How a Ship Engine Works - 2-Stroke Marine Diesel Engine

Summary

This video explains the workings of a two-stroke marine diesel engine, used in large cargo ships. It highlights the engine's slow speed, typically running between 60-120 RPM, and its massive size—standing 42 feet tall. Key processes, including fuel injection, air compression, exhaust gas removal, and cooling systems, are described in detail. The video also covers the engine's starting mechanisms, valve operations, and lubrication systems, emphasizing safety features like explosion relief valves. Additionally, the role of the turbocharger, the cooling system, and the fuel heating process are explored. The history of the diesel engine, pioneered by Rudolph Diesel, is also mentioned.

Takeaways

• 😀 A two-stroke marine diesel engine completes a full power cycle in just two piston strokes: one downstroke and one upstroke.
• 😀 Unlike high-speed car engines, large ship engines operate at very low speeds, typically between 60-120 RPM.
• 😀 The size of a ship's engine is immense, with some models standing as tall as 42 feet, roughly the height of a four-story building.
• 😀 A marine engine uses starting air, highly compressed air blown into the cylinder, to begin its rotation before combustion starts.
• 😀 Fresh air is drawn into the engine through scavenge ports, pushing out exhaust gases and reducing pollutants via a scrubber system.
• 😀 The turbocharger has two sides: a turbine powered by exhaust gases and a compressor that draws in fresh air, which is then cooled and filtered.
• 😀 Cooling water flows through the cylinders to absorb heat, ensuring the engine runs at optimal temperatures.
• 😀 Exhaust valves in the engine are controlled hydraulically, using oil pressure to open and close them as part of the combustion cycle.
• 😀 The electronic control system (ECS) precisely manages fuel and hydraulic oil timing to ensure the piston motion is synchronized.
• 😀 In large cargo ships with low-speed engines, there's no gearbox; the propeller is directly connected to the engine, and it can be reversed by stopping and restarting the engine.
• 😀 Heavy fuel oil, used in marine engines, is heated to a high temperature to allow it to be injected as a fine mist for combustion, offering high energy output at a lower cost.

Q & A

What is the basic function of a two-stroke marine diesel engine?

A two-stroke marine diesel engine completes a full power cycle in two piston strokes: one where combustion occurs and the piston moves downward, and a second where the piston moves upward, compressing air.

How does the RPM of a marine diesel engine compare to a car engine?

Marine diesel engines operate much slower than car engines. They typically run between 60 to 120 RPM, and rarely exceed 200 RPM, while car engines often operate at thousands of RPM.

Why are marine diesel engines built for low speed rather than high speed?

Marine diesel engines are designed to be steady and strong, optimized for power and reliability to move massive cargo ships, not for speed or quick acceleration.

What is the size of a typical large two-stroke marine diesel engine?

A large two-stroke marine diesel engine can be 42 feet tall, roughly the height of a four-story building.

How does the starting process of a marine diesel engine work?

Starting a marine diesel engine involves using highly compressed starting air from the starting air valve to push the piston downward and begin the engine's rotation. Combustion does not happen right away during startup.

What role does the turbocharger play in the engine's operation?

The turbocharger uses exhaust gas to spin a turbine, which powers a compressor that draws in fresh air. This air is cooled, filtered, and sent to the cylinders to replace the exhaust gas in the combustion cycle.

What is the purpose of the exhaust valve's rotator?

The rotator on the exhaust valve ensures even wear on the valve disc by causing the valve to rotate slightly each time it opens, preventing uneven wear from repeated contact with the valve seat.

How does the engine reverse direction to move the ship astern?

To reverse the ship, the engine must first stop completely. Then, starting air is sent to the cylinders, and the crankshaft is reversed. Once the engine rotates in the opposite direction, normal combustion resumes, and the ship moves backward.

What is the function of the explosion relief valves in the crankcase?

Explosion relief valves are designed to release internal pressure in the crankcase due to vaporized lubricant. These valves prevent crankcase explosions by safely venting pressure while preventing outside air from entering, which could trigger a secondary explosion.

Why do large ships use heavy fuel oil instead of regular diesel?

Heavy fuel oil is cheaper and provides more energy output than regular diesel. It is thick and dense, so it is heated before being injected into the combustion chamber to ensure proper atomization and combustion.