Linear Alternator

Shake Flashlight
Shake Flashlight
The simplest type of linear alternator is the shake flashlight. This is an electric flashlight which contains a coil and a permanent magnet. When the appliance is shaken back and forth, the magnet oscillates through the copper coil and induces an electric current. This current is used to charge a capacitor that can then supply an LED lamp with power for a longer time.

Video: Shake Flashlight

​The simple construction of a free-piston engine in combination with a linear alternator represents the (theoretically) simplest possible construction of a power generator. Although - it seems that in practice it is not quite that simple, as some examples will reveal in the following.

Eugène Jordan, France
1923 Eugène Jordan, France
1923 Eugène Jordan, France

Generator of Electric Current

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1925 Noack, Freudenreich, Switzerland
1925 Noack, Freudenreich, Switzerland
1925 Noack, Freudenreich, Switzerland

Revolutionary proposal: The power take-off occurs on both the exhaust gases (2, 3) as well as electric (10, 4) with a linear alternator. The engine had a supercharger too (5). The proposal was never realized.

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1943 Pontus Ostenberg, USA
1943 Pontus Ostenberg, USA
1943 Pontus Ostenberg, USA

Electric Generator

Early proposal of an inherently balanced opposed piston engine with linear alternators.

Download Patent

1960 Ralph James, Esso Co. USA
1960 Ralph James, Esso Co. USA
1960 Ralph James, Esso Research and Engineering Co. USA

Free-Piston Generator of Electric Current


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1964 Harold Kosoff, USA
1964 Harold Kosoff, USA
1964 Harold Kosoff, USA

Harold Kosoff developed an opposed piston engine in which the pistons are synchronized pneumatically rather than mechanically.
As early as 1964 he had a vision of a linear generator, which powered cars and supplied houses with electricity and heat. The engine was not developed further.

1962 Stirling A. Colgate, USA
1962 Stirling A. Colgate, USA

1962 Stirling A. Colgate, Livermore, CA

Free Piston Electrical Generator

Based on the Pescara free-piston design, Colgate proposed an opposed free piston linear alternator.

Download US Patent


1965 Robert Huber, Société des Générateurs Jarret, France
1965 Robert Huber, Société des Générateurs Jarret, France
1965 Robert Huber, Société des Générateurs Jarret, France

The Colgate patent (USA, FR, GB) forced Robert Huber to switch to another engine instead of "his" own Pescara design (cooperation with Jarret).

Download US Patent

Electromagnetic Oscillator EMO150
Electromagnetic Oscillator EMO150
1965 Robert Huber, Société des Générateurs Jarret, France 


Robert Huber designed his electromagnetic Oscillator EMO 150. The enormously heavy electromagnetic components made ​​it difficult to achieve a sufficiently high frequency.

1972 Jarret, France
1972 Jarret, France

1972 Jarret 

The Colgate patent still made it impossible to integrate the magnets on the bouncer pistons according to the Pescara system.
Jarret tried it with this construction.

Download Patent


1976 Jarret, France
1976 Jarret, France
1976 Jarret

Hydraulic bouncer chambers, same system

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The Jarret engine
The Jarret engine

Download Jarret Article (English language)

The time was not ready yet for a free-piston linear generator, because no rare-earth magnets with sufficiently high flux density were available.

Only with extremely powerful magnets, the piston mass can be reduced to an acceptable range.

Jarret Linear Alternator principle
Jarret Linear Alternator principle
The magnetic field of permanent magnets decreases with increasing temperature. Modern NdFeB magnets can be used up to 130 °C, the more expensive SmCo magnets up to about 250 °C. 

In Jarret-like free-piston designs, the permanent magnets are thermally stressed.

1994 Galileo Research
1994 Galileo Research
1997 Galileo Research
1997 Galileo Research
1994-1997 Galileo Research

A prototype made by Galileo, using commercially available weed wacker engine cylinders and a linear alternator from a Stirling engine. Double-acting type.

The 
privately funded company had to abandon its research for lack of money. Two govt institutes began their work instead:

  • West Virginia University
  • Sandia National Laboratories


Sources:
"A High Specific Energy Output Free Piston Engine-Generator (HISEN-FPEG) for Hybrid Electric Vehicles and Electric Utility Power Generation" by Dr. Robert Law / Kenneth A. Galitello, Jr. March 1996
et al.

