Piston Motion Research Articles

Tracer-Based High-Speed Laser-Induced Fluorescence Measurements Of Temperature And Fuel Concentration Fields In A Rapid Compression Expansion Machine

Tracer planar laser-induced fluorescence (PLIF) using 1-methylnaphthalene (1-MN) is applied to study temperature and fuel courses during compression in a rapid compression expansion machine (RCEM). A burst mode Nd:YAG-laser at 266 nm is utilized for excitation of tracer fluorescence at a repetition rate of 7.5 kHz. A high-speed intensified CMOS camera equipped with an image doubler is applied for 2-color LIF (2c-LIF). The measurements were conducted in nitrogen atmosphere for which a calibration curve is presented that was generated in a flow cell. The temperature and fuel concentration fields are very homogeneous at early points in time during compression, however, inhomogeneities in terms of millimeter-sized hot and cold gas regions can be found especially near top dead center (TDC). These inhomogeneities were also visible in the fuel partial density field and are due to the distinct heat transfer between the hot gas and the cool walls, and probably also because of roll-up vortices induced by the piston movement. Especially at TDC the minimal gas temperature is about 300 K lower than the peak temperature near the cylinder head. These temperature differences are much larger than in piston engines and in other RCEMs reported in the literature at comparable conditions. This is because of the special design of the present layout of the machine. A relatively large difference to the adiabatic temperature can be overserved particularly at TDC. About 70 K lower temperatures were measured, which can be explained by these temperature inhomogeneities in the cylinder.

Thermo-Fluid Analysis on the Efficiency of Wet Compression Process

Wet compression has been well known as a promising technology to effectively increase the power output of the gas turbine engine by introducing fine droplets of water into the compressor stages. This lessens the temperature rise throughout the compression process of gas, thus leading to the reduction in the compressor work. A considerable amount of research on the wet compression process has been performed to date, but the detailed compression process of the two-phase gas media and fine droplets is not well understood yet. In the present study, the thermo-fluid analysis has been done on a simple flow model that has a spherical droplet of water inside a cylinder-piston system. The model is validated by using a quasi-steady D2 – Law of evaporation model. The compression rate is varied by employing the piston movement under various flow conditions such as percentage of overspray, water droplet diameter, relative humidity, and temperature. The results obtained show that for a higher percentage of overspray, smaller droplet diameters and a slower compression rate the efficiency obtained is high. Which results in lesser compressor work. The effects of compression rate, droplet diameter, overspray, and the efficiency of the wet compression have been explained and analyzed in detail.

Design and Fabrication of Exoskeleton Arm for Lifting Weight

Abstract: For centuries now, humans have developed machines for tasks which are too labour intensive for species cannot do. So, creative imagination and subtle engineering has led to the development of the powered exoskeleton. It is a device which can be worn over the human body. The robotic exoskeleton systems are developed significantly to be used for human power assist and haptic interaction with human Motion. The designed pneumatic arm consists of cylinders, a shaft efforts with lead screw mechanism able of converting a movement of piston to rotational movement of arm by utilizing the compressed air from pneumatic system. The designed processes of the suit is carried out based on some integrated information of kinematic, dynamics and structural analysis of the desired exoskeleton configuration as a whole. Since, such exoskeleton directly interacts with a human body there are some mechanical limitations to its design. While designing such exoskeleton movable range of arms, safety and comfort Wearing, low inertia, adaptability are considered.

Effect of control flow on main jet switching for single and double feedback channels fluidic oscillator

The fluidic down-the-hole (DTH) hammer controlled by the single feedback channel fluidic oscillator (SFO) has been to be effective in hard rock drilling. However, the unstable motion of the piston limits the performance of the fluidic DTH hammer in some cases. In this paper, a double feedback channels fluidic oscillator (DFO) is proposed to improve the smoothness of the piston motion, and the relationship between the control flow and main jet is observed through numerical simulation. The results show that the flow rate and symmetry of the control flow are the main factors affecting the switching of the main jet and the smoothness of the piston motion. The elevation of the flow rate of control flow shortens the switching time of the main jet. The symmetrical control flow of DFO is beneficial to the stable growth of the vortex and the wall attachment of the main jet. Compared with the SFO, the flow rate at the control nozzle of DFO is increased by 15.8%, and the switching time of the main jet is reduced by 25%. The bench test results show that the pause time is decreased by 61.4% and the impact frequency is raised by 38%.

