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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. / <p>QC 20150327</p>

The goal of this study is to assess the potential of the Stirling engine in alternative energy applications including combined cooling, heating, and power (CCHP) and novel waste heat recovery (WHR) technologies. A first and second law model is developed to quantify Stirling engine performance and realize the crucial parameters in Stirling engine design. In addition, analysis of systems employing the Stirling engine as a prime mover can help justify particular design interests for the engine regarding certain applications. A model of a CCHP system is developed with a Stirling engine prime mover. Sensitivity analysis is performed on the CCHP system to gain a deeper understanding of how each component affects the overall performance of the CCHP system. The main objective of these analyses is to provide information on the feasibility of Stirling CCHP on the basis of primary energy consumption and cost. Finally, the potential of the Stirling engine as a waste heat recovery device is investigated. A thermodynamic model is developed to provide estimates of Stirling engine performance based on an available waste heat stream from any specific heat source, while suggesting practical design constraints on the engine based on bounds from the second law. These results are provided to strengthen the feasibility of the Stirling engine as a bottoming prime mover rather than the central power plant.

Micro Combined Heat and Power systems or microCHP systems generate heat and electricity for a home. Stirling engines are widely used as prime movers in microCHP applications. Stirling engine is an external combustion engine having an enclosed working fluid (as helium) that is alternately compressed and expanded to operate a piston. The displacer shuttles the working fluid between the hot and cold ends. The piston is coupled to a transmission and to an electrical machine to generate power. Conventional Stirling engines are not controllable to a great degree. The piston and displacer are connected to the same crank and they maintain the same phase difference throughout the cycle. Also the piston and displacer are normally constructed to move in a sinusoidal fashion. The Active Stirling Engine is a new concept introduced in this thesis which has a free displacer. The displacer is driven separately compared to a coupled drive in conventional Stirling engines. The displacer motion can be non-linear with dwell at each ends of the stroke, opening up the possibilities to increase the pressure volume diagram which indicates the work done by the engine. A separately driven displacer also allows introducing phase control and stroke control to improve the controllability of a Stirling engine. This thesis examines the effect of non-linear displacer motion and phase control of the displacer on Stirling engine performance. Simulations are performed in Sage, the leading Stirling engine simulation software, to understand the effect of displacer phase control. A test rig is constructed with the actively controlled displacer connected to a linear machine controlled by a programmable servo. Heat is applied to the test rig though an electric heating coil. The test rig is charged with nitrogen at 20Bar pressure. The power piston is connected to a rotating electrical machine via the transmission. The rotating electrical machine is used to start the engine and to act as the generator. The test rig is instrumented to determine the linear position of the displacer and piston, angular position of the rotating electrical machine shaft, temperatures, pressures and flow. A LabVIEW™ based data acquisition system is set up to capture data from the test rig. Data is collected at various test cases. The simulation result is compared against post processed data. An efficiency improvement of 15% is achieved using this method and is demonstrated experimentally. Applications in micro combined heat and power systems utilising the improved efficiency due to non linear motion and controllability due to phase control are explored in this thesis.

