Background
Cylinder lubrication on slow-speed two-stroke marine engines has evolved through several technology generations. The earliest designs used mechanical lubricators driven by cams or chains; these gave acceptable timing but limited control over dose quantity. The Alpha Lubricator introduced full electronic control via solenoid-driven pumps. Pulse lubrication systems represent a third approach: hydraulically actuated pumps that produce dose pulses with high injection velocities, often optimised for fine atomisation and good distribution within the cylinder.
The most prominent pulse lubricator in marine practice is the Hans Jensen SIP (Swirl Injection Principle) system, developed in Denmark and widely adopted as both new-build equipment and as retrofit upgrade for older engines. Other manufacturers offer similar pulse-based products. The common feature is that the dose is delivered as a short, high-velocity pulse rather than as a metered displacement.
Pulse lubrication is particularly valuable for retrofit applications. Older MAN B&W MC engines and Sulzer/WinGD RTA engines were originally fitted with mechanical lubricators. Replacing these with full Alpha Lubricator systems would require substantial engine modifications, but pulse lubricator retrofits can usually be installed with minimal mechanical changes, providing electronic-quality dose precision while leaving the engine architecture largely intact.
This article describes pulse lubrication architecture, the swirl injection principle, retrofit considerations, and the operational characteristics that distinguish pulse lubricators from solenoid-driven systems.
System architecture
Pulse pump construction
A pulse pump consists of:
- Hydraulic actuator chamber containing system oil at high pressure (typically 25 to 50 bar)
- Pump piston that displaces a measured volume of cylinder oil when driven by hydraulic pressure
- Cylinder oil chamber receiving cylinder oil from the supply manifold
- Outlet check valve preventing backflow
- High-velocity nozzle at the outlet, designed to produce a fine jet of cylinder oil
The hydraulic actuator is triggered by a separate solenoid valve that opens to admit high-pressure system oil to the actuator chamber, driving the pump piston rapidly through its stroke.
Hydraulic supply
Pulse lubricators typically use the engine’s system oil as the hydraulic medium. The system oil is supplied at moderate pressure (10 to 25 bar) and is intensified by the pulse pump’s hydraulic stage to higher pressures during the actuation stroke.
Some installations use a dedicated hydraulic supply (separate from system oil) for cleanliness and precise pressure control.
Solenoid valves
A small solenoid valve gates the high-pressure hydraulic supply to each pulse pump. Valve actuation triggers each dose pulse. Solenoid valves are similar in principle to those used in Alpha Lubricators but operate at typically lower pressures and lower duty cycles (one event per cylinder cycle rather than continuous high-frequency operation).
Electronic control
The engine control system or a dedicated lubricator controller commands each solenoid valve at the desired crank angle. Modern pulse lubricators include:
- Crank angle sensors for timing reference
- Engine load signals for dose quantity calculation
- Communication interfaces to the central engine control system
- Diagnostic monitoring of pump operation
Distribution
Each pulse pump’s output connects to a high-pressure delivery pipe leading to a cylinder oil quill. The pulse arrives at the quill as a short, high-velocity column of oil that ejects into the cylinder through the quill nozzle.
Swirl Injection Principle (SIP)
The Hans Jensen SIP is a particular implementation of pulse lubrication with a focus on optimised oil distribution within the cylinder.
Atomisation through high velocity
The SIP nozzle accelerates the oil pulse to high velocities (typically 30 to 80 m/s) at the quill outlet. At these velocities, the oil jet breaks up into fine droplets through aerodynamic instability with the surrounding cylinder air. Droplet size distributions are typically 50 to 200 micrometres, finer than what mechanical lubricators or simple positive-displacement systems achieve.
Swirl interaction
The fine droplets are entrained in the cylinder’s scavenge air swirl, distributing them around the circumference and along the axial extent of the cylinder. Swirl interaction is the principal mechanism for spreading oil from a few quill points to the entire cylinder running surface, ensuring uniform film thickness despite limited quill count.
Droplet impingement
Some droplets impinge on the liner running surface directly, depositing oil at impact points. Other droplets remain airborne and reach the upper cylinder, where they impinge on the cylinder cover or piston crown and contribute to upper-cylinder lubrication.
Combustion participation
A small fraction of the injected oil burns during combustion, contributing to total fuel energy but also producing combustion deposits. Modern oils are formulated to minimise deposit formation; SIP-equipped engines typically show acceptable deposit patterns at standard feed rates.
Comparison with Alpha Lubricator
| Feature | Pulse Lubricator (e.g. SIP) | Alpha Lubricator |
|---|---|---|
| Dose generation | Hydraulic intensification | Solenoid-driven piston |
| Dose velocity | High (30-80 m/s) | Lower |
| Atomisation | Fine droplets | Coarser jets |
| Distribution mechanism | Swirl entrainment | Liner spreading by piston rings |
| Quill count | Often fewer (3-6) | More (6-12) |
| Hydraulic supply needed | Yes | No (electrical only) |
| Retrofit suitability | Excellent | Major modification needed |
| Typical applications | New build and retrofits | New build |
| Maintenance complexity | Moderate (hydraulic + electronic) | Lower (electronic only) |
The two systems achieve similar end results in terms of cylinder lubrication quality. Choice between them is typically driven by:
- Engine type (new build vs retrofit)
- Manufacturer preference and standardisation
- Operator experience with each system
- Total cost of ownership
Retrofit applications
Target engines
Pulse lubricators are particularly suited to retrofitting older slow-speed two-stroke engines:
- MAN B&W MC engines (mechanical camshaft) from the 1980s and 1990s
- Sulzer/WinGD RTA engines from the same era
- Mitsubishi UEC LSII and similar generations
- Some smaller engines that were never offered with electronic lubrication from new
For these engines, replacing the original mechanical lubricator with a pulse lubricator typically:
- Reduces cylinder oil consumption by 15 to 30 percent at the same wear performance
- Provides per-cylinder feed rate adjustability
- Enables skip-cycle operation for very-low-load running
- Adds electronic monitoring and diagnostics
Installation
Pulse lubricator retrofit involves:
- Removing the original mechanical lubricator
- Installing the pulse lubricator unit on existing or new mounting brackets
- Connecting cylinder oil supply to the new unit
- Connecting hydraulic supply (system oil tap-off or dedicated supply)
- Connecting electrical wiring to the control system
- Connecting outlet pipework to existing oil quills
- Commissioning and feed rate calibration
The mechanical work is typically completed during a short port stay; commissioning may take several days of operating time.
