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The free-piston linear generator (FPLG) with a dual-piston air-driven system is a novel type of energy conversion device that converts mechanical energy into electric power through a linear generator. This paper investigates a novel FPLG utilising different generator stator core configurations (GA, GB, GC, GD, and GD) with an optimised valve opening control and the inlet pressure of 5 bar and 8 bar. The effect of generator configuration on the translator motion characteristics, root mean square (RMS) power output, as well as the system stability and the conversion efficiency, are duly discussed. The results show that the piston motion is affected by the generator configuration and the inlet pressure. The maximum RMS power achieved is 203.9 W when GB is used, whereas the maximum operating frequency of 13.8 Hz and a peak power output of 396 W are achieved when GD is used. The FPLG stability within the range for all generator configurations except for GA when the inlet pressure is 5 bar. The FPLG system conversion efficiency (thermal to work and work to electrical) is duly discussed.

The presented work discusses a methodology for analysis of noise emissions from a diesel engine. A numerical model of the piston motion, analyzing its lateral, reciprocating and rotation motion, has been presented in order to investigate the lateral motion of the piston skirt assembly and resulting vibrations induced as a result of these motions in the engine block. Various parameters of modal analysis were obtained using the mobility analysis. The presented methodology was validated by data obtained from a diesel engine test set up. The predicted results matched well with those of measured data, hence validating the presented scheme.

The presented work discusses a methodology for analysis of noise emissions from a diesel engine. A numerical model of the piston motion, analyzing its lateral, reciprocating and rotation motion, has been presented in order to investigate the lateral motion of the piston skirt assembly and resulting vibrations induced as a result of these motions in the engine block. Various parameters of modal analysis were obtained using the mobility analysis. The presented methodology was validated by data obtained from a diesel engine test set up. The predicted results matched well with those of measured data, hence validating the presented scheme. [ABSTRACT FROM AUTHOR]

We study, in a unified manner the motion of a uniformly advancing piston in the planar ( m = 0 ), cylindrically symmetric ( m = 1 ) and spherically symmetric ( m = 2 ) isentropic flow governed by Euler's equations. In the three dimensional space the piston is replaced by an expanding cylinder or a sphere which produces a motion in the medium outside. Under the hypothesis of self symmetry pair of ordinary differential equations is derived from Euler's equations of fluid flow. Based on the analysis of critical solutions of this system of ordinary differential equations, unified treatment of motion of uniformly advancing piston is given with different geometries viz. planar, cylindrically symmetric and spherically symmetric flow configuration. In case of nonplanar flows, solutions in the neighbourhood of nontransitional critical points approach these critical points in finite time. Transitional solutions exist in nonplanar cases which doesn't correspond to the motion of a piston. In the planar case, it is found that solutions take infinite time to reach critical line. [ABSTRACT FROM AUTHOR]

The free-piston engine has a lot of potential to alter the conventional combustion engine due to mechanical structural simplicity, high engine efficiency, reducing hazardous gas emission and fuel flexible combustion. However, accuracy of piston motion control is a major challenge in all types of free-piston engine as well a dual free piston engine generator (DFPG) because of not having a crankshaft mechanism. This article describes a simulation investigation of a predictive-fuzzy logic control method conducted on the DFPG prototype in University of Ulsan. First, the simulation model of the DFPG consisted of a free-piston engine and a linear alternator is established and running in Matlab/Simulink environment. Then simulation result is validated against experimental data to prove validity of the simulation model. Second, a predictive-fuzzy logic (PFL) control method is proposed to apply to the DFPG and its performance is carried out using the full-cycle simulation model. The PFL strategy is demonstrated to improve the DFPG performance and more effective than the PID one in terms of settling time, TDC error, and cycle-to-cycle variation. According to results, the PFL controller reduces settling time 30 % in comparison to PID controller. The PFL controller has also 0.52 mm better TDC position error than the PID controller is 0.76 mm. Coefficient of variation values is found to be 1.0 %, and 1.9 % for the PFL controller and PID controller, respectively. This means that the PFL controller is a powerful method to dampen cycle to cycle variations in the DFPG. [ABSTRACT FROM AUTHOR]