The Effectiveness of the Device for Vacuum Fine-Needle Aspiration Biopsy in Focal Thyroid Pathology

Purpose: Determination of the effectiveness of using vacuum fine-needle aspiration biopsy under ultrasound control in patients with focal thyroid pathology. Material and methods: The modified original experimental sample for vacuum fine-needle aspiration biopsy (patent RU No. 2757525) was developed with the help of which 48 vacuum fine-needle aspiration biopsy were performed under the control of ultrasound navigation in patients with focal thyroid pathology. The device is a full-fledged vacuum compressor that creates a negative pressure in the range from –0.1 to –0.8 bar, which is connected to a syringe using a metal container, foot switches, electromagnetic valves, high-strength hoses and an adapter, where a high discharge power is created and fragmentation and aspiration of cellular material occurs. The degree of discharge depended on the assumed morphological structure of thyroid nodes, which were determined using multiparametric ultrasound. The average vacuum level was selected in the range from –0.3 to –0.5 bar, which is significantly higher than the level of discharge created by a 10 ml syringe (–0.2 bar). Results: During the vacuum fine-needle aspiration biopsy, no complications were detected during and after the manipulation. In the group of patients, 72.1 % (n = 32) women prevailed, the average age was 59.0±5.5 years. The collection of cytological material was carried out much easier, since when using v-TAB, the discharge in the syringe is formed using an apparatus that is kept at a constant level, which eliminated the need for translational movements of the syringe piston and needle in the focus for greater collection of cytological material, this indicates a low level of uninformative cytological conclusion (Bethesda I), n = 5 (11.2 %). Conclusions: 1. The implementation of vacuum fine-needle aspiration biopsy allows to improve the quality of sampling of cellular material, which affects the informativeness of cytological examination of nodular formations of the thyroid gland. 2. The vacuum fine-needle aspiration biopsy allows you to individualize the procedure depending on the ultrasound semiotics of the nodular formation of the thyroid gland. 3. The vacuum fine-needle aspiration biopsy minimizes the number of uncontrolled needle movements during a biopsy, which reduces the risk of complications.

Study on the Three-Dimensional Tribo-Dynamic Analysis of Piston Ring Pack Considering the Influence of Piston Secondary Motion

Abstract More detailed and accurate modeling is very important for analyzing and optimizing the tribological performance of the piston-ring-cylinder liner system. However, due to the difficulty of modeling and solving, theoretical studies on the three-dimensional (3D) tribodynamics of piston rings are limited. The tribodynamic model which couples the dynamics, mixed lubrication, and blow-by of piston-ring pack assemblies has not been found yet. Therefore, in this study, a 3D tribodynamic model of the piston-ring pack is developed considering the influence of piston secondary motion and the interaction forces and moments between piston ring and cylinder liner as well as between piston ring and ring groove. In addition to the ring end gaps, the influence of ring dynamics is also contained in the blow-by model. Coupled with gas flows and piston rotation, ring motions in the ring groove are investigated. It is found that ring dynamics has significant effects on the tribological performance, the axial reversing movement of piston ring is the main cause of gas pressure oscillation, piston motion has an obvious influence on the ring dynamics, the interaction forces and moments between piston and rings increase the secondary motion amplitude of piston, especially near the fire top dead center.

Analysis of the Dynamic Characteristics of the Pump Valve System of an Ultra-High Pressure Liquid Hydrogen Reciprocating Pump

This paper developed a 3D physical model of the hydraulic end of a high-pressure liquid hydrogen reciprocating pump to research the dynamic characteristics of the pump valve system. Based on dynamic mesh technology, we analyzed the coupling characteristics of pump valve and plunger motion and spool force considering the leakage model, closure model of valve gap, and compressibility of liquid hydrogen. Further, we analyzed the effect of the spring stiffness and preload force on the laws of motion of the pump valve. Finally, a liquid hydrogen pressurization test was conducted to revise the simulation model and verify the accuracy of the simulation. The results of the simulation and test show that the simulation method in this paper can simulate the liquid hydrogen pressurization process more accurately and obtain the motion law of the suction and discharge valves. Both the suction and discharge valves have an opening hysteresis angle of about 40°, and there is a strong coupling relationship between the spool motion and the piston motion and forces. The greater the preload force of the suction valve, the more obvious the oscillation effect of the suction valve. As the preload of the discharge valve increases, the opening hysteresis angle of the discharge valve increases significantly and the closing hysteresis angle decreases. The results of the research can provide some useful reference for the design of pump valves of high-pressure liquid hydrogen reciprocating pumps.

