Most of the marine diesel engines are adaptations of industrial engines used as well in automotive, their reliability is widely proved. They all share the engine block, what is different is the refrigeration system. Either marine and industrial engines use the benefits of a turbocharged system instead of an atmospheric aspiration.
What a turbocharger is and how it works
The first turbocharger was created in the beginnings of XX century and its development has been slow until it was equipped in non-stationary diesel engines. In the decade of 40’s it was developed a turbocharger by Alfred J Buchi wich has been implemented in industrial and marine power plants. The detonation in diesel engines takes place through compression. The fuel does not go into the cylinder until the top dead center (TDC), where ends the compression phase. The turbocharger increases the volume of air that enters the cylinder by increasing its pressure. With the same displacement and engine revolutions it is possible to reach higher pressure, particularly in the expansion phase. Whe it is introduced more oxygen in the cylinder, the engine is able to transform more fuel in energy, so increases its power.
How to increase the pressure
As its name indicates, the turbocharger is a turbine activated by the exhaustion gases and turning jointly with a centrifugal compressor. This second one take air from the atmosphere through the air filter and introduces it into the cylinder at a higher pressure. The exhaustion gases give their energy to the turbine and get out axially. By means of the intercooler, the inlet gases temperature lows down at the same time of its volume, so we can introduce even more oxygen and deliver a higher power. The energy taken by the turbine comes from the internal energy of the exhaustion gases, this energy does not mean a substantial power loss in front of all the benefits of the turbocharging system.
Components and types of turbochargers
Turbo supercharged engines have a turbine that rotates to the exhaust gases and a compressor . The compressor is the one responsible for taking the air coming from the filter and pressed into cylinders. It is joint by an axis.
4.- Wastegate Valve
Non Variable Geometry Turbochargers
The non variable geometry turbochargers have been used both in diesel and gasoline engines, they have very few mobile parts and slower response time. They are more economic and very reliable thanks to their simplicity, fixed blades turbochargers do not have the same capacity at increasing the engine performance as the VGT.
Variable Geometry Turbochargers (VGT)
Nowadays the most common turbocharger in the market. This sophisticated and technologically advanced turbine has a steerable-blades crown that changes the attack angle of the exhaustion gases respect the rotor blades. At low engine rpms, the deflectors attack angle decreases. When the engine speed rises, the deflector blades increases quickly as well as the turbocharger performance.
2.- Steerable blades or deflectors
7.- Adjusting nut
8.- Pneumátic regulator
In the picture below we can see graphically the deflector orientation at low rpm’s (left) and high rpm’s (right)
1.- manometric regulator
3.- Orientable blades
Compresor twin scroll
It is the most actual system. It has two air entrances that move independently each cylinder. It provides a more constant performance on all the revolutions range, since it optimices the exhaust gas pressure to move the turbine.
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