Chapter 8 Lyes KADEM [Thermodynamics II] 2007 STIRLING and ERICSSON Cycles Robert Stirling; Scotland (1790 –1878) John Ericsson; Sweden (1803 - 1889) When we take a look at the ideal Otto and Diesel cycles, we can notice that they both are only internally reversible. This is because the heat supply and rejection are not performed at a constant temperature (isothermal process). Therefore, for the same high and low temperatures, the ideal Otto and Diesel cycles will have a thermal efficiency lower than Carnot efficiency (where the heat transfer is isothermal). Hence, to approach the Carnot efficiency we have to reduce the difference in temperature between points 2 and 3 and between 4 and 1. This is objective of Stirling and Ericsson cycles. How? By using a regenerator. What is a regenerator? It is a heat exchanger that transfers the wasted heat at (1-4) to (23). As a consequence, the T1 will increase (ideally approaches T2) and T3 will decrease (ideally approaches T4) A generator induces a significant increase in thermal efficiency Figure 8.12. The components of the Sterling and Ericsson cycles. Gas power cycles 23 Chapter 8 Lyes KADEM [Thermodynamics II] 2007 Stirling Engine Ericsson Engine Figure.8.13. T-s and P-v diagrams of Stirling and Ericsson cycles. Why don’t we use the Stirling and Ericsson cycles? This is due to some technical difficulties. In deed, Stirling and Ericsson cycles are difficult to achieve in practice because they involve heat transfer through a differential temperature difference (small difference in temperature), which necessitates a long surface areas for heat transfer or allowing an infinitesimally long time for the process. Example A Stirling cycle operates on air with a compression ratio of 10. If the low pressure is 200 kPa, the low temperature is 100ºC, and the high temperature is 600ºC, calculate the work output and the heat input. Gas power cycles 24