Simulation of a Two-Stroke Free-Piston Engine for Electrical Power Generation

Free-piston linear generators (FPLGs) have attractive application prospects for hybrid electric vehicles (HEVs) owing to their high-efficiency, low-emissions and multi-fuel flexibility. In order to achieve long-term stable operation, the hybrid system design and full-cycle operation strategy are essential factors that should be considered. A 25 kW FPLG consisting of an internal combustion engine (ICE), a linear electric machine (LEM) and a gas spring (GS) is designed. To improve the power density and generating efficiency, the LEM is assembled with two modular flat-type double-sided PM LEM units, which sandwich a common moving-magnet plate supported by a middle keel beam and bilateral slide guide rails to enhance the stiffness of the moving plate. For the convenience of operation processes analysis, the coupling hybrid system is modeled mathematically and a full cycle simulation model is established. Top-level systemic control strategies including the starting, stable operating, fault recovering and stopping strategies are analyzed and discussed. The analysis results validate that the system can run stably and robustly with the proposed full cycle operation strategy. The effective electric output power can reach 26.36 kW with an overall system efficiency of 36.32%.

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“…Assuming that the load is resistive, the LEM model can be described by the phase equivalent circuit model shown in Figure 5 [11,18,29]. …”

Section: Lem Model Under Generating Modementioning

confidence: 99%

Hybrid System Modeling and Full Cycle Operation Analysis of a Two-Stroke Free-Piston Linear Generator

et al. 2017

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“…The piston dynamics and output electric power can be predicted directly from the input parameters with acceptable accuracy, without solving the coupled differential equations. From Equation (11) to Equation (16), the influence of the design parameters (m, L, A, and k v ) on the system oscillation characteristics and power output is shown in Table 3. It will provide useful general guidance for the design process, as well as accurate prediction for the future control of piston dynamics.…”

Section: Sensitivity Analysis Of Design Parametersmentioning

confidence: 99%

A Decoupled Design Parameter Analysis for Free-Piston Engine Generators

et al. 2017

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Abstract:The free-piston engine generator (FPEG) is a novel power generation device with an estimated brake efficiency (energy contained in the fuel that is transformed into useful work) of up to 46%, compared to the 25-35% reported in conventional reciprocating engines. This paper seeks to address a major challenge in the development of new and complex technologies-how do we effectively communicate and understand the influence of key design parameters on its operating performance? In this paper, the FPEG is described using a simple numerical model, a model which is reduced to a forced mass-spring vibration system under external excitation, enabling all the major input parameters to be decoupled. It proved that the engine piston position as a function of time and output power could be predicted directly from the input parameters with acceptable accuracy. The influence of the key FPEG design parameters on the piston oscillation characteristics and electric power output can be characterised with respect to one another and summarised. Key design parameters include piston mass, compression stroke length, piston cross sectional area, and electric load. Compared with previous and more complex numerical models, the presented methods can be used to simply describe the sensitivity of key design parameters on the FPEG performance. It will provide useful general guidance for the FPEG hardware design process.

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“…For the same geometry size, a flat permanent magnet LG is easily constructed and exhibits good excitation; meanwhile, its output voltage, current effective value, efficiency, and specific power are slightly higher than those of the tubular permanent magnet LG with the same load [33,34]. Therefore, a flat permanent magnet LG is selected to match with the FPEs in this research.…”

Section: Working Principle and Function Of The Free Piston Expander-lmentioning

confidence: 99%

Preliminary Development of a Free Piston Expander–Linear Generator for Small-Scale Organic Rankine Cycle (ORC) Waste Heat Recovery System

Zhang

Yang

et al. 2016

Energies

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Abstract:A novel free piston expander-linear generator (FPE-LG) integrated unit was proposed to recover waste heat efficiently from vehicle engine. This integrated unit can be used in a small-scale Organic Rankine Cycle (ORC) system and can directly convert the thermodynamic energy of working fluid into electric energy. The conceptual design of the free piston expander (FPE) was introduced and discussed. A cam plate and the corresponding valve train were used to control the inlet and outlet valve timing of the FPE. The working principle of the FPE-LG was proven to be feasible using an air test rig. The indicated efficiency of the FPE was obtained from the p-V indicator diagram. The dynamic characteristics of the in-cylinder flow field during the intake and exhaust processes of the FPE were analyzed based on Fluent software and 3D numerical simulation models using a computation fluid dynamics method. Results show that the indicated efficiency of the FPE can reach 66.2% and the maximal electric power output of the FPE-LG can reach 22.7 W when the working frequency is 3 Hz and intake pressure is 0.2 MPa. Two large-scale vortices are formed during the intake process because of the non-uniform distribution of velocity and pressure. The vortex flow will convert pressure energy and kinetic energy into thermodynamic energy for the working fluid, which weakens the power capacity of the working fluid.

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Simulation of a Two-Stroke Free-Piston Engine for Electrical Power Generation

Cited by 110 publications

References 14 publications

Hybrid System Modeling and Full Cycle Operation Analysis of a Two-Stroke Free-Piston Linear Generator

Hybrid System Modeling and Full Cycle Operation Analysis of a Two-Stroke Free-Piston Linear Generator

A Decoupled Design Parameter Analysis for Free-Piston Engine Generators

Preliminary Development of a Free Piston Expander–Linear Generator for Small-Scale Organic Rankine Cycle (ORC) Waste Heat Recovery System

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