Forced breathing: Turbocharger and Supercharger
To fully understand the concept of performance enhancement by charging the engine, you first have to know how an engine works. The most common used engine these days for regular cars, is a direct injection four-stroke reciprocating engine. The four working steps are:
1. Intake: The stroke of the piston begins at top dead center. The piston descends from the top of the cylinder to the bottom of the cylinder, increasing the volume of the cylinder. A mixture of fuel and air is sucked into the cylinder by the resulting vacuum through the intake port.
2. Compression: With both, intake and exhaust valves closed, the piston returns to the top of the cylinder compressing the air or fuel-air mixture into the cylinder head.
3. Power: While the piston is close to the top dead center, the compressed air–fuel mixture is ignited. In a diesel engine the mixture ignites itself due to the resulting heat from the compression. In a gasolin engine this has to be done by a spark plug. The resulting pressure from the combustion of the compressed fuel-air mixture forces the piston back down toward the bottom dead center.
4. Exhaust: During the exhaust stroke, the piston once again returns to the top dead center while the exhaust valve is open. This action expels the burnt fuel-air mixture through the exhaust valve.
This cycle continues until the engine is turned off.
The power of the engine can now be increased by these three basic principles:
1. Increase the cylinders capacity: By enlarging the combustion chamber, more fuel can be burned per cycle.
2. Increase the engines revolutions: The engine works faster and can complete more cycles in a given time.
3. Charging the engine: By doing so, we are modifying the engines air intake. The engine does not just suck in the air from the surrounding environment anymore. Instead, the air is compressed and put under pressure. The engine still gets the same volume of air, but because of the higher denisty, it get's more mass into the combustion chamber and therefore more oxygen. With more oxygen it is possible to burn more fuel, resulting in more power without increasing the cylinders capacity or the engines revolutions.
The formula for calculating the internal engine power (Pi) reads as follows:
Pi = pi * Vh * z * n * i
Pi = internal power
pi = mean effective pressure
Vh = displacement per cylinder
z = cylinder count
n = revolutions per minute
i = working cycles per revolution ( 0.5 for a four-stroke-engine)
The turbocharger: A turbocharger is a turbine, which is powered by the engines exhaust stream. The compressor rotor is propelled by that power and sucks in the air from it's surroundings. This air is then directed to the engines air intake. By this principle, the pressure varies with the amount and speed of the engines exhaust gases. To counter this effect and make the turbocharger more steady and efficient, it is common to use adjustable variable-geometry turbochargers (VGT). By altering the geometry of the turbine housing as the engine accelerates, the turbo's ratio can be maintained at its optimum. Because of this, VGTs have a minimal amount of lag, have a low boost threshold and are very efficient at higher engine revolutions. Within a twin-turbo or biturbo engine, two turbochargers are installed in parallel. This technique is often used in V-engines and there is one charger per manifold. There are even engines with more than two chargers connected in series
The supercharger: A supercharger compresses the surrounding air like a turbocharger. But it is powered in a different way. The supercharger is propelled by a v-ribbed belt just like the alternator or air conditioning. On the downside, for this to work the engine has to start with putting up to 15% of it's power just into powering the supercharger. On the other hand, the supercharger can run with a constant speed and without the thermal stresses of a turbocharger. This also has a positive effect on the durability of the supercharger. There are many ways to build a supercharger. The most common is the roots type supercharger. The first use of superchargers by Mercedes was in racing - almost 100 years ago. In 1920 they constructed the "28/95 PS", a racecar with 140 HP that was unmatched for a long time. Soon after that, the first regular cars with superchargers were produced. Probably the most legendary mercedes racecar is the "Typ 720 SSKL" (W06 RS). Due to it's supercharger, the 6-cylinder engine with 7000 ccm generated 300 HP and was able to reach a top speed of 235 km/h. The regular version of the W06 had only 225 HP.
The intercooler: By compressing air with a turbocharger or supercharger, this air get's very hot due to friction. The turbocharger, which is powered by the hot exhaust gases, even adds additional heat to the air, because the charger itself is very hot. In order to get the desired power boost, the compressed air should be cooled down. Hot air has less oxygen due to it's higher volume and furthermore, cooler air intake has higher antiknock properties, which allow for higher ignition timing. In regular cars, air-to-liquid intercoolers are coming out on top. There are multiple advantages over air-to-air intercoolers. The airflow is irrelevant, therefor the intercooler can be installed underneath the intake manifold and supercharger. The air has a much shorter path and therefore the loss in pressure is reduced. The cooling efficiency of a water-based cooler is also much higher and stable compared to regular air-to-air intercoolers.
