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Thermodynamic analysis of Stirling engine systems: Applications for combined heat and power
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.ORCID iD: 0000-0002-9254-3453
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Increasing energy demands and environmental problems require innovative systems for electrical and thermal energy production. In this scenario, the development of small scale energy systems has become an interesting alternative to the conventional large scale centralized plants. Among these alternatives, small scale combined heat and power (CHP) plants based on Stirling Engines (SE) have attracted the interest among research and industry due to the potential advantages that offers. These include low maintenance, low noise during operation, a theoretically high electrical efficiency, and principally the fuel flexibility that the system offers. However, actual engine performances present very low electrical efficiencies and consequently few successful prototypes reached commercial maturity at elevated costs.Considering this situation, this thesis presents a numerical thermodynamic study for micro scale CHP-SE systems. The study is divided in two parts: The first part covers the engine analysis; and the second part studies the thermodynamic performance of the overall CHP-SE system. For the engine analysis a detailed thermodynamic model suitable for the simulation of different engine configurations was developed. The model capability to predict the engine performance was validated with experimental data obtained from two different engines: The GPU-3 Stirling engine studied by Lewis Research Centre; and the Genoa engine studied on the experimental rig built at the Energy Department at the Royal Institute of Technology (KTH). The second part of the research complemented the study with the analysis of the overall CHP-SE system. This included numerical simulations of the different CHP components and the sensitivity analysis for selected design parameters.The complete study permitted to assess the different operational and design configurations for the engine and the CHP components. These improvements could be implemented for test field evaluations and thus foster the development of more efficient SE-CHP systems. In addition, the detailed thermodynamic-design methodology for the SE-CHP systems was established and the numerical tool for the design assessment was developed.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , xx, 93 p.
Series
TRITA-KRV, ISSN 1100-7990 ; 15:02
Keyword [en]
Stirling engine; Thermodynamic analysis
National Category
Engineering and Technology Energy Engineering
Research subject
Energy Technology
Identifiers
URN: urn:nbn:se:kth:diva-163048ISBN: 978-91-7595-498-1 (print)OAI: oai:DiVA.org:kth-163048DiVA: diva2:798500
Public defence
2015-04-13, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Sida - Swedish International Development Cooperation Agency
Note

QC 20150327

Available from: 2015-03-27 Created: 2015-03-26 Last updated: 2015-03-27Bibliographically approved
List of papers
1. Non-ideal Stirling engine thermodynamic model suitable for the integration into overall energy systems
Open this publication in new window or tab >>Non-ideal Stirling engine thermodynamic model suitable for the integration into overall energy systems
2014 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, ISSN 1359-4311, Vol. 73, no 1, 203-219 p.Article in journal, Meeting abstract (Refereed) Published
Abstract [en]

The reliability of modelling and simulation of energy systems strongly depends on the prediction accuracy of each system component. This is the case of Stirling engine-based systems, where an accurate modelling of the engine performance is very important to understand the overall system behaviour. In this sense, many Stirling engine analyses with different approaches have been already developed. However, there is a lack of Stirling engine models suitable for the integration into overall system simulations. In this context, this paper aims to develop a rigorous Stirling engine model that could be easily integrated into combined heat and power schemes for the overall techno-economic analysis of these systems. The model developed considers a Stirling engine with adiabatic working spaces, isothermal heat exchangers, dead volumes, and imperfect regeneration. Additionally, it considers mechanical pumping losses due to friction, limited heat transfer and thermal losses on the heat exchangers. The predicted efficiency and power output were compared with the numerical model and the experimental work reported by the NASA Lewis Research Centre for the GPU-3 Stirling engine. This showed average absolute errors around ±4% for the brake power, and ±5% for the brake efficiency at different frequencies. However, the model also showed large errors (±15%) for these calculations at higher frequencies and low pressures. Additional results include the calculation of the cyclic expansion and compression work; the pressure drop and heat flow through the heat exchangers; the conductive, shuttle effect and regenerator thermal losses; the temperature and mass flow distribution along the system; and the power output and efficiency of the engine.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Stirling engine; simulation; thermodynamics;CHP;
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-150576 (URN)10.1016/j.applthermaleng.2014.07.050 (DOI)000346543400021 ()2-s2.0-84906080788 (Scopus ID)
Projects
Micro-Scale Biomass Polygeneration
Funder
Sida - Swedish International Development Cooperation Agency
Note

QC 20140912

Available from: 2014-09-06 Created: 2014-09-06 Last updated: 2017-12-05Bibliographically approved
2. Development and validation of a thermodynamic model for the performance analysis of a gamma Stirling engine prototype
Open this publication in new window or tab >>Development and validation of a thermodynamic model for the performance analysis of a gamma Stirling engine prototype
Show others...
2015 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 83, 16-30 p., 6439Article in journal (Refereed) Published
Abstract [en]