The free-piston engine generator becomes a new-type potential substitute for the conventional crankshaft combustion engine. This article presents a simulation to study the fuel spray and mixing characteristics of a diesel free-piston engine generator by comparing a corresponding crankshaft combustion engine. A full-cycle model which couples with piston dynamics, combustion, and gas exchange is developed to simulate the fuel spray, atomization, and mixing in the free-piston engine generator. The result indicates that compared with the crankshaft combustion engine, the free-piston engine generator provides a higher temperature and pressure for fuel spray and mixing during the ignition delay, but its ignition delay lasts shorter. The free-piston engine generator shows a shorter spray penetration and more fuel impingement due to its smaller combustion chamber volume during the injection process. The free-piston engine generator exhibits a lower level of air utilization and worse uniformity of fuel--air mixture in combustion chamber. In addition, the shorter ignition delay of free-piston engine generator makes the time of atomization, evaporation, and mixing of fuel shorter, and the mixing effect of free-piston engine generator is worse, resulting in less combustible mixture formed during the ignition delay. In addition, some guiding suggestions have been proposed to improve the fuel spray and fuel--air mixing characteristics of free-piston engine generator. [ABSTRACT FROM AUTHOR]

The model test investigates the temporal and spatial distribution characteristics of the slamming effects in the stepped moonpool under wave excitation with ship forward speed. An analysis is conducted to compare and examine the variations in the duration and extreme value of slamming at different positions along the moonpool wall. The mechanism of the slamming formation on the moonpool wall during the piston and sloshing motion of the fluid in the moonpool is studied in depth. The results indicate that the slamming phenomenon of the stepped moonpool is limited to one side of the step, while the opposite side does not exhibit any noticeable slamming phenomenon. The existence of the step leads to a similar phenomenon of the 'dam-break effect', which in turn produces a slamming phenomenon. The slamming on the wall of the moonpool is significantly influenced by the motion mode of the fluid within the moonpool, which in turn affects its temporal and spatial distribution characteristics. The duration and magnitude of slamming vary with the vertical location of the wall. The presence of steps in the moonpool is a crucial structural element that leads to the slamming of the moonpool, regardless of whether the fluid inside is in piston or sloshing action. This paper provides citations and recommendations for the design of moonpools and the mitigation of slamming phenomena within them. • The slamming phenomenon of the stepped moonpool is limited to one side of the step, while the opposite side does not exhibit any noticeable slamming phenomenon. The existence of the step leads to a similar phenomenon of 'dam-break effect', which in turn produces a slamming phenomenon. • The slamming on the wall of the moonpool is significantly influenced by the motion mode of the fluid within the moonpool, which in turn affects its temporal and spatial distribution characteristics. • The presence of steps in the moonpool is a crucial structural element that leads to the slamming, regardless of whether the fluid inside is in piston or sloshing action. [ABSTRACT FROM AUTHOR]

The results of kinematic analysis of the ASz-62IR radial engine crankshaft was presented. In addition, the one-dimensional model of the working cycle of the engine was created in AVL BOOST system. Differences in the waveforms for each pistons causes the differences in the filling process what reflects in the mass of the load supplied to cylinders. Additionally, due to one dimensional model computation. The results show differences in the value of maximum pressure. This causes differences in mean effective pressure of up to 4% and which also affects the vibrations of the whole engine.

