Modelling and Optimisation of a Free Piston Stirling Engine for Micro-CHP Applications

This study is carried out to investigate the solar thermal energy conversion for generating power. This form of renewable energy can be utilised for power production deploying the free piston Stirling engines, which convert thermal energy into mechanical energy. Such systems have an advantage of production of work using low and high temperature differences in the cycle which could be created by different sources of heat including solar energy, combustion of a fuel, geothermal energy, nuclear energy or waste heat. The thermodynamic analysis of the free piston Stirling engine have been carried out and implemented in past studies with different methods of approach with various difficulties exhibited. In the present study isothermal, ideal adiabatic and Quasi steady flow models have been produced and used for investigation of the engine performance. The approach in this study deals with simultaneous mathematical modelling of thermodynamic processes and pistons dynamics. The steady state operation of the engine depends on the values of damping coefficients, spring stiffness and pressure drop within the heat exchangers during the engine’s operation, which is also a result of the energy transfer in each engine’s component. In order to design effective high performance engines it is necessary to develop such advanced mathematical models to perform the analysis of the engine’s operation and to predict its performance satisfactorily. The aim of this study was to develop several levels of mathematical models of free piston Stirling engines and to evaluate their accuracy using experimental and theoretical results available in published sources. The validation of the developed free piston Stirling engine models demonstrates a good agreement between the numerical results and experimental data. The validated model then was used for optimisation of the engine, deploying Genetic Algorithm approach with the purpose to determine its optimal design parameters. The developed optimisation procedure provides a noticeable improvement in the engine’s performance in terms of power output and efficiency

End-gas autoignition propensity and flame propagation rate measurements in laser-ignited rapid compression machine experiments

2019 Summer.Includes bibliographical references.Knock in spark-ignited (SI) engines is initiated by autoignition and detonation in the unburned gases upstream of spark-ignited, propagating, turbulent premixed flames. Knock propensity of fuel/air mixtures is typically quantified using research octane number (RON), motor octane number (MON), or methane number (MN; for gaseous fuels), which are measured using single-cylinder, variable compression ratio engines. In this study, knock propensity of SI fuels was quantified via observations of end-gas autoignition (EGAI) in unburned gases upstream of laser-ignited, premixed flames at elevated pressures and temperatures in a rapid compression machine. Stoichiometric primary reference fuel (PRF; n-heptane/isooctane) blends of varying reactivity (50 ≤ PRF ≤ 100) were ignited using an Nd:YAG laser over a range of temperatures and pressures, all in excess of 545 K and 16.1 bar. Laser-ignition produced outwardly-propagating premixed flames. High-speed pressure measurements and schlieren images indicated the presence of EGAI. The fraction of the total heat release attributed to EGAI (i.e., EGAI fraction) varied strongly with fuel reactivity (i.e., octane number) and the time-integrated temperature in the end-gas prior to ignition. Flame propagation rates, which were measured using schlieren images, did not vary strongly with octane number but were affected by turbulence caused by variation in piston timing. Under conditions of low turbulence, measured flame propagation rates agreed with the theoretical premixed laminar flame speeds quantified by 1-D calculations performed at the same conditions. Experiments were compared to a three-dimensional CONVERGE™ model with reduced chemical kinetics. Model results accurately captured the measured flame propagation rates, as well as the variation in EGAI fraction with fuel reactivity and time-integrated end-gas temperature. Model results also revealed low-temperature heat release and hydrogen peroxide formation in the end-gas upstream of the propagating laminar flame, which increased the temperature and degree of chain branching in the end-gas and ultimately led to EGAI

Condition Monitoring and Fault Diagnosis of Fluid Machines in Process Industries

Condition Monitoring (CM) of fluid machines plays a critical role in maintaining efficient productivity in many processing industries. Conventional vibration techniques generally provide more localised information with the need for many sensors, associated data acquiring and processing efforts, which are difficult for system deployment and are reluctantly accepted by those industries, for example paper mills and food production lines making marginal profits. To find adequate CM techniques for such industries this research investigates a new cost- effective scheme of implementing CM, which combines the high diagnostic capability of using Surface Vibration (SV) with the global detection capability of using the Instantaneous Angular Speed (IAS) measurements and Airborne Sound (AS). To address specific techniques involved in the scheme, this research is arranged in three consecutive Phases: Phase I is the technical evaluation; Phase II is the field implementation practices and Phase III is the application of AS through Convolution Neural Networks (CNN). In Phase I, widely used reciprocating compressor is investigated numerically and experimentally, which clarifies the performances of SV, IAS, AS, pressure and motor current in a quantitative way for differentiating common faults such as leakages happening in valves and intercoolers, faulty motor drives and mechanical transmission systems. It paves the foundations for the field implementation in Phase II. In Phase II, this novel scheme is realised on three sets of vacuum pumps in a paper mill. Based on an analytic study of dynamic responses to common faults on these pumps, a field test was conducted to verify the feasibility of the scheme and the preliminary study shows that airborne sound can show the relative spectral components for each machine to a good degree of accuracy. Knowledge gained from the preceding phases of study is now applied to Phase III. New techniques based on airborne signal differences through CNN have been demonstrated to give a good indication of the sound propagation and location of noise sources under all operating discharge pressure conditions at 100% validation accuracy, proving that the state of the art deep leaning approaches can be used to deal with complicated acoustic data

