An approximate calculation of the working cycle for a specific cylinder of your choice can be carried out with the program below. The original version of this program was compiled by Mr. Matthias Kornfeld, TU Vienna on the occasion of the 5th EFRC- workshop in 2008.
When using this program you can chose quality criteria for clearance volume, the compressor valves and the wear condition of the cylinder in question as “very good” or “less good”. According to your choice the program then defines the clearance volume ratio, the temperature and mass factor of the performance ratio, the polytropic exponent and the effective valve area in relation to the piston area. Thereby it is possible to assess the influence of these quality criteria on compressor throughput and power consumption .
The overall proceedings in the working chamber are called the working cycle. To start let us assume the compressor working without any losses. The clearance volume as is necessary by the design is Vo. By cooling the cylinder the compression will be polytropic, which is between the isothermal and isentropic compression.
The working cycle can be shown with a p,V diagram (indicator diagram), which shows both the change in the conditions of state and the changes of masses.
The polytropic compression starts in bottom dead center UT (1) at suction conditions and ends when the delivery pressure has been reached (2). Then the delivery valve opens and gas is pushed out at constant pressure up to top dead center OT (3). There the sign of the volume change alters and the delivery valve closes. The reexpansion of the remaining gas from the clearance volume back to suction pressure follows (4). The suction valve now opens and fresh gas is sucked in at suction conditions up to bottom dead center UT (1).
The suction and discharge process are ideally pure changes in mass and are called (similar to the combustion engines) load changes.
In the case of ideal process the changes of state of compression and reexpansion have the same polytropic exponent. The clearance volume then only causes a diminished flow of gas.