What is the difference between a primary and secondary fuel filter on a marine diesel?

A. Primary (Racor/CAV type): large housing with a water separator bowl and coarse filter — removes water and large particles, inspected regularly. Secondary (fine filter): smaller, close to the injection pump, removes very fine particles — protects the high-pressure injection system from abrasive damage

B. Only the secondary filter needs regular replacement — the primary is self-cleaning

C. The primary filter is inside the fuel tank; the secondary is between tank and engine

D. Primary and secondary filters are identical — either can be replaced independently

A. Compression ignition: diesel fuel is ignited by the heat of highly compressed air (compression ratio ~22:1) — no spark plugs are used. Fuel is injected into the compressed air at the moment of ignition

B. Diesel engines work at lower compression ratios than petrol engines for safety

C. Diesel engines use spark plugs but fire in a different sequence to petrol engines

D. Diesel engines use carburettors to mix fuel and air before compression

A. Compression, ignition, induction, exhaust — the compression happens before air enters

B. Induction (air in): piston down, air drawn into cylinder. Compression: piston up, air compressed to high temperature. Power (ignition): fuel injected, combustion drives piston down. Exhaust: piston up, exhaust gases expelled

C. Ignition, compression, induction, exhaust

D. Induction, power, compression, exhaust