Analysis and Design of a Linear Tubular Electric Machine for Free-piston Stirling Micro-cogeneration Systems

The UE investments for the renewable source development, in order to achieve the set goals (Kyoto protocol and “20-20-20” targets), push to investigate in new technologies and to develop the existing. In this context, the cogeneration (CHP) plays a fundamental role, and in particular, the micro-CHP has wide development margins. Among the different cogeneration process, the systems driven by a free-piston Stirling engine are one of the most significant challenges in the research area. In such systems, the thermal energy, coming from primary energy source (for example renewable energy), is converted into mechanical energy through a Stirling engine, and then a linear generator converts the mechanical energy into electrical energy, finally, the generator is connected to the electric grid or to the load by means of an electric converter. The use of the linear generator, instead of the traditional systems of linear to alternating motion conversion (rod-crank system), allows achieving several advantages, including: improving the system reliability, noise and cost reduction. Finally, this kind of system, if well-designed, allows improving the system efficiency. In this thesis a linear generator, directly coupled to a free-piston Stirling engine in a CHP system, was developed and analysed. It was found, after a first phase of the study and literature review, that the most convenient choice, from the technical and economic point of view, is a single-phase tubular permanent magnet linear generator. In particular, the magnets are made of plasto-neodymium, while, for the realization of the stator magnetic circuit, due to the geometrical complexity, soft magnetic composites (SMC) materials have been considered. In order to determine the generator performance, an analysis method based on FEAs was developed. This simplified method (HFEA) allows the study and the comparison of different magnetization patterns and current supply strategies. The proposed methodology exploits the representation of the magnetization spatial harmonics through an analytical processing that allows taking into account different magnetization profile of the permanent magnets. Thus, it was possible to reconstruct the most important quantities, such as the flux density and the flux linkage, superposing the effect of each harmonic obtained through the Fourier analysis. Furthermore, a procedure, able to reproduce the effects of magnetic saturation of the mover, generally not negligible in such kind of machines, was developed. For this purpose, an appropriate surface current distribution on the yoke of the mover was introduced, in order to reproduce the demagnetizing effect due to the saturation. By means of the air gap flux density, the force provided by linear generator was calculated, while, by means of the flux density sampled on suitable points on the stator and mover yokes, the iron losses were estimated and then the machine efficiency. By means of the flux linkage the emf provided by linear generator was determined. The results show a very good agreement with corresponding FEAs. The proposed analysis method allows carrying out a parametric analysis with a lower computational effort. Thanks to this feature, different magnetization patterns, supply strategies and SMC materials can be compared in order to optimize the machine design. A prototype based on the design guidelines was built; then, a procedure based on experimental measurement was developed to characterize the electromagnetic parameters. To determine the magnetization profile of the magnets, the flux density on the mover surface was carried out by means of a Gaussmeter. As regards the SMC materials that compose the stator core, a calculation method was developed from suitable experimental elaborations, in order to determine the most important magnetic properties, such as the BH curve and core loss coefficients. From experimental results, it can be noted that the actual characteristics are poorer than those provided by the manufactured datasheets, likely due to the manufacturing processes and spurious air gaps between the SMC modules. The update electromagnetic parameters are used to determine the actual performance of the machine, particularly to estimate the efficiency, the emf and the force. Finally, a simplified model of the cogeneration system was developed in order to predict the dynamic behaviour and particularly, the actual values of the speed, output power and efficiency. This model allows developing the control strategy of the linear generator acting on the electric converter

Volume 1 – Symposium: Tuesday, March 8

Group A: Digital Hydraulics Group B: Intelligent Control Group C: Valves Group D | G | K: Fundamentals Group E | H | L: Mobile Hydraulics Group F | I: Pumps Group M: Hydraulic Components:Group A: Digital Hydraulics Group B: Intelligent Control Group C: Valves Group D | G | K: Fundamentals Group E | H | L: Mobile Hydraulics Group F | I: Pumps Group M: Hydraulic Component

Internal Combustion Engines and Powertrain Systems for future Transport 2019

Internal Combustion Engines and Powertrain Systems for Future Transport 2019 provides a forum for IC engine, fuels and powertrain experts, and looks closely at developments in powertrain technology required to meet the demands of the low carbon economy and global competition in all sectors of the transportation, off-highway and stationary power industries

Internal Combustion Engines and Powertrain Systems for future Transport 2019

Internal Combustion Engines and Powertrain Systems for Future Transport 2019 provides a forum for IC engine, fuels and powertrain experts, and looks closely at developments in powertrain technology required to meet the demands of the low carbon economy and global competition in all sectors of the transportation, off-highway and stationary power industries