Automobile Emission Control Questions and Answers

Q: Assertion (A): Nitrogen oxide emissions peak when the mixture is rich. Reason (R): Thermal formation requires a high flame temperature. Select the correct answer from the options below.

Correct answer: A is false but R is trueThe reason is correct as far as it goes, but incomplete - and the omission is what makes the assertion false. Thermal formation needs available oxygen as well as a high flame temperature.A rich mixture is hot but oxygen-starved, so nitrogen oxide formation falls. The peak occurs slightly lean of stoichiometric, where both conditions are met. That is why the emission curves for nitrogen oxides and for carbon monoxide peak on opposite sides of stoichiometric, and why no single mixture minimises both.

Q: Consider the following statements about the three-way catalyst: 1. It treats carbon monoxide, hydrocarbons and nitrogen oxides together. 2. It requires the mixture to be held close to stoichiometric. 3. It works equally well in a diesel's lean exhaust. Which of the statements given above is or are correct?

Correct answer: 1 and 2 onlyThe first two are correct and the second follows from the first. Treating all three pollutants together means oxidising two of them while reducing the third, and only exhaust close to stoichiometric suits both chemistries.The third is false for exactly that reason. A diesel's exhaust is oxygen-rich, and reduction cannot proceed with oxygen present - which is why a diesel needs an oxidation catalyst, a filter and a separate nitrogen oxide measure instead.

Q: Consider the following statements about emissions and mixture strength: 1. Rich running raises carbon monoxide and hydrocarbons. 2. Nitrogen oxides peak slightly lean of stoichiometric. 3. Deeply lean running raises nitrogen oxides further still. Which of the statements given above is or are correct?

Correct answer: 1 and 2 onlyThe first two are correct: rich running gives incomplete combustion and so raises carbon monoxide and hydrocarbons, and nitrogen oxides peak slightly lean of stoichiometric where flame temperature and available oxygen coincide.The third reverses the trend beyond the peak. Deeply lean running lowers nitrogen oxides, because the excess air cools the flame - which is the principle a lean-burn engine exploits, at the cost of losing catalytic reduction.

Q: Consider the following statements about diesel particulate filters: 1. They trap soot in wall-flow channels. 2. They must periodically be regenerated by raising the exhaust temperature. 3. Short cold journeys assist regeneration. Which of the statements given above is or are correct?

Correct answer: 1 and 2 onlyThe first two describe the device correctly: soot is trapped as exhaust is forced through porous channel walls, and the accumulation must periodically be burnt off by raising the exhaust temperature.The third is the opposite of the truth. Short cold journeys never reach the regeneration threshold, so soot accumulates unburnt until back pressure forces the engine to derate - the commonest cause of a blocked filter in urban use.

Q: Consider the following statements about evaporative emissions: 1. They arise from the fuel tank and fuel system rather than the exhaust. 2. A carbon canister stores the vapour until it can be purged into the engine. 3. They are negligible compared with exhaust hydrocarbons. Which of the statements given above is or are correct?

Correct answer: 1 and 2 onlyThe first two are correct: evaporative emissions are fuel vapour escaping the tank and fuel system, and a carbon canister adsorbs it until the engine can be purged of it.The third understates them badly. Before evaporative control they were a substantial share of a vehicle's total hydrocarbon emission, and on a modern car with a very effective catalyst they can rival or exceed the exhaust contribution - which is why they are separately regulated and separately tested.

Q: Match each device in List I with the duty it performs in List II. List I A. Three-way catalyst B. Carbon canister C. Positive crankcase ventilation D. Urea injection List II 1. Exhaust carbon monoxide, hydrocarbons and nitrogen oxides 2. Fuel vapour from the tank 3. Blow-by gases from the crankcase 4. Oxides of nitrogen in a lean diesel exhaust Select the correct match.

Correct answer: A-1, B-2, C-3, D-4Each device addresses a different pathway out of the vehicle. The three-way catalyst treats the exhaust, handling all three regulated gases at stoichiometric.The carbon canister handles fuel vapour from the tank, which never passes through the engine. Positive crankcase ventilation handles blow-by past the piston rings. Urea injection handles nitrogen oxides in lean diesel exhaust, where a three-way catalyst cannot work. Four escape routes, four devices.

