Automobile Emission Control Questions and Answers

Q: Fuel vapour stored while a vehicle is parked is held in a _____ canister.

Correct answer: carbonThe canister is filled with activated carbon, whose very large internal surface adsorbs the fuel vapour escaping from the tank while the vehicle is parked.When the engine runs under suitable conditions, air is drawn through the canister to desorb the vapour and carry it to the intake, where it is burnt. The same adsorption principle serves organic vapours in air cleaning generally - the carbon holds the molecules until conditions favour their release.

Q: Unreacted reagent passing through a vehicle's reduction catalyst is called ammonia _____.

Correct answer: slipAmmonia slip is unreacted ammonia passing through the reduction catalyst and out of the tailpipe. It arises when urea is overdosed, or when the catalyst is too cold or too small to consume what is supplied.It matters because ammonia is itself a pollutant and a precursor of secondary particulate. Systems therefore dose carefully against temperature and load, and often carry a small oxidation catalyst downstream specifically to destroy any that escapes.

Q: Aftertreatment devices on a modern heavy diesel. DeviceDutyConsumable Oxidation catalystCarbon monoxide and hydrocarbonsNoneParticulate filterSootFuel for regenerationUrea reduction catalystOxides of nitrogenUrea solutionExhaust gas recirculationOxides of nitrogen in-cylinderNone Why does a diesel need several devices where a petrol engine needs one?

Correct answer: Lean exhaust prevents reductionRead the table's duty column. Oxidation and filtration both work in oxygen-rich exhaust, but nitrogen oxide reduction does not - reduction requires the removal of oxygen, and a diesel's exhaust is full of it.A three-way catalyst avoids the problem by working at stoichiometric, where oxidation and reduction can proceed together. A diesel cannot run there, so it needs separate devices: one to oxidise, one to filter, and either recirculation or urea to deal with nitrogen oxides.

71.

Fuel vapour stored while a vehicle is parked is held in a _____ canister.

A.zeolite
B.cyclone
C.carbon
D.ceramic

Answer: C

Correct answer: carbon

The canister is filled with activated carbon, whose very large internal surface adsorbs the fuel vapour escaping from the tank while the vehicle is parked.

When the engine runs under suitable conditions, air is drawn through the canister to desorb the vapour and carry it to the intake, where it is burnt. The same adsorption principle serves organic vapours in air cleaning generally - the carbon holds the molecules until conditions favour their release.

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72.

Unreacted reagent passing through a vehicle's reduction catalyst is called ammonia _____.

A.excess
B.carryover
C.breakthrough
D.slip

Answer: D

Correct answer: slip

Ammonia slip is unreacted ammonia passing through the reduction catalyst and out of the tailpipe. It arises when urea is overdosed, or when the catalyst is too cold or too small to consume what is supplied.

It matters because ammonia is itself a pollutant and a precursor of secondary particulate. Systems therefore dose carefully against temperature and load, and often carry a small oxidation catalyst downstream specifically to destroy any that escapes.

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73.

Petrol engine emissions against air-fuel ratio.

Air-fuel ratio	Lambda	CO	HC	NOx
12.5	0.85	Very high	High	Low
14.7	1.00	Moderate	Moderate	High
15.5	1.05	Low	Low	Highest
18.0	1.22	Very low	Rising	Low

Why can no single air-fuel ratio minimise all three pollutants at once?

A.The two groups move in opposite directions
B.All three fall together as the mixture leans
C.All three rise together as the mixture leans
D.The three are unrelated to mixture strength

Answer: A

The map runs in opposite directions for the incomplete combustion products and for the thermal nitrogen oxides. It is exactly why the three-way catalyst was developed, since it treats all three at one point rather than trading them.

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74.

Catalyst conversion efficiency against temperature.

Bed temperature (C)	CO conversion	HC conversion	NOx conversion
150	5	3	2
250	60	45	40
350	97	94	93
500	98	96	95

What does the table imply about short journeys?

A.Temperature has little effect on conversion
B.Almost nothing is converted until light-off
C.Conversion is complete from the moment of starting
D.Conversion falls at high temperature

Answer: B

Between 150 and 350 degrees the conversion goes from almost nothing to almost everything, and reaching that band takes a minute or two from cold. A five kilometre trip may therefore emit more than a fifty kilometre one.

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75.

Aftertreatment devices on a modern heavy diesel.

