Automobile Emission Control Questions and Answers

Q: Arrange the events of a cold start in order: 1. The engine starts on a rich mixture for stability 2. Untreated exhaust passes through a cold catalyst 3. The catalyst reaches light-off temperature 4. Conversion efficiency rises above ninety per cent Select the correct sequence.

Correct answer: 1, 2, 3, 4The sequence explains why cold start emissions are so high. The engine starts rich, because a cold intake condenses fuel and a lean mixture will not run smoothly.That rich exhaust passes through a catalyst still at ambient temperature, which converts almost nothing. Only when the exhaust has warmed the substrate to light-off, around 250 to 300 degrees, does conversion begin, and efficiency then rises above 90 per cent. The worst exhaust meets the least effective catalyst.

Q: Consider the following pairs of device and the pollutant it addresses: Three-way catalyst - Carbon monoxide, hydrocarbons and nitrogen oxides Diesel particulate filter - Soot Carbon canister - Evaporative hydrocarbons Exhaust gas recirculation - Carbon monoxide How many of the pairs given above are correctly matched?

Correct answer: Only threeThe first three are correctly matched: the three-way catalyst treats all three regulated gases, the particulate filter traps soot, and the carbon canister holds evaporative hydrocarbons.The fourth is wrong. Exhaust gas recirculation lowers peak flame temperature and so reduces nitrogen oxides; it does nothing for carbon monoxide, and by degrading combustion it can slightly increase it. Each device addresses the pollutant its physics acts on.

Q: Consider the following pairs of mixture condition and its emission effect: Rich of stoichiometric - High carbon monoxide and hydrocarbons Slightly lean - Peak nitrogen oxides Deeply lean - Lower nitrogen oxides but poor catalyst reduction Exactly stoichiometric - Peak nitrogen oxides How many of the pairs given above are correctly matched?

Correct answer: Only threeThe first three are right. Rich running gives incomplete combustion and therefore high carbon monoxide and hydrocarbons; slightly lean gives peak nitrogen oxides, having both flame temperature and oxygen; deeply lean lowers them but takes the exhaust outside the window in which a three-way catalyst can reduce.The fourth is wrong and contradicts the second. The nitrogen oxide peak lies slightly lean of stoichiometric, not at it - which is what makes precise control around stoichiometric a compromise rather than an optimum for any single pollutant.

Q: Consider the following pairs of fuel change and its purpose: Removal of lead - Allowing catalytic converters to survive Reduction of sulphur - Allowing filters and reduction catalysts to work Control of volatility - Limiting evaporative emissions Raising aromatic content - Reducing particulate How many of the pairs given above are correctly matched?

Correct answer: Only threeThe first three pair each fuel change with what it enabled: lead removal for catalytic converters, sulphur reduction for filters and reduction catalysts, and volatility control for evaporative emissions.The fourth has the sign wrong. Aromatics are limited rather than raised, because they promote soot formation and benzene emission. Every genuine fuel change in the list removes something; raising a constituent that makes particulate would be a step backwards.

Q: Consider the following pairs of term and its meaning: Lambda - Actual air-fuel ratio divided by stoichiometric Light-off - The temperature at which a catalyst becomes effective Regeneration - Burning off trapped soot in a particulate filter Purge - Injecting urea into the exhaust How many of the pairs given above are correctly matched?

Correct answer: Only threeThe first three define their terms correctly. Lambda is the actual air-fuel ratio divided by the stoichiometric one, so lambda of 1 is exactly stoichiometric. Light-off is the temperature at which a catalyst becomes effective. Regeneration is burning off trapped soot.The fourth confuses two operations. Purge is releasing stored vapour from the carbon canister into the intake; urea injection is dosing, and belongs to selective catalytic reduction on a diesel.

Q: Consider the following pairs of engine type and its characteristic emission problem: Spark ignition - Carbon monoxide and hydrocarbons when rich Compression ignition - Particulate from locally rich zones Compression ignition - Nitrogen oxides from lean high-temperature combustion Spark ignition - Sulphate particulate from fuel sulphur How many of the pairs given above are correctly matched?

Correct answer: Only threeThe first three are right and reflect how each engine burns. A spark ignition engine running rich emits carbon monoxide and hydrocarbons; a diesel makes particulate in locally rich zones within a globally lean charge, and nitrogen oxides from the high temperatures of that lean combustion.The fourth misassigns sulphate particulate, which is a diesel problem - diesel fuel historically carried far more sulphur, and a diesel's particulate is measured by weight where sulphate matters.

Q: Three of the following treat exhaust emissions. Which treats evaporative emissions? Carbon canister Three-way catalyst Particulate filter Oxidation catalyst

Correct answer: Carbon canisterThe canister holds fuel vapour that escapes from the tank and fuel system while the vehicle is parked - hydrocarbons that never enter the engine and so never reach the exhaust.The other three are exhaust devices: the three-way catalyst treats all three regulated gases on a petrol engine, an oxidation catalyst treats carbon monoxide and hydrocarbons, and a particulate filter traps soot. Evaporative and exhaust emissions are separate problems needing separate hardware.

