How Does A Turbo Work: Unveiling the Power of Boost

How Does A Turbo Work

Ahoy, fellow sea enthusiasts! Ever wondered about the engine powerhouse that propels those mighty marine diesel engines? In this post, we will try to put in our best effort to explain the Turbochargers from their working principles to design operation, and maintenance. Imagine a massive ship gliding through waves with astonishing speed, driven by a remarkable force. That power comes from something called a turbocharger, a really important piece that makes marine diesel engines work better.

From the spinning turbine to the intricate dance of air and fuel, understanding the inner workings of a marine diesel engine’s turbocharger is like peering into the heart of sea propulsion. engines. By the end, you’ll have a clear understanding of the world of turbochargers for marine diesel engines. Prepare yourself as we get into the specifics of marine diesel engine turbochargers.

Working Principle of Diesel Engine Turbocharger

The Exhaust gases from the Diesel Engine enter the Turbocharger through the gas inlet casing and nozzle ring to the turbine wheel. Exhaust heat energy is utilized by the turbine wheel to rotate the compressor wheel.

The compressor sucks the fresh air and sends the air to cylinders after compressing. Exhaust gases pass out to the atmosphere through the exhaust manifold connected to the gas outlet casing. Air for the engine operation is compressed in the Turbocharger. This air is drawn through the suction filter silencers and sent to the compressor wheel. Compressed air leaves the turbocharger through the casing via a diffuser.

As per the design of the turbocharger, the rotor operates in radial plain or ball bearings. Bearings are lubricated either with the engine lubricating system or with its pump as per the design and type of Turbocharger. We will explain the bearing Lubrication system and the type of bearings used further in a detailed description.

Method of Turbocharger For Diesel Engine

Constant Pressure Turbocharging

This system is used in main Engine Turbochargers. In a Turbocharger, if we supply the gas at constant pressure. There is an arrangement for taking the exhaust gas at constant pressure from each cylinder. The Exhaust gas from cylinders is discharged into a standard manifold at a pressure higher than the atmosphere.

The exhaust gases from cylinders expand in the exhaust valve of an engine to constant pressure in the exhaust manifold and then deliver to Turbine. In the Turbine, exhaust gases expand, and the mechanical work is done. In the Turbine, blown-down energy by exhaust in Thermal Energy gets converted into valuable work.

This type of turbocharger maintains constant pressure for the exhaust gases.

Pulse Turbo Charging

This system is used in generators. In this turbocharging short and small exhaust pipe connects each cylinder port to the Turbine. The kinetic energy associated with the blow-down exhaust gases is utilized. Exhaust pipes are so grouped in a manner that the overlap of exhaust gases doesn’t take place. There is no instability of the gases entering the turbocharger.

Immediately upon the exhaust valve opening, the top part of the blown-down exhaust energy is converted into pulses. Thermal energy into mechanical is converted by the pulses supplied to the turbocharger through narrow opening pipes.

Rapid action is desired due to the use of this system in low-pressure turbines. This system is not suitable for single-cylinder engines. Pulse turbocharging is mainly used in large diesel engines

Pulse Converter Turbocharging

In the Pulse Converter Turbocharging system, various exhaust manifolds are connected in a specially designed venturi junction. In the nozzle section of the century pressure, a pulse is converted to kinetic energy. Its design of the century as an ejector creates a suction effect in the exhaust lines and helps in the engine’s scanning process. The diffuser section of the century pressure gradually increases, supplying the high-pressure exhaust to the Turbine. Due to the engine’s quick response, this system is suitable and efficient even at part load conditions for low-pressure turbines.

Construction of a Turbocharger

Marine Engine Turbocharger has two parts, Turbine and blower side.   The turbine is impulse type and the compressor is centrifugal type, both sides are connected through the shaft.

Both sides are provided with a casing that carries the Turbine and Blower. A filter is provided on the blower side casing to fitter the air and supply clean air to avoid damage to the compressor blades. The pressure of the air is enhanced with the help of a diffuser.

Exhaust gases to the turbine blades are guided by the inlet casing on the turbine side. The pressure energy of the gases is converted into kinetic energy by the nozzle ring fitted before the turbine.

The shaft is supported by bearings. These bearings make it possible to run the shaft at a high speed of about 20000 to 40000 revolutions per minute. The design of bearings will be as per the speed of the turbocharger. For the extreme higher speed bush bearings are suitable and the roller bearings are suitable for the medium speed.

Turbocharger Parts And Function

The compressor Impeller

A Compressor Impeller is a radial centrifugal type component. Air is induced to the Impeller’s eye through the filter. The rotating compressor creates a low-pressure area, accelerates to the periphery of the Impeller, and leaves with high velocity.
The material of the Impeller is either titanium or aluminum alloy. The aluminum impeller has a short life due to the creep. The final Air temperature decides the creep.

