Question 34 MODE01 - Chief MODU Engineer

The Correct Answer is D **Explanation for Option D (Diluted with fuel oil):** The flash point of a lubricating oil is the lowest temperature at which its vapors will ignite momentarily in the presence of an ignition source. Diesel engine lube oils typically have a relatively high flash point (often above $200^\circ\text{C}$ or $400^\circ\text{F}$). Diesel fuel oil (or marine gas oil) has a much lower flash point (typically between $60^\circ\text{C}$ and $100^\circ\text{C}$ for marine fuels). When the high-flash-point lube oil is mixed with the low-flash-point fuel oil (a condition known as "fuel dilution"), the overall mixture's flash point drops significantly, often to a value closer to that of the contaminant fuel. Therefore, a decrease in the lube oil's flash point is the primary and most reliable indicator of fuel oil contamination (dilution). **Explanation for Incorrect Options:** * **A) contaminated with carbon:** Carbon (soot) contamination is a common issue in diesel engines, often indicated by an increase in viscosity and the Total Base Number (TBN) decreasing rapidly. While soot can affect the oil's performance, it is a solid particulate and does not typically lower the flash point; rather, it often increases viscosity. * **B) contaminated with sludge:** Sludge is a mixture of oxidized oil, water, and insoluble contaminants. Sludge formation usually results from severe oil degradation or poor filtration. Like carbon, sludge is composed primarily of high-molecular-weight compounds that do not volatilize easily and therefore do not lower the flash point. * **C) diluted with water:** Water contamination, while harmful to engine components and potentially causing foaming, does not lower the flash point. Water boils at $100^\circ\text{C}$ ($212^\circ\text{F}$) and will flash off during the initial heating stage of the flash point test, leaving the oil behind. If anything, water presence can sometimes interfere with the test, but it does not chemically or physically reduce the flammability temperature of the remaining oil like fuel dilution does.