eWAVE is the first ring that disperses oil around the bore in a homogeneous layer, protecting against local oil film breakdown, improving the sealing of combustion gases, reducing wear and ensuring more uniform liner temperatures. This means the amount of oil injected into the cylinder can be greatly reduced and, because two-stroke engines expel their lubricant in the exhaust, less oil means lower carbon emissions as well as reduced operating costs.

—Richard Mittler, Federal-Mogul’s Senior Expert Manager, Analysis and Product Development, Technology, Rings & Liners

Conventional two-stroke piston rings are predominantly designed using principles very similar to those used in four-stroke engines, in which there is a flow of oil from the crank case around the entire circumference of the ring. However, in two-stroke engines the lube oil is sprayed against the cylinder liner in proportion to the engine load. This feed oil is not uniformly distributed on the cylinder wall.

With a standard piston ring system, around the Bottom Dead Center (BDC) point of the liner the oil that was not distributed formed an ‘oil nose’ and no longer provided lubrication. Click to enlarge.		The eWAVE piston ring system lubricated an area ten times bigger than a standard system. No oil drops were visible, indicating that there was no loss of oil. Click to enlarge.

To ensure a safe minimum coverage of all areas of the liner, surplus oil is injected in order to compensate for the uneven distribution. Because there is no mechanism to distribute the oil circumferentially around the bore much of the surplus is pushed downwards in the direction of the ports, meaning that approximately 30 to 40 percent of the oil supplied passes through to the exhaust without ever performing a useful function.

The eWAVE piston ring changes the axial position of the pivot point multiple times around the circumference. Click to enlarge.

The geometry of the eWAVE piston ring creates a circumferential pressure difference that generates controlled oil flow around the bore as the piston reciprocates, improving the uniformity of the oil film. It achieves this by varying, around the circumference, the point about which the ring pivots in its groove as the piston reverses direction. Tests have shown that the eWAVE ring distributes oil over an area around 10 times the size of that achieved by conventional ring profiles, which generate less than one percent of their oil flow in a circumferential direction.

Long term trials since 2013 in a number of vessels with different oil injection technologies have confirmed the economic and environmental advantages of eWAVE rings. In over 8000 hours of testing, we have seen improved wear resistance while reducing oil consumption by up to 20 percent, helping to reduce operating costs while improving the marine environment.

—Richard Mittler

The detail of the eWAVE design can be optimized to suit individual types and arrangements of feed nozzle and different engine strokes and operating speeds.