modelDryAirNASA

Information

Example of an Otto cycle engine model. See TUMExercisesThermodynamicCycles.Exercise3OttoEngine for the problem description.

This example makes use of the following components and settings:

• DryAirNasa medium (ideal gas with temperature-dependent cp)
• Adiabatic process model (which is only available for systemSpec = Flow)

The calculation of outlet pressure for given outlet density is achieved by the use of the InverseBlockConstraints model. An implicit nonlinear equation is introduced, which requires suitable start values.

The Adiabatic model defines isentropic efficiency based on shaft work (i.e., changes in specific enthalpy), whereas for a closed-cycle process the isentropic efficiency is commonly defined based on the net expansion work (i.e., changes in specific internal energy). In general both definitions are not equivalent and discrepancies can arise. The results will however be identical when the isentropic efficiency is equal to unity, or when the working fluid is an ideal gas with constant isentropic exponent.

This setup is based on the fact that the specific work of a thermodynamic cycle is given by the closed integral in the p–v diagram (pressure - specific volume). Therefore, integrating with respect to volume, p*dv (boundary work as typically transferred in a piston–cylinder system), and integrating with respect to pressure, v*dp (“artificial” shaft work of a dual stationary-flow process), yield the same net cycle work, even though the individual contributions of each process step differ.

Components

Revisions

• 2026, by Raphael Gebhart (raphael.gebhart@dlr.de):
  Initial version.