CarnotCycle_abg.tex ( -ss -o)

MTT command:

mtt -ss -o CarnotCycle abg tex

Figure 8.1: System CarnotCycle: acausal bond graph

The acausal bond graph of system CarnotCycle is displayed in Figure 8.1 (on page ) and its label file is listed in Section 8.1.1 (on page ). The subsystems are listed in Section 8.1.2 (on page ).

The Carnot cycle is a simple closed thermodynamic cycle with four parts:

1. Isentropic compression
2. Heat injection at constant temperature
3. Isentropic expansion
4. Heat extraction at constant temperature

The subsystem Cycle (Section 13.1.4 (on page )) is a two-port component describing an ideal gas. It has two energy ports which, with integral causality correspond to

1. Entropy flow in; temperature out
2. Volume rate of change in; pressure out

In contast to the Otto cycle (see Table 13.1 (on page ) where each table entry gives the causality on the heat and work ports respectively). The ideal Carnot cycle has derivative causality on the [Heat] port for two parts of the cycle.

To avoid this causlity change, the Carnot cycle is approximated by applying the heat from a temperature source via a thermal resistance RT component. During the heat injection and heat extraction parts of the cycle, the resistance parameter $r\approx 0$, but during the isentropic compression and isentropic expansion parts of the cycle, the resistance parameter $r\approx \inf$.

The simulation parameters appear in Section (on page ). The results are plotted against time as follows:

• Volume (Figure (on page ))
• Pressure (Figure (on page ))
• Entropy (Figure (on page ))
• Temperature (Figure (on page ))

These values are replotted as the standard PV and TS diagrams in Figures (on page ) and (on page ) respectively.

The PV diagram shows the long and thin form typical of the Carnot cycle - this implies a poor work ratio. The TS diagram is not informative; it is not the expected rectangle because both T and S change in a stepwise manner.