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Sulzer

6RTA72U-B

Name: Sulzer 6RTA72U-B
Brand: Sulzer
SKU: OSE-38648

The Sulzer 6RTA72U-B is a low‑speed, two‑stroke diesel main engine delivering 21.6 MW at 91 rpm, distinguished by its large 720 mm bore and conventional camshaft design.

21600.0 kW

Power

Engine Specifications

Cylinders

720 mm

Bore

2500 mm

Stroke

21,600 kW

MCR Power

91.0 rpm

MCR RPM

2-stroke

Stroke Type

Family: Sulzer RTA · Tier: IMO Tier I · Fuel: HFO, MDO

Inspector Detail ✓ verified

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Designation decoded

Sulzer RTA72U-B – 6-cylinder two-stroke crosshead engine with gear-driven camshaft valve drive, 720 mm bore, 2500 mm stroke. U=Ultra-long-stroke (speed-optimized), B=improved design with optimized combustion and extended service intervals.

Background

The RTA72U-B combines the speed optimization of the U-variant with the constructional improvements of the B-upgrade. B-improvements include optimized combustion chamber geometry, improved piston ring packages, redesigned fuel injectors and adapted scavenge air routing. This combination targets maximum fuel efficiency at lowest speed, reduced emissions and extended TBO intervals (Time Between Overhaul). VIT with B-optimized characteristic, improved PLS and CLU.

Calculated metrics

Stroke To Bore Ratio

3.47

Mean Effective Pressure Bar

19.8

Inspector checklist

Camshaft and drive gears

Check gear flanks for wear and fatigue cracks – U-B combination produces highest torque
Nockenwellenlager-Spiel messen
Examine cam profiles for wear
Control drive gear alignment and tooth flank clearance

Cylinder liners and piston rings (B-design)

Compare cylinder liner wear with B-specific limit values
Check B-piston rings for correct type, end gap and side clearance
CLU bores to check for continuity and correct distribution
Laufflächenprofil auf B-typische Tragbildentwicklung beurteilen

VIT-System (B-optimiert)

VIT characteristic curve of the U-B version to verify – differs from U and standard
Fuel injectors to check for B-specific type and opening pressure
Brennstoffpumpen-Timing gemäß U-B-Spezifikation kontrollieren
VIT servo motor function and response behaviour to test

Crosshead and running gear

Kreuzkopflager-Spiel messen – höchste Drehmomentbelastung in der Baureihe
Main bearing clearance and temperature to check
Kolbenstangen-Stopfbuchse auf Leckage prüfen
Pleuelschrauben-Vorspannung kontrollieren

Combustion optimization and power output

Cylinder pressure diagrams to record and compare with B reference values
Abgastemperatur-Spreizung – B-Version fordert engere Toleranzen
Specific fuel consumption to calculate and compare with B guarantee values
Turbocharger efficiency at U speed to check

Pulse Lubrication (B-optimiert)

PLS-Dosierung gemäß B-Empfehlung prüfen – typischerweise reduzierbar
Schmierimpuls-Timing an U-Drehzahl verifizieren
Oil quality and BN value to check
Zylinderweise Verbrauchsanalyse durchführen

Logbook reference values

Parameter	Expected	Deviation means
Exhaust gas temperature per cylinder	320–375 °C at 85 % MCR	B-optimized combustion shows lower and more uniform values – increase indicates component wear
Spezifischer Brennstoffverbrauch	Gemäß U-B-Testprotokoll, niedrigster Wert der Baureihe	Anstieg auf U-Niveau deutet auf Verlust der B-Optimierung hin – Ersatzteilverwendung prüfen
Cylinder liner wear	0,03–0,07 mm/1000 Bh (B-optimiert, niedrigste Rate)	Higher wear rates indicate incorrect piston rings or insufficient lubrication
Spitzendruck (Pmax)	Gemäß U-B-Testprotokoll, typisch 150–165 bar	U-B-Variante hat höchste Spitzendrücke – Zylinderungleichheit >3 bar erfordert sofortige VIT-Justierung
Kompressionsdruck	Gemäß U-B-Herstellerangabe	Decrease indicates ring wear or exhaust valve leakage
PLS-Schmierölverbrauch	0,4–0,7 g/kWh (B-optimiert, niedrigster Verbrauch)	Deviations require inspection of dosing valves and running surface condition
Kurbelwellendurchbiegung	Gemäß U-B-Herstellergrenzwerte	Bei U-B kritischste Variante wegen höchstem Drehmoment – engmaschig überwachen
Hauptlager-Temperatur	58–70 °C	Elevated values at U-B particularly critical – immediate root cause analysis required

