• 한국수소및신에너지학회논문집
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• 제25권6호
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• pp.648-655
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• 2014

This paper describes the continuing effort to develope a single acting free-piston Stirling engine/alternator combination for use of the household cogeneration. Free piston Stirling engines(FPSE) use variations of working gas pressure to drive mechanically unconstrained reciprocating elements. Stirling cycle free-piston engines are driven by the Stirling thermodynamic cycle which is characterized by an externally heated device containing working gas that is continuously re-used in a regenerative, reversible cycle. The ideal cycle is described by two isothermal process connected by two constant volume processes. Heat removed during the constant volume cooling process is internally transferred to the constant volume heating process by mutual use of a thermal storage medium called the regenerator. Since the ideal cycle is reversible, the ideal efficiency is that of Carnot. Free-piston Stirling engine is have no crank and rotating parts to generate lateral forces and require lubrication. The FPSE is typically comprised of two oscillating pistons contained in a common cylinder. The temperature difference across the displacer maintains the oscillations, and the FPSE operate at natural frequency of the mass-spring system. The power is generated from a linear alternator. The purpose of this paper is to describe the design process of the single acting free-piston Stirling engine/alternator. Electrical output of the single acting free-piston Stirling engine/alternator is about 0.95 kW.

• 한국수소및신에너지학회논문집
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• 제27권1호
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• pp.114-120
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• 2016

This paper describes generating efficiency characteristics of the double acting Stirling engine/generator for domestic small-scale CHP (Combined Heat and Power) system. In small distributed generation applications, Stirling engine has competition from fuel cell, microturbine and etc. In order to be economical in the applications, a long life with minimum maintenance is generally required. Free piston Stirling engine (FPSE) has no crank and rotating parts to generate lateral forces and require lubrication. Double acting Stirling engine/generator has one displacer and two power piston which are supported by flexure springs. Two power pistons oscillate with symmetric displacement and are connected with moving magnet type linear generators for power generation from PV work. In experiments, 1 kW class double acting free piston Stirling engine/generator is fabricated and tested. Heat is supplied to hot end of engine by the combustion of natural gas and converted to electric power by linear generators which are assembled with power pistons. The electric parameters such as voltage, current and phase are measured with for variable flow rate of fuel gas. Especially, generating efficiency of FPSE is measured with three different measurement methods. Generating efficiency of the double acting Stirling engine/alternator is about 24%.

• 한국소음진동공학회논문집
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• 제23권7호
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• pp.654-661
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• 2013

The dynamic characteristics of a free-piston stirling engine(FPSE) with regard to the working frequency is investigated from theoretical and experimental studies. The FPSE is modeled as a two degree-of-freedom linear vibration system. A theoretical expression on the working frequency is derived from the instability condition for self-excitation based on the linear vibration model. A ${\gamma}$-type free-piston stirling engine is fabricated for experimental studies, and its working frequency is measured on various heater temperatures. Comparisons between the theoretical and experimental results reveal that the working frequency of the test FPSE depends on both the temperature of the compression space and the temperature difference between the expansion and compression spaces.

• 한국수소및신에너지학회논문집
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• 제26권6호
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• pp.638-644
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• 2015

This paper describes the continuing effort to analysis and design on dynamic and electrical behavior of gamma-type free piston Stirling engine/generator with dual-opposed linear generator for domestic micro-CHP (Combined Heat and Power) system. The double acting Stirling engine/generator has one displacer and two power piston which are supported by flexure springs. Two power pistons oscillate with symmetric sinusoidal displacement and are connected with moving magnet type linear generators for power generation. To operate Stirling engine/generator, combustion heat of natural gas is supplied to hot-end and heat is rejected from cold-end by cooling water. The temperature difference across the displacer induces the oscillating motion, and it can be explained with mass-spring vibration system. The purpose of this paper is to describe the design process of linear generator for the double acting free-piston Stirling engine.

• 대한기계학회논문집
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• 제18권7호
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• pp.1751-1758
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• 1994

A new set of governing equations is derived for the dynamic analysis of the Free-Piston Stirling Engines(EPSE). Equations from the ideal adiabatic model for the thermodynamic analysis of the working fluid are incoporated with the equations of motion for the moving masses of the system, resulting in a set of nonlinear differential equations. The coupled set of equations are numerically integrated with proper intial conditions to obtain a steady state response of the engine. The proposed method is compared with the conventional method of analyzing EPSE based mainly on the ideal isothermal model. The results clearly shows the limitationsl of the conventional methods and the relative advantages of the method proposed in the present study.