Combustion engines bring a lot of pollution products to human living environment. This study introduced a green engine called free-piston linear engine (FPLE), and performed an evaluation on the pollutant emissions of a diesel FPLE by comparison with a corresponding conventional crankshaft engine (CCE). The combustion reaction and pollutant formation were described by a comprehensive model which considers the special operation mechanism of the FPLE. The effect of dynamic and fuel quantity on the unclean combustion products of the FPLE and the CCE was compared. Results indicate that in the case of the fuel quantity of 7.1 mg condition, the pollutant forming in the FPLE is generally later than that in CCE because of the higher speed of FPLE around the reverse point of stroke, and a significant advantage in nitric oxide (NO) emission is found for the FPLE, although it emits more carbon monoxide (CO) and soot. Moreover, compared with the CCE, the FPLE is cleaner in lean fuel conditions because the NO production of the FPLE is only half of that of the CCE, and that of other pollutants is almost at the same level. However, in heavy fuel conditions, the FPLE shows a disadvantage in CO and soot emission due to the serious afterburning effect and poor oxygen environment in some local areas, although its NO production is still lower than that of the CCE. [ABSTRACT FROM AUTHOR]

The free-piston engine generator is an attractive alternative to the conventional reciprocating engine due to the feature that it moves without crankshaft system. This paper presented a simulation for the investigation on the characteristic of in-cylinder gas motion and heat transfer in a compression ignited free-piston engine generator. An operation experiment was performed to obtain the precise piston motion for the modeling of heat transfer and gas flow. The development of the multi-dimensional model was described, and simulation results were presented and showed good similarity with the experimental data. Then, the heat transfer and gas motion in the free-piston engine generator were discussed, on which the influences of piston motion were also investigated compared with a corresponding conventional reciprocating engine. The results indicated that compared with the conventional reciprocating engine, a higher level of squish and reverse squish effect was found for the free-piston engine generator due to its faster motion around top dead center, while its slower piston motion led to weaker gas turbulence in the compression process. Moreover, the free-piston engine generator and conventional reciprocating engine did not show a significant difference in heat transfer during the compression process, however, an obvious advantage of heat transfer was indicated for the free-piston engine generator in combustion and expansion processes due to its lower combustion temperature and the reduced time that is available for heat transfer caused by its faster expansion. The mechanism for such differences is that the free-piston engine generator moves with uneven equivalent speed. [ABSTRACT FROM AUTHOR]

Free-piston engine generator is a new alternative to traditional reciprocating engine, which moves without mechanical restriction of crankshaft system. This article investigated numerically the friction characteristics of piston rings in a free-piston diesel engine generator by adopting coupled models of dynamic and friction. The development of the dynamic model and friction model was described, and an iterative calculation method was presented, giving insight into the coupled parameters of these two models. The detailed effects of the dynamic on friction and lubrication were investigated compared with a corresponding traditional crank engine. The friction characteristics of the free-piston engine generator were found to differ clearly from those of the traditional engine due to its special piston motion. Compared with the traditional engine, the minimum lubricant film thickness of piston rings in the free-piston engine generator is thicker and lasts shorter at the dead center regions, but it is generally thinner at other positions. The average friction force, friction power, and friction work of the piston rings in the free-piston engine generator are less than the traditional engine due to the better lubrication in endpoints region. Meanwhile, the friction power of the free-piston engine generator increases with the increase in fuel mass or decrease in load. The friction efficiency varies in correlation with the generator load; the optimum friction efficiency can be obtained by either increasing or decreasing from a certain generator load. [ABSTRACT FROM AUTHOR]

The wide employment of the moonpool on marine vessels and offshore platforms shelters the activities and operations from the external wave environment to a high degree. However, under certain resonant conditions, violent water motions with relatively large amplitudes can be excited within the moonpool. This paper describes the numerical simulations and physical experiments in an offshore basin carried out specifically to investigate the behaviour and characteristics of the resonant water motions within a large rectangular moonpool of a typical drilling vessel. By tracking the dynamic free surface evolution in the moonpool, it was observed that complex water motions consisting of vertical piston motions, longitudinal sloshing motions, wave run-up and impacts are coupled in the moonpool. The relative water motion amplitudes were quantified. It was identified that multiple water motions coexist even when there is only one external excitation source provided by a regular wave train. It was further demonstrated that the encountered waves travelling along the vessel have significant effects on the excitation of the resonant water motions in the moonpool. Close coherences were found revealed between the water elevations inside and outside the moonpool. [ABSTRACT FROM AUTHOR]

