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Questions and Answers
What is the main topic of Unit 3 in the Applied Sciences course at Antwerp Maritime Academy?
Propulsion
Which of the following is NOT a fuel type discussed for marine engines?
The Lubrication oil system for marine engines includes a Main lubrication oil system.
True
The connection between piston and ______ can be achieved through a Crosshead engine or a Trunk piston engine.
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What parts of the engine are lubricated by the main lubrication system?
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What are the different sections the lubrication oil system is split into?
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The high temperature fresh water system is used to cool down the engine cylinders and exhaust valves.
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The low temperature fresh water system cools down different parts of the installation, such as the _____ and the turbo.
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What is the purpose of the safety valve in a marine diesel engine?
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What component of a diesel engine transforms the piston's translation into rotation?
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A turbocharger in a diesel engine is powered by the combustion of fuel.
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The distance traveled by the piston between the Top Dead Centre (TDC) and Bottom Dead Centre (BDC) is known as the _______ length.
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What is the residuum from the thermal cracking process that cannot be used as fuel but is used in asphalt and membrane roofing?
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Which of the following statements about LPG is true?
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Methane has a higher knock resistance compared to hydrogen.
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In the crosshead engine, the piston is _ connected with the piston rod, a crosshead supports and the connecting rod.
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Match the alternative marine fuel with its description:
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What is the primary purpose of the turbine in the propulsion system?
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What is the purpose of the PTI (Power Take In) in the turbine system?
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Exhaust gases should have a temperature above 200°C to prevent soot in the boiler.
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What is the purpose of electric accumulators in the emergency system? Electric accumulators start the emergency system in ___ conditions.
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Match the component of the boiler with its description:
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What is the purpose of controlling the viscosity of the fuel in a crosshead engine with an exhaust valve?
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A vessel equipped with two daily tanks for heavy fuel can run every day on a single tank.
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What is used to start the engine in a crosshead engine with an exhaust valve?
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At what minimal pressure is the compressed air produced for starting the engine?
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Match the following engine components with their functions:
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What transformation occurs in the superheater?
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Fire tube boilers are used to generate saturated steam for heating purposes. (True/False)
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What is the primary purpose of a water tube boiler?
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The flow rate of the supply pump is controlled with the rotational speed of the pump or with a control valve and directed with a signal indicating the water level in the _______ collector.
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What is the rotational speed range of a turbine as mentioned in the content?
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What is the main purpose of a turbine in driving most rotating machines?
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Which is NOT a characteristic of isentropic expansion?
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A turbine seal must be contactless due to the high rotational speeds involved.
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The turbines are positioned to compensate the axial forces by another turbine if a system exists out of more than one ____________.
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What are the two turbines used for propulsion?
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What is the purpose of sending the lowest possible amount of steam to the condenser?
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What type of turbines are the turbo alternators described in the text?
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What is the purpose of the secondary steam system mentioned in the text?
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Why is the secondary steam system separated from the primary system?
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What is the purpose of the steam-steam generator mentioned in the text?
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Study Notes
Propulsion I
- The course Propulsion I aims to describe the entire drive train of a merchant vessel, starting from the properties of marine fuel and how it is refined, to the engine and propeller.
Diesel Engine
- A marine diesel engine is composed of a number of cylinders, with a cylinder liner made of cast iron, rigidly connected to the engine block.
- The cylinder liner is at the top side closed with the cylinder cover, which contains fuel injectors, safety valves, starting air valves, inlet valves, and exhaust valves.
- A piston moves up and down in the cylinder, made gas-tight by three to five piston rings.
- The continuous translation of the piston takes place between the Top Dead Centre (TDC) and the Bottom Dead Centre (BDC).
- The distance traveled by the piston in one motion is known as the stroke or stroke length.
- The translation of the piston is transformed into a rotation by a connection rod – crank system.
Engine Cycles
- A four-stroke engine has four cycles: compression, power, exhaust, and intake.
- A two-stroke engine has two cycles: compression and power, with scavenging occurring at the end of the power stroke.
- Two types of scavenging can be distinguished: uniflow-scavenged and loop-scavenged.
Comparison between 2 Stroke and 4 Stroke Engine
- A two-stroke engine can deliver more power than a four-stroke engine for the same engine speed and dimensions.
- A two-stroke engine produces power every rotation, while a four-stroke engine needs two rotations for one power stroke.
- A two-stroke engine can use ports, while a four-stroke engine uses valves.
Fuel
- Atmospheric distillation, vacuum distillation, catalytic cracking, and thermal cracking are methods of refining fuel.
- LPG, LNG, and CNG are alternative marine fuels.
- Knock resistance is a key factor in fuel selection.
The Connection between Piston and Crankshaft
- The connection between the piston and crankshaft can be done using a crosshead engine or a trunk piston engine.