• 대한기계학회논문집A
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• 제39권10호
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• pp.985-993
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• 2015

자유피스톤 스털링 엔진(Free-piston Stirling Engine, FPSE)은 석유자원 고갈로 인한 에너지 비용 상승으로 활발하게 연구되고 있는 신재생 에너지와 폐에너지 회수를 위한 핵심 에너지 변환장치로 주목받고 있다. 기존 스털링 엔진은 두 개의 피스톤과 기구부로 구성되어 열에너지를 기계동력을 변환한다. FPSE 는 기존 스털링 엔진의 단점인 기구부를 제거하고 각각의 피스톤에 스프링을 연결하여 진동 시스템으로 구성된 엔진으로서, 올바른 엔진 설계 및 운전 제어를 위하여 정교한 동역학 성능 예측이 필수적이다. 본 논문에서는 FPSE 의 외부 부하를 고려한 동역학 성능 예측 모델을 제시하고 선형 및 비선형 해석을 통한 성능 예측 방법론을 제시하였다. 선형 해석은 고유치 해석을 통한 근궤적 선도를 이용하여 엔진의 작동점을 예측한다. 비선형 해석은 외부 부하 감쇠의 선형항과 비선형항을 고려하여 수치적분을 통해 엔진 피스톤의 진폭을 예측한다. 이러한 동역학 성능 데이터는 엔진 출력 성능 예측에 활용된다. 또한, 본 논문의 해석 모델은 대표적인 FPSE 인 RE-1000 의 실험결과 및 기존 해석 연구들과 비교/검증하여 신뢰성을 검토하였다.

• 한국소음진동공학회논문집
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• 제26권3호
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• pp.248-257
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• 2016

Recently, researches on the free-piston Stirling engines(FPSEs) are actively investigated. FPSEs have merits in its light weight, simple structure, and little need for maintenance, thus becoming a promising solution for the power conversion of renewable energy and waste heat recycle. This paper presents the methodology that estimates damping coefficients using analytical models of linear and nonlinear dynamics for FPSEs, and validates the methodology by comparing with existing experimental results. The analysis model predicts an operable range of linear damping coefficients forming limit cycles by using the root locus, and time responses obtained by numerical integration determines nonlinear damping coefficients. The model predictions are compared with experimental results of the well-known FPSE B-10B. We also investigate the damping characteristics regarding heater temperatures and power piston motions.

• Nuclear Engineering and Technology
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• 제53권2호
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• pp.637-646
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• 2021

The free-piston Stirling engine (FPSE) has been widely used in aerospace owing to its advantages of high efficiency, high reliability, and self-starting ability. In this paper, a 20-kW FPSE is proposed by analyzing the requirements of space nuclear power reactor. A code was developed based on an improved simple analysis method to evaluate the performance of the proposed FPSE. The code is benchmarked with experimental data, and the maximum relative error of the output power is 17.1%. Numerical results show that the output power is 21 kW, which satisfies the design requirements. The results show that: a) reducing the pressure shell's thickness can improve the output power significantly; b) the system efficiency increases with the wire porosity, while the growth of system efficiency decreases when the porosity is higher than 80%, and system efficiency exhibits a linear relationship with the temperatures of the cold and hot sides; c) the system efficiency increases with the compression ratio; the compression ratio increases by 16.7% while the system efficiency increases by 42%. This study can provide valuable theoretical support for the design and analysis of FPSEs for space nuclear power reactors.

• Nuclear Engineering and Technology
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• 제53권7호
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• pp.2184-2194
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• 2021

The Free-Piston Stirling engine (FPSE) is of interest for many research in aerospace due to its advantages of long operating life, higher efficiency, and zero maintenance. In this study, a 1-kW FPSE was proposed by analyzing the requirements of Space Reactor Power Systems (SRPS), of which performance was evaluated by developing a code through the Simple Analysis Method. The results of SAM showed that the critical parameters of FPSE could satisfy the designed requirements. The heater of the FPSE was designed with the copper rectangular fins to enhance heat transfer, and the parametric study of the heater was performed with Computational Fluid Dynamics (CFD) software STAR-CCM⁺. The Performance Evaluation Criteria (PEC) was used to evaluate the heat transfer enhancement of the fins in the heater. The numerical results of the CFD program showed that pressure drop and Nusselt number ratio had a linear growth with the height of fins, and PEC number decreased as the height of fins increased, and the optimum height of the fin was set as 4 mm according to the minimum heat exchange surface area. This paper can provide theoretical supports for the design and numerical analysis of an FPSE for SRPSs.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 추계학술대회 논문집
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• pp.479-480
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• 2013