Free-piston engine generator is an unconventional engine, which abandons the crank and connecting rod mechanism. This paper focused on a numerical simulation for the research on the combustion characteristics of a free-piston diesel engine generator. An iteration numerical simulation method was presented by adopting coupled models of zero-dimensional dynamics, multidimensional scavenging and combustion. According to the coupled parameters of these models, the effects of the piston motion on combustion process were investigated compared with a corresponding traditional crank engine. The results indicate that compared with the conventional engine, the free-piston engine generator has a longer combustion duration due to its faster piston mean velocity in combustion process. While the heat release before top dead center, the isochoric heat release, and the heat release during the premixed combustion period both were lower than the traditional engine, and the post-combustion became more intense for the free-piston engine, thus a slight disadvantage of indicated efficiency was found. In addition, the in-cylinder average gas temperature and pressure were generally lower than the traditional engine, which contribute to the distinct advantages in NO discharge of the free-piston engine generator. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to introduce and investigate a new application of hydrogen to a special internal combustion engine (free-piston engine generator). The development of a full-cycle zero-dimensional dynamic simulation model is described, and an extensive coupled research method is presented by the iteration simulation between the zero-dimensional dynamic model and a multi-dimensional computational fluid dynamics engine model of combustion process, giving insight into the operating characteristics and performances of the new hydrogen fueled engine. The influences of the piston motion on combustion process are analyzed. The performance characteristics of the new hydrogen engine are found to differ significantly from those of a corresponding traditional hydrogen engine and a free-piston gasoline engine. The results indicate that compared with the above-mentioned traditional hydrogen engine, the free-piston hydrogen engine has a higher piston acceleration around top dead center (TDC) and a advantage in terms of emissions formation due to faster power stroke expansion, but the indicated efficiency is slightly lower due to the longer late combustion process. Moreover, the indicated efficiency, combustion velocity and peak pressure are both larger, compared with the free-piston engine combusting gasoline, and the concentration of NO emission also has an advantage. [ABSTRACT FROM AUTHOR]

The aim of this work is to develop various analytical models for studying the piston slapping motion. The results of various methods are compared to the experimental results using block vibrations measurements on a diesel engine test rig. Both results correlate, validating the considered theoretical methods. [ABSTRACT FROM AUTHOR]

A four-stroke free-piston engine with internal and external irreversibilities of finite combustion rate of the fuel, heat transfer and friction is investigated in this paper. Under the condition of the fixed fuel consumption per cycle, the optimal piston motion trajectory for maximizing the net work output of different cases is derived by applying optimal control theory. Considering the path constraints and boundary conditions of this free-piston Miller cycle, a Gauss pseudospectral method (GPM) is presented for solving optimal motion trajectory. The results show that the optimal piston trajectory improves the efficiency by more than 10% and also suitably reduces the heat transfer losses compared to the conventional piston motion. By optimizing the piston motion around the top dead center (TDC), the in-cylinder gas pressure and temperature have a remarkable improvement while the heat transfer losses have a suitable reduction. The effects of other parameters, such as combustion duration and the frictional coefficient on the piston trajectory, are also investigated. It is shown that optimizing the piston motion trajectory is a good approach for the free-piston engine to improve the efficiency and it can provide guidelines for the optimal control of the practical free-piston engine. [ABSTRACT FROM AUTHOR]

Highlights: [•] The control method of an opposed hydraulic free piston engine was proposed. [•] Grey model prediction can provide better performance in piston position control. [•] The piston motion on one side influences that of the other side. [•] A satisfactory synchronization of the compression stroke can be achieved. [•] Better real-time control performance was obtained in the hardware-in-the-loop test. [ABSTRACT FROM AUTHOR]

