A review of free-piston linear engines

Hung, Nguyen Ba; Lim, Ocktaeck

doi:10.1016/j.apenergy.2016.06.038

Cited by 118 publications

(49 citation statements)

References 73 publications

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“…Although the manufacturing of the flat-type LEM is relatively simple, it has some drawbacks in structure, such as end-windings. So far, both types are under investigation by the researchers all over the world [4]. J. Wang from the University of Sheffield analyzed the design and experimental characterization of a three-phase tubular modular PM machine equipped with quasi-Halbach magnetized magnets, as shown in Figure 5.…”

Section: Different Topology Structures Of Pmlemsmentioning

confidence: 99%

“…The FPLG being used as a range extender can be an effective measure to solve this drawback [2]. Benefitting from the elimination of the slider-crank mechanism, it has the advantages of a variable compression ratio, compact size, and highly-efficient power generation [3,4]. The compression ratio depends on the distance between the piston position and the cylinder head.…”

Section: Introductionmentioning

confidence: 99%

“…Repeating this process above, FPLG can keep the continuous reciprocating motion and generate electrical energy.The combustion chamber is the energy input port of FPLG, and it is one of the crucial components. The number of combustion chambers determines the complexity of the energy input and piston motion control, as well as the design of LEMs [4]. Furthermore, the FPLG's vibration behavior is affected by the layout structure of combustion chambers [3].…”

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confidence: 99%

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A Review of the Design and Control of Free-Piston Linear Generator

et al. 2018

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The Free-piston linear generator (FPLG) is a novel energy converter which can generate electrical energy and is regarded as a potential technology for solving the restriction of the short driving range of electric vehicles. Getting rid of the crank and flywheel mechanism, FPLG obtains some advantages of a variable compression ratio, compact size, and highly-efficient power generation. Linear electric machine (LEM) design and piston motion control are two key technologies of FPLG. However, they are currently the main obstacles to the favorable performance of FPLG. LEM being used to drive the piston motion or generate electric energy is an integrated design including a motor/generator. Various types of LEMs are investigated, and suitable application scenarios based on advantages and disadvantages are discussed. The FPLG's controller is used to ensure stable operation and highly-efficient output. However, cycle-to-cycle variations of the combustion process and motor/generator switching make it difficult to improve the performance of the piston motion control. Comments on the advantages and disadvantages of different piston motion control methods are also given in this paper.The piston moves freely between TDC and bottom dead center (BDC), and its motion is determined by the resultant force that is acting upon it, including gas pressure force, electro-magnetic force, and rebound force [8][9][10]. The piston motion must be controlled by an electronic control system-an electronic crankshaft, which is an integrated control of combustion parameters or control variables of the LEM and rebound devices [5]. Moreover, there are cycle-to-cycle variations and periodic large disturbances during the combustion process. As a result, piston motion control is still the biggest challenge of FPLG [11]. Besides, LEM is not only used as a power output unit but also a control unit for adjusting the movement of the piston. For the FPLG, LEM requires high reliability, high precision, high efficiency, and so on. Various structures of LEM designed by many teams around the world have been investigated, but none of these meet all of the requirements due to the short stroke, high frequency, and high acceleration.In order to lucubrate the current existing problems, this paper reviews the key technologies of LEM design and FPLG motion control. Firstly, several basic structures of FPLG are introduced, and both their advantages and disadvantages are analyzed. Afterwards, according to the different types of structure, corresponding advantages and disadvantages of LEMs are presented. With respect to the existing LEMs, they are classified according to the different flux path and topology structures in the third section. Finally, different starting methods are introduced based on the FPLG's structure. In terms of power generation stage, piston motion control strategies are divided into three forms and introduced based on their control variables. They include three categories: active combustion parameters control, active LEM control, and the mixed cont...

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Section: Different Topology Structures Of Pmlemsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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A Review of the Design and Control of Free-Piston Linear Generator

et al. 2018

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“…the scavenging process in a two-stroke free piston linear engine has been modelled and simulated successfully based on the combination of a dynamic model and a CFD model, see [16]. The authors of [17] reviewed in detail conventional internal combustion engines and indicated two-stroke ones as investigated most frequently for their advantageous construction and control.…”

Section: Introductionmentioning

confidence: 99%

CFD Analysis of Charge Exchange in an Aircraft Opposed-Piston Diesel Engine

2019

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The paper presents a description of geometric models, computational algorithms, and results of numerical analysis of charge exchange in an opposed-piston two-stroke engine. The research engine is a newly designed internal diesel engine. This unit is composed of three cylinders in which operate three pairs of opposed-pistons. The engine generates a power output equal to 100 kW at a crankshaft rotation speed of 3800-4000 rpm. The numerical investigations were carried out using ANSYS FLUENT solver. The geometrical model includes an intake manifold, a cylinder and an outlet manifold. The study was conducted for a series of modifications of manifolds and intake and exhaust ports to optimise the charge exchange process in the engine. In addition, we attempted to verify the effect of the combustion chamber shape on the charge exchange process in the engine. The calculations specified a swirl coefficient obtained under steady conditions for fully open intake and exhaust ports as well as the CA value of 280° for all cylinders. In addition, mass flow rates were identified separately in all of the intake and exhaust ports to achieve the best possible uniformity of flow in particular cylinders. The paper includes comparative analyses of all of the intake and exhaust manifolds of the designed engine.

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“…A free-piston linear generator is a novel energy converter which normally consists of an internal combustion engine (ICE), a linear electric machine (LEM) and a rebounding device [1,2]. The hybrid electric vehicle equipped with this energy conversion device can increase the runtime or reduce the demand of charging.…”

Section: Introductionmentioning

confidence: 99%

A Free-Piston Linear Generator Control Strategy for Improving Output Power

Zhang

Chen

et al. 2018

Energies

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This paper presents a control strategy to improve the output power for a single-cylinder two-stroke free-piston linear generator (FPLG). The comprehensive simulation model of this FPLG is established and the operation principle is introduced. The factors that affect the output power are analyzed theoretically. The characteristics of the piston motion are studied. Considering the different features of the piston motion respectively in acceleration and deceleration phases, a ladder-like electromagnetic force control strategy is proposed. According to the status of the linear electric machine, the reference profile of the electromagnetic force is divided into four ladder-like stages during one motion cycle. The piston motions, especially the dead center errors, are controlled by regulating the profile of the electromagnetic force. The feasibility and advantage of the proposed control strategy are verified through comparison analyses with two conventional control strategies via MatLab/Simulink. The results state that the proposed control strategy can improve the output power by around 7-10% with the same fuel cycle mass.

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A review of free-piston linear engines

Cited by 118 publications

References 73 publications

A Review of the Design and Control of Free-Piston Linear Generator

A Review of the Design and Control of Free-Piston Linear Generator

CFD Analysis of Charge Exchange in an Aircraft Opposed-Piston Diesel Engine

A Free-Piston Linear Generator Control Strategy for Improving Output Power

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