A supercharger is an air compressor used for forced induction of an internal combustion engine. The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally-aspirated engine, which allows more fuel to be provided and more work to be done per cycle, increasing the power output of the engine.
A supercharger can be powered mechanically by a belt, gear, shaft, or chain connected to the engine's crankshaft. It can also be powered by an exhaust gas turbine. A turbine-driven supercharger is known as a turbosupercharger or turbocharger.
OBJECTS OF SUPERCHARGING
The increase in the amount of air inducted per unit time by supercharging is obtained mainly to burn a greater amount of fuel in a given engine and thus increase its power output. The objects of supercharging include one or more of the following.
1. To increase the power output for a given weight and bulk of the engine. This is important for aircraft, marine and automotive engines where weight and space are important.
2. To compensate for the loss of power due to altitude. This mainly relates to aircraft engines which lose power at an approximate rate of one percent 100 meters altitude. This is also relevant for others engines which are used at high altitudes.
The first functional supercharger can be attributed to German engineer Gottlieb Daimler who received a German patent for supercharging an internal combustion engine in 1885. Louis Renault patented a centrifugal supercharger in France in 1902. An early supercharged race car was built by Lee Chadwick of Pottstown, Pennsylvania in 1908 and reportedly reached a speed of 100 miles per hour (160 km/h).
Types of supercharger
There are two main types of supercharger defined according to the method of compression: positive displacement and dynamic compressors. The former deliver a fairly constant level of boost regardless of engine speed (RPM), whereas the latter deliver increasing boost with increasing engine speed.
Positive displacement pumps deliver a nearly fixed volume of air per revolution at all speeds (minus leakage which is nearly constant at all speeds for a given pressure and so its importance decreases at higher speeds). The device divides the air mechanically into parcels for delivery to the engine, mechanically moving the air into the engine bit by bit.
Major types of positive displacement pumps include:
- Roots
- Lysholm screw
- Sliding vane
- Scroll-type supercharger, also known as the G-lader
- Piston as in Bourke engine
- Wankel engine
Positive displacement pumps are further divided into internal compression and external compression types.
Roots superchargers are typically external compression only (although high helix roots blowers attempt to emulate the internal compression of the Lysholm screw).
- External compression refers to pumps which transfer air at ambient pressure into the engine. If the engine is running under boost conditions, the pressure in the intake manifold is higher than that coming from the supercharger. That causes a back flow from the engine into the supercharger until the two reach equilibrium. It is the back flow which actually compresses the incoming gas. This is a highly inefficient process and the main factor in the lack of efficiency of roots superchargers when used at high boost levels. The lower the boost level the smaller is this loss and roots blowers are very efficient at moving air at low pressure differentials, which is what they were first invented for (hence the original term "blower").
All the other types have some degree of internal compression.
- Internal compression refers to the air being compressed within the supercharger itself and this compressed air, already at or close to boost level, can be delivered smoothly to the engine with little or no backflow. This is more efficient than backflow compression and allows higher efficiency to be achieved. Internal compression devices usually use a fixed internal compression ratio. When the boost pressure is equal to the compression pressure of the supercharger, the backflow is zero. If the boost pressure exceeds that compression pressure, backflow can still occur as in a roots blower. Internal compression blowers must be matched to the expected boost pressure in order to achieve the higher efficiency they are capable of, otherwise they will suffer the same problems and low efficiency of the roots blowers.
[edit] Supercharger drive types
Superchargers are further defined according to their method of drive (mechanical—or turbine).
Mechanical:
- Belt (V belt, Toothed belt, Flat belt)
- Direct drive
- Gear drive
- Chain drive
Exhaust gas turbines:
- Axial turbine
- Radial turbine
Other:
- Electric motor
All types of compressor may be mated to and driven by either gas turbine or mechanical linkage. Dynamic compressors are most often matched with gas turbine drives due to their similar high-speed characteristics, while positive displacement pumps usually use one of the mechanical drives. However, all of the possible combinations have been tried with various levels of success.