An existing model of the interface between a parallel-sided piston skirt and the cylinder wall in an internal combustion engine is extended to allow the modelling of barrelling of the piston skirt. The effects of the skirt profile on the secondary motion of the piston and on the distribution of pressure in the lubricant film are examined. It is shown that piston secondary motion, and in particular rotation of the piston about the gudgeon pin, which might contribute to wear of the cylinder, can be reduced by appropriate positioning of the maximum diameter of the piston skirt in relation to the gudgeon pin and the centre of mass of the piston. [ABSTRACT FROM AUTHOR]

Based on the hydraulic free piston engine fundamental theory, the analytical model of the system was built. The asymmetry of the piston motion and the influencing factors were investigated by simulation and prototype tests. The results indicate that the piston motion around top dead center of the single piston hydraulic free piston engine appears asymmetry. The energy transfer characteristics and the forces on the piston around top dead center determined that the asymmetry characteristic is inherent. The piston motion around top dead center is mainly determined by the cylinder gas pressure. The faster the compression procession is, the faster the expansion process is. The responses of the distributing valves affect the piston motion around top dead center little. The operation position of the load pressure mainly affects the end of the expansion process. [ABSTRACT FROM AUTHOR]

An existing model for the dynamic analysis of the piston motion in an internal combustion engine has been modified to incorporate a simpler representation of the piston–cylinder interaction, and to represent the main and big-end bearings as lubricated rather than dry journal bearings. The results demonstrate that the differences in calculated bearing forces and output torques are negligible, indicating that the simple dry journal bearing model is sufficient, but show that the modelling of the interaction between piston and cylinder is considerably improved. [ABSTRACT FROM AUTHOR]

A Diesel cycle heat engine with internal and external irreversibilities of heat transfer and friction, in which the finite rate of combustion is considered and the heat transfer between the working fluid and the environment obeys Newton's heat transfer law ≈ D(T), is studied in this paper. Optimal piston motion trajectories for minimizing entropy generation per cycle are derived for the fixed total cycle time and fuel consumed per cycle. Optimal control theory is applied to determine the optimal piston motion trajectories for the cases of with piston acceleration constraint on each stroke and the optimal distribution of the total cycle time among the strokes. The optimal piston motion with acceleration constraint for each stroke consists of three segments, including initial maximum acceleration and final maximum deceleration boundary segments, respectively. Numerical ex-amples for optimal configurations are provided, and the results obtained are compared with those obtained when maximizing the work output with Newton's heat transfer law. The results also show that optimizing the piston motion trajec-tories could reduce engine entropy generation by more than 20%. This is primar-ily due to the decrease in entropy generation caused by heat transfer loss on the initial portion of the power stroke. [ABSTRACT FROM AUTHOR]

A dynamic model is presented for the internal combustion engine in which the primary motion of the pistons is determined by the gas pressure in the cylinders rather than by an assumed steady rotation of the crank, and the secondary motion of the pistons is determined by the interaction of the pistons with the cylinder walls under non-lubricated and fully flooded lubricated conditions. Results are presented for the simulation of a single-cylinder engine and show clearly the variations in the secondary translation and rotation of the piston throughout the engine cycle for the non-lubricated condition, and the significant damping of such secondary motions in the fully flooded lubricated condition. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we construct the exact solution for fluid motion caused by the uniform expansion of a cylindrical or spherical piston into still air. Following Lighthill , we introduce velocity potential into the analysis and seek a similarity form of the solution. We find both numerical and analytic solutions of the second order nonlinear differential equation, with the boundary conditions at the shock and at the piston. The results obtained from the analytic solutions justify numerical solution and the approximate solution of Lighthill . We find that although the approximate solution of Lighthill gives remarkably good numerical results, the analytic form of that solution is not mathematically satisfactory. We also find that in case of spherical piston motion Lighthill’s solution differs significantly from that of our analytic and numerical solutions. We use Pade′ approximation to extend the radius of convergence of the series solution. We also carry out some local analysis at the boundary to obtain some singular solutions. [Copyright &y& Elsevier]

