Abstract
The reported discrepancy between theory and experiment for external combustion Stirling engines is explained by the addition of thermal resistance of the combustion gasses to the standard Carnot model. In these cases, the Stirling engine ideal efficiency is not as is normally reported equal to the Carnot cycle efficiency but is significantly lower. A new equation for ideal Stirling engine efficiency when the heat is obtained through external combustion without pre-heating the air, is presented and results for various fuels tabulated. The results show that petrol and diesel, internal combustion engines (Otto cycle) have a higher ideal efficiency than the Stirling engine. When comparing thermoacoustic engines heated by wood, efficiency should not be quoted as a percentage of the Carnot efficiency, but against a figure 48% lower than Carnot. The effect is not seen with electrically heated rigs, solar or nuclear fission heated engines.
Highlights
The maximum theoretical efficiency of the Stirling cycle is often quoted as the same as the Carnot efficiency [1]: η= 1− Tc Th (1)The rationale behind writing this paper is to provide a new upper limit to the efficiency of external combustion Stirling engines and an explanation for the often reported low measured efficiency of Stirling enginesHow to cite this paper: Riley, P.H. (2015) The Myth of the High-Efficiency External-Combustion Stirling Engine
Use of plutonium as a heat source in a thermoacoustic engine [3] has an agreement of 15% between simulation and experiment with a stated thermodynamic efficiency of 18%
By modelling the entire system, including combustion, this paper presents a more accurate upper bound for external combustion Stirling engine cycle efficiency and better explains the discrepancies
Summary
Riley in real-world external-combustion situations, compared with theoretical or rig results. Thermoacoustic rig test results using electrical heating on the hot heat exchanger have shown impressive thermal efficiencies of over 18% [2] that are not reproduced using external combustion processes. This is because (1) is only true where the heat is supplied at a fixed temperature, such as in solar, through electrical heating, or a fission source. Use of plutonium as a heat source in a thermoacoustic engine [3] has an agreement of 15% between simulation and experiment with a stated thermodynamic efficiency of 18%. In thermoacoustic tests with electrical heaters agreement between DeltaEC [4] simulation and experiment varies between about 40% [5] and 15% [6]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
