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.

Outlines

00:00

🚢 Marine Engine Operations and Ship Stopping Mechanism

This paragraph delves into the complexities of ship operations, focusing on the crucial role of the marine engine or propulsion plant. It clarifies that ships lack brakes and instead rely on the marine engine to stop by reversing the propeller direction. The explanation outlines the process of engine reversal, emphasizing the absence of clutch and gear systems in large marine diesel engines. It highlights the importance of adjusting fuel pump timing and air injection timing to achieve the reverse thrust. The paragraph also describes the components involved in this process, such as the fuel pump, camshaft, and pneumatic valve, and explains how compressed air is utilized to actuate the reversal mechanism. The summary underscores the intricate nature of marine engine operations and the significance of the reversing process in ship maneuvering.

05:04

🔧 Advanced Reversing Techniques in Two-Stroke Marine Engines

The second paragraph expands on the technical aspects of reversing two-stroke marine engines, which are integral to ship navigation. It discusses the unique absence of clutch and gear systems in these engines and the necessity of reversing the entire engine rotation to change the direction of thrust. The paragraph explains how fuel pump timing is altered using a pneumatic valve and a cam follower, which is shifted to change the injection timing during the reversing process. It also details the use of a radial air start distributor operated by two cams to supply air to the cylinders according to the new firing order. The description includes the process of starting the engine in both ahead and astern directions, illustrating how the telegraph signal and air signals interact with the starting air cutoff valve and air distributor to deliver the correct sequence of starting air to the combustion chamber. The summary provides a comprehensive understanding of the advanced mechanisms that enable two-stroke marine engines to reverse direction efficiently.

Keywords

💡Cargo

Cargo refers to goods or produce transported by a ship. In the context of the video, cargo is a fundamental aspect of ship operations, highlighting the importance of the various processes involved in its transportation, including loading and discharging.

💡Ship Operations

Ship operations encompass all activities related to the functioning of a ship, such as navigation, mooring, and maneuvering. The video emphasizes that these operations are central to the marine industry and are intricately linked to the ship's propulsion plant.

💡Marine Engine

A marine engine, also known as a propulsion plant, is the primary machinery on a ship that enables it to move. The video script underscores its significance in allowing the vessel to maneuver, accelerate, and stop, which is crucial for safe and efficient ship operations.

💡Maneuvering

Maneuvering refers to the process of controlling a ship's movement to navigate safely. The script mentions maneuvering as one of the operations involved in ship transportation, highlighting the marine engine's role in this process.

💡Anchoring

Anchoring is the action of securing a ship in place by dropping an anchor. It is one of the several operations mentioned in the script that the marine engine supports, particularly when a ship needs to stop and hold its position.

💡Propulsion Plant

The propulsion plant is the system that powers a ship, including its engine and propeller. The script describes it as the heart of ship operations, emphasizing its central role in enabling the ship to move and stop.

💡Reversing Marine Engine

Reversing a marine engine involves changing the direction of the propeller's thrust to slow down or stop the ship. The script explains this process as a key operation for halting a ship, which is achieved without the use of brakes.

💡Two-Stroke Marine Engine

A two-stroke marine engine is a type of engine that completes a power cycle in two strokes of the piston. The script discusses this engine type, noting that it lacks a clutch and gear system, and instead requires reversing the entire engine rotation to change direction.

💡Fuel Pump Timing

Fuel pump timing is the synchronization of fuel delivery with the engine's operation. The script explains that altering this timing is a critical step in reversing the marine engine, as it changes the moment of fuel injection.

💡Air Injection Timing

Air injection timing refers to the precise moment when air is supplied to the engine's cylinders. The video script describes how adjusting this timing is essential for the engine to operate in reverse, ensuring the air is supplied according to the new firing order.

💡Firing Order

Firing order is the sequence in which the engine's cylinders are ignited. The script explains that changing the firing order is necessary for engine reversal, as it affects the timing of fuel injection and air supply to the cylinders.

💡Camshaft

A camshaft is a part of the engine that controls the opening and closing of the engine's valves. The script details how the camshaft, through its design and operation, is integral to the process of reversing the marine engine by altering the fuel pump and air injection timings.

💡Pneumatic Valve

A pneumatic valve is a valve that uses air pressure to operate. In the context of the script, it is used to shift the cam follower roller, changing the timing for reversing the engine, which is a critical component in the operation of the fuel pump.

💡Starting Air System

The starting air system is used to initiate the engine's operation. The script describes how compressed air from this system is utilized to actuate the pneumatic cylinder and piston, which in turn displaces the follower units for engine reversal.

💡Telegraph

A telegraph is a device used on ships to communicate commands between the bridge and the engine room. The script mentions that moving the telegraph to the 'ahead' position signals the engine to move in the forward direction, which is part of the ship's operation control.

Highlights

Transportation of cargo and ships involves various operations beyond loading and discharging, such as navigation, mooring, and maneuvering.

The propulsion plant or marine engine is central to ship operations, allowing the vessel to maneuver, accelerate, and stop.

Ships do not have brakes; they stop by reversing the marine engine or propeller direction to generate opposite thrust.

The reversing process of the marine engine is complex and involves changing fuel pump timing and air injection timing.