 Turbine

The turbine rotates the compressor impeller using exhaust gas.

• The material of Turbine blades is Nickel chrome alloy or nimonic material with excellent resistance to creep, fatigue, and corrosion.
• Positive fixing of blades is ensured by the special design of the blade root ( fur-tree shape)
• To facilitate the thermal expansion, blade fixing is loose.

Diffuser

Once air leaves from compressor it passes through the diffuser. The diffuser consists of vanes as shown. Due to the configuration air slows down when it leaves the diffuser that is there is a conversion from kinetic energy to pressure energy.

Nozzle ring

The nozzle ring has to be resistant to high temperatures and corrosion. It is made from a chromium-nickel alloy to resist the creep. Heat-resisting molly-grown nickel steel or Nemonic alloy. The cross-sectional area of each nozzle decreases as the exhaust gas passes through that. Because of this gas is forced to speed up kinetic energy will increase through this and pressure and heat energy will decrease.

Labyrinth seal

To prevent exhaust gas leakages and the drawing of oil into the compressor, a labyrinth seal is provided on the shaft

Types of Turbocharger

Axial flow type ( TCA Type Turbocharger)

Axial flow turbine after the nozzle ring gas moving with high velocity is directed to the turbine blades as the gas changes direction due to the blade profile. a force is imparted onto the blade causing it to turn the turbine wheel.

Radial flow type (TCR Type Turbocharger)

Radial flow turbine nozzles work in a similar way as in the axial flow type. that is pressure energy is converted into kinetic energy and the gas is directed onto the turbine wheel as the gas passes through the turbine wheel it changes direction and this change of direction produces an impulsive force that turns the wheel.

Turbocharger Bearing

Ball/ Roller type

Ball and roller-type bearings with resilient mounting and spring damping are used to prevent damage to the bearings. These bearings support the rotor shaft at both ends.

On the blower side, there’s a double-row ball bearing that handles the axial load of the shaft. It has thrust packings on both sides of the housing.

Leaf springs are used to prevent vibration and excessive movement of the balls. The bearing is fully enclosed in the casing, and the bottom part of the casing holds lubricating oil.

Lubrication for this type of bearing is done through a gear pump. This pump is driven by the turbine shaft and provides oil to the bearing. An oil level indicator is present for checking the oil level. There are plugs for oil filling and draining in the casing.

The turbine side of the bearing has a single row and allows for the linear expansion of moving parts. Lubrication is similar to the compressor side-bearing lubrication.

Journal sleeve/Bush-type bearing

This bearing arrangement is shown in the following diagram. The sketch shows radial flow type Turbo arrangement. In this type of arrangement, Lubrication is a forced lubrication type. Oil is supplied either by a gear-driven pump or pressure lubrication by the engine lube oil system itself. This arrangement is employed in radial-type turbochargers.

Bering support is the board. The turbine and compressor wheel are fitted outboard on both ends of the shaft. Due to the high speed, a sleeve type of Bearing is used for this type of Turbocharger. Bearing Lubrication is through the engine oil system. Lubricating oil is available all the time at Turbocharger. In the event of starting and stopping, the Bearing is lubricated by an engine lube oil priming pump,

Variable Geometry Turbocharger

In turbochargers with Variable Geometry (VGT), there’s something special called nozzle rings. These rings can move, and they’re in charge of changing the angle of the blades. Why? Well, it’s because they help control how the exhaust gas flows.

So, with a VGT turbocharger, the engine can change how much air it gets along with the fuel. This is really handy because it means the engine can work just right, no matter how heavy or light the job is. It’s kind of like having a gas pedal that adjusts itself automatically!

In simple words, a VGT turbocharger helps the engine work better by changing the angle of the blades to control how much air and fuel go in. It’s like giving the engine exactly what it needs to do its job well, whether it’s working hard or taking it easy.

Advantages 

1. Works on the entire range of the Engine
2.    No need for the Auxiliary Blower
3.    Reduces fuel consumption
4.    Reduces exhaust stroke emissions and reduces air pollution
5.    Lowers CO2, SOX, NOx Emissions
6.    No Soot and carbon deposits.
7.    Reduces fouling of Parts
8.    Improved Overall efficiency of Engine

K Value in Turbochargers

The distance between the rotor shaft end and the bearing cover flange is known as the K value. The measurement of the K value is taken from the blower side.

Importance of k value

To prevent contact between the impeller and the blower casing in the event of wearing out of the thrust bearing, the K Value is maintained.