- Crosshead engines have a piston rod attached to a crosshead, which makes a vertical translation, allowing for a stuffing box to separate the chambers.
- Trunk piston engines have a piston attached directly to the crankshaft.
The Different Systems
- The lubrication oil system, cooling water system, fuel oil system, and starting procedure are essential systems in a diesel engine.
- The lubrication oil system includes lubrication of the cylinder liner, camshaft, and main lubrication oil system.
- The cooling water system includes high temperature fresh water system, low temperature fresh water system, seawater system, and piston cooling water system.
- The fuel oil system includes storage, settling, and service tanks, as well as supply of fuel to the injection pumps.
Diesel Generators
- Diesel generators are used as emergency systems or auxiliaries.
- They are used to provide power in case of main engine failure or when the ship is at anchor.
Steam Turbine
- The steam turbine is a type of engine that uses steam to generate power.
- The steam turbine is connected to a generator to produce electricity.
- The steam turbine has a geometry that allows for efficient energy conversion.
- The turbine steam condenser is used to cool the steam and convert it back into liquid.
- The turbine bearings and seal are essential components of the steam turbine.
Steam Boiler
- The steam boiler is a critical component of the steam turbine system.
- The boiler is used to produce steam, which is then used to generate power.
- The boiler includes components such as the economiser, evaporator, and superheater.
- The boiler is classified into two types: fire tube boiler and water tube boiler.
- The boiler is equipped with safety valves, supply pumps, and desuperheater.
Examples
- The LNG carrier Methania is an example of a steam system with a turbine.
- The steam system is used to generate power for the ship's propulsion.### Fuel Refining Process
- The refining process is necessary to understand the nuances of fuel quality
- Four main steps in the refining process:
- Atmospheric distillation
- Vacuum distillation
- Catalytic cracking
- Thermal cracking
Atmospheric Distillation
- Crude oil is heated to 360°C at atmospheric pressure
- Lighter components vaporize and rise in the column
- Temperature decreases higher in the column
- Different levels of the column yield different qualities of fuel
- Top of the column: LPG (Methane, Propane, Butane) and gases with a boiling point below 125°C
- Lower in the column: atmospheric distillates (benzene, naphtha, kerosene, gasoil)
- Bottom of the column: atmospheric residuum (70-90% of the original crude oil)
Vacuum Distillation
- Temperature limited to 400°C to prevent cracking
- Vacuum simplifies vaporization and yields more fuel
- Outcomes: vacuum gasoil and slop wax
- Vacuum gasoil is used as gasoil after dilution with atmospheric distillate
- Slop wax is used as raw material for catalytic cracking
Catalytic Cracking
- Slop wax is treated to crack long molecules into shorter ones
- Process carried out at high temperatures (250°C) with aluminosilicates
- Outcomes: LPG, gasoil, olefins (ethylene), and unsaturated compounds
- Hydrogenation adds H to unsaturated compounds for stability
Thermal Cracking
- Final step to extract fuels and chemicals from residuum
- Two types: visbreaker and flexicoker
- Visbreaker: yields a small amount of LPG and distillates
- Flexicoker: yields more distillates and a more stable residuum
Concluding Remarks on Refining
- Different refining processes yield different fuel properties
- Residual fuel is a mixture of residuum and can be diluted with distillates
- Cracking makes residuum less stable, and catalytic cracking yields catalytic fines
Alternative Marine Fuels
- Hydrogen:
- Hard to store due to high pressure and low temperature
- Origin can be "brown" or "green"
- Produces water after combustion
- Methanol and Ethanol:
- Can be made from CO2 and H2
- Produce CO2 and H2O after combustion
- Fluid and easy to store
- Methane and Ethane:
- Methane slip
- Greenhouse gas
- Ammonia:
- Zero carbon
- Toxic and corrosive
- Fluid
- Electric:
- Storage (battery) is problematic
- Simple, reliable, and low maintenance
- Torque and autonomy
Connection between Piston and Crankshaft
- Crosshead Engine:
- Principle: piston is connected to piston rod and crosshead, which supports the connecting rod and crankshaft
- Consequences:
- Large and heavy pistons
- Limited rotational speed
- Reliability increases
- Specific fuel consumption is better
- Applications: large two-stroke engines for propulsion
- Issues: lubrication, scavenging, and cooling
- Trunk Piston Engine:
- Principle: connection rod connects piston and crankshaft directly
- Consequences:
- Smaller pistons
- Higher rotational speed
- More power per cylinder
- Four-stroke engine is more suitable
- Applications: smaller engines for gensets, RoRo-vessels, and high-speed vessels
- Issues: maintenance cost, reliability, and fuel quality
Lubrication Oil System
- Lubrication of the cylinder liner:
- Obtained by injecting lube oil between cylinder segments
- System includes storage tank, make-up tank, lubrication pump, and lubricators
- Lubrication of the camshaft:
- Dedicated system sometimes used
- Main system used as standard
- Main lubrication oil system:
- Provides lubrication oil to crankshaft, gears, connection rod, and crosshead
- Cools the piston
