Automobile Emission Control Questions and Answers

Answer: A

Correct answer: Both Statement I and Statement II are correct

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.

Filters and reduction catalysts therefore could not be introduced until fuel sulphur had been reduced by a factor of tens, which is why the refinery investment and the emission standards were sequenced together. Cleaning the fuel was a precondition rather than a parallel improvement.

Answer: B

Correct answer: Statement I is incorrect but Statement II is correct

The second statement is true and it defeats the first. New vehicle standards govern the emission of a vehicle when new and correctly maintained, and nothing more.

Control equipment degrades with age and mileage, and some is deliberately defeated - removed filters, disabled recirculation valves. A small proportion of poorly maintained vehicles accounts for a disproportionate share of fleet emissions, which is why inspection and maintenance programmes are run alongside the standards rather than instead of them.

Answer: C

The loop is a switching controller rather than a proportional one, which is why the mixture oscillates about stoichiometric rather than settling on it. That small oscillation is actually useful, since it keeps oxygen storage in the catalyst cycling.

Answer: D

The oxidation catalyst also raises the temperature and the nitrogen dioxide fraction that helps the filter regenerate passively. Urea must be injected and mixed before the reduction catalyst if the ammonia is to be distributed evenly across it.

Answer: A

Correct answer: 1, 2, 3, 4

The chain is causal and each step follows from the one before. Short cold journeys mean the exhaust never reaches the temperature at which trapped soot burns off.

Regeneration therefore does not occur, soot accumulates and back pressure rises. Eventually the engine management derates the engine to protect it, and the filter must be cleaned or replaced. Note the order of the first two steps: the usage pattern is the cause and the low temperature its consequence, not the reverse.

Answer: B

Correct answer: 1, 2, 3, 4

The order runs from the simplest measure to the most demanding. Positive crankcase ventilation came first in the early 1960s, routing blow-by back to the intake - cheap and requiring nothing of the fuel.

Evaporative canisters and exhaust gas recirculation followed. Catalytic converters came next and required unleaded fuel to survive. Diesel particulate filters and urea reduction came last, and required sulphur to be removed. Each step needed a fuel change the previous one did not.

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.

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.

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.

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.