Main Diesel Engines

How a genset engine runs

A generator engine holds one speed and lets torque follow the electrical load. An electronic governor meters fuel to keep frequency constant. Running sets share load in droop or isochronous mode under the power management system. Turbocharging and charge-air cooling set the power density, so the turbocharger and aftercooler decide much of an engine's condition. Most offshore engines burn marine gas oil. Some newer units are dual-fuel.

High-speed or medium-speed

High-speed engines such as the Caterpillar 3500 series are compact and quick to exchange, with shorter overhaul intervals. Medium-speed engines from makers such as Wärtsilä, Everllence (MAN Energy Solutions until 2025) and Bergen Engines run longer between overhauls and suit high continuous load. They are heavy, and an engine change usually means opening a hatch or deck.

Key specifications

Standards and what they require of a used engine

Under MARPOL Annex VI and the NOx Technical Code 2008, every engine above 130 kW subject to Regulation 13 carries an Engine International Air Pollution Prevention (EIAPP) certificate and a NOx technical file. The file lists NOx-critical components and settings, such as injection timing, injectors, turbocharger and charge-air cooler. Changes to any of them must be recorded, or the certificate no longer describes the engine. A non-identical replacement engine meets the tier in force when fitted. Where Tier III is not possible for a replacement, Regulation 13.2.2 allows Tier II under IMO guidelines, at the Administration's discretion.

Class rules require crankcase explosion relief valves on larger engines. IACS UR M10 adds oil mist detection or bearing temperature monitoring for engines above 2,250 kW or with cylinder bores over 300 mm. The MODU Code sets limits on where engine air intakes and exhaust outlets may sit relative to hazardous areas.

Failure modes and inspection

• Cylinder liners and rings. Look for polishing, scuffing and cavitation erosion on the coolant side of wet liners. Borescope through the injector bore.
• Crankshaft and main bearings. Take web deflection readings against OEM limits. Inspect bearing shells, and run magnetic particle testing on fillets after any bearing failure.
• Turbocharger. Check rotor axial and radial play, compressor fouling and nozzle ring erosion.
• Cylinder heads. Check for cracks between valve seats and for valve recession.
• Oil analysis. Rising iron and chromium point to liner and ring wear, silicon to dirt ingress, and sodium or potassium to coolant leaks.
• Load test. Run on a load bank or the rig board. Record firing pressures, exhaust temperature spread between cylinders, blow-by and lube oil consumption.

Documentation that makes a used engine credible

• EIAPP certificate, NOx technical file and record book of engine parameters
• Class product certificate from manufacture
• Engine log with total hours and hours since top-end and major overhaul
• Overhaul reports listing parts replaced and measurements taken
• Oil analysis history and the last crankshaft deflection readings
• Preservation record if stacked, including barring-over intervals

Integration and compatibility

Match the flywheel housing and coupling to your alternator. Check that the governor and engine controller can take your power management system's speed and load signals. Confirm cooling water flow and temperature, fuel supply pressure and exhaust back-pressure. A different make or model on an existing alternator needs a new torsional vibration calculation approved by class.

Overhaul and recertification

A major overhaul replaces liners, pistons, rings, bearings and usually the turbocharger cartridge, and reconditions heads, injection equipment and the crankshaft to OEM limits. An OEM exchange engine or a dealer overhaul with a measurement report carries more weight than a lower-hours engine with no history. Matching alternators are under Generators, and the set that backs them up is under Emergency power systems.