Wärtsilä Corporation has introduced a new, electronically-controlled cylinder lubricating system to meet the demand for lower cylinder oil feed rates: the Pulse Lubricating System (PLS). Developed for application in Wärtsilä RTA and RT-flex low-speed marine diesel engines, it delivers reduced cylinder oil consumption without compromising piston-running reliability.
The Pulse Lubricating System makes it possible to reduce the cylinder oil feed rate compared with the existing accumulator system through an improved distribution of cylinder lubricating oil to the cylinder liner, and the fully flexible, precise timing of oil delivery.
The guide feed rate for Wärtsilä RTA and RT-flex engines equipped with the Pulse Lubricating System as original equipment is 0.7 g/kWh of cylinder lubricating oil.
Thus the cost savings achievable with the Pulse Lubrication System are significant. In the case of a 12-cylinder Wärtsilä RT-flex96C engine of 68,640 kW maximum continuous output, running at 85 per cent load for 7000 hours a year with cylinder oil costing US$ 1700/tonne, the reduction from the guide feed rate of 1.1 g/kWh (0.8 g/bhph) with the existing accumulator system to the new guide feed rate of 0.7 g/kWh (0.5 g/bhph) can generate cost savings of more than US$ 270,000 a year. This corresponds to a cost saving of about 36 per cent for cylinder lubricating oil.
The key feature of the Pulse Lubricating System is that it delivers accurately metered, load-dependent quantities of lubricating oil to the cylinder liner running surface at the precise timing required. Electronic control ensures the accurate dosage and timing, with full flexibility in settings.
The cylinder lubricating oil is sprayed as a pulse of multiple jets on to the liner surface from a single row of lubricators arranged around the liner, each lubricator having a number of nozzle holes. The oil jet sprays ensure better distribution of the oil over the liner running surface than with the existing accumulator system. There is no atomisation and no loss of lubricating oil to the scavenge air.
Cylinder oil is delivered under pressure to the lubricators by a newly-developed dosage pump which is powered by pressurised servo oil drawn from the engine’s system oil. The feed rate and timing are electronically controlled through a solenoid valve at the lubricator pump. There is full flexibility in the setting of the lubricator timing point, and volumetric metering ensures constant spray patterns across the engine’s load range. The dosage is precisely regulated even for low feed rates.
The Pulse Lubricating System is available from January 2007 for newly-built Wärtsilä RT-flex96C, RTA96C, RT-flex84T-D and RTA84T-D engines. Additional engine types will be added to these in 2007. The new RT-flex82C, RTA82C, RT-flex82T and RTA82T engine types will be equipped with the Pulse Lubricating System from the beginning.
Service experience with the Pulse Lubricating System has been very successful with excellent liner and piston ring conditions. Trials have been carried out both on the Wärtsilä research engine inWinterthur and on shipboard engines. The first production engine fully fitted with PLS successfully passed its shop test in May 2006, with other engines following.
The first PLS test started on the research engine in June 2003. Shipboard testing began with a Wärtsilä RTA58T engine in July 2004, followed by an RT-flex96C engine in June 2005. Shipboard testing has accumulated more than 18,000 running hours. Throughout the outstanding performance of the Pulse Lubricating System was confirmed, with all testing being at or below the guide feed rate of 0.7 g/kWh.
For example, a cylinder in an RT-flex96C engine equipped with the PLS in the newbuilding execution was inspected at the end of August 2006. The engine had run for 6503 hours since the PLS had been installed, together with new cylinder liner and piston rings. The last 3500 running hours had been with a cylinder oil feed rate of around 0.7 g/kWh.
The rings and liner were all in excellent condition. The specific cylinder liner wear was measured as 0.080 mm/1000 hours on the diameter. The measurements were made using the dimple method.
Also retrofit version
The Pulse Lubricating System is also provided for retrofit to RTA and RT-flex low-speed engines. The major cost savings delivered by Retrofit PLS make for a quick return on the capital investment.
As the PLS in new engines involves a different execution of cylinder liner than for the Wärtsilä accumulator system, the Retrofit PLS has been adapted to suit the existing cylinder liners in RTA and RT-flex engines.
Much of the hardware is the same for both newbuilding and retrofit versions of PLS. The key difference is in the lubricators. For Retrofit PLS, lubricators are fitted in the lower quill openings in the cylinder liner. Instead of multiple oil sprays, the retrofit lubricators feed the pressurised pulse of cylinder oil exactly into the piston ring package and on to the piston skirt from where it is evenly distributed around the circumference of the liner.
The Retrofit PLS can be fitted during commercial operation of the vessel. It is an independent system with only few connections or interfaces to other systems. Thus preparation and installation are easy and fast. All equipment including prefabricated piping is supplied, with installation and commissioning being undertaken by Wärtsilä service engineers.
To a substantial extent this material can be installed during the voyage considerably reducing port time required for final installation and commissioning. Installation of controls, pumps, wiring and interface connections to remote and alarm monitoring systems is executed during the voyage as well. Ample attention is paid to commissioning, fine adjustment and running-in of the Retrofit PLS in port and during a confirmation voyage.
The Pulse Lubricating System is available now for retrofitting to RT-flex96C and RTA96C engines, and for RT-flex84T-D and RTA84T-D engines from January 2007, with additional engine types to be added during 2007.
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Notes to the editor:
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