This work presents the development and validation of a numerical model that represents the performance of a gamma Stirling engine prototype. The model follows a modular approach considering ideal adiabatic working spaces; limited internal and external heat transfer through the heat exchangers; and mechanical and thermal losses during the cycle. In addition, it includes the calculation of the mechanical efficiency taking into account the crank mechanism effectiveness and the forced work during the cycle. Consequently, the model aims to predict the work that can be effectively taken from the shaft. The model was compared with experimental data obtained in an experimental rig built for the engine prototype. The results showed an acceptable degree of accuracy when comparing with the experimental data, with errors ranging from +/- 1% to +/- 8% for the temperature in the heater side, less than +/- 1% error for the cooler temperatures, and +/- 1 to +/- 8% for the brake power calculations. Therefore, the model was probed adequate for study of the prototype performance. In addition, the results of the simulation reflected the limited performance obtained during the prototype experiments, and a first analysis of the results attributed this to the forced work during the cycle. The implemented model is the basis for a subsequent parametric analysis that will complement the results presented.

Keyword
Energy technology, Simulation and modelling, Stirling engine, Thermodynamic analysis
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-163046 (URN)10.1016/j.applthermaleng.2015.03.006 (DOI)000355349700003 ()2-s2.0-84925614881 (Scopus ID)
Funder
Sida - Swedish International Development Cooperation Agency
Note

QC 20150817. Updated from e-pub head of print to published.

Available from: 2015-03-26 Created: 2015-03-26 Last updated: 2017-12-04Bibliographically approved
3. Numerical simulation for the performance analysis of a gamma Stirling engine prototype
Open this publication in new window or tab >>Numerical simulation for the performance analysis of a gamma Stirling engine prototype
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Computer assisted modelling and simulation of energy systems asses the performance and suggest improvements to achieve energy efficient solutions. This is the case of the Stirling engine technology, where computer simulations combined with experimental work have helped to the development of different prototypes. Following this trend, the current work aims to study possible improvements towards the design of a gamma Stirling engine prototype through numerical simulations. The prototype was first experimentally studied and presented low performances. For this reason and considering a lack of reports for this prototype, the numerical simulation was the approach to identify the possible problems that limited the performance. In this regard, this paper presents the development and validation of a numerical model that represent the performance of the Stirling prototype. The model follows a modular approach considering ideal adiabatic working spaces; limited internal and external heat transfer through the heat exchangers; and mechanical and thermal losses during the cycle. In addition, it includes the calculation of the mechanical efficiency taking into account the crank mechanism effectiveness and the forced work during the cycle. Consequently, the model aims to predict the work that can be effectively taken from the shaft. The model was compared with experimental data obtained in an experimental rig built for the engine prototype. The results showed an acceptable degree of accuracy when comparing with the experimental data, with errors ranging from 1%-8% for the temperature in the heater side, less than 1% error for the cooler temperatures, and 1-8% for the brake power calculations. Therefore, the model was probed adequate for study the prototype performance. In addition, the results of the simulation reflected the limited performance obtained during the prototype experiments, and a first analysis of the results attributed this to the forced work during the cycle. The implemented model is the basis for a subsequent parametric analysis that will complement the results presented.

Keyword
Stirling engine; simulation
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-163051 (URN)
Funder
Sida - Swedish International Development Cooperation Agency
Note

QS 2015

Available from: 2015-03-26 Created: 2015-03-26 Last updated: 2015-03-27Bibliographically approved
4. Integration of Stirling engines into residential boilers for combined heat and power services: Thermodynamic modelling and analysis
Open this publication in new window or tab >>Integration of Stirling engines into residential boilers for combined heat and power services: Thermodynamic modelling and analysis
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The use of simulation techniques for the study of Combined Heat and Power systems based on Stirling Engines (CHP-SE) has been focused on dynamic simulations that guide the sizing of the system components. These are valuable tools for the performance evaluation of determined designs. However, there is a need to complement these studies with additional analysis that could permit to assess the design improvement and the integration of the system components. For this reason, the present work developed a model that coupled the design equations of each component with the equations that describe the thermal interactions presented in the overall system.

This integration allowed to obtain a deeper insight into the thermodynamic characteristics of the overall system, and thus was used for the study of a micro CHP-SE experimental rig.  The results for this case study allowed to quantify the main energy outputs, the energy losses, and the influence of different parameters on the system. The overall efficiency under the original conditions presented values ranging from 60%-64% with very low exergy efficiencies ranging from 5%-7%. The simulation analysis permitted to identify design and operational parameters that would increase the overall efficiency to values closer to 80% and the exergy to values closer to 14%. These increments would correspond to the reduction of the energy losses, improvements on the conditions for the biomass combustion, and the use of engines with higher electrical outputs. 

Keyword
Stirling engine; Combined Heat and Power
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-163052 (URN)
Funder
Sida - Swedish International Development Cooperation Agency
Note

QS 2015

Available from: 2015-03-26 Created: 2015-03-26 Last updated: 2015-03-27Bibliographically approved

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