Yanmar 6N21AL Specifications
| Engine Model: Yanmar 6N21AL |
| Engine Type: 4-stroke inline 6-cylinder turbocharged water-cooled diesel |
| Total Displacement: 3,678 cu.in (60.27 L) |
| Rated Engine Power: 1000-1368 Hp (745-1020 kW) at 900-1000 rpm |
| Fuel System Type: Direct injection |
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The Yanmar 6N21AL is a medium-speed, 4-stroke
vertical water-cooled diesel engine. Primarily utilized as an auxiliary
engine for marine generator sets, it is engineered for high reliability
and superior combustion performance. The 6N21AL belongs to the N21
series of Yanmar industrial diesel engines, designed for continuous duty
in marine auxiliary and prime power applications.
This engine is found on oceangoing vessels, offshore platforms, and
large yachts where reliable electrical power generation is critical. The
Yanmar 6N21AL incorporates direct injection combustion, exhaust gas
turbocharging with air cooling, and a two-line cooling system, all
packaged in a robust inline six-cylinder configuration. The engine
complies with IMO Tier II emission requirements, reflecting its
suitability for international maritime operation.
The Yanmar 6N21AL engine is recognized for its high power output in a
medium-speed configuration, fuel efficiency, and extended service
intervals suitable for continuous marine generator duty. The 6-cylinder
inline configuration provides inherent balance and reduced vibration
compared to V-configuration engines of comparable displacement. The
direct injection combustion system with an optimally shaped air intake
port improves air-fuel mixing, resulting in complete combustion and
reduced specific fuel consumption.
The exhaust gas turbocharger with air cooler increases volumetric
efficiency and power density while reducing exhaust temperatures. The
two-line cooling system separates the freshwater cylinder jacket circuit
from the seawater cooling circuit, preventing corrosion in the engine
block. The air motor starting system provides reliable cranking in
marine environments where electrical starting may be compromised. The
engine's dry weight of approximately 8,700 kg (19,180 lb) reflects its
heavy-duty construction for continuous commercial operation.
Engine Type: Vertical inline 6-cylinder, 4-stroke, water-cooled
turbocharged diesel.
Displacement: 60.27 liters (3,678 cu.in).
Bore: 210.0 mm (8.27 in).
Stroke: 290.0 mm (11.42 in).
Compression Ratio: 15.6:1 to 15.8:1, varying with combustion chamber
design and injection timing.
Combustion System: Direct injection.
Aspiration: Turbocharged with air cooler (charge air cooler /
intercooler).
Firing Order: 1-4-2-6-3-5-1.
Rated Speed (Generator applications): 900 rpm or 1,000 rpm, depending on
generator frequency (50 Hz or 60 Hz) and pole count.
Rotation: Counter-clockwise or clockwise as specified for generator
coupling.
Power (6N21AL-DV): 745 kW (1000 hp) at rated speed.
Power (6N21AL-UV): 800 kW (1,073 hp).
Power (6N21AL-SW): 880 kW (1,180 hp).
Power (6N21AL-EW): 970 kW (1,301 hp).
Power (6N21AL-GW): 1,020 kW (1,368 hp).
Peak Torque: 8,000-9,000 Nm (5,900-6,640 lb-ft) at 700-800 rpm.
Low Idle Speed: 350-400 rpm for generator starting sequences.
Governor Type: Electronic or mechanical isochronous governor for precise
frequency control.
The cylinder block is constructed from high-strength cast iron with a
closed-deck design. The block features a deep-skirt configuration
extending below the crankshaft centerline, with reinforced bulkheads at
each of the seven main bearing locations. Individual cylinder liner
bores are machined into the block to accept replaceable wet cylinder
liners. The wet liner design allows coolant to circulate directly around
each cylinder bore, providing superior heat transfer from the combustion
chamber to the cooling system.
