Knowledge - Damage Pattern 02
Clover leafing in cylinder liners
How the pattern forms
Burning high-sulphur fuel produces sulphur oxides. Wherever the liner wall is cold enough for combustion water to condense, they form sulphuric acid on the running surface. The alkaline additive in the cylinder oil (its BN) is there to neutralise that acid - but the oil is injected at discrete lubricator points around the circumference.
Close to each injection point the fresh, alkaline oil protects the surface. Halfway between the points the film is older, its BN depleted, and the acid attacks the cast iron. Corrosive wear concentrates in those in-between zones. Measured over thousands of hours, the bore develops lobes: maximum diameter between the quills, minimum at the quills - the clover-leaf shape that gives the pattern its name.
Why it matters
- Ring seal loss - a lobed bore is not round, so the ring cannot follow the wall everywhere. Blow-by increases and local hot gas attack accelerates the damage.
- Hidden by conventional gauging - a two-point hand gauge measured at the wrong orientation can miss the lobes almost entirely. The pattern only becomes obvious when wear is measured in many directions.
- It is a system problem - the liner is the victim; the cause is the balance of fuel sulphur, cylinder oil BN, feed rate and liner wall temperature. A replacement liner inherits the same environment.
What measurement shows
Clover leafing is where multi-directional measurement earns its keep. The polar view of an in-situ 3D measurement shows the bore in eight directions per measuring height: a healthy liner plots as a circle, a clover-leafed liner as a lobed polygon with ovality values well above the wear values suggested by a single diameter. The 3D surface map locates the corrosion zones vertically - cold corrosion typically sits in the mid-stroke region where wall temperatures pass through the dew point.
Countermeasures
- Match cylinder oil BN and feed rate to the actual fuel sulphur content, following the engine maker's guidance.
- Keep liner wall temperatures above the acid dew point - cooling water temperature control and load profile both matter.
- Trend the condition: a follow-up measurement shows whether the corrosion rate has stopped or the lobes are still growing.
As with all damage patterns, the measurement quantifies the condition; the corrective decision remains subject to the engine maker's instructions and the vessel's operating conditions.
