250+ TOP MCQs on Engine Emissions and Answers

Automobile Engineering Multiple Choice Questions on “Engine Emissions”.

1. Which of the following is one of the major exhaust emissions from CI engines compared to SI engines?
a) Oxides of nitrogen
b) Particulates
c) CO and CO₂
d) Unburnt hydrocarbon
Answer: b
Clarification: Unburnt hydrocarbons are one of the major exhaust emissions from CI engines. The components in diesel fuel have higher molecular weight.

2. Which of the following causes the photochemical smog?
a) Excess O₂
b) CO and CO₂
c) Soot and particulate matter
d) NO_x and HC
Answer: d
Clarification: NO_x is one of the primary causes of photochemical smog. This smog is formed by the photochemical reaction of automobile exhaust and atmospheric air in the presence of sunlight.

3. What does the blue smoke in diesel engine indicate?
a) Unburnt oil
b) HC
c) NO_x
d) CO
Answer: a
Clarification: Blue smoke comes out from the exhaust when there is unburnt oil in the diesel engine. A very thin layer of the oil gets deposited on the cylinder wall to provide the lubrication between the walls and the moving piston.

4. During which condition of the vehicle does NO_x emission in SI engine will be lowest?
a) Cruising
b) Idling
c) Accelerating
d) Decelerating
Answer: b
Clarification: NO_x emissions are lowest in SI engine during idling. NO_x is created from nitrogen in the air. Nitrogen can also be found in fuel blends.

5. For what purpose is the Rhodium used?
a) To reduce CO and HC
b) To reduce NO_x
c) To reduce CO
d) To reduce HC
Answer: b
Clarification: Rhodium is used to reduce NO_x. It is used to clean vehicle emission. It is mixed with the other two metals – platinum and palladium.

6. Why is the fumigation technique used?
a) To control HC
b) To control NO_x
c) To control CO
d) To control smoke
Answer: d
Clarification: The fumigation technique is used to control smoke. Fumigation is injecting gaseous or liquid fuel into the intake of air steam of CI engines. There are two types of smoke: hot smoke and cold smoke.

7. Why are lead compounds added in petrol?
a) Reduce knocking
b) Reduce HC emission
c) Reduce exhaust temperature
d) Increase power output
Answer: b
Clarification: The lead compounds are added in petrol to reduce the HC emission. The additive TEL (Tetraethyl Lead) was added to increase the octane number. The resulting lead in the engine exhaust was a poisonous pollutant.

8. Which of the following cannot be reduced by thermal converters?
a) CO
b) HC
c) Soot
d) NO_x
Answer: d
Clarification: NO_x emission cannot be reduced using a thermal converter. Thermal converters are high-temperature chambers through which the exhaust gas flows.

9. What can be reduced by using exhaust gas recirculation (EGR) effectively?
a) CO
b) NO_x
c) HC
d) CO and HC
Answer: b
Clarification: The most effective way of reducing NO_x emission is to hold combustion chamber temperatures down. Using this also reduces the thermal efficiency of the engine.

10. Three-way catalytic converters reduce the emission of CO, HC, and soot.
a) True
b) False
Answer: b
Clarification: Three-way catalytic converters reduce the emission of CO, NO_x, and HC. They are chambers contain catalytic material. It promotes the oxidation of the emission contained in the exhaust flow.