Automobile Emission Control Questions and Answers

Answer: C

A diesel runs lean, so there is ample oxygen for oxidation but no possibility of reducing nitrogen oxides on the same bed. That is precisely why a diesel needs separate devices for the two duties while a petrol engine does not.

Answer: D

Correct answer: Fuel vapour escaping from the tank and fuel system

Evaporative emissions are hydrocarbons that never pass through the engine at all - petrol vapour escaping from the tank, the fuel lines and the injectors, driven off by ambient warmth and by the day's temperature cycle.

They are controlled by a carbon canister that adsorbs the vapour while the vehicle is parked and releases it to be burnt when the engine runs. The exhaust, crankcase and catalyst are all sources of emissions, but of combustion products rather than raw fuel vapour.

Answer: A

Vapour is held on activated carbon while the engine is off and drawn into the intake once it is running warm. The purge must be scheduled carefully, since an uncontrolled purge upsets the fuelling and drives the mixture rich.

Answer: B

Gases forced past the piston rings carry unburnt fuel and oil vapour, and venting them was once a substantial source of hydrocarbon emission. Routing them back to be burnt was among the earliest and cheapest control measures adopted.

Answer: C

Lead deposits coat the precious metal sites and destroy the catalyst irreversibly, so unleaded fuel was a precondition for the whole technology. Its own toxicity, particularly to children, made the case unanswerable in any event.

Answer: D

Correct answer: Poisons catalysts and forms sulphate particulate

Sulphur attacks aftertreatment twice over. It adsorbs onto the precious metal sites and suppresses catalytic activity, and it is oxidised to sulphate which condenses and is weighed as particulate.

Both effects made low sulphur fuel a precondition rather than a refinement: particulate filters and reduction catalysts could not be introduced until the fuel supply was cleaned up, which is why sulphur limits and emission standards advanced in step. It does not affect atomisation or cetane appreciably.

Answer: A

It is meant to represent typical use so that vehicles can be compared on a common basis. How well the cycle reflects real driving has been a long-running controversy, and real driving emissions testing was introduced to address it.

Answer: B

Until the bed reaches roughly three hundred degrees the conversion efficiency is very low, and a large share of a short trip's total emission occurs in those first minutes. Close-coupled converters and electrical heating both attack this directly.

Answer: C

New vehicle standards do nothing about a fleet whose control equipment has degraded or been tampered with. A small proportion of badly maintained vehicles typically accounts for a large share of a fleet's total emission.

Answer: D

Excess air dilutes and cools the charge, and the emission falls once the mixture is lean enough. The difficulty is that a three-way catalyst cannot reduce nitrogen oxides in the resulting oxygen-rich exhaust, so a lean NOx trap or reduction catalyst is needed.