1998 West Virginia University
1998 West Virginia University
1998 West Virginia University

First prototype similar to the Galileo project. Double-acting type. Homelite chainsaw cylinders were used.

1999 West Virginia University
1999 West Virginia University
1999 West Virginia University

Second prototype (diesel), not a working engine.

Sources:
"Optimization of a Brushless Permanent Magnet Linear Alternator for Use With a Linear Internal Combustion Engine", William R. Cawthorne, West Virginia University
"Free-Piston Diesel-Fueled Linear Alternator for Auxiliary Power Unit Applications, 1996-1999", Atkinson, Famouri, Clark, West Virginia University
et al.

2000 FEV Engine Technology
2000 FEV Engine Technology
2000 FEV Engine Technology

Source:
"Free Piston Engine Its Application and Optimization", Martin Goertz and Lixin Peng

(theoretical work only)
1998 Sandia National Laboratories
1998 Sandia National Laboratories
1998 Sandia National Laboratories
1998 Sandia National Laboratories
1998-Present Sandia National Laboratories, Livermore, CA

To date, Sandia has worked one of the most comprehensive studies on free-piston engines. However, the permanent magnets of this version are thermally stressed.

2011 Sandia National Laboratories
2011 Sandia National Laboratories
2011 Sandia National Laboratories
2011 Sandia National Laboratories

2011 Sandia National Laboratories, Livermore, CA

Research status 2012

Research Status 2015


2011 Sandia National Laboratories
2011 Sandia National Laboratories
1962 Stirling A. Colgate, USA
1962 Stirling A. Colgate, USA
2011 Sandia National Laboratories, Livermore, CA

Sandia chose a Jarret-like design with thermally highly stressed permanent magnets.

Stirling A. Colgate, Livermore, CA realized almost 50 years earlier: The magnets must be placed at a cool area.

Sources:
"ADVANCED INTERNAL COMBUSTION ELECTRICAL GENERATOR", Peter Van Blarigan, Sandia National Laboratories, Livermore, USA
"Developing a Thermodynamic Fuel Cell", Peter Van Blarigan, Sandia National Laboratories, Livermore, USA
et al.

2002 Frank Stelzer
2002 Frank Stelzer
2002 Frank Stelzer

The engine - virtually the same since 1980 - was coupled with a linear alternator developed in Chemnitz, Germany.

The engine stalled as power was taken off. The alternator did not work as a starter, a demonstration never took place.

​2003 Deutsches Luft- und Raumfahrtzentrum DLR
​2003 Deutsches Luft- und Raumfahrtzentrum DLR
2003 Deutsches Luft- und Raumfahrtzentrum DLR
2003 Deutsches Luft- und Raumfahrtzentrum DLR
​2003 Germany's national research center for aeronautics and space DLR

Single-acting recoil-operated engine, later on combined to an opposed piston engine.

Download Patent

The engine was then combined to an opposed piston engine with a center bounce chamber and two outer expansion chambers. The proposal is similar to the '72 Jarret engine.

Sources:
"Der Freikolbenlineargenerator FKLG Stromerzeugung mit hohem Wirkungsgrad", Dr.-Ing. Markus Gräf, Institut für Fahrzeugkonzepte, DLR
et al.

2013 DLR
2013 DLR
​2013 DLR

A single-acting design with flat type linear alternator. The alternator design was described in 2008 by the Shanghai Jiaotong University.
The engine has a single combustion chamber and an opposite bouncer chamber. Similar engines were built by INNAS and TU Dresden.
The vibrations of this engine design must be damped by a foundation, note the massive side brackets.

Download Patent

2013 DLR
2013 DLR
2013 DLR
2013 DLR
Electromagnetic Oscillator EMO150
Electromagnetic Oscillator EMO150
2013 DLR

Based on the above-described experimental apparatus, this machine is to arise.

The machine looks very similar to EMO150 engine that was invented by Huber / Jarret in the 1960s, but the bounce chambers of this newer version seem to be surprisingly small in relation to the alternators.

