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p-V-Diagramm 1

Changes in the state of gases
1IsobaricThe pressure remains the same.
2IsochoricThe volume remains the same.
heat delivery left, absorption right
3IsothermalThe temperature remains the same.
4IsentropicNo heat exchange takes place.

In a cyclic process, the changes in the state of gaseous substances always follow in the same order. In the Joule and Brayton (figure 4), these are e.g., 2 isentropes and two isothermal changes, which succeed one another.

Fundamental possibilities for cyclic processes
Thermal energy creates kinetic energy.
Kinetic energy creates heat / cold.

In the technical realisation the degree of effectivity is particularly important. It can however, only measure itself against ideal conditions. As a matter of fact, the degree of effeciency, shows how far a process is removed from the ideal condition. The definition for an ideal process states, that no other process is better.

Because of the ideal-line shown in curve No. 2, the processes in the petrol engine are sometimes also described as
constant-volume combustion.

Exemplary for all thermodynamic processes is that from Carnot, which itself is only theoretically possible. There are variations for the Otto- and the Diesel engine, which come a little closer to reality. The Seiliger- process on the other hand, shows a variation, which corresponds even better to the actual processes in the Diesel engine.

Because only the abovementioned four changes of state are theoretically ascertainable, the congruence with the actual processes is impossible. This is only a demonstration of approaching reality by using mathematically determinable functions. Only the p-v-diagramm shown here is measurable. 10/10