This thesis presents the design and construction of a low temperature differential (LTD) Stirling engine for electric power generation. The target energy sources were geothermal, industrial waste heat or solar heated water. These sources would supply a source temperature of around 90 °C. Assuming that the sink is kept at around 20 °C, the engine was designed based on a temperature difference of approximately 70 °C. The initial design and basic structure of the engine was completed in a previous project utilising first order design methods. The goal was to develop a low cost prototype engine capable of producing up to 500W electrical output power. A novel gamma type engine was proposed utilising a rotary reciprocating displacer and industrial steam piping to form a low cost pressurised chamber. This project concentrated on advancing the design and construction towards completion with particular emphasis on the electrical control, measurement/instrumentation components, and gas flow through the regenerator. At the completion of this project the displacer piston actuation system has been redesigned. In order to achieve the displacer’s specified 2 ㎐ actuation, both the displacer’s structure and the actuation system were altered. The displacer’s aluminium shell and foam centre were removed and replaced with a pine superstructure coated in depron foam, reducing the moment of inertia from 0.4488 ㎏ ∙ ㎡ to 0.0984 ㎏ ∙ ㎡. A secondary motor was added to the actuation system to increase the actuation power. The gearing ratio was also altered from 10:1 to 2:1 to increase the peak displacer speed. The regenerator was designed and built to suit the unusual wedge shape requirements of the original design. A ribbed structure was conceived to allow fluid flow to be manipulated within separate sections, producing an even pressure drop over varying regenerator lengths. Simulations were run to optimise both the number of sections and the mass of wire wool to be placed in each segment. The final regenerator design has axial ribs placed at radii of 93, 134, 192, 276 and 392mm, creating four sections. These sections are filled with 0.68, 0.97, 1.40 and 1.90kg of #0 mild steel wire wool. As Stirling engines are not self-starting the generator was required to be run as a motor when starting the Stirling engine. To achieve bidirectional flow of current within the starter motor/generator control system, a field oriented control (FOC) inverter from Texas Instruments was purchased and set up to run the 1kW, 3 phase, permanent magnet generator in both motor and generation modes. This will allow the Stirling engine to be brought up to speed with the generator operating as a motor and then switch to generation mode when the motoring current falls below a set limit. Both pressure and temperature measurement systems were developed, constructed and tested in order to collect information about the performance of the engine under operation. Three pressure transducer circuits were designed and constructed with measurement ranges of 10 ㎪, ±0.99 ㎪ and ±6.66 ㎪. These circuits were integrated with a PiocLog1012 analog to digital converter and PicoLog recording software. Eight K-type thermocouples were used for temperature recording. These were sampled with a Pico Technology TC-08 temperature thermocouple data logger which in turn was connected, via USB, to a computer running PicoLog Recorder software. Thus far all component testing has been carried out with test rigs that model the relevant parts of the engine. The displacer actuation system and phase angle control of the displacer and power piston has been tested. Temperature and pressure measurement systems have been independently tested. Motor/generator speed control and switching has been simulated and tested. Unfortunately completion of the engine assembly was not achieved within the scope of this project and therefore fully integrated testing of all components was not carried out. Once mechanical assembly is completed fully integrated testing of displacer actuation, piston position, generator speed control and measurement systems can be achieved.

This study examined the performance of a residential micro–cogeneration system based on a Stirling engine and fuelled by diesel and ethanol. An extensive number of engine tests were conducted to ensure highly accurate and reproducible measurement techniques. Appropriate energy efficiencies were determined by performing an energy balance for each fuel. Particulate emissions were measured with an isokinetic particulate sampler, while a flame ionization detector was used to monitor unburned hydrocarbon emissions. Carbon monoxide, nitric oxide, nitrogen dioxide, carbon dioxide, water, formaldehyde, acetaldehyde and methane emissions were measured using a Fourier transform infrared spectrometer. When powered by ethanol, the system had slightly higher thermal efficiency, slightly lower power efficiency and considerable reductions in emission levels during steady state operation. To further study engine behaviour, parametric studies on primary engine set points, including coolant temperature and exhaust temperature, were also conducted.

This study examined the performance of a residential micro–cogeneration system based on a Stirling engine and fuelled by diesel and ethanol. An extensive number of engine tests were conducted to ensure highly accurate and reproducible measurement techniques. Appropriate energy efficiencies were determined by performing an energy balance for each fuel. Particulate emissions were measured with an isokinetic particulate sampler, while a flame ionization detector was used to monitor unburned hydrocarbon emissions. Carbon monoxide, nitric oxide, nitrogen dioxide, carbon dioxide, water, formaldehyde, acetaldehyde and methane emissions were measured using a Fourier transform infrared spectrometer. When powered by ethanol, the system had slightly higher thermal efficiency, slightly lower power efficiency and considerable reductions in emission levels during steady state operation. To further study engine behaviour, parametric studies on primary engine set points, including coolant temperature and exhaust temperature, were also conducted.

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Sustainable Built Environments Senior Capstone Project / This paper provides a study on the configuration of Stirling engines and the effect using a solar dish as a heat source on efficiency. The Stirling engine was based on the MIT 2.670 design - a Gamma configuration, low temperature differential Stirling engine. Temperature and speed were measured for the base model Stirling engine to determine the initial efficiency. Modifications were planned to add a parabolic mirror as a solar dish and compare the efficiency to the initial design, however, the completed solar Stirling engine testing and data collection is to be performed in the following summer. The work performed by the engine was to be calculated using the Schmidt formula to then find the power output. Results from the completion of this study would indicate how the solar dish effects the power output of the Stirling engine.

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