Investigation of Friction and Wear Behavior of Cast Aluminum Alloy Piston Skirt with Graphite Coating Using a Designed Piston Skirt Test Apparatus.

A piston skirt friction and wear apparatus that simulates the contact and the relative motion of piston and cylinder liner in a real engine has been designed and constructed. With this apparatus, the friction and wear behavior of a cast aluminum alloy piston with a graphite coating under different loads was studied, and the effectiveness of the apparatus was confirmed. The total wear of the piston skirt was higher under a higher load, and the upper part of the skirt surface (around the height of the piston pin) was worn more severely. The wear mechanisms were studied and, based on the test results and surface analyses, three main wear modes were believed to occur in the wear process of the piston skirt: abrasive, adhesive, and fatigue wear. The effects of skirt profile design, coating, and surface texturing on the friction and wear behavior of the piston skirt can be investigated well using the proposed apparatus, which can truly reflect actual working conditions and is useful to improve the tribological performances of piston skirts.

HIDRA-MAT liquid metal droplet injector for liquid metal applications in HIDRA

A liquid metal droplet injector was explicitly designed for the Hybrid Illinois Device for Research and Applications Material Analysis Test-stand (HIDRA-MAT) at the University of Illinois Urbana-Champaign to prepare liquid metal plasma-facing components (PFCs) for plasma exposure. The design goals were to create a compact, reliable, and robust design that could apply liquid metal droplets in-vacuo to a variety of samples. The injector was designed for liquid metal use, and results discussed pertain to lithium. The injector can produce lithium droplets of consistent size by utilizing programmable piston movement. Droplet formation data is presented for four different piston step sizes (0.125 mm, 0.25 mm, 0.5 mm, and 1 mm) at three different nozzle temperatures (185 °C, 230 °C, and 270 °C). Droplets are formed on the injector nozzle tip and a linear shift mechanism vertically translates the droplet to the substrate for application. This design prevents the droplet from inadvertently detaching off the nozzle and falling to the sample. Application of the liquid metal droplet ensures placement consistency on the substrate and helps avoid damage to components in HIDRA-MAT that should not interact with liquid metals. A description of the liquid lithium droplet creation and application results is given and provides additional insight into the cooling and oxidation of lithium droplets under vacuum conditions. A second nozzle was fabricated and demonstrated repeatability in droplet diameter creation having a variance of ±0.14 mm for droplets created from the same number of piston steps. The end-use for the injector on HIDRA-MAT is to apply liquid metals to PFCs and expose them to HIDRA's plasma with subsequent intershot in-vacuo surface analysis in HIDRA-MAT for plasma-material interaction studies.

The real-time interaction model for transient mode investigations of a dual-piston free-piston engine generator

A free-piston engine generator is being developed worldwide as a novel means of electrical power generator for light vehicle application, which can provide a complementary solution towards reducing carbon dioxide emissions of road vehicles in general. However, the absence of a crank-slider mechanism in free-piston engines resulted in poor transient operations. Transient real-time modelling and simulation can provide the interaction between in-cylinder combustion with dynamics of piston motion, which has not been fully explored previously. This paper presents a real-time interaction model between dynamics of the piston motion and thermodynamics of the in-cylinder combustion of a two-stroke spark ignition dual-piston free-piston engine generator for transient operation investigations. The simulation model was developed based on the working prototype and comprised of zero- and one-dimensional sub-models interacted in real-time governed by a single timestep. The study focuses on three critical transient modes: motoring, starting and generating for the transient performance investigation. A series of experimental results during motoring was used for validating the simulation model, which showed good agreement between simulation and experiment results with 2–5% errors. The targeted brake thermal efficiency is around 20–30% at 50–60 Hz engine speed which has been shown achievable. Transient speeds of 10 and 25 Hz produced higher combustion pressure around the top dead centre but suffered pumping loss at the end of the expansion stroke. The lower peak pressures at 50 and 60 Hz have contributed to the lower brake mean effective pressure values. Maximum brake thermal efficiency of 25.8% lies in the mid-range of compression ratios between 10:1 to 15:1 while at the cyclic speeds of 50 Hz to 60 Hz. Maximum brake mean effective pressure contour occurs between 5 and 12.5 compression ratios and corresponding speeds of 10 to 30 Hz. It was observed that the excess energy from combustion results in piston overshoot condition while insufficient energy prevents the piston from achieving the targeted stroke and compression ratio. Knock events were observed for high compression ratio cases regardless of engine speed. Predictive stroke control and knock detection capability are the main contribution of the real-time interaction model presented in this paper for realistic transient operation investigation and performance prediction of the dual-piston free-piston engine generator.