Liners are sealed at the bottom with rubber O-rings and at the top with
a compressed copper or steel gasket. The block incorporates integrated
oil galleries supplying the main bearings, connecting rod bearings,
camshaft bearings, and piston cooling jets. Access covers on the block
sides provide inspection access to the connecting rod bolts and
bearings. The bedplate design reinforces the lower block structure for
crankshaft stability.
The cylinder head is manufactured from cast iron and is supplied as
individual heads per cylinder or as a multi-cylinder casting depending
on the variant. Each cylinder head houses the overhead valve (OHV)
arrangement with two valves per cylinder (intake and exhaust). Intake
valves measure 80.0 mm (3.15 in) in diameter, while exhaust valves
measure 70.0 mm (2.76 in). The valvetrain consists of a single camshaft
located in the cylinder block, operating the valves through hardened
pushrods and forged steel rocker arms.
Valve seat inserts are replaceable and manufactured from heat-resistant
alloy material. Valve clearance is adjusted by a screw and locknut on
each rocker arm, requiring periodic inspection. The cylinder head
incorporates the direct injection combustion chamber with centrally
positioned injector nozzles. The cylinder head is secured by four or six
head bolts per cylinder, requiring a multi-step torque sequence with
hydraulic tensioners for final tightening.
The fuel system employs a mechanical direct injection architecture using
an in-line injection pump (Bosch or Yanmar-built). The injection pump is
flange-mounted to the timing gear housing and driven by the engine's
gear train. The in-line pump design provides individual plungers and
barrels for each cylinder, delivering precise fuel metering across the
engine speed range. An electronic governor or mechanical governor,
depending on the variant, maintains engine speed under varying loads for
precise generator frequency control.
High-pressure injection lines deliver fuel to multi-hole injectors
mounted in each cylinder head. Injector opening pressure is factory set
between 250 and 300 bar (3,625-4,350 psi). A fuel feed pump, driven by
the camshaft, draws fuel from the day tank and supplies it through
primary and secondary fuel filters. A fuel cooler may be fitted for
operation in high ambient temperature conditions.
The lubrication system is a forced-feed, dry-sump or wet-sump type
utilizing a gear-type oil pump mounted to the timing gear housing. The
pump is driven by the crankshaft gear, ensuring immediate oil pressure
upon startup. A full-flow spin-on or cartridge-type oil filter is
mounted externally on the cylinder block. A separate full-flow oil
centrifuge (bypass filter) may be fitted for extended oil change
intervals. The system supplies lubricant to the crankshaft main
bearings, connecting rod bearings, camshaft bearings, timing gears,
pushrods, rocker shaft, valve tips, turbocharger center bearing, and air
motor drive.
Piston cooling oil jets are mounted in the cylinder block, directing
continuous oil streams to the underside of each piston crown. A
seawater-cooled oil cooler maintains oil temperature under sustained
load. The oil sump capacity ranges from 150 to 200 liters (40-53 gal)
depending on installation. An oil priming pump is fitted for
pre-lubrication before starting.
The cooling system is a two-line (dual-circuit) system. The
high-temperature freshwater circuit circulates coolant through the
cylinder block and cylinder head jackets. A centrifugal fresh-water
pump, gear-driven from the camshaft, provides circulation. A wax-type
thermostat with a rated opening temperature of 80-85°C (176-185°F)
regulates the engine operating temperature.
The low-temperature seawater circuit draws seawater through a sea chest
and strainer, circulates it through a rubber-impeller or centrifugal
seawater pump, and passes it through the fresh-water heat exchanger, oil
cooler, and charge air cooler before discharge overboard. The charge air
cooler reduces turbocharged intake air temperature, increasing air
density and combustion efficiency. The expansion tank is pressurized and
incorporates a coolant level sensor. Freshwater capacity is 150 liters
(40 gal) for the engine block and head only.
| Intake and Exhaust Systems |
Intake System: Air is drawn through a dry-type paper element air filter
or a dry-type inertial separator (for dusty environments) before
entering the turbocharger compressor inlet. After compression and
cooling, air enters the intake manifold. The intake manifold is cast
from cast iron and distributes air evenly to each cylinder.