- System includes service tank, cooling system, and filters
Cooling Water System
- High-temperature fresh water system (HTFW):
- Cools engine, cylinders, and cylinder covers
- Temperature of the water needs to be warm enough
- May be cooled by mixing with low-temperature fresh water system or heat exchangers
- Low-temperature fresh water system (LTFW):
- Cools the HTFW system, lubrication systems, and other components
- Temperature of the water is around 32°C
- Can be cooled by seawater system via heat exchangers
- Seawater system:
- Cools the LTFW system
- Two concepts: decentralized and centralized seawater cooling systems### Cooling Systems
- Various parts of the engine require low temperatures, which are achieved by directly connecting them to the seawater system (e.g., air conditioning, refrigerators, steam condenser)
- More fragile or temperature-sensitive parts are cooled with a centralised cooling system
- There are three types of cooling systems:
- Seawater cools freshwater, which in turn cools lube oil, exhaust gases, and the engine (jacket)
- Seawater cools exhaust gases and freshwater, which then cools lube oil and the engine
- Seawater cools lube oil, exhaust gases, and freshwater, which then cools the engine
MAN Cooling System
- The MAN system is a centralised cooling system that cools:
- LTFW (Low Temperature Fresh Water)
- Air-conditioning
- Steam condenser
- Condenser and oil cooling system of the cooling installation
- The system has two main pumps and one auxiliary pump, with the auxiliary pump used in harbour conditions
- There are two seawater chests: one at the bilge and one at a higher position
SULZER Cooling System
- The SULZER system is similar to the MAN system
- It is used to replace the LTFW if there is no centralised cooling system
- The control of the temperature of the seawater is important
Piston Cooling Water System
- Sometimes, pistons are cooled with water, which requires a dedicated cooling water system
- The system is used only for large engines and has a high risk of corrosion due to the presence of air
Fuel Oil System
- Overview of the fuel oil system:
- Storage tanks (1) with fuel at 30-50°C to be pumpable
- Settling tank (2) with fuel at 70°C to remove impurities
- Daily tank (or service tank) (3) with clean fuel
- Fuel is cleaned in purifiers before entering the daily tank
- Fuel pumps are sometimes incorporated into the purifiers
- Switching fuel type (e.g., from heavy fuel oil to diesel oil) requires carefulmanagement of viscosity and temperature to avoid damage to the engine
High-Pressure Injection
- Fuel is injected into the cylinder through injectors
- The fuel is atomized, resulting in smooth self-ignition and integral combustion
- The injection pump is specific to each cylinder
- The pressure in the injection pipes is about 600-1500 bar, depending on the injection speed, nozzle dimensions, and fuel viscosity
- The viscosity of the fuel is monitored and controlled to ensure proper injection
Starting Procedure for the Main Engine
- Production of compressed air:
- Compressed air is produced with two compressors with different stages and intercooling
- Both compressors are connected in parallel and start automatically when the compressed air pressure drops below a minimal pressure
- The compressed air is cooled before being stored, and condensation of the air cannot be avoided
- Switching the engine on:
- Compressed air enters the cylinder at the same time as the piston reaches the position where combustion is expected
- The starting valves are opened pneumatically with a starting air valve
- Minimal number of cylinders to start an engine:
- For a two-stroke engine, at least 4 cylinders are necessary
- For a four-stroke engine, at least 6 cylinders are necessary
- Failed engine start:
- The engine may not start due to various reasons, such as sedimentation of soot in the starting valves
- A slow start procedure is used to avoid this issue
- Slow start:
- A second master valve with a small air capacity allows the engine to run slowly without fuel supply
- This is used to check the performance of all parts and to drain fluids collected in the cylinder
- Changing the direction of the engine:
- The engine must be able to run in both directions
- The camshaft, valves, and fuel cams must be repositioned
- A hydraulic servomotor is used to shift the camshaft
Protection
- The engine is equipped with different types of protection systems:
- The master valve cannot be opened while the 'torn machine' of the engine is active
- The master valve cannot be opened as long as the starting cams are not in the correct position
- Compressed air cannot enter the cylinder as long as the cylinder pressure is too high or the rotational speed of the engine is too high
- Fuel oil cannot be injected as long as the direction of the engine is in the desired rotational direction
Turbocharger
- A turbocharger consists of a turbine and a compressor
- The turbine is driven by exhaust gases and compresses air
- The compressed air is used for scavenging and combustion in the cylinders
- The amount of air available for combustion is the limiting factor for the amount of fuel injected in the cylinder and the total power of the engine
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Description
Part 1 of Propulsion course for 3rd-year Bachelor students in Nautical Science at Antwerp Maritime Academy, covering principles of propulsion systems.