Experimental investigation on helium valved linear compressors with different active offsets

Piston offset in the helium valved linear compressor (VLC) deteriorates the cooling performance and operating life of Joule-Thomson (JT) refrigerators, especially in aerospace applications. To clarify the influence of piston offset on the VLC performance, an experimental investigation was carried out. Based on a laboratory developed VLC, the effects of piston offset on the suction and discharge pressure, pressure ratio, mass flow rate, motor efficiency, volume efficiency and adiabatic efficiency are systematically studied under two piston motion states (fixed piston displacements and full strokes). The results show that when the piston stroke is constant, the offset will increase the discharge pressure and mass flow rate, and decrease suction pressure. When the piston moves at full stroke, the offset will reduce the discharge pressure and mass flow rate, and increase suction pressure. Regardless of the working conditions, the existence of offset will affect the efficiency of the compressor, hence increasing the power consumption.

Gas chromatograph calibration of gas mixtures using a versatile precision volumetric apparatus

A compact, volumetric apparatus was developed for accurate automated preparation of standard gas and gas-liquid mixtures for gas chromatograph detector calibration, with accuracies comparable to those from gravimetric or Coriolis flow methods. The method developed by the principal author is not an adaptation or extension of any other apparatus or technology, and measurements involve only stepper motor steps, temperature, and pressure ratios. Mixture preparation is accomplished via the displacement of gas between chambers in a highly uniform cylinder, separated by a movable piston. Piston movement, with piston end rods of exactly equal diameter, ensures that there is no change in interior volume, and the volume of gas displaced from the bottom into the top compartment is exactly proportional to the piston travel measured to within 10μm. The apparatus, operation, and previously unpublished measurements on common refinery gas mixtures over large concentration ranges are described in detail. These confirmed the accuracy and versatility of the apparatus and also the principle of no pressure change during mixture preparation, from sensitive pressure measurements. Conservative expanded uncertainties in prepared mixture mole fraction ranged from 0.001 to 0.002 over extended composition ranges. Absolute average deviations for the detector response factor for the mixtures ranged from 0.001 to 0.002. An exact new mathematical solution procedure permits the use of impure "pure" gases without loss of accuracy and can be applied to other procedures for standard gas mixture preparation. An exact expression is listed for determining "pure" gas purity.

Approximation of the compression process to isothermal in a reciprocating compressor with a liquid piston

• Theoretical and experimental study of bringing the compression process to isothermal. • Designed two-stage piston hybrid power machine with liquid piston. • The kinematics of liquid piston motion has three zones: two isothermal (hyperisothermic) and one non-isothermal compression. • With a decrease in the temperature of the surface of the working chamber and its diameter, the average velocities of the liquid piston of the real and isothermal compression process converge. • According to the obtained results, new highly efficient designs of hybrid power machines are proposed. The implementation of the isothermal process of gas compression in the compressor increases the indicator efficiency up to 20%, which is a determining increase in their operation and saves a significant amount of energy and financial resources, as compressor units consume up to 10% of the energy consumed by production sector. Its implementation is possible in many ways: by changing the heat exchange surface (injection of coolant during compression), changing the heat transfer coefficient, changing the speed of gas compression, etc. The article considers a scheme for gas compression in a cylinder with a liquid piston having a variable speed to ensure an isothermal compression process, and a design of piston hybrid power machine, which brings the gas compression process closer to isothermal. According to theoretical studies, we determine the speed of the liquid piston for the implementation of the isothermal compression process, the amount of liquid required to supplied to the cylinder and the amount of liquid to be be drained from the pump into the gas cap. Using the method of mathematical modeling, according to the fundamental laws of conservation of energy, mass and motion, a mathematical model of a two-stage piston hybrid power machine with a liquid piston and a gas cap has been developed. The performance of the machine is verified by the created prototype, a test stand for its research and a series of experimental studies. As a result of the numerical experiment, we determined the physical picture of the processes in the machine, the absolute and relative flow rates of liquid into the gas cap and into the working cavity for isothermal compression process. The comparative analysis of the relative and absolute flow rates of the liquid and the instantaneous velocities of the piston identified areas by the angle of rotation where the isothermal compression process or close to it is carried out and where it is difficult. The performed parametric analysis verified that reducing the temperature of the walls and the diameter of the cylinder improves the implementing of the isothermal compression process. Using the findings, the results of the conducted patent analysis on the design features of the PHPM, we offered ways to implement the isothermal compression process, new two-stage PHPM designs with a liquid piston having high weight, size and energy indicators.

