Particulate Filters Questions and Answers

Answer: A

Plugging alternate ends forces the gas through the porous walls, which trap the soot. The last option describes exactly that construction, which makes it a correct and more detailed version. Flow through filters exist but trap far less. The order in which the effects act is what decides the outcome, so it is worth establishing first. Reading the definition literally, rather than recalling a summary, avoids the usual confusion.

Answer: B

Wall flow filters remove well over ninety per cent of the particulates. The last option adds the number efficiency, which makes it a correct and fuller version of the same answer. Checking which component actually carries the load settles most questions of this kind at once. Most errors here come from carrying across a result from a neighbouring case where it does not hold. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: C

Cordierite is cheaper and silicon carbide tolerates higher temperatures. The last option explains exactly that choice, which makes it a correct and more instructive version. Metal foam filters exist but are uncommon. Tracing the requirement back to the physical constraint that produces it makes the answer follow. Naming what changes and what stays the same is the reliable route through questions of this shape. Checking the units of each quantity catches a wrong formula before the arithmetic begins.

Answer: D

Silicon carbide survives the temperature excursions that destroy cordierite. The last option explains exactly that advantage, which makes it a correct and more instructive version. It is considerably more expensive. The shared behaviour explains why these belong together and the differences explain why both exist. Working the distinction through on a single concrete case fixes it more firmly than any rule of thumb. The quantity that varies and the quantity that does not are worth naming before any substitution is attempted.

Answer: A

The soot is burnt rather than removed, and leaves as carbon dioxide. The last option explains exactly that, which makes it a correct and more instructive version of the same answer. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision. A symptom that appears under one condition and not another is what narrows the diagnosis quickly. Most errors here come from carrying across a result from a neighbouring case where it does not hold.

Answer: B

Oxygen burns soot only around six hundred degrees, which ordinary driving rarely reaches. The last option explains exactly that difficulty, which makes it a correct and more instructive version. Nitrogen dioxide works far lower. Reading the definition literally, rather than recalling a summary, avoids the usual confusion. The order in which the effects act is what decides the outcome, so it is worth establishing first. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: C

Nitrogen dioxide oxidises soot from around two hundred and fifty degrees. The last option explains exactly where it comes from, which makes it a correct and more detailed version. It underpins passive regeneration. Most errors here come from carrying across a result from a neighbouring case where it does not hold. Checking which component actually carries the load settles most questions of this kind at once. Framing the question as which quantity the change acts upon makes the answer follow without calculation.

Answer: D

Passive regeneration removes soot continuously without any special measures. The last option explains exactly that, which makes it a correct and more instructive version. Active regeneration is the fallback. Naming what changes and what stays the same is the reliable route through questions of this shape. Tracing the requirement back to the physical constraint that produces it makes the answer follow. The quantity that varies and the quantity that does not are worth naming before any substitution is attempted.

Answer: A

Urban driving keeps the exhaust too cool for passive regeneration. The last option explains exactly that, which makes it a correct and more instructive version. Motorway driving is what clears a filter. Working the distinction through on a single concrete case fixes it more firmly than any rule of thumb. The shared behaviour explains why these belong together and the differences explain why both exist. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: B

Fuel injected late passes to the catalyst and burns there. The last option describes exactly that mechanism, which makes it a correct and more detailed version of the same answer. A symptom that appears under one condition and not another is what narrows the diagnosis quickly. Reading the definition literally, rather than recalling a summary, avoids the usual confusion. The quantity that varies and the quantity that does not are worth naming before any substitution is attempted.