Exam Question

(a) Three properties required of crankcase oil for a trunk piston main engine
Thermal and Oxidation Stability: The oil must resist degradation under the high temperatures and oxidative conditions within the engine. Deterioration leads to sludge formation, increased viscosity, and reduced lubricating effectiveness. The oil needs to remain stable for extended periods under normal operating conditions.
Viscosity:  Appropriate viscosity is essential for maintaining an adequate oil film thickness between moving engine components. This prevents metal-to-metal contact, reducing wear and preventing damage. Too high a viscosity hinders oil flow, increasing friction and temperature. Conversely, viscosity that is too low increases the risk of metal-to-metal contact. The viscosity grade must be selected based on the engine's operating temperature and load.
Total Base Number (TBN):  TBN measures the oil's alkalinity and its ability to neutralise acidic byproducts of combustion. Acids formed during combustion are corrosive and can damage engine parts. Sufficient alkalinity is crucial to neutralise these acids, protecting against corrosion and extending the oil's service life. A minimum TBN is usually specified for the oil to ensure sufficient protection.