Q: Three of the following reduce nitrogen oxides. Which does not? Oxidation catalyst Exhaust gas recirculation Selective catalytic reduction The reduction function of a three-way catalyst

Correct answer: Oxidation catalystAn oxidation catalyst adds oxygen to carbon monoxide and hydrocarbons, converting them to carbon dioxide and water. Oxidation is the opposite of what nitrogen oxides need.The other three do reduce them: exhaust gas recirculation by lowering peak flame temperature so fewer form, selective catalytic reduction by using ammonia from urea to convert them to nitrogen, and the reduction function of a three-way catalyst by the same chemistry within its narrow window.

Q: Three of the following are needed for a three-way catalyst to work. Which is not? A high sulphur fuel Unleaded fuel Closed loop fuelling control A lambda sensor

Correct answer: A high sulphur fuelSulphur is a poison, not a requirement. It adsorbs onto the precious metal sites and suppresses activity, which is why sulphur limits had to fall before modern aftertreatment could work.The other three are genuinely necessary: unleaded fuel, because lead destroys the catalyst irreversibly; a lambda sensor to measure the exhaust oxygen; and closed loop control to hold the mixture within the narrow window where oxidation and reduction can proceed together.

51.

Arrange the events of a cold start in order:

1. The engine starts on a rich mixture for stability

2. Untreated exhaust passes through a cold catalyst

3. The catalyst reaches light-off temperature

4. Conversion efficiency rises above ninety per cent

Select the correct sequence.

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

Answer: C

Correct answer: 1, 2, 3, 4

The sequence explains why cold start emissions are so high. The engine starts rich, because a cold intake condenses fuel and a lean mixture will not run smoothly.

That rich exhaust passes through a catalyst still at ambient temperature, which converts almost nothing. Only when the exhaust has warmed the substrate to light-off, around 250 to 300 degrees, does conversion begin, and efficiency then rises above 90 per cent. The worst exhaust meets the least effective catalyst.

Discuss in Forum

52.

Consider the following pairs of device and the pollutant it addresses:

Three-way catalyst - Carbon monoxide, hydrocarbons and nitrogen oxides

Diesel particulate filter - Soot

Carbon canister - Evaporative hydrocarbons

Exhaust gas recirculation - Carbon monoxide

How many of the pairs given above are correctly matched?

A.Only one
B.Only two
C.All four
D.Only three

Answer: D

Correct answer: Only three

The first three are correctly matched: the three-way catalyst treats all three regulated gases, the particulate filter traps soot, and the carbon canister holds evaporative hydrocarbons.

The fourth is wrong. Exhaust gas recirculation lowers peak flame temperature and so reduces nitrogen oxides; it does nothing for carbon monoxide, and by degrading combustion it can slightly increase it. Each device addresses the pollutant its physics acts on.

Discuss in Forum

53.

Consider the following pairs of mixture condition and its emission effect:

Rich of stoichiometric - High carbon monoxide and hydrocarbons

Slightly lean - Peak nitrogen oxides

Deeply lean - Lower nitrogen oxides but poor catalyst reduction

Exactly stoichiometric - Peak nitrogen oxides

How many of the pairs given above are correctly matched?

A.Only three
B.Only one
C.Only two
D.All four

Answer: A

Correct answer: Only three

The first three are right. Rich running gives incomplete combustion and therefore high carbon monoxide and hydrocarbons; slightly lean gives peak nitrogen oxides, having both flame temperature and oxygen; deeply lean lowers them but takes the exhaust outside the window in which a three-way catalyst can reduce.

The fourth is wrong and contradicts the second. The nitrogen oxide peak lies slightly lean of stoichiometric, not at it - which is what makes precise control around stoichiometric a compromise rather than an optimum for any single pollutant.

Discuss in Forum

54.

Consider the following pairs of fuel change and its purpose:

Removal of lead - Allowing catalytic converters to survive

Reduction of sulphur - Allowing filters and reduction catalysts to work

Control of volatility - Limiting evaporative emissions

Raising aromatic content - Reducing particulate

How many of the pairs given above are correctly matched?

A.All four
B.Only three
C.Only one
D.Only two

Answer: B

Correct answer: Only three

The first three pair each fuel change with what it enabled: lead removal for catalytic converters, sulphur reduction for filters and reduction catalysts, and volatility control for evaporative emissions.

The fourth has the sign wrong. Aromatics are limited rather than raised, because they promote soot formation and benzene emission. Every genuine fuel change in the list removes something; raising a constituent that makes particulate would be a step backwards.