Exhaust System: A cast-iron exhaust manifold collects exhaust gases and
directs them to the turbocharger turbine inlet. After the turbocharger,
exhaust gases pass through an exhaust silencer and may be routed to a
waste heat recovery boiler for vessel heating systems. An exhaust gas
bypass may be fitted for wastegate control.
Timing System: The camshaft is driven by a gear train from the
crankshaft. Hardened steel timing gears at the front of the engine
provide fixed timing without belts or chains requiring replacement. The
gear train sequentially drives the crankshaft gear, idler gear, camshaft
gear, injection pump gear, and accessory drives. Timing marks on each
gear must align during assembly. No timing tensioner is present due to
the fixed gear arrangement.
Turbocharging System: A single exhaust gas turbocharger (ABB, MAN, or
Mitsubishi Heavy Industries) is flange-mounted to the exhaust manifold.
The turbocharger utilizes exhaust gas energy to compress intake air,
increasing volumetric efficiency and power output. A charge air cooler
(intercooler) reduces compressed air temperature before entry to the
intake manifold. The turbocharger bearing housing is supplied with
engine oil through a dedicated feed line with an orifice restrictor. A
water-washing system may be fitted for cleaning the compressor and
turbine stages.
Starting System: An air motor starting system is standard. Compressed
air at 15-30 bar (215-435 psi) is supplied from a starting air receiver.
An air distributor mounted to the camshaft directs starting air to each
cylinder in firing order sequence. A manual or electrically operated
starting air valve controls air flow. An electric starter motor may be
fitted as an alternative starting method for smaller variants.
Engine Monitoring System: The engine is equipped with a local control
panel with gauges for oil pressure, coolant temperature, exhaust
temperature, fuel rack position, and engine speed. Electronic variants
include a remote monitoring interface for integration with the vessel's
automation system. Shutdown switches protect against low oil pressure,
high coolant temperature, and engine overspeed.
Overall Engine Length: 3,166 mm (124.6 in).
Overall Engine Width: 1,544 mm (60.8 in).
Overall Engine Height: 2,032 mm (80.0 in).
Dry Weight (Engine only): 8,600-8,800 kg (18,960-19,400 lb), varying
with auxiliary systems and generator configuration.
Generator Set Weight (with alternator and base frame): Up to 14,700 kg
(32,400 lb).
Engine Oil Capacity (Sump): 150-200 liters (40-53 U.S. gal, 33-44
imperial gal), varying with oil pan configuration. Engine Oil
Specification: API CD, CE, CF, CF-4, or CI-4 grade; SAE 30 or SAE 40
viscosity recommended. SAE 10W-50 may be used in cold climates. Marine
diesel engine oil with alkaline reserve (TBN) of 20-30 is required for
high-sulfur fuel operation. Oil Change Interval: 3,000-4,000 operating
hours for diesel engine oil with centrifuge purification; 500-1,000
hours without centrifuge.
Coolant Capacity (Freshwater): 150 liters (40 gal) inclusive of the
engine block and head. Coolant Specification: Ethylene glycol-based
antifreeze with corrosion inhibitors for diesel engines.
Nitrite-containing coolant is required for wet sleeve cylinder liner
cavitation prevention. Thermostat Opening Temperature: 80-85°C
(176-185°F). Air Filter Service: Dry element replacement when
restriction indicator shows vacuum exceeding 635 mm water gauge (25 in
H2O) or at 2,000 hours.
Fuel Filter Replacement Interval: 1,000 operating hours or with each
major service. Fuel Injection Pressure: 250-300 bar (3,625-4,350 psi,
255-306 kgf/cm2). Valve Clearance (Cold): Intake: 0.35-0.45 mm
(0.014-0.018 in); Exhaust: 0.55-0.65 mm (0.022-0.026 in). Adjustment is
performed by loosening the rocker arm locknut and turning the adjusting
screw while holding the appropriate feeler gauge. Valve Clearance
Inspection Interval: 4,000 operating hours or 2 years.