Two-stroke marine engines in ships lack clutch and gear systems for propeller direction reversal; the entire engine rotation must be reversed.

In large marine diesel engines, exhaust and scavenging timing are symmetrical in reverse and ahead directions.

Fuel pump timing is altered using a pneumatic valve that shifts the cam follower roller to change the timing for reversing the engine.

Compressed air from the starting system is used to actuate the pneumatic cylinder and piston for fuel pump timing adjustment.

A sensor on each pump ensures that if the position is not properly locked, fuel delivery is stopped.

Altering the fuel pump timing changes the firing order, which is crucial for the engine reversal process.

Large MC engines use a radial air start distributor operated by two cams to supply air according to the new reverse firing order.

The pilot valve follower in the air start distributor is pushed onto different cam profiles for ahead or astern starting.

When the ahead command is given, the starting air is supplied to the air distributor according to the firing order.

The astern command shifts the distributor cam for the astern firing order, supplying starting air to the combustion chamber in reverse sequence.

In Mitsubishi engines, the camshaft contains two cams for ahead and astern directions, with the entire camshaft moved axially to change the firing order.

Sulzer engines move the cam alone with respect to the shaft using a servo motor to change the firing order.

Camshafts are integral to two-stroke engines, as without them, fuel injection would not occur.

Transcripts

when it comes to transportation of cargo and ship

it is not just about loading and discharging

there are several other operations involved such as

navigation, mooring, maneuvering, anchoring, channel crossing and so on but at the

heart of the ship operations is the most important machinery, that is the

propulsion plant of the ship or marine engine.

The marine engine allows the vessel to maneuver

accelerate and stop whenever required

now as you all must be aware of, ships do not have brakes

which can be used whenever they want to stop. So how do ships actually

stop? let's understand in this video, but before that please do subscribe to

our youtube channel and press the bell icon to view all our

future videos. Back to the topic, the halting of the

ship is done using the marine engine. Whenever a ship

needs to be stopped, reversing of the marine engine or the

propeller direction is carried out to generate an opposite

thrust which ultimately reduces the ship's

speed and makes it stop as required. This whole process

might sound very simple but the engine is a complex machinery and so is the

reversing operation it undergoes. Let's understand how the reversing

process is carried out. The two-stroke marine engine used in

ships is made up of several parts which help it to operate

efficiently and safely. some of these components work together

in order to reverse the engine.

unlike medium or small sized internal combustion engines

the two-stroke marine engine does not have a clutch and

gear systems to reverse the direction of the propeller.

The entire engine rotation needs to be reversed

for change of thrust direction which in turn will reverse

the ship motion. In large marine diesel engines the exhaust and

scavenging timing are almost symmetrical in reverse and ahead direction, hence

in order to carry out reverse direction, the two important components

which needs to be changed are fuel pump timing

and air injection timing. Now let's understand how each of these

can be done. Fuel pump comprises a camshaft a

negative cam and a cam follower which operates the

plunger of the pump. The fuel pump will deliver the fuel when

the cam follower operates on top of the cam. Here a

pneumatic valve is installed which shifts the cam follower roller to

alter the timing when the reverse or astern command is given.

Compressed air from the starting system is used to actuate the pneumatic

cylinder and piston which displaces each follower

unit. If the position is not properly locked

in its place the fuel delivery will be stopped.

This is done by a sensor fitted to each pump

now once the engine is reversed and cam follower is shifted

the timing when the injection happens will change

when the fuel pump timing is altered for reversing of the engine

that is the firing order is altered it is important

to supply the air into the cylinder as per the new reverse firing order

else the reversal of engine will not take place

for this purpose the large mc engines use

a radial air start distributor operated by two cams

fixed on the end of the camshaft

The pilot walls arranged radially in housing

are either pushed by pilot air onto the inner cam profile when starting

ahead or onto the outer profile when starting

astern. When not in use a spring holds the pilot

valve follower clear of both profiles thus reducing

wear. If the engine needs to be moved in

forward direction the telegraph is moved to the ahead

position. Till now the starting air is not

supplied to the air distributor

once the ahead signal is given, the air signal goes to the starting air cutoff

valve, making it inactive. This allows the

starting air to go to the air distributor

and all the air starting valves via the air control valve.

Now the air from the air distributor will be supplied to different cylinders

as per the firing order. As the ahead cam rotates

the plunger which falls on the cam will move

allowing the air to pass through, delivering starting air to the

combustion chamber. When the astern command is given, the

astern air signal will shift the distributor cam and the

second cam which is responsible for astern firing

order will come into play. The astern air signal will make the air

cutoff valve inactive supplying the starting air from the air

manifold to the air distributor.

Now the air from the air distributor will be supplied to different cylinders

as per the reverse firing order, because the astern cam will operate

each unit plunger in aseron firing sequence as it rotates

allowing the starting air to go to the combustion chamber.

In other engines like mitsubishi, the camshaft contains

two cams one for ahead and one for astern direction for each unit.

The entire camshaft is axially moved to change the cam and hence the firing

order

in Sulzer engines, the cam alone is moved with respect to the shaft by use of

servo motor. Cam shaft are an integral part of any two stroke

engine as without them there will not be any fuel injection