Yanmar 6N18AL Specifications
| Engine Model: Yanmar 6N18AL |
| Engine Type: 4-stroke inline 6-cylinder turbocharged water-cooled diesel |
| Total Displacement: 2,609 cu.in (42.75 L) |
| Rated Engine Power: 610-897 Hp (455-669 kW) at 720-900 rpm |
| Fuel System Type: Direct injection |
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The Yanmar 6N18AL is a medium-speed, 4-stroke
marine diesel engine designed primarily for auxiliary power generation
on commercial vessels. Developed by Yanmar Diesel Engine Co. in the late
1990s, this engine belongs to the N18 series and is engineered for
robust construction, high reliability, and the capability to operate on
both Marine Diesel Oil (MDO) and Heavy Fuel Oil (HFO) up to 700 cSt
viscosity.
The Yanmar 6N18AL generates electrical power for shipboard systems,
including lighting, navigation equipment, refrigeration, and cargo
handling, serving a critical role in vessel safety and operational
efficiency. The engine is commonly paired with generator sets producing
500-600 kW output at 900 rpm or 660-750 kVA at 900 rpm.
The Yanmar 6N18AL represents a dedicated auxiliary generator engine
architecture developed from Yanmar's extensive experience in
medium-speed diesel engines. Its inline 6-cylinder configuration with a
180 mm bore and 280 mm stroke provides the smooth, vibration-damped
operation required for continuous generator service. The cast iron
cylinder block and head are constructed for heavy fuel combustion,
addressing the specific challenges of HFO operation including vanadium
and sodium corrosion.
The direct injection combustion system achieves efficient fuel
atomization and combustion, while the turbocharged and intercooled
aspiration provides consistent air density at all generator operating
speeds. The engine is classified for 720 rpm (50 Hz) or 900 rpm (60 Hz)
operation, matching standard generator frequencies used worldwide. The
air motor starting system is standard for this engine class, providing
reliable cold starts in marine environments. The engine meets IMO
emission standards through combustion optimization and fuel system
design.
Engine Type: Vertical inline 6-cylinder, 4-cycle, water-cooled,
turbocharged diesel
Family: Yanmar N18 Series
Displacement: 42.75 liters (2,609 cu.in)
Bore x Stroke: 180.0 mm x 280.0 mm (7.09 in x 11.02 in)
Compression Ratio: Estimated 13:1-14:1 (medium-speed diesel range)
Firing Order: 1-5-3-6-2-4
Aspiration: Turbocharged with intercooler (air-to-seawater)
Maximum Output: 455-669 kW (610-897 hp), model dependent
Generator Output: 500 kW (625 kVA) at 900 rpm for 60 Hz operation
Rated Speed (50 Hz): 720-750 rpm
Rated Speed (60 Hz): 900 rpm
Idle Speed: 400-500 rpm (estimated)
Rotation: Counter-clockwise (CCW) when viewed from flywheel end
Valvetrain: 4 valves per cylinder (24 total) with exhaust valve rotators
The cylinder block is constructed from cast iron with a deep-skirt
design, providing the structural rigidity required for sustained
medium-speed diesel operation. The block utilizes replaceable wet-type
cylinder liners, each sealed with rubber O-rings, permitting in-chassis
overhaul. This design is essential for HFO operation, as cylinder liner
wear occurs at higher rates than with distillate fuels. Six main
bearings support the crankshaft.
The water jacket surrounds each liner completely, with cast-in coolant
passages optimized for uniform thermal distribution across all six
cylinders. The block incorporates mounting positions for the
turbocharger, intercooler, and generator frame coupling. The camshaft is
located on the side of the block, driven by a gear train from the
crankshaft.
The cylinder head is manufactured from cast iron with recessed valve
seats hardened for HFO combustion residue resistance. The engine employs
a 4-valve-per-cylinder configuration (24 valves total), with two intake
valves and two exhaust valves per cylinder. Exhaust valves are equipped
with rotators that incrementally rotate the valve during operation,
preventing localized hot spots and ensuring even wear when burning heavy
fuels.
Valve actuation is achieved via overhead camshaft (OHC) or mechanical
pushrods, depending on the specific variant. The direct injection
combustion chamber is machined directly into the piston crown.
The engine operates on a mechanical direct injection fuel system
designed for heavy fuel oil compatibility up to 700 cSt at 50°C. An
in-line injection pump provides individual elements for each cylinder,
delivering fuel at high pressure (600-1,000 bar).
