A design method for selecting the physical parameters of a free piston Stirling engine

A new design method for selecting the physical parameters of a free piston Stirling engine (FPSE) is presented. The dynamics of FPSE are described in the form of a transfer function including the inherent feedback mechanism. The simplified Nyquist stability criterion is used to derive the operation condition, where the indices of the magnitude amplification factor (MAF) and the operation limit factor (OLF) are introduced in terms of the physical parameters. Further, a measure for the efficiency of the engine is defined as the damping ratio of the power piston system (DRP). Parametric studies of these quantities are carried out as well as benchmarking against the design values of the standard RE-1000 engine. A design method is presented that defines the physical parameters of an FPSE which is working at a given operation frequency.

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Design and Performance of a Diaphragm Free-Piston Stirling Engine for Power Production From Low-Temperature Heat Sources

Volume 2: Heat Exchanger Technologies; Plant Performance; Thermal Hydraulics and Computational Fluid Dynamics; Water Management for Power Systems; Student Competition ◽

10.1115/power2018-7396 ◽

2018 ◽

Author(s):

Anas Nawafleh ◽

Khaled R. Asfar

Keyword(s):

Low Temperature ◽

Waste Heat ◽

Engine Performance ◽

Surface Friction ◽

Stirling Engine ◽

Operating Conditions ◽

Physical Parameters ◽

Free Piston ◽

And Performance ◽

Free Piston Stirling Engine

This paper addresses modeling, design, and experimental assessment of a Gamma type low-temperature differential free-piston Stirling engine. The most advanced third-order design analysis method is used to model, simulate and optimize the engine. Moreover, the paper provides an experimental parametric investigation of engine physical parameters and operating conditions on the engine performance. The experimental test results are presented for a model validation, which shows about a 5% to 10% difference in the simulation results. The aim of this study is to design a Stirling engine capable of harvesting low-temperature waste heat effectively and economically and convert it to power. The engine prototype is designed to increase the engine performance by eliminating the main losses occurred in conventional Kinematic engines. Thus, elastic diaphragm pistons are used in this prototype to eliminate the surface friction of the moving parts, the use of lubricant, and to provide appropriate seals. In addition, flat plate heat exchangers, linear flexure bearing, a stainless-steel regenerator and a polyurethane displacer are outlined as the main components of the engine. Experiments successfully confirm the design models for output power and efficiency. Furthermore, it is revealed that the displacer-to-piston natural frequency ratio is an important design point for free-piston Stirling engines and should be addressed in the design for optimum power output.

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