Discuss in Forum

55.

Consider the following pairs of term and its meaning:

Lambda - Actual air-fuel ratio divided by stoichiometric

Light-off - The temperature at which a catalyst becomes effective

Regeneration - Burning off trapped soot in a particulate filter

Purge - Injecting urea into the exhaust

How many of the pairs given above are correctly matched?

A.Only two
B.All four
C.Only three
D.Only one

Answer: C

Correct answer: Only three

The first three define their terms correctly. Lambda is the actual air-fuel ratio divided by the stoichiometric one, so lambda of 1 is exactly stoichiometric. Light-off is the temperature at which a catalyst becomes effective. Regeneration is burning off trapped soot.

The fourth confuses two operations. Purge is releasing stored vapour from the carbon canister into the intake; urea injection is dosing, and belongs to selective catalytic reduction on a diesel.

Discuss in Forum

56.

Consider the following pairs of engine type and its characteristic emission problem:

Spark ignition - Carbon monoxide and hydrocarbons when rich

Compression ignition - Particulate from locally rich zones

Compression ignition - Nitrogen oxides from lean high-temperature combustion

Spark ignition - Sulphate particulate from fuel sulphur

How many of the pairs given above are correctly matched?

A.Only one
B.Only two
C.All four
D.Only three

Answer: D

Correct answer: Only three

The first three are right and reflect how each engine burns. A spark ignition engine running rich emits carbon monoxide and hydrocarbons; a diesel makes particulate in locally rich zones within a globally lean charge, and nitrogen oxides from the high temperatures of that lean combustion.

The fourth misassigns sulphate particulate, which is a diesel problem - diesel fuel historically carried far more sulphur, and a diesel's particulate is measured by weight where sulphate matters.

Discuss in Forum

57.

Three of the following treat exhaust emissions. Which treats evaporative emissions?

Carbon canister

Three-way catalyst

Particulate filter

Oxidation catalyst

A.Carbon canister
B.Three-way catalyst
C.Particulate filter
D.Oxidation catalyst

Answer: A

Correct answer: Carbon canister

The canister holds fuel vapour that escapes from the tank and fuel system while the vehicle is parked - hydrocarbons that never enter the engine and so never reach the exhaust.

The other three are exhaust devices: the three-way catalyst treats all three regulated gases on a petrol engine, an oxidation catalyst treats carbon monoxide and hydrocarbons, and a particulate filter traps soot. Evaporative and exhaust emissions are separate problems needing separate hardware.

Discuss in Forum

58.

Three of the following reduce nitrogen oxides. Which does not?

Oxidation catalyst

Exhaust gas recirculation

Selective catalytic reduction

The reduction function of a three-way catalyst

A.The reduction function of a three-way catalyst
B.Oxidation catalyst
C.Exhaust gas recirculation
D.Selective catalytic reduction

Answer: B

Correct answer: Oxidation catalyst

An oxidation catalyst adds oxygen to carbon monoxide and hydrocarbons, converting them to carbon dioxide and water. Oxidation is the opposite of what nitrogen oxides need.

The other three do reduce them: exhaust gas recirculation by lowering peak flame temperature so fewer form, selective catalytic reduction by using ammonia from urea to convert them to nitrogen, and the reduction function of a three-way catalyst by the same chemistry within its narrow window.

Discuss in Forum

59.

Three of the following are needed for a three-way catalyst to work. Which is not?

A high sulphur fuel

Unleaded fuel

Closed loop fuelling control

A lambda sensor

A.Closed loop fuelling control
B.A lambda sensor
C.A high sulphur fuel
D.Unleaded fuel

Answer: C

Correct answer: A high sulphur fuel

Sulphur is a poison, not a requirement. It adsorbs onto the precious metal sites and suppresses activity, which is why sulphur limits had to fall before modern aftertreatment could work.

The other three are genuinely necessary: unleaded fuel, because lead destroys the catalyst irreversibly; a lambda sensor to measure the exhaust oxygen; and closed loop control to hold the mixture within the narrow window where oxidation and reduction can proceed together.

Discuss in Forum

60.

Three of the following raise cold start emissions. Which reduces them?

Close-coupling the converter to the manifold

A long run of exhaust pipe before the converter

Very short journeys

A large thermal mass in the converter

A.A long run of exhaust pipe before the converter
B.Very short journeys
C.A large thermal mass in the converter
D.Close-coupling the converter to the manifold

Answer: D

Correct answer: Close-coupling the converter to the manifold

Mounting the converter close to the exhaust manifold puts it where the gas is hottest, so it reaches light-off sooner and the untreated period is shortened.

The other three all lengthen that period or repeat it: a long pipe run lets the gas cool before it arrives, a large thermal mass takes longer to warm through, and very short journeys mean the catalyst may never reach light-off at all. Every cold start measure aims at the same ninety seconds.

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