Reversing of Marine Diesel Engine
Summary
TLDRThis 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
🚢 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.
🔧 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.
Mindmap
Keywords
💡Cargo
💡Ship Operations
💡Marine Engine
💡Maneuvering
💡Anchoring
💡Propulsion Plant
💡Reversing Marine Engine
💡Two-Stroke Marine Engine
💡Fuel Pump Timing
💡Air Injection Timing
💡Firing Order
💡Camshaft
💡Pneumatic Valve
💡Starting Air System
💡Telegraph
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
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