Question 21 AEL01 - Assistant Engineer - Limited

The Correct Answer is D **Explanation for Option D (Heating the engine coolant):** Starting a large low-speed diesel engine, especially in cold weather, requires overcoming high resistance due to viscous lubricating oil and achieving the necessary compression temperature for ignition. Heating the engine coolant (using a jacket water heater) raises the overall temperature of the engine block, cylinder liners, and surrounding components. This heating achieves three critical goals that ease starting: 1. **Reduces Viscosity:** It warms the engine components that are lubricated, significantly lowering the viscosity of the lubricating oil. This reduces the rotational drag (resistance) on the crankshaft and pistons, allowing the engine to turn over more easily and reach starting speed faster. 2. **Improves Atomization and Ignition:** By warming the combustion chamber walls (cylinder liners), the heat reduces the chilling effect on the incoming starting air and the injected diesel fuel. This ensures the air reaches a higher compression temperature, which is necessary to reliably ignite the fuel spray (improving atomization and reducing ignition delay). 3. **Protects Components:** Pre-heating also minimizes thermal stress and wear during the initial cold start. **Explanation of Incorrect Options:** **A) Increasing the quantity of starting air:** While the engine needs sufficient starting air pressure and volume, simply increasing the *quantity* of air available in the storage bottles (assuming the pressure and receiver capacity are already adequate for the standard starting procedure) does not address the fundamental problem of cold, viscous oil and low compression temperatures. The engine will still struggle to turn over rapidly enough to achieve reliable ignition. **B) Increasing the lube oil pressure:** The lube oil system is pressurized to deliver oil to bearings and moving parts *once the engine is running*. Attempting to increase the pressure before starting (assuming the stand-by pump is operating) does not reduce the viscosity of the cold oil, which is the root cause of the starting difficulty. High pressure with cold, thick oil simply increases the load on the stand-by pump and may not effectively reach critical areas, whereas heating the engine (Option D) reduces the oil's resistance everywhere. **C) Heating the engine fuel supply:** Diesel fuel heating is primarily done to reduce viscosity for proper pumping and injection, especially with heavy or high-viscosity fuels (like Heavy Fuel Oil). While standard low-sulfur marine diesel fuel (MGO/MDO) can benefit from slight heating in extreme cold, heating the fuel *alone* does not solve the primary mechanical issue—the resistance from cold, viscous lube oil—nor does it significantly raise the combustion chamber temperature needed for reliable ignition of the large engine. Pre-heating the block (Option D) is far more effective.