Question 1

The engine has stopped 5nm from the nearest harbour on a falling tide. Fuel is present and the filters are clear. What is the troubleshooting sequence?

Accepted Answer

Anchor immediately if in tide or near hazards. Check: 1) Raw water seacock — if overheated and shut down automatically; 2) Fuel stop solenoid — some engines have a fuel cut solenoid that fails open; 3) Air in fuel — re-bleed if any filter was changed; 4) Alarm condition (oil pressure, temperature) — engine may have shut down via alarm; 5) Battery voltage — engine management may have reset. Call Coastguard if unable to restart within 20 minutes Engine stopped at sea — most resolve within 20 minutes if approach is systematic: the anchor buys time. A fuel stop solenoid that fails de-energised cuts fuel supply — the solenoid can be held open manually (or bridged temporarily) as an emergency measure. Air in the fuel system from a filter change is the most common cause of engine stopping shortly after a maintenance task. An engine management ECU alarm shutdown (oil pressure or temperature sensor fault, not necessarily actual fault) is increasingly common on modern engines. Do not exhaust the battery cranking — keep reserve for VHF and distress.

Question 2

What is the fundamental operating principle of a diesel engine that distinguishes it from a petrol engine?

Accepted Answer

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 Diesel (compression ignition): air is compressed to ~22:1 ratio, reaching ~500-700°C. Diesel fuel (which ignites at ~250°C) is injected directly into this hot compressed air and spontaneously ignites. Petrol engines use ~8:1 compression and require a spark to ignite. The high compression ratio makes diesel engines more thermally efficient (~40% vs ~25% for petrol) and safer (diesel is much less volatile than petrol).

Question 3

Describe the four strokes of a diesel engine cycle in the correct order

Accepted Answer

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 The four-stroke diesel cycle (suck, squeeze, bang, blow): 1) Induction — intake valve open, piston moves down drawing in air only (no fuel). 2) Compression — both valves closed, piston moves up, air compressed to ~22:1. 3) Power — injector fires, combustion, piston driven down. 4) Exhaust — exhaust valve open, piston moves up expelling gases. Two complete crankshaft revolutions per power stroke per cylinder. Multiple cylinders provide smoother, overlapping power strokes.