Marine Diesel Engine: Working Principle, Types & Maintenance
Table of Contents
1. What is a Marine Diesel Engine?
A marine diesel engine is the main power source of ships such as container vessels, tankers, and bulk carriers. It is designed for continuous operation, high reliability, and long service life in harsh sea conditions.
2. Working Principle (Very Important)
Marine diesel engines work on the compression ignition principle. The cycle follows these steps:
- Air Intake: Air is taken into the cylinder.
- Compression: Air is highly compressed (raising temperature and pressure).
- Fuel Injection: Fuel is injected at high pressure near top dead center.
- Ignition: Fuel ignites automatically due to the heat of the compressed air.
- Power Stroke: Expanding gases push the piston down, producing power.
3. Types of Marine Diesel Engines
3.1 Two-Stroke Marine Diesel Engine
- Cycle: Power stroke every revolution.
- Feature: High torque at very low speed.
- Design: Simple and efficient.
- Used for: Main propulsion of large ships.
- Speed Range: 60–120 RPM (slow-speed).
3.2 Four-Stroke Marine Diesel Engine
- Cycle: Power stroke every two revolutions.
- Design: Compact and flexible.
- Used for: Diesel generators (Auxiliary engines) and small vessels.
- Speed Range: 500–1800 RPM.
4. Main Parts of Marine Diesel Engine
- Bedplate: The engine foundation supporting the crankshaft.
- Cylinder Liner: Replaceable sleeve forming the combustion chamber.
- Piston: Receives power from combustion.
- Connecting Rod: Transfers power from piston to crankshaft.
- Crankshaft: Converts reciprocating motion into rotational motion.
- Cylinder Head: Houses valves and fuel injector.
5. Maintenance (Short Notes)
- Daily: Check oil levels, cooling water pressure, and check for leaks.
- Weekly: Clean air filters and inspect the turbocharger.
- Monthly: Check fuel injectors and cylinder liner condition.
- Annual: Major inspection and component overhaul.
6. Common Problems (Oral Ready)
- Black Smoke: Indicates poor combustion (air starvation or bad injectors).
- High Exhaust Temp: Engine overload or fouled turbocharger.
- Low Compression: Worn piston rings or leaking valves.
- Vibration: Misalignment or loose mounting.
7. Safety & Environment (Short)
- Pre-start checks are mandatory before any operation.
- PPE: Ear muffs, helmets, and safety shoes must be used in the engine room.
- Follow MARPOL Annex VI rules for emissions (NOx and SOx).
- Use low-sulfur fuel in ECA (Emission Control Area) zones.
8. Frequently Asked Questions (FAQ)
Scavenging is the process of removing exhaust gases from the cylinder and replacing them with fresh air for the next cycle. In 2-stroke engines, this happens near the bottom of the stroke.
Marine engines need to produce massive torque at low RPM (60-100 RPM) to drive the propeller directly without a gearbox. A longer stroke and larger bore are required to achieve this.
TBN stands for Total Base Number. It measures the oil's ability to neutralize acids formed during combustion, especially when using high-sulfur fuel.
No, car engines operate at high RPM and are not designed for the continuous, heavy-load operation required for ship propulsion.