Performance investigation of a novel Franchot Engine design

Ja'far Daoud, Daniel Friedrich

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

The double‐acting Franchot engine is inferior to the double‐acting Siemens engine under configurations limited by the Siemens engine. In this contribution, the performance of a novel Franchot engine design without the Siemens engine limitations is investigated with a new mathematical definition of the regenerator end temperatures, and the initial statement is challenged. The main advantages of the Franchot engine compared with the Siemens engine are the free control of the phase angle and the thermal separation of the cylinders. Here, the performance of a cylinder‐heated/cooled air‐filled Franchot engine is investigated at medium temperature under variations of engine speed, phase angle, geometry, dead volume, and gas density. A second‐order thermodynamic model with nonconstant, polytropic heat transfer is developed and implemented in Matlab/Simulink for this investigation. The nonconstant heat transfer is crucial to accurately model the behaviour of the direct cylinder heating and cooling. The results show that the phase angle and air charge density have the largest effect on the engine performance. An increase of the phase angle from 90o to 150o at a speed of 1000 RPM led to an increased output power of 58 W compared with a maximum power less than 20 W for a phase angle of 90o. The efficiency at a phase angle of 150o is approximately 25% which is slightly lower than the ideal Curzon and Ahlborn efficiency of 29.3%. This discrepancy can be explained by the nonconstant, polytropic heat transfer. In addition to the increase in engine power, the operation at higher phase angles reduces the pressure difference across the power piston by a factor larger than 4 which leads to a significant reduction in gas leakage across the power pistons. This shows that at higher phase angles, the 2 main disadvantages compared with the Siemens engine are at least reduced and arguably completely removed. Thus, the Franchot engine has the potential to be superior to the Siemens engine if freed from the operational restrictions of the Siemens engine.
Original languageEnglish
JournalInternational Journal of Energy Research
Early online date15 Aug 2017
DOIs
Publication statusE-pub ahead of print - 15 Aug 2017

Keywords / Materials (for Non-textual outputs)

  • Stirling
  • Franchot engine
  • Stirling engine
  • Polytropic heat transfer
  • Direct cooled/heated
  • Performance evaluation

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