Common Failure Modes

Verlust der B-Verbrennungsoptimierung

Symptoms: ['Spezifischer Brennstoffverbrauch steigt auf U-Niveau', 'Abgastemperaturspreizung nimmt zu', 'Spitzendrücke weichen von B-Referenz ab']

Causes: Use of non-B spare parts during overhaul, Wear of B-specific combustion chamber components, Incorrect VIT setting after maintenance

Preventive: Use exclusively B-specific spare parts, adjust VIT after every overhaul in accordance with U-B service letter and carry out regular power measurement

Hauptlager-Überlastung

Symptoms: ['Erhöhte Lagertemperaturen', 'Veränderte Kurbelwellendurchbiegung', 'Lagerschalen-Auslauf']

Causes: Highest torque in the series at U speed and B pressure level, Fundamentverformung, Schmierölmangel

Preventive: Crankshaft deflection to measure quarterly, bearing temperatures to monitor and foundation bolts to check at every docking

Turbocharger mismatching at part load

Symptoms: ['Ladedruck-Schwankungen', 'Surging noises at part load', 'Leistungsabfall unter 50 % MCR']

Causes: U-B-specific turbocharger characteristic curve at part load critical, Turbolader-Verschmutzung verschlechtert Wirkungsgrad, Fehlende Teillast-Anpassung

Preventive: Turbocharger to flush regularly, operating points to document and part load operation to maintain in accordance with manufacturer recommendations

Nockenwellen-Antriebszahnrad-Ermüdung

Symptoms: ['Geräuschveränderungen am Steuerungsgehäuse', 'Metallpartikel in Ölfilteranalyse', 'Einspritztiming-Drift']

Causes: Höchstes Drehmoment der Baureihe belastet Zahnräder maximal, Material fatigue during continuous operation, Korngrenzenversagen

Preventive: Gears inspection every 20,000 operating hours with MT/PT, perform oil analysis monthly and have spare parts ready at first signs of pitting

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Related components

Turbolader (Kennlinie, Wirkungsgrad, Surging-Verhalten) Spülluftkühler (Verschmutzung, Druckverlust) Exhaust valve (B-specific seat geometry and material) Kolbenkühlung (Ölfluss, Rücklauftemperatur) Main bearing and crankshaft deflection (Priority!) Torsionsschwingungsdämpfer Foundation bolts and engine installation Wellenstrang-Ausrichtung

Classification & regulatory

IACS UR Z10.5 for machinery survey. U-B combination requires both U-specific and B-specific documentation in EIAPP Technical File. NOx-relevant components (fuel injectors, VIT setting, timing) must match U-B certificate. Measure crankshaft deflection at each intermediate and class survey. Torsional vibration report for U-rated speed must be on board.

Reference content for inspector orientation. Always verify against manufacturer's manual, latest service letters and class society requirements.

Other Cylinder Configurations 50

Components & Design

Component data being added…

Technical Data

unified from engine model True

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Manuals

operating
Sulzer RTA Operating Manual
Wärtsilä Switzerland (historical Sulzer)
maintenance
Sulzer RTA Maintenance Manual
Wärtsilä Switzerland (historical Sulzer)
spare_parts
Sulzer RTA Spare Parts Catalogue
Wärtsilä Switzerland (historical Sulzer)

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Equipment Model #38648 · ✓ still in production