Liner with installed Anti Polishing Ring (APR), which prevents formation of deposits on the piston crown top land. The APR does not need to be specifically fixated, as the thermal expansion of the hot ring keeps it perfectly and tightly in place. |
The so-called piston-running behaviour is a critical factor in a two-stroke engine. It regulates the time between overhauls (TBO) and has a direct impact on the reliability, overhaul costs and, through the cylinder oil feed rate, the engine operating costs.
In the Wärtsilä TriboPack solution, co-ordinated design measures have been brought together to substantially improve the piston-running behaviour. The TriboPack design covers every aspects of the tribological interaction between piston, piston ring and cylinder liner. The results are extended TBO and reduced cylinder oil consumption.
Direct savings
The limiting factors in a two-stroke engine influencing the TBO are usually the top piston ring wear and the cylinder liner wear. Since TriboPack improves the piston-running performance by reducing the piston ring and liner wear rates it is possible to extend the TBO and achieve the benefits of:
- more freedom to schedule maintenance work
- off-hire risk reduction
- reduced operating costs by minimising parts consumption.
In addition to an extended TBO, TriboPack allows the reduction of cylinder oil consumption. The savings that can be achieved by using this retrofit package are substantial. After fuel, cylinder oil has the second highest cost on an engine’s operational cost structure and savings of just 0.1 g /kWh can make a visible economical difference.
Advanced features behind operational safety
These are the design features that improve the piston running conditions:
- The fully deep-honed liner with multi-level lubrication and special insulation.
- Special insulation providing a correct temperature distribution allowing uniform wear and therefore good piston-running condition.
- The profiled chromium-ceramic coated (CC) top piston ring reduces ring and liner wear and provides high operational safety.
- The profiled running-in coated (RC) lower piston rings, have a soft layer on their running-face to allow a fast sealing effect. The soft layer disappears after a few hundred running hours unveiling a hard running-face with scuffing prevention features.
- The anti-polishing ring (APR) prevents formation of deposits on the piston crown top land. Deposits which build up from over lubrication and/or high cylinder oil alkalinity (BN). The presence of these deposits is harmful since they disturb the oil film on the liner, which leads to liner polishing and therefore scuffing. The use of low-sulfur fuel also contributes to the development of such deposits.
Most of the design measures in TriboPack have been employed in Sulzer RTA engines for several years. It is only now in TriboPack that they have been brought together as a standard package. TriboPack is now standard in all Sulzer RTA low-speed marine engines built today and is also available as a retrofit package for all Sulzer RTA engines in service.