A fuel supply system includes viscosity control, fuel heating, and a
centrifugal purifier system to remove contaminants and water from HFO.
Injection timing is adjustable via shims. The governor system is an
isodromic speed-regulating governor, model Yanmar NZ61, which maintains
stable generator frequency under varying electrical loads.
The lubrication system is a forced lubrication configuration using a
gear-type oil pump driven by the crankshaft. The system includes a
bypass strainer and a centrifugal purifier for continuous cleaning of
lubricating oil. An oil cooler of the seawater-cooled type maintains oil
temperature within operational limits.
Oil galleries within the block and cylinder head supply pressurized oil
to the main bearings, connecting rod bearings, camshaft bearings, and
turbocharger bearing housing. The system uses a wet sump or dry sump
depending on installation configuration. Total oil capacity is
engine-specific, ranging from 120-200 liters for this engine class.
The cooling system is a dual-circuit configuration: high-temperature
fresh water cooling the cylinder jackets and cylinder head, and
low-temperature seawater cooling the lubricating oil cooler and charge
air intercooler. A belt-driven centrifugal fresh water pump circulates
coolant through the engine.
A seawater pump supplies cooling water directly from the sea chest,
discharging overboard after passing through the coolers. A heat
exchanger transfers heat from the fresh water circuit to the seawater
circuit. A wax-type thermostat regulates fresh water flow.
Starting System: Compressed air motor starting, standard for
medium-speed marine diesels.
Timing System: Gear-driven camshaft from crankshaft. Gear train
eliminates belt/chain replacement.
Turbocharger System: Fixed geometry turbocharger manufactured by IHI or
similar , with an air-to-seawater intercooler reducing intake
temperatures.
Governor System: Yanmar NZ61 isodromic speed-regulating governor with
pilot valve ports and isodromic needle for frequency stability.
Emission Compliance: IMO Tier II and Tier III standards depending on
variant and tuning.
Dry Weight (Bobtail): 4,200 kg (9,260 lb)
Overall Length: 3,200-3,600 mm (126-142 in)
Overall Width: 1,600 mm (63 in)
Overall Height: 2,600 mm (102 in)
Bore Pitch: 230 mm (9.06 in)
Engine Oil Capacity: 150-220 liters (158-232 qt) depending on sump
design
Engine Oil Specification: SAE 30 or 40 meeting API CF or higher for HFO
service
Coolant Capacity: 100-150 liters (26-40 gal) fresh water circuit
Intake Valve Clearance (Cold): 0.35 mm (0.014 in)
Exhaust Valve Clearance (Cold): 0.45 mm (0.018 in)
Valve Clearance Inspection Interval: Every 4,000 operating hours
Injector Opening Pressure: 250-300 bar (3,625-4,350 psi)
Fuel Injection Timing: 8°-12° before top dead center (BTDC)
Oil Change Interval: 4,000-8,000 operating hours, oil analysis dependent
Cylinder Liner Re-boring Interval: 24,000-36,000 operating hours
Cylinder Head Bolts, Stage 1: 200 Nm (148 lb-ft)
Cylinder Head Bolts, Stage 2: 400 Nm (295 lb-ft)
Cylinder Head Bolts, Stage 3: 600 Nm (443 lb-ft)
Main Bearing Cap Bolts, Stage 1: 500 Nm (369 lb-ft)
Main Bearing Cap Bolts, Stage 2: 900 Nm (664 lb-ft)
Connecting Rod Cap Bolts: 300 Nm (221 lb-ft) + 90° angle
Flywheel Bolts: 250 Nm (184 lb-ft) + 90° angle
Crankshaft Pulley Bolt: 1,200 Nm (885 lb-ft)
Turbocharger Mounting Nuts: 80 Nm (59 lb-ft)
Commercial Vessel Generator Sets: The 6N18AL provides shipboard
electrical power for large tankers, container ships, bulk carriers, and
passenger vessels.
Offshore Support Vessels: Platform supply vessels, anchor handling tugs,
and crew boats utilize the engine for auxiliary power.
Workboats and Tugs: Harbor tugs, push boats, and dredgers rely on the
6N18AL for reliable auxiliary generation.
Fishing Vessels: Large factory trawlers and long-liners use the engine
for refrigeration and processing power.
Ferries and Ro-Ro Vessels: Passenger roll-on/roll-off ferries use the
6N18AL for hotel load and cargo handling systems.
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