In-Cylinder Cold-Flow Analysis - ‘A Comparison of Crank-Slider Engine and Crank-Rocker Engine’

Researchers and engineers are continuously working to improve the overall efficiency of internal combustion engines by modifying the engine designs and configurations. As new engine designs are introduced, the in-cylinder flow behaviour becomes more and more complex. The maximum output and efficiency that can be achieved from a single cylinder engine depends upon the amount of air entrapped in the combustion chamber during intake stroke. A novel crank-rocker (C-R) engine was designed and fabricated in Universiti Teknologi PETRONAS (UTP), Malaysia and is currently under optimization phase. This paper narrates the in-cylinder cold-flow analysis of the C-R engine considering widely used industrial automotive software, Converge CFD. The turbulent behaviour of the C-R engine was compared with that of the conventional crank-slider engine. The initial and boundary conditions for the C-R engine simulations were set according to the benchmarked crank-slider engine. RNG k-ε turbulence model was used to generate the data plots for tumble & swirl ratios, cylinder pressure, TKE, turbulent dynamic viscosity and vorticity at cold-flow conditions. It was observed that the C-R engine has better air scavenging properties and can achieve better air-fuel mixing that can lead to emission-free combustion. This study will help in understanding the turbulent airflow behaviour within the curved cylinder under the influence of rocking piston motion, and its advantageous flow properties compared to those in crank-slider engines.

WCSPH simulation of the forced response of an attenuator oscillating water column wave energy converter

In this study, a weakly compressible smoothed particle hydrodynamics (WCSPH) model was used to simulate the forced piston motion of water inside a fixed oscillating water column (OWC) wave energy converter. The considered device was a chamber with a complex entrance geometry attached to the rear wall of the wave flume. The effect of an impulse turbine on the chamber was modeled by an equivalent orifice damping force applied on a thin plate. This way, a balance is established between numerical accuracy and efficiency. The simulations were performed for two different wave steepness values of 0.025 and 0.04. To validate the model results, the experimental work performed in the Technical University of Denmark was used. Fourier Transform analysis was performed on the SPH model results and experimental data to obtain the first-harmonic amplitude of the desired parameters. In general, a good correspondence was found between the SPH calculations and the experimental results for the piston motion of the water inside the chamber. However, the SPH results were slightly larger, especially around the resonance period. A possible reason is the placing of the plate above the free surface which might reduce the small sloshing motions of water inside the chamber. Finally, from the heaving velocity of the plate, the flux and pressure drop through the orifice were evaluated. It is shown that all three parameters reach their maximum around the resonance period of the chamber.

Study of the Cylinder Deactivation on Tribological Parameters and Emissions in an Internal Combustion Engine

In the present investigation, a study is carried out using numerical simulation on the effects of cylinder deactivation on tribological parameters and emissions in an internal combustion engine. For the development of the research, a tribological model was used to predict the characteristics of the lubrication film, friction conditions, blow-by gas, and deformation of the piston rings. Additionally, the construction of a CFD model was carried out to describe the kinematic movement of the engine piston. The analysis of results allowed for the demonstration of the active cylinders presenting an increase of 21.53% and 7.65% in the pressure and temperature in the cylinder wall. Additionally, the active cylinders present a reduction of 11.33% in the minimum thickness of the lubrication film and an increase in the friction force due to asperities, which implies an increase of 33% in power losses due to friction. The implementation of technologies such as cylinder deactivation causes an increase in combustion gas leaks caused by the increase in pressure of the active cylinders. However, the use of this technology allows reducing 9.09%, 8.26%, and 7.41% in CO, HC, and NO emissions. Although the use of technologies such as cylinder deactivation allows significant fuel savings, it is necessary to consider the negative effects caused by this technology, such as the increase in combustion gas leaks and the increase in power loss by the greatest frictional forces.

