Question 1

What is the correct annual engine service schedule for a typical marine auxiliary diesel doing 100-150 hours per season?

Accepted Answer

Every 100-150h or annually: engine oil and filter; primary fuel filter element; secondary fuel filter; raw water impeller; check coolant antifreeze concentration; check V-belt condition and tension; check all hose clamps; clean raw water strainer; check zinc anodes; test battery condition; check engine mount condition; check alignment; log all work with dates and hours Marine auxiliary diesel service intervals are shorter than car engine equivalents because: 1) The engine sits in a damp, salty environment year-round; 2) Marine engines often run at high load (pushing a displacement hull) for extended periods; 3) Maintenance access is poor compared to a car (no drive-through oil change); 4) Failure consequences at sea are severe. A full service typically costs £200-400 professionally, or £80-120 DIY in parts. An engine that fails mid-passage can cost £500-2000 in RNLI/commercial salvage, not counting repair costs. The ROI on preventive service is significant.

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.