81.

Assertion (A): Short urban journeys produce disproportionately high emissions.

Reason (R): The catalyst converts almost nothing until it reaches its light-off temperature.

Select the correct answer from the options below.

A.Both A and R are true, and R is the correct explanation of A
B.Both A and R are true, but R is not the correct explanation of A
C.A is true but R is false
D.A is false but R is true

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the second is the mechanism. The catalyst converts almost nothing below light-off, so the first ninety seconds or so passes essentially untreated exhaust - and that exhaust is itself worse, the engine running rich while cold.

The quantity is roughly fixed per start, so a short journey carries the whole of it over very few kilometres. Close-coupled converters, low thermal mass substrates and electrical heating all attack the same interval.

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82.

Assertion (A): Exhaust gas recirculation is scheduled rather than applied continuously.

Reason (R): Excessive recirculation costs power and drivability.

Select the correct answer from the options below.

A.A is false but R is true
B.Both A and R are true, and R is the correct explanation of A
C.Both A and R are true, but R is not the correct explanation of A
D.A is true but R is false

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the second explains the scheduling. Recirculated exhaust displaces fresh charge and slows the burn, so too much of it costs power, worsens drivability and can raise particulate and hydrocarbon emissions.

The rate is therefore mapped against speed and load: high at part load where nitrogen oxides matter and power does not, reduced or cut at full load and during warm-up. It is a trade managed continuously rather than a setting applied once.

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83.

Assertion (A): Inspection and maintenance programmes are worth running alongside new vehicle standards.

Reason (R): A small proportion of badly maintained vehicles accounts for a large share of fleet emissions.

Select the correct answer from the options below.

A.A is true but R is false
B.A is false but R is true
C.Both A and R are true, and R is the correct explanation of A
D.Both A and R are true, but R is not the correct explanation of A

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the second is the reason such programmes repay their cost. Emissions across a fleet are heavily skewed: a small fraction of vehicles, poorly maintained or with equipment defeated, produces a disproportionate share.

New vehicle standards cannot reach them, since those vehicles were compliant when new. Testing in service finds them and repair fixes them, so the two instruments address different parts of the problem and are complementary rather than alternative.

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84.

Assertion (A): Nitrogen oxide emissions peak when the mixture is rich.

Reason (R): Thermal formation requires a high flame temperature.

Select the correct answer from the options below.

A.Both A and R are true, and R is the correct explanation of A
B.Both A and R are true, but R is not the correct explanation of A
C.A is true but R is false
D.A is false but R is true

Answer: D

Correct answer: A is false but R is true

The reason is correct as far as it goes, but incomplete - and the omission is what makes the assertion false. Thermal formation needs available oxygen as well as a high flame temperature.

A rich mixture is hot but oxygen-starved, so nitrogen oxide formation falls. The peak occurs slightly lean of stoichiometric, where both conditions are met. That is why the emission curves for nitrogen oxides and for carbon monoxide peak on opposite sides of stoichiometric, and why no single mixture minimises both.

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85.

Assertion (A): Fuel sulphur reduction was necessary before diesel particulate filters could be adopted.

Reason (R): Sulphur poisons catalysts and is oxidised to sulphate that adds to measured particulate.

Select the correct answer from the options below.

A.Both A and R are true, and R is the correct explanation of A
B.Both A and R are true, but R is not the correct explanation of A
C.A is true but R is false
D.A is false but R is true

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the second gives both mechanisms. Sulphur adsorbs onto catalyst sites and suppresses their activity, and it is oxidised to sulphate that condenses and is weighed as particulate.

A filter fitted to high-sulphur fuel would therefore be defeated twice over: its regeneration catalyst poisoned, and sulphate added to the very quantity it was fitted to reduce. Cleaning the fuel was a precondition, which is why sulphur limits and the filter mandate were sequenced together.

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86.

Consider the following statements about the three-way catalyst:

1. It treats carbon monoxide, hydrocarbons and nitrogen oxides together.

2. It requires the mixture to be held close to stoichiometric.

3. It works equally well in a diesel's lean exhaust.

Which of the statements given above is or are correct?

