Question 44 MODE01 - Chief MODU Engineer

The Correct Answer is B **Explanation for Option B (Increased exhaust valve wear):** Heavy fuel oils (HFOs) contain various impurities, including ash-forming compounds (primarily vanadium, sodium, nickel, and sulfur-related compounds). When HFO is combusted in a diesel engine (especially large, slow-speed marine engines), these ash components are deposited on hot surfaces. * **Vanadium and Sodium:** These elements combine to form low-melting point ash compounds (e.g., sodium vanadates). * **Corrosion/Wear:** These molten or semi-molten ash particles accumulate on the surfaces of the exhaust valves and valve seats. Due to the high temperature, high pressure, and movement of the valves, this corrosive ash layer accelerates high-temperature corrosion and abrasive wear, leading to pitting, guttering, and eventually failure of the exhaust valves. An increase in the average ash content directly translates to a greater quantity of these abrasive and corrosive materials passing through the combustion space and over the exhaust components, thus increasing exhaust valve wear. **Explanation of Why Other Options Are Incorrect:** * **A) Excessive bearing wear:** Bearing wear is primarily caused by lubrication issues, contaminants (like water or metal particles) in the lubricating oil, or high loads/temperatures transmitted through the crankshaft. While ash could potentially contaminate the crankcase oil via blow-by, the immediate and direct consequence of increased ash content in the *fuel* is combustion component wear, not bearing wear. * **C) Glazing of the cylinder liners:** Glazing, or bore polishing, occurs when the lubrication oil film is excessively stable and combustion temperatures are too low, preventing complete removal of the oil film. This smooths the liner surface, inhibiting the retention of lubrication oil. While poor combustion (which can be exacerbated by contaminants) might indirectly relate, bore polishing is typically linked to low load operation or improper lubrication viscosity, not directly to increased fuel ash content. Fuel ash's main effect on the liners is usually abrasive wear (scuffing) from hard particles, not glazing. * **D) Increased MEP (Mean Effective Pressure):** MEP is a measure of the average pressure driving the piston throughout the power stroke and is directly related to engine torque and power output. Increased ash content signifies lower fuel quality and higher impurity levels. While the fuel energy content (calorific value) might not change drastically, the negative effects of the ash (fouling of injectors, reduced turbocharger efficiency, increased friction due to wear) generally lead to *decreased* engine efficiency and thus either maintained or *reduced* MEP, not an increase.