Power cycle

Thermodynamic power cycles are the basis for the operation of heat engines, which supply most of the world's electric power and run the vast majority of motor vehicles. Power cycles can be divided according to the type of heat engine they seek to model. The most common cycles used to model internal combustion engines are the Otto cycle, which models gasoline engines, and the Diesel cycle, which models diesel engines. Cycles that model external combustion engines include the Brayton cycle, which models gas turbines, the Rankine cycle, which models steam turbines, the Stirling cycle, which models hot air engines, and the Ericsson cycle, which also models hot air engines.

For external combustion engines it is recommended to use the thermodynamic plot since the points of the cycle correspond to variables at inlets and outlets of system components.

For internal combustion engines the cycle uses the variations of variables at only one location where the combustion occurs. To perform this kind of plot, you can switch the modulo plot that contains the pressure and volume variable to an XY curve. Therefore you get a P-v diagram of the power cycle of the system.

You first need to create a modulo plot that contains the variations of the pressure and the volume from a single cylinder. The modulo variable has to refer to the crank angle with a [0-720] degree range. You may need to adjust the offset so that the starting point of the cycle is at the top dead center.

Procedure

1. Click the icon in the plot toolbar, or use the Tools > XY curve(s) menu option.

2. Click on the first graph.

   Figure 96: Pressure and volume modulo plot

Results

The curve is now an XY curve that corresponds to the P-v diagram.

Figure 97: Diagram P-v

The modulo variable is no longer used as the X axis variable. You can have access to the modulo variable value by using the replay cursor.