Supercharging and turbocharging

Supercharging can be defined as the introduction of air (air fuel mixture) into an engine cylinder at a density greater than ambient. This is allows a proportional increase in the fuel that can be burned and hence raised the potential power output.
The principle objective is to increase power output not to improve efficiency, although the efficiency may be benefit.
Figure 1 show an ideal naturally aspirated dual combustion cycle. Point 1 denotes the beginning of the compression stroke.
compare a naturally aspirated and supercharged ideal cycle. The supercharged cycle start at a higher (and density) point 1
??. Extra fuel can be burned between 2
???4
??because more air is available (the same volume but higher density). Two things are clear: the supercharged engine has a greater power output and much higher maximum pressure. Unless the engine is designed to be supercharged, the high maximum pressure may not be acceptable; the engine may not be with stand the stress involved.
Compressors
The compressor used in the supercharger uses energy to produce work. Where the compressor gets this energy is essential in determining total engine efficiency. Because the power output of the engine increases when using a supercharger some of this power is used to drive the compressor. The amount of work that is produced by the piston is therefore divided into running the compressor and running the engine. In a turbocharger the exhaust gas is used to drive the compressor, therefore all the work from the cylinder is in running the engine. The work input into the compressor can be computed from the 1st law of thermodynamics.