Question 40 3AE01 - Third Assistant Engineer

The Correct Answer is C ### Why Option C (Neutralize Acids) is Correct The TBN value stands for **Total Base Number**. It is a crucial measure used for determining the remaining useful life of engine lubricating oil, especially in diesel engines. Diesel combustion inherently produces acidic byproducts (such as sulfuric acid, especially when high-sulfur fuel is used, and nitric acids). These acids cause corrosion of engine components and lead to premature wear. The TBN value quantifies the reserve alkalinity of the oil, indicating the amount of base additive (alkaline detergents and dispersants) present in the oil. This reserve alkalinity is specifically designed to **neutralize these acids**, thereby preventing corrosion and protecting the engine. A high initial TBN indicates a strong ability to neutralize acids over time; when the TBN drops to a critical low point, the oil is considered depleted and must be changed. ### Why Other Options Are Incorrect **A) resist changes in viscosity with changes in temperature:** This property is primarily measured by the **Viscosity Index (VI)**. A high VI indicates the oil's ability to maintain its viscosity stability across a wide temperature range, which is separate from its acid-neutralizing capability (TBN). **B) resist emulsification:** The ability of oil to resist mixing with water (emulsification) is related to the oil's formulation, including specific demulsifying additives and its inherent water separation characteristics. While important for lubricating oils, it is not what the TBN measures. **D) resist oxidation at high temperatures:** The resistance to oxidation is determined by the quality and quantity of **antioxidant additives** in the oil. Oxidation resistance is often measured through tests like RPVOT (Rotating Pressure Vessel Oxidation Test) or various stability tests, not directly by the TBN value. Although detergent and dispersant additives (which contribute to TBN) can sometimes have mild antioxidant properties, their primary function, as quantified by TBN, is acid neutralization.