Reversing of Marine Diesel Engine

Summary

This video script delves into the intricacies of halting a ship, highlighting the marine engine's crucial role in navigation. Unlike vehicles, ships lack brakes and rely on reversing the engine's thrust for stopping. The script explains the complex process of engine reversal in two-stroke marine engines, detailing the adjustments in fuel pump timing and air injection timing. It also describes the mechanisms of starting air distributors and camshaft adjustments that facilitate the change in firing order, essential for maneuvering the ship in reverse.

Takeaways

• 🚢 The core of ship operations is the propulsion plant, specifically the marine engine, which enables the vessel to maneuver, accelerate, and stop.
• 🛑 Unlike cars, ships do not have brakes and rely on reversing the marine engine or propeller direction to stop.
• 🔄 The reversing process of a marine engine is complex and involves changing the fuel pump timing and air injection timing.
• 💡 Two-stroke marine engines, commonly used in ships, do not have clutch and gear systems like smaller engines to reverse the propeller direction.
• 🔧 Large marine diesel engines have symmetrical exhaust and scavenging timing in both forward and reverse directions, simplifying the reversing process.
• ⏱️ Fuel pump timing is adjusted using a pneumatic valve that shifts the cam follower roller, altering when fuel is delivered to the engine.
• 🌬️ Air injection timing is managed by a radial air start distributor, which is operated by two cams to supply air to the cylinders in the correct firing order.
• 🔄 When reversing, the firing order is changed, and the air distributor must supply air to the cylinders according to the new order to successfully reverse the engine.
• 📡 The telegraph is used to signal the desired direction of the ship, with the ahead and astern positions controlling the engine's direction.
• 🔧 In some engines like Mitsubishi, the entire camshaft moves axially to change the firing order, while in Sulzer engines, the cam moves relative to the shaft using a servo motor.
• 🛠️ Camshafts are integral to two-stroke engines, as they control fuel injection timing, which is essential for engine operation.

Q & A

What are the various operations involved in ship transportation besides loading and discharging?

Besides loading and discharging, ship operations include navigation, mooring, maneuvering, anchoring, and channel crossing.

What is the most important machinery in ship operations?

The most important machinery in ship operations is the propulsion plant of the ship, also known as the marine engine.

How do ships stop without brakes?

Ships stop by reversing the marine engine or the propeller direction to generate an opposite thrust, which reduces the ship's speed and brings it to a halt.

What components are crucial for reversing the direction of the propeller in a two-stroke marine engine?

In a two-stroke marine engine, the crucial components for reversing the propeller direction are the fuel pump timing and air injection timing.

How does the fuel pump timing work in a two-stroke marine engine?

The fuel pump timing is controlled by a camshaft, a negative cam, and a cam follower which operates the plunger of the pump. A pneumatic valve shifts the cam follower roller to alter the timing when a reverse command is given.

What is the role of the pneumatic valve in the reversing process of a marine engine?

The pneumatic valve is used to shift the cam follower roller, altering the timing of the fuel pump and enabling the engine to reverse.

How is the air injection timing adjusted for the reverse operation of a marine engine?

The air injection timing is adjusted using a radial air start distributor operated by two cams fixed on the end of the camshaft. The pilot valves are pushed onto different cam profiles for ahead or astern starting.

What happens if the position of the cam follower is not properly locked during the reversing process?

If the position of the cam follower is not properly locked, the fuel delivery will be stopped by a sensor fitted to each pump.

How does the firing order change when the marine engine is reversed?

When the marine engine is reversed, the firing order is altered by changing the fuel pump timing, which affects the sequence of fuel injection into the cylinders.

What is the purpose of the telegraph in controlling the direction of the ship?

The telegraph is used to signal the desired direction of the ship, either ahead or astern, which in turn controls the firing order and the direction of the marine engine.

How do different engines like Mitsubishi and Sulzer handle the firing order change during engine reversal?

In Mitsubishi engines, the entire camshaft is axially moved to change the cam and the firing order. In Sulzer engines, the cam is moved with respect to the shaft using a servo motor.