Force and energy analysis of single-piston free-piston expander—linear generator

The movement of piston in free-piston expander-linear generator (FPE-LG) mainly depends on the dynamic force balance among four kinds of forces (air impetus, air resistance, electromagnetic resistance and frictional resistance). In this paper, the Newton's Second Law and the first law of thermodynamics are used to analyze the single-piston FPE-LG, the change of four kinds of forces and work produced by the four kinds of forces are analyzed. Nominal work-electricity conversion loss coefficient is proposed for the firs time to represent the energy loss. The experiment results show that the work produced by four forces from top dead center (TDC) to bottom dead center (BDC) are higher than those from BDC to TDC. The minimum proportion of air resistance energy consumption is also more than 50%, the proportion of electromagnetic resistance energy consumption is less than 20%, and the proportion of frictional resistance energy consumption is more than 20%. Therefore, the total nominal work-electricity conversion loss can be effectively reduced by increasing intake time or intake pressure.

The effect of electromagnetic load fluctuation on the gas exchange stability of a free-piston hybrid power system

The free-piston hybrid power system (FPHS) is affected by the dynamic coupling of combustion drive, power transmission, piston motion, excitation generation and gas exchange, and its operating state is very different from that of traditional engines. In this paper, the influence of the change of electromagnetic load on the ventilation stability of the whole system is studied by combining the method of system simulation and experimental validation. A dynamic-ventilation one-dimensional coupled gas exchange model was established, and the influence of the fluctuation of the electromagnetic load on the gas exchange is simulated by combining the thermodynamic model with the magnetic inductive load model. The results show that the scavenging efficiency is positively correlated with the load fluctuation, while the trapping efficiency changes with the opposite rule. Specifically, increasing the electromagnetic load properly will increase the time of gas exchange and obtain more fresh charge. The reduction of the electromagnetic load will make the compression process have higher gas pressure and temperature, which the mixture of oil and gas is more homogeneous and the combustion rate is faster after ignition. The stability of the ventilation performance of FPHS is very sensitive to electromagnetic fluctuations. The control of FPHS system can be achieved by adjusting the electromagnetic load.

Robust Tracking Control for Electrohydraulic System Using an Internal Model-Based Sliding Surface

Abstract An electrohydraulic system, which is widely applied in practice, is a highly nonlinear system with uncertainty. In order to improve the control performance, the nonlinearity and uncertainty should be taken into consideration. In this context, a lot of researches have been carried out, and most of them need the derivatives of the tracking error to construct their controllers. However, the accurate values of the derivatives are difficult to be obtained in practice. What's more, without considering the characteristics of the reference signal, the direct applications of these control methods in the periodic motion tracking problem of electrohydraulic systems are difficult to achieve satisfactory control performances. Therefore, a novel internal model principle (IMP)-based sliding mode control (SMC) is proposed in the paper. First, an ideal driving force for the second-order piston motion dynamics is designed based on the IMP with the measurement of piston position. And then, the deviation between the ideal and measured driving force is selected as the sliding mode variable. At last, the SMC is formed to guarantee the actual driving force can converge to the ideal one in finite time. As the main contribution of this paper, the proposed IMP-based SMC does not need the derivatives of the tracking error and can achieve a better performance by eliminating the reference frequency related component in the tracking error. To verify the control performance of the proposed method, a 20 Hz sinusoidal reference tracking scenario is considered, and the finite-time exact differentiator (FTD)-based SMC and the FTD-based high-order SMC (HOSMC) are selected as comparison methods. A group of simulations are performed on an electrohydraulic system used in the controlled trajectory rapid compression and expansion machine (CT-RCEM). The simulation results show that the 20 Hz component in the tracking error is eliminated under the proposed controller, but the 20 Hz error components are still remaining as 2.58 mm and 0.64 mm under the FTD-based SMC and the FTD-based HOSMC, respectively.

Power-Optimal Control of a Stirling Engine's Frictional Piston Motion.

The power output of Stirling engines can be optimized by several means. In this study, the focus is on potential performance improvements that can be achieved by optimizing the piston motion of an alpha-Stirling engine in the presence of dissipative processes, in particular mechanical friction. We use a low-effort endoreversible Stirling engine model, which allows for the incorporation of finite heat and mass transfer as well as the friction caused by the piston motion. Instead of performing a parameterization of the piston motion and optimizing these parameters, we here use an indirect iterative gradient method that is based on Pontryagin’s maximum principle. For the varying friction coefficient, the optimization results are compared to both, a harmonic piston motion and optimization results found in a previous study, where a parameterized piston motion had been used. Thus we show how much performance can be improved by using the more sophisticated and numerically more expensive iterative gradient method.