Abstract: A piston motion controller for a free-piston internal combustion engine is presented. To improve dynamic performance in the control of the piston motion and engine compression ratio, the controller response is determined from a prediction of engine top dead centre error rather than the measured value from the previous cycle. The proposed control approach showed superior performance compared with that of standard PI feedback control known from the literature due to a reduced control action time delay. The manipulation of fuel injection timing to reduce in-cylinder pressure peaks and cycle-to-cycle variations was also studied, indicating that with the piston motion estimation, the injection timing is a powerful control variable for this purpose. [Copyright &y& Elsevier]

This paper reports a new actuating method of a micromirror with piston motion by the electrowetting effect. Liquid metals drops (LMD), gallium and mercury, instead of conventional electrolyte solution, are used in the electrowetting experiments to reduce the vapor pressure and to increase the conductivity. An approximate formula of LMD height changes versus actuated voltage is deduced and the electrowetting setup is improved for actuating the mirror. The actuating performance of the LMD as a pivot is investigated. The hysteresis of contact angle is effectively minimized with argon sputtering the surface of the insulating layer, which makes the deformation of the LMD highly repeatable. The frequency response (0.01 Hz-3 kHz) and 6 vibration modes of the mercury drop are observed. The maximum acceleration of the drop during the actuation is 300 g (g = 9 · 8 In/s²). We fabricated a 1000 µm × 1000 µm × 20 µm, 50 µg micromirror and an actuating circuit based on the electrowetting of liquid metal. With the LMD confine spot, a mercury drop of 500 µm in diameter is placed between the mirror and the actuating electrodes. A 440-Hz sinusoidal voltage of 75 V actuates the micromirror, with a maximum of 60 µm displacement. [ABSTRACT FROM AUTHOR]

In this paper, we study the piston motion of a mercury droplet that is confined in a metal-plated microhole. This droplet is actuated by the electrocapillary effect and large displacements of up to 210 µm are achieved with very low voltages (∼2 V). We use a high-speed camera (10,000 frames/s) to capture the piston motion and we find the resonance frequency is ∼50 Hz. The mercury droplet geometry in equilibrium state is analyzed based on Laplace equation and volume conservation. A mathematical model is developed; it predicts that the resonant frequency of mercury droplet is 150 Hz. A prototype of piston-motion micromirror is also demonstrated in the experiment, with a frequency of 400 Hz and amplitude of ∼8 µm at 2 V. [ABSTRACT FROM AUTHOR]

In order to improve the operation of a high-enthalpy free piston shock tunnel its tuned operation was studied analytically and experimentally. First, the piston motion in the free piston driver tube was analytically solved by proposing a simple piston/gasdynamic model, and the tuned operation condition was formulated as an eigenvalue with which the piston has sufficiently high speed at the moment of diaphragm rupture, so as to maintain a constant driver gas pressure, and reduces its speed to come to rest when very closely approaching the end of the driver tube. Second, the result of this analysis was validated by its comparison with experiments which were conducted in the medium-sized free piston shock tunnel HEK installed at the NAL Kakuda Research Center. By observing the detail of piston landing at the end of the driver tube the present tuned operation was found to be successfully achieved with the operating condition given here. Its advantages in improving the pressure recovery factor and in enhancing the stagnation enthalpy were successfully demonstrated. [ABSTRACT FROM AUTHOR]

Excessive recoil severely restricts the loading of high-power traditional guns on modern vehicles. To reduce the recoil without breaking the continuous firing mode and reducing the projectile velocity, a recoil reduction method that controls the lateral ejecting of propellant gas by a piston was proposed. The recoil reduction device is symmetric about the barrel axis. First, a one-dimensional two-phase flow model of interior ballistic during the gun firing cycle was established. Next, the MacCormack scheme was used to simulate, and the piston motion was gained. Then the propagation of the rarefaction wave in the barrel was presented. Finally, the propulsion difference between the piston-controlled gun and the traditional gun was discussed. The results showed that the recoil momentum was reduced by 31.80%, and the muzzle velocity was decreased by just 1.30% under the reasonable matching of structural parameters. [ABSTRACT FROM AUTHOR]