Turbocharger For Diesel Engine
In this post on Turbocharger for Diesel Engine, I will discuss about the Turbo chargers for the marine and industrial Diesel engines application. I have an experience of working on several make of Turbochargers during my career in Shipping and Industries. This post on Turbocharger For Diesel Engine will be useful to the readers.
Turbocharger was invented by the Swish Engineer Alfred Buchi
Turbocharger is the most important part of a Diesel Engine. Turbocharger recovers the waste heat energy for rotating the turbine. The compressor wheel mounted on the same shaft, compresses the atmospheric air and supplies the compressed air to engine.
Working Principle of Diesel Engine Turbocharger
The Turbocharger is a machine consists of following main components.
Both Turbine and Compressor are mounted on a common shaft
Description of Turbocharger For Diesel Engine Principles
The Exhaust gases from Diesel Engine enter the Turbocharger through gas inlet casing and nozzle ring to the turbine wheel. Exhaust heat energy is utilised 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 filters silencers and sends to the compressor wheel. Compressed air leaves the turbocharger through the casing via diffuser.
As per the design of turbocharger, 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.
The function of a Turbocharger For Diesel Engine
1) Turbocharging will increase the power for an Engine of the same size, or in other words, it would reduce the size of an engine with the same power output.
2) It will reduce SFOC ( Specific Fuel Consumption).
3) Thermal loading of the engine will get reduced by the shorter burning period of fuel.
Method of Turbocharger For Diesel Engine
There are the following three methods of Turbo Charging.
- Constant Pressure Turbo charging
2. Pulse Turbo Charging
3. Pulse Converter
Description of Turbo charging methods
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.
Advantages of Constant pressure type system
1.The design of the exhaust pipe is simple.
2. Efficient Turbine can be used.
3. The pressure ratio is higher in compressor and Turbine, making it more efficient in recovery of exhaust energy.
4. This type of arrangement lowers the specific fuel consumption compared to other turbo charging methods (Pulse-type).
5. This system makes the Turbine run at higher efficiency by supplying the exhaust gases at constant pressure and temperature.
6. There is no limitation on Engine speed by the pressure wave in the exhaust pipes.
Disadvantages of Constant pressure type systemfor Turbocharger For Diesel Engine
1.Exhaust pipe size is significant to maintain the constant pressure.
2. Inefficient scavenging
3. At part load, turbine efficiency reduces due to the partial entry of exhaust gases.
4. Losses latent in mixing this high-velocity gas with a large volume of low velocity can’t be recovered.
5. Due to sluggish acceleration against the increased load, the system’s response is considerably poor and is unsuitable for two-stroke engines.
Pulse Turbo Charging
This system is used in generators. In this turbo charging 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 takes 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 in to mechanical is converted by the pulses supplied to 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 engine. Pulse turbocharging is mainly used in large diesel engines
Advantages of Pulse Turbo Charging
- Less space requirement due to the short and smaller diameter exhaust pipes.
2. Enhanced scavenging is achieved at less loads due to decreased pressure below the scavenge pressure.
3. Efficient recovery of blown-down energy as compared to constant pressure system.
4. Exhaust process of cylinders doesn’t interface with each other due to separate exhaust pipes.
Disadvantages of Pulse Turbo Charging
- Recovery of energy is poor due to the high-pressure ratio in Turbine.
2. Arrangements of Inlet and exhaust pipe are not simple in Multi-cylinder Engines.
3. Engine speed is limited.
4. Disturbed scavenging process in case the distance traveled by waves is long to reach the Turbine.
5. Turbine efficiency is low in case of the non-multi cylinder engine.
Pulse Converter Turbocharging
In the Pulse Converter Turbo charging system, various exhaust manifolds are connected in a specially designed ventury junction. In the nozzle section of the century pressure, a pulse is converted to kinetic energy. Its design of 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.
Best Book On Turbochargers
Turbocharging the Internal Combustion Engine
This is the most authoritative text on turbo charging for internal combustion engines. I essentially had to look no further to indulge in the intricate technicalities of how turbo’s 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 neither are many topics covered in the as the highly effective/relevant chapters on diesel engine exhaust emissions and noise, turbo charging for petrol engines and the nearly 100 pages on modelling.
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.