Automobile Emission Control Questions and Answers

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.

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.

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.

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.

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.

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.

Answer: C

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

Each pollutant has its own formation mechanism. Carbon monoxide is incomplete oxidation where oxygen is short; unburnt hydrocarbons are fuel that escaped the flame in crevices and in the quench layer at cool walls.

Nitrogen oxides form from atmospheric nitrogen and oxygen at high flame temperature. Particulate forms by pyrolysis in the fuel-rich zones of a diffusion flame - which is why it is characteristically a diesel problem, the charge being locally rich even when globally lean.

Answer: D

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

Each change removed an obstacle to a specific technology. Lead had to go before catalytic converters, since it destroys the precious metal sites permanently.

Sulphur had to fall before particulate filters and reduction catalysts, which it poisons and whose measured output it inflates as sulphate. Volatility limits made evaporative control effective, and aromatics limits reduced benzene and soot. Every device was waiting on a refinery investment.

Answer: A

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

The four terms belong to four different parts of the system. Lambda is the mixture measure, the actual air-fuel ratio over the stoichiometric one.

Light-off is a catalyst property, the temperature at which it becomes substantially active. Regeneration is a filter operation, burning off accumulated soot. Ammonia slip is a reduction-system fault, unreacted reductant escaping the tailpipe. Mixture, catalyst, filter and reductant - one term each.

Answer: B

Correct answer: Carbon dioxide

Carbon dioxide is a product of the catalyst's work, not a target of it. Oxidising carbon monoxide and hydrocarbons produces carbon dioxide and water, so the converter increases it.

The other three are exactly what the device is named for: the three ways are oxidation of carbon monoxide, oxidation of hydrocarbons and reduction of nitrogen oxides. Reducing carbon dioxide is a matter of burning less fuel, which is an engine efficiency question rather than an aftertreatment one.