A.1, 2 and 3
B.1 and 2 only
C.1 and 3 only
D.2 and 3 only

Answer: B

Correct answer: 1 and 2 only

The first two are correct and the second follows from the first. Treating all three pollutants together means oxidising two of them while reducing the third, and only exhaust close to stoichiometric suits both chemistries.

The third is false for exactly that reason. A diesel's exhaust is oxygen-rich, and reduction cannot proceed with oxygen present - which is why a diesel needs an oxidation catalyst, a filter and a separate nitrogen oxide measure instead.

Discuss in Forum

87.

Consider the following statements about emissions and mixture strength:

1. Rich running raises carbon monoxide and hydrocarbons.

2. Nitrogen oxides peak slightly lean of stoichiometric.

3. Deeply lean running raises nitrogen oxides further still.

Which of the statements given above is or are correct?

A.2 and 3 only
B.1, 2 and 3
C.1 and 2 only
D.1 and 3 only

Answer: C

Correct answer: 1 and 2 only

The first two are correct: rich running gives incomplete combustion and so raises carbon monoxide and hydrocarbons, and nitrogen oxides peak slightly lean of stoichiometric where flame temperature and available oxygen coincide.

The third reverses the trend beyond the peak. Deeply lean running lowers nitrogen oxides, because the excess air cools the flame - which is the principle a lean-burn engine exploits, at the cost of losing catalytic reduction.

Discuss in Forum

88.

Consider the following statements about diesel particulate filters:

1. They trap soot in wall-flow channels.

2. They must periodically be regenerated by raising the exhaust temperature.

3. Short cold journeys assist regeneration.

Which of the statements given above is or are correct?

A.1 and 3 only
B.2 and 3 only
C.1, 2 and 3
D.1 and 2 only

Answer: D

Correct answer: 1 and 2 only

The first two describe the device correctly: soot is trapped as exhaust is forced through porous channel walls, and the accumulation must periodically be burnt off by raising the exhaust temperature.

The third is the opposite of the truth. Short cold journeys never reach the regeneration threshold, so soot accumulates unburnt until back pressure forces the engine to derate - the commonest cause of a blocked filter in urban use.

Discuss in Forum

89.

Consider the following statements about evaporative emissions:

1. They arise from the fuel tank and fuel system rather than the exhaust.

2. A carbon canister stores the vapour until it can be purged into the engine.

3. They are negligible compared with exhaust hydrocarbons.

Which of the statements given above is or are correct?

A.1 and 2 only
B.1 and 3 only
C.2 and 3 only
D.1, 2 and 3

Answer: A

Correct answer: 1 and 2 only

The first two are correct: evaporative emissions are fuel vapour escaping the tank and fuel system, and a carbon canister adsorbs it until the engine can be purged of it.

The third understates them badly. Before evaporative control they were a substantial share of a vehicle's total hydrocarbon emission, and on a modern car with a very effective catalyst they can rival or exceed the exhaust contribution - which is why they are separately regulated and separately tested.

Discuss in Forum

90.

Match each device in List I with the duty it performs in List II.

List I

A. Three-way catalyst

B. Carbon canister

C. Positive crankcase ventilation

D. Urea injection

List II

1. Exhaust carbon monoxide, hydrocarbons and nitrogen oxides

2. Fuel vapour from the tank

3. Blow-by gases from the crankcase

4. Oxides of nitrogen in a lean diesel exhaust

Select the correct match.

A.A-4, B-2, C-3, D-1
B.A-1, B-2, C-3, D-4
C.A-2, B-1, C-4, D-3
D.A-1, B-3, C-2, D-4

Answer: B

Correct answer: A-1, B-2, C-3, D-4

Each device addresses a different pathway out of the vehicle. The three-way catalyst treats the exhaust, handling all three regulated gases at stoichiometric.

The carbon canister handles fuel vapour from the tank, which never passes through the engine. Positive crankcase ventilation handles blow-by past the piston rings. Urea injection handles nitrogen oxides in lean diesel exhaust, where a three-way catalyst cannot work. Four escape routes, four devices.

Discuss in Forum

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