Economic case
The economic case for retrofit depends on:
- Cylinder oil cost savings from reduced feed rate (typically the largest item)
- Reduced cylinder wear from optimised feed rate (extending overhaul intervals)
- Operational flexibility from skip-cycle and per-cylinder adjustment
- Capital cost of the pulse lubricator system and installation
- Remaining engine life (longer life justifies more capex)
Typical payback periods are 1 to 3 years for ships operating regularly on heavy fuels.
Operational characteristics
Feed rate management
Pulse lubricators support feed rate adjustment through the same channels as Alpha Lubricators: software-driven dose quantity, skip-cycle operation, per-cylinder offsets. The numerical feed rates achievable are similar (0.6 to 1.5 g/kWh on modern engines, lower on slow-steaming optimised installations).
Distribution quality
The high injection velocity and fine atomisation can achieve good cylinder coverage with relatively few quills. Some pulse lubricator installations use only 3 to 6 quills per cylinder, compared to 6 to 12 for Alpha Lubricators. Reduced quill count simplifies the cylinder liner machining and reduces ongoing wear at quill nozzle locations.
Combustion interaction
The fine droplets produced by pulse injection mix more readily with combustion gases. This can lead to slightly higher in-cylinder oil consumption (i.e. more oil burned rather than scavenged out), with implications for both feed rate and emissions. The effect is small but measurable.
Compatibility with low-sulphur fuels
Pulse lubricators work well with low-BN cylinder oils used for low-sulphur fuels. The fine atomisation distributes the limited alkalinity reserve more uniformly across the cylinder, maintaining acceptable acid neutralisation despite the lower BN.
Maintenance
Routine maintenance
Pulse lubricator maintenance includes:
- Hydraulic supply filtering: filtering of system oil before it enters the hydraulic actuator chambers
- Solenoid valve inspection: similar to Alpha Lubricator solenoid maintenance
- Pump piston inspection: at major intervals
- Quill nozzle inspection: for blockage or wear that affects atomisation
- Pressure transducer calibration
Hydraulic maintenance
Pulse lubricators add a hydraulic subsystem not present on Alpha Lubricators. The hydraulic supply must be:
- Adequately filtered
- Free of water or particulates
- Maintained at correct pressure
- Free of cavitation or excessive aeration
Hydraulic supply problems are a leading cause of pulse lubricator faults, often manifesting as pulse delivery variation between cylinders or between cycles.
Failure modes
Common pulse lubricator failure modes include:
- Hydraulic supply contamination causing pump piston wear
- Solenoid valve sticking or failure
- Quill nozzle erosion from high-velocity oil flow
- Outlet check valve failure allowing combustion gas backflow
- Sensor faults in pressure transducers or position sensors
Most failures produce gradual performance degradation detectable through routine monitoring before they cause acute cylinder damage.
Future developments
Pulse lubricator technology continues to evolve, with developments in:
- Higher injection pressures for finer atomisation
- Variable nozzle geometry for spray pattern adjustment
- Sensor integration for closed-loop control based on cylinder pressure or oil distribution measurements
- Machine learning for adaptive feed rate optimisation
- Compatibility with alternative fuels including methanol, ammonia, and hydrogen-bearing fuels
These developments aim to extend the operational envelope of pulse lubricators and to maintain their competitive position relative to Alpha Lubricators and other electronic systems.
Related Calculators
- Cylinder Oil Feed Rate Calculator
- Lubricator Dose Volume Calculator
- Pulse Lubricator Sizing Calculator
- Cylinder Oil Atomisation Calculator
- Cylinder Oil Cost Calculator
See also
- Alpha Lubricator Electronic Cylinder Lubrication
- Cylinder Lubrication Systems for Two-Stroke Marine Engines
- Cylinder Liner Wear Monitoring on Marine Engines
- Two-Stroke Marine Diesel Engine Fundamentals
Additional calculators:
- Cylinder Oil Feed Rate - MAN ACC
- Fuel Pump - Delivery Stroke
- Cylinder Oil Feed Rate - WinGD LCD
- Engine - Pcomp vs Pmax Ratio
Additional formula references:
Additional related wiki articles:
References
- Hans Jensen Lubricators. (2023). SIP Cylinder Lubrication System Technical Manual. Hans Jensen Lubricators A/S.
- MAN Energy Solutions. (2023). Cylinder Lubrication Retrofit Guidelines. MAN Energy Solutions.
- CIMAC. (2020). Recommendations Concerning Cylinder Oils. CIMAC Working Group 8.
- Wakuri, Y. et al. (2003). Tribology in Marine Diesel Engines. Wiley.
- Lloyd’s Register. (2022). Guidance Notes for Cylinder Lubrication Retrofits.