Device	Duty	Consumable
Oxidation catalyst	Carbon monoxide and hydrocarbons	None
Particulate filter	Soot	Fuel for regeneration
Urea reduction catalyst	Oxides of nitrogen	Urea solution
Exhaust gas recirculation	Oxides of nitrogen in-cylinder	None

Why does a diesel need several devices where a petrol engine needs one?

A.Diesel fuel contains more sulphur
B.Its emissions are larger in total
C.Lean exhaust prevents reduction
D.Its exhaust is cooler

Answer: C

Correct answer: Lean exhaust prevents reduction

Read the table's duty column. Oxidation and filtration both work in oxygen-rich exhaust, but nitrogen oxide reduction does not - reduction requires the removal of oxygen, and a diesel's exhaust is full of it.

A three-way catalyst avoids the problem by working at stoichiometric, where oxidation and reduction can proceed together. A diesel cannot run there, so it needs separate devices: one to oxidise, one to filter, and either recirculation or urea to deal with nitrogen oxides.

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76.

Fleet emission contribution by vehicle condition.

Group	Share of fleet	Emission per vehicle	Share of total
Well maintained	70 per cent	1.0	43 per cent
Degraded	20 per cent	2.0	24 per cent
Malfunctioning	10 per cent	5.0	31 per cent
Whole fleet	100 per cent	1.6 average	100 per cent

What policy does the table most directly support?

A.Tighter new vehicle standards
B.Reducing the size of the fleet
C.Improving fuel quality further
D.Inspection and targeted repair

Answer: D

A tenth of the vehicles carries nearly a third of the emission, and repairing them is far cheaper than tightening standards on vehicles not yet built. Standards and inspection address different parts of the same problem.

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77.

Fuel quality changes and the technology each enabled.

Change	Enabled technology
Removal of lead	Catalytic converters
Sulphur to 10 ppm	Particulate filters and reduction catalysts
Volatility control	Effective evaporative control
Aromatics limits	Lower particulate and benzene emissions

What general point does the table make?

A.Aftertreatment technology and fuel quality had to advance together
B.Fuel quality is irrelevant to emissions
C.Aftertreatment alone determines emissions
D.Fuel quality changes were made for engine durability

Answer: A

Correct answer: Aftertreatment technology and fuel quality had to advance together

Every row pairs a fuel change with a technology that could not have been introduced without it. Lead destroys catalysts, sulphur poisons them and adds sulphate particulate, volatility drives evaporative losses, and aromatics promote soot and benzene.

Each device was therefore waiting on a refinery investment, which is why standards and fuel specifications were legislated in step. Neither could deliver alone, and the durability of engines was a secondary benefit rather than the motive.

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78.

Assertion (A): The three-way catalyst made closed loop fuelling control essential.

Reason (R): It can oxidise and reduce simultaneously only within about one per cent of stoichiometric.

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 is the reason. The catalyst must oxidise and reduce simultaneously, and those chemistries want opposite exhaust conditions - oxygen for one, its absence for the other.

Only a narrow band around stoichiometric satisfies both, and holding a carburettor there is impossible across the operating range. A lambda sensor and closed loop control became necessary, which is why electronic fuel injection and the three-way catalyst arrived together rather than by coincidence.

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79.

Assertion (A): Unleaded petrol was a precondition for catalytic converters.

Reason (R): Lead deposits coat the precious metal sites and destroy catalytic activity irreversibly.

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 why the change was mandatory rather than desirable. Lead compounds deposit on the precious metal sites and block them permanently - a single tank of leaded fuel ruins a converter.

Unleaded fuel therefore had to be available before catalytic converters could be fitted, and the two were legislated together. It is the clearest example of the general point that aftertreatment and fuel quality advanced in step.

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80.

Assertion (A): A diesel needs separate devices for oxidation and for nitrogen oxide reduction.

Reason (R): Its exhaust is oxygen-rich, and reduction cannot proceed in the presence of excess oxygen.

Select the correct answer from the options below.

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

Answer: D

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. A diesel runs lean, so its exhaust carries substantial oxygen - which suits oxidation perfectly and prevents reduction entirely, since a reducing reaction cannot compete with the oxygen present.

Separate devices are therefore required: an oxidation catalyst, and either exhaust gas recirculation to prevent nitrogen oxides forming or a urea system supplying ammonia to reduce them selectively. A petrol engine at stoichiometric needs only one device because both chemistries can proceed together there.

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