: For complete combustion of fuels, it is necessary to supply sufficient amount of air. If air supplied is not sufficient then combustion will be incomplete. This means carbon in the fuel burns to produce carbon monoxide (CO) instead of carbon dioxide (CO2), and thus reducing the amount of oxygen required and amount of heat generated.

5. C + O2 →_____
a) CO
b) CO2
c) CO3
d) 2CO

Explanation: Based on molecular weight, 12kg of carbon combines with 32kg of oxygen forming 44kg of carbon dioxide.
i.e., 12kg of C + 32 kg of O2 => 44kg of CO2
1kg of C + 8/3kg of O2 => 11/3kg of CO2
Reaction type: synthesis.
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6. C + O2 => _______
a) CO
b) 2CO2
c) 2CO
d) CO3

Explanation: Balanced equation: 2C + O2 => 2CO [Synthesis reaction] Oxygen is left in excess, based on the molecular weight, 24kg of carbon combines with 32kg of oxygen forming 56kg of carbon monoxide
24kg of C + 32kg of O2 => 56kg of CO
1kg of C + 4/3kg of O2 => 7/3kg of CO.

7. CO + O2 => _______
a) 2CO2
b) CO2
c) CO
d) CO3

Explanation: Based on molecular weight, 56kg of carbon monoxide combines with 32kg of oxygen forming 88kg of CO2
Balanced equation: 2CO + O2 => 2CO2
56kg of CO + 32kg of O2 => 88kg of CO2
1kg of CO + 4/7kg of O2 => 11/7kg of CO2.

8. H2 + O2 => _____
a) H2O
b) OH
c) H3O
d) 2H2O

Explanation: Based on molecular weight, 32kg of sulfur combines with 32kg of oxygen forming 36kg of water.
Balanced equation: 2H2 + O2 => 2H2O
4kg of H2 + 32kg of O2 => 36kg of H2O
1kg of H2 + 8kg of O2 => 9kg of H2O.

9. S + O2 => ______
a) SO3
b) SO2
c) S2-
d) 2SO2

Explanation: Based on molecular weight, 32 kg of sulfur combines with 32 kg of oxygen forming 64 kg of SO2
S + O2 => SO2
32 kg of S + 3 2 kg of O2 => 64 kg of SO2
1 kg of S + 1 kg of O2 => 2 kg of SO2.

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