Testing scuffing resistance of materials for marine 2-stroke engines – Difficulties with lab scale testing of a complex phenomenon

Abstract

Optimising sliding materials of marine two-stroke diesel engine cylinders for reduced risk of scuffing is imperative because of the high costs associated with replacing the cylinder liner. But how can a complex and poorly understood phenomenon such as scuffing be tested? This study investigates the potential of material selection based on lab tests. Experience from ship operation is combined with analysis of lab scale scuffing tests to evaluate the possibilities of gaining applicable knowledge from scuffing testing. Two piston ring materials, a grey cast iron and a plasma sprayed cermet coating, both currently used in engines, were tested. Each of the materials was tested with two surface characters, achieved by run-in in a real engine and by fine grinding respectively. The ranking of the two materials proved to differ between the two surface characters. In the tests, scuffing could only be detected when all oil had become removed from the contact by being adsorbed by agglomerated wear debris and scraped away. This and other critical mechanisms behind scuffing in the tests are thoroughly discussed and compared to possible mechanisms taking place in the engine.

An experimental investigation of the corrosive influence of SO2 relative to H2SO4 of marine engine cylinder liners

“…Moreover, the use of exhaust gas recirculation (EGR) can promote engine wear when sulphur is present . The cylinder liner wear in marine engines is normally stated in units of millimeters per 1000 h. In large two‐stroke marine diesel engines, a normal cylinder liner (bore) wear rate is less than 0.1 mm/1000 h, and wear rates exceeding 1 mm/1000 h are critical …”

Scuffing resistance testing of piston ring materials for marine two-stroke diesel engines and mapping of the operating mechanisms

“…Will the scuffing resistance ranking of materials be the same in the engine as in the test? Difficulties with evaluating the relevance of scuffing tests like the present were discussed in previous work [3]. For example, the ranking between ring samples of PS cermet and grey iron where reversed when testing with different surface preparation of the ring sample.…”

“…It shows that the effect of selecting between the tested materials is comparable to the effect of the sources of scatter in the tests. The possible sources of scatter were discussed in previous work [3].…”

“…Any problems with the lubrication would move the cylinder closer to a scuffing failure. Nonetheless ship operators report that using excessive amount of cylinder oil also can cause scuffing problems [3]. Many papers have reviewed the scuffing problem through the years, e.g.…”

“…This type of understanding is needed to analyse the critical mechanisms in actual engines and thereby enable validation of the relevance of specific scuffing tests. Some of the results were presented in earlier work [3], but are repeated here to simplify comparisons.…”