To fully understand the concept of performance enhancement by charging the engine, you first have to know how an engine works. The most common used engine these days for regular cars, is a direct injection four-stroke reciprocating engine. The four working steps are:
1. Intake: The stroke of the piston begins at top dead center. The piston descends from the top of the cylinder to the bottom of the cylinder, increasing the volume of the cylinder. A mixture of fuel and air is sucked into the cylinder by the resulting vacuum through the intake port.
2. Compression: With both, intake and exhaust valves closed, the piston returns to the top of the cylinder compressing the air or fuel-air mixture into the cylinder head.
3. Power: While the piston is close to the top dead center, the compressed air–fuel mixture is ignited. In a diesel engine the mixture ignites itself due to the resulting heat from the compression. In a gasolin engine this has to be done by a spark plug. The resulting pressure from the combustion of the compressed fuel-air mixture forces the piston back down toward the bottom dead center.
4. Exhaust: During the exhaust stroke, the piston once again returns to the top dead center while the exhaust valve is open. This action expels the burnt fuel-air mixture through the exhaust valve.
This cycle continues until the engine is turned off.
The power of the engine can now be increased by these three basic principles:
1. Increase the cylinders capacity: By enlarging the combustion chamber, more fuel can be burned per cycle.
2. Increase the engines revolutions: The engine works faster and can complete more cycles in a given time.
3. Charging the engine: By doing so, we are modifying the engines air intake. The engine does not just suck in the air from the surrounding environment anymore. Instead, the air is compressed and put under pressure. The engine still gets the same volume of air, but because of the higher denisty, it get's more mass into the combustion chamber and therefore more oxygen. With more oxygen it is possible to burn more fuel, resulting in more power without increasing the cylinders capacity or the engines revolutions.
The formula for calculating the internal engine power (Pi) reads as follows:
Pi = pi * Vh * z * n * i
Pi = internal power
pi = mean effective pressure
Vh = displacement per cylinder
z = cylinder count
n = revolutions per minute
i = working cycles per revolution ( 0.5 for a four-stroke-engine)
The turbocharger: A turbocharger is a turbine, which is powered by the engines exhaust stream. The compressor rotor is propelled by that power and sucks in the air from it's surroundings. This air is then directed to the engines air intake. By this principle, the pressure varies with the amount and speed of the engines exhaust gases. To counter this effect and make the turbocharger more steady and efficient, it is common to use adjustable variable-geometry turbochargers (VGT). By altering the geometry of the turbine housing as the engine accelerates, the turbo's ratio can be maintained at its optimum. Because of this, VGTs have a minimal amount of lag, have a low boost threshold and are very efficient at higher engine revolutions. Within a twin-turbo or biturbo engine, two turbochargers are installed in parallel. This technique is often used in V-engines and there is one charger per manifold. There are even engines with more than two chargers connected in series
The supercharger: A supercharger compresses the surrounding air like a turbocharger. But it is powered in a different way. The supercharger is propelled by a v-ribbed belt just like the alternator or air conditioning. On the downside, for this to work the engine has to start with putting up to 15% of it's power just into powering the supercharger. On the other hand, the supercharger can run with a constant speed and without the thermal stresses of a turbocharger. This also has a positive effect on the durability of the supercharger. There are many ways to build a supercharger. The most common is the roots type supercharger. The first use of superchargers by Mercedes was in racing - almost 100 years ago. In 1920 they constructed the "28/95 PS", a racecar with 140 HP that was unmatched for a long time. Soon after that, the first regular cars with superchargers were produced. Probably the most legendary mercedes racecar is the "Typ 720 SSKL" (W06 RS). Due to it's supercharger, the 6-cylinder engine with 7000 ccm generated 300 HP and was able to reach a top speed of 235 km/h. The regular version of the W06 had only 225 HP.
The intercooler: By compressing air with a turbocharger or supercharger, this air get's very hot due to friction. The turbocharger, which is powered by the hot exhaust gases, even adds additional heat to the air, because the charger itself is very hot. In order to get the desired power boost, the compressed air should be cooled down. Hot air has less oxygen due to it's higher volume and furthermore, cooler air intake has higher antiknock properties, which allow for higher ignition timing. In regular cars, air-to-liquid intercoolers are coming out on top. There are multiple advantages over air-to-air intercoolers. The airflow is irrelevant, therefor the intercooler can be installed underneath the intake manifold and supercharger. The air has a much shorter path and therefore the loss in pressure is reduced. The cooling efficiency of a water-based cooler is also much higher and stable compared to regular air-to-air intercoolers.