Most Common Issues with Turbochargers

Surging

To understand the phenomenon of surging in Turbocharging Diesel Engines, let us consider the following conditions.

P1 Compressor outlet pressure.

P2 (Pressure 2) Pressure from Charge Air Cooler

M (mass Flow)

Case A: – P2/P1=1, and M is on the Higher side. In this case, it indicates no restriction to the flow of mass since boot the pressures are equal, and the mass flow of air is also on the higher side.

Case B:- P2/P1 ≥1 and mass flow M offer is a little less

Case C:-P2/P1 ˂ one and Mass flow is wholly decreased.

Case C is when the Pressure ratio of P2 /P1 is less than one and mass flow is Negligible, and in this condition, surging occurs.

Leading Causes for the Turbocharger Surging

• High exhaust backpressure
•  Chocked scavenged ports
•  Excessive turbo outlet restriction
• Fouled Nozzle ring blades
• Leaky Exhaust valves
• Misfiring in one or more cylinders
• Fouled Compressor wheel Blades
• Chocked Charge Air Cooler
• Turbo outlet pressure leak
• Erratic engine or engine control operation
• A muffler with a large amount of water in it.
• Sudden Load Change
• Fire in Scavenge space or Exhaust Trucking
• A collapsed air cleaner filter element.
• Several cylinders were misfiring.
• A badly worn fuel control linkage.
• An improperly adjusted governor.
• A worn governor actuator.
• A voltage regulator with an intermittent output fault.
• Damaged turbine and compressor blades on the turbo.

Checking Turbocharger Efficiency While in Operation

Turbine Efficiency= Turbine Efficiency (Drop in Turbine side) + Blower Efficiency (Filter chocked) + Mechanical Efficiency

1. If the temperature difference is more than, it indicates that the Turbocharger is running efficiently. If the difference in temperature is more than it suggests, the fouling of internal Turbocharger moving parts
2. The readings of the Manometer at the compressor side. There is an absolute pressure gauge before the filter, and after the filter, a manometer is installed. The reading at the Manometer will indicate the choking of the filter. If the filter is choked, then the air-induced mass flow will be less, and combustion will be poor.
3. If the charge air cooler is choked, then the air-induced density will be less and will result in poor combustion. The difference in water temperature between the inlet and Outlet of the charge air cooler should not be ˂ 5⁰C
4. The temperature difference of air across the charge air cooler should be between 35⁰C to 40⁰C.

Guidelines for Dealing with a Blocked Turbocharger in Diesel Engines

No action is to be taken for the 4-stroke engine with one turbocharge and separate air receiver. It is possible to run the engine as a naturally aspirated engine.

Common air receiver

Remove the compensator of the broken turbocharger and isolate the air ducting on the engine side.
Power pulses will be applied on the locked rotor for the pulse-type turbocharger. Maintain the following operating parameters.

1. The engine can be operated up to a maximum of 25% engine load.
2. The pressure in the charge-air receiver must not exceed 0.9 bar
3. With pulse supercharging (2…4 gas inlets), the engine can be operated up to a maximum of 20% engine load.
4. The pressure in the charge-air receiver must be less than 0.5 bar

Turbine Side water washing

Blog Post Conclusion

In the end, think of turbochargers as secret helpers for marine diesel engines, giving them more power and efficiency. Exhaust gases come out to rotate the turbine and the compressor gets rotated which is mounted on the same shaft. The compressor compresses the air and sends it to the Engine. More air induced in the cylinder will help in burning more fuel efficiently and increasing the Engine efficiency.

Understanding the working of a Turbocharger is a bit complex since these are highly rotating machines.
In this blog post, we have tried to explain the working of a Turbocharger in a very simple easy-to-understand way for Beginners. Happy learning!!

Best Book On Turbochargers

Turbocharging the Internal Combustion Engine

This is the most authoritative text on turbocharging for internal combustion engines. I essentially had to look no further to indulge in the intricate technicalities of how turbos work and how they affect the engine as a system. Don’t be fooled by Nicholas Baines’ Introduction to Turbochargers. It is not a replacement for this book nor are many topics covered in the as the highly effective/relevant chapters on diesel engine exhaust emissions and noise, turbocharging for petrol engines, and the nearly 100 pages on modeling.

I’m thrilled to write that Watson and Janote have compiled several topics and ideas in the most lucid style I have ever come across, such that a complex subject is made easy to understand.

That said, it is not a simple book to read by any means and it is highly recommended that you have a strong interest in engines and turbochargers before you pursue this text. It also is highly research-oriented in nature so I would not recommend using this book to get something practically done with your turbo project. For those, there are several coffee table auto books written on turbochargers. You may, however, understand a lot of the science behind turbochargers.

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