Injector Inspection Interval: 3,000 operating hours for opening pressure
testing, spray pattern inspection, and flow testing. Injection Pump
Timing: Static timing set at 12-16 degrees before top dead center,
verified by aligning marks on the pump flange and timing gear housing or
by using a dial indicator on the pump plunger. Turbocharger Inspection:
Bearing shaft end-play and radial clearance inspection at 4,000
operating hours. Cylinder Liner Protrusion: 0.15-0.25 mm (0.006-0.010
in) above the block deck, measured with a dial indicator and straight
edge. Starting Air Receiver: Condensate drain daily; safety valve
inspection annually.
Cylinder Head Bolts, Step 1: 200 Nm (20.4 kgf-m, 148 lb-ft).
Cylinder Head Bolts, Step 2: 400 Nm (40.8 kgf-m, 295 lb-ft).
Cylinder Head Bolts, Step 3: 600 Nm (61.2 kgf-m, 443 lb-ft).
Main Bearing Cap Bolts: 500 Nm (51.0 kgf-m, 369 lb-ft).
Connecting Rod Cap Bolts: 300 Nm (30.6 kgf-m, 221 lb-ft).
Flywheel Bolts: 400 Nm (40.8 kgf-m, 295 lb-ft).
Crankshaft Pulley Bolt: 1,500 Nm (153 kgf-m, 1,106 lb-ft).
Camshaft Bearing Cap Bolts: 100 Nm (10.2 kgf-m, 74 lb-ft).
Rocker Arm Shaft Bolts: 80 Nm (8.2 kgf-m, 59 lb-ft).
Intake Manifold Bolts: 60 Nm (6.1 kgf-m, 44 lb-ft).
Exhaust Manifold Nuts: 80 Nm (8.2 kgf-m, 59 lb-ft).
Injection Pump Mounting Nuts: 50 Nm (5.1 kgf-m, 37 lb-ft).
Injector Hold-Down Clamp Bolts: 60 Nm (6.1 kgf-m, 44 lb-ft).
Turbocharger Mounting Nuts: 100 Nm (10.2 kgf-m, 74 lb-ft).
Oil Filter (Spin-on Type): 25 Nm (2.5 kgf-m, 18 lb-ft).
Oil Pan Bolts: 30 Nm (3.1 kgf-m, 22 lb-ft).
Starter Air Motor Mounting Bolts: 80 Nm (8.2 kgf-m, 59 lb-ft).
Generator Coupling Bolts: 400 Nm (40.8 kgf-m, 295 lb-ft).
The Yanmar 6N21AL engine is utilized in marine auxiliary power
generation and prime power applications.
Marine Auxiliary Generator Sets
Cargo vessels: Container ships, bulk carriers, and tankers requiring
ship service power.
Passenger vessels: Cruise ships and ferries with hotel load electrical
requirements.
Offshore supply vessels: Platform support vessels with dynamic
positioning systems.
Tugboats and workboats: Auxiliary power for winches, pumps, and ship
systems.
Large yachts: Mega-yachts and super-yachts with high electrical load
requirements.
Marine Main Propulsion (limited
applications)
Small coastal freighters: Direct drive or diesel-electric propulsion
configurations.
Fishing vessels: Trawlers and purse seiners with auxiliary generator
requirement.
Land-Based Prime Power
Emergency generator sets: Hospitals, data centers, and industrial
facilities.
Island power generation: Remote communities and industrial sites.
Rental power fleets: Temporary power for construction and events.
Generator Configurations
50 Hz applications (1,000 rpm): 800-1,020 kW generator sets for European
and Asian markets.
60 Hz applications (900 rpm): 745-970 kW generator sets for North
American markets.
Diesel-electric propulsion: Variable speed generator sets for hybrid
marine systems.
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