Sources: DLR Homepage

2001 Pempek Systems, Australia
2001 Pempek Systems, Australia
2001 Pempek Systems, Australia

This engine is designed as a two-stroke diesel. The vibrations are eliminated by connecting 4 units that run in 2 pairs at 180 degrees phase shifted.

2001 Pempek Systems, Australia
2001 Pempek Systems, Australia
2001 Pempek Systems, Australia
Pempek prototype on a test bench

Sources:
"The Free Piston Power Pack: Sustainable Power for Hybrid Electric Vehicles", Douglas Carter and Edward Wechner, Pempek Systems, Australia
et al.

2003 D. Hagen, Switzerland
2003 D. Hagen, Switzerland
2003 D. Hagen, Switzerland

First Prototype with integrated starter / alternator.
Thermal separation of the linear alternator from the engine cylinders. Displacement 30 ccm, frequency 160 Hz, compression ratio 1:24
2004 Volvo Free Piston Energy Converter
2004 Volvo Free Piston Energy Converter
2004 Volvo Free Piston Energy Converter
2004 Volvo Free Piston Energy Converter

2004 Volvo Free Piston Energy Converter (FPEC)
EU funded project

Double-acting type with the same known thermic problem of the permanent magnets.
    
Download project paper

Partners: Volvo Technology, SE, ABB SE, NOAX and INNAS, NL, Institut Francais Du Petrole, FR, Chalmers University of Technology, SE, Royal Institute of Technology, SE, University of Sheffield, UK

Sources:
"Analysis and Control of a Hybrid Vehicle Powered by a Free-Piston Energy Converter", Jörgen Hansson, Royal Institute of Technology (KTH), Stockholm, Sweden
et al.

2011 Volvo opposed piston type
2011 Volvo opposed piston type
2011 Volvo opposed piston type

"Volvo has earlier developed and built a prototype of a dual free piston engine and also made some testing on it. Conclusions made from the FPEC prototype resulted in that a free piston engine of opposed piston type would be used."

Citation from "Development of Linear Bearing for Free Piston Engine", Luleå University of Technology, Department of Engineering, Science and Mathematics.
1972 Jarret, France
1972 Jarret, France
2011 Volvo >> 1972 Jarret: Thermic decoupling of permanent magnets not yet solved.

2003 Czech Technical University
2003 Czech Technical University
2003 Czech Technical University
2003 Czech Technical University
2003 Czech Technical University

Double-acting engine similar to Galileo and West Virginia University

Sources:
"Modelling and Control of Linear Combustion Engine (LCE)", Pavel Němeček, Ondřej Vysoký, Michal Šindelka, Czech Technical University in Prague
et al.

2006 Malaysia
2006 Malaysia
2006 Malaysia

Source:
"SIMULATION OF A TWO-STROKE SPARK IGNITION FREE PISTON LINEAR ENGINE MOTION", N. A. N. MOHAMED, A. K. ARIFFIN & S. FONNA, Universiti Teknologi Malaysia

2007 Newcastle University
2007 Newcastle University
​2007 Newcastle University

Single-acting Free-Piston Engine Project

Source: "The design and simulation of a two-stroke free-piston compression ignition engine for electrical power generation", R. Mikalsen, A.P. Roskilly, Newcastle University,UK (basic research)


2008 Malaysia
2008 Malaysia
2008 Malaysia
2008 Malaysia
2008 Malaysia, investigation of the starting procedure of a free-piston engine

Source: "Starting of a Free-Piston Linear Engine-Generator by Mechanical Resonance and Rectangular Current Commutation", Zulkifli, Karsiti, Rashid A-Aziz, Universiti Teknologi PETRONAS, Malaysia
et al.

Starting of a free-piston engine means to swing-up the engine piston(s) taking advantage of the kinetic energy and the air cushions. The starter energy is not strong enough to achieve the necessary compression directly, because the starter has no transmission gear. The Malaysian paper describes this specific starting procedure perfectly.
2008 Korea
2008 Korea
2008 Korea
2008 Korea
2008 Korea

Source: "The performance characteristics of a  hydrogen-fuelled free piston internal  combustion engine and linear generator system", Youngmin Woo, Youngjae Lee, Yonggyun Lee, Automobile Energy and Environment Research Center, Korea et al.


2008 China
2008 China
2008 China

Source: "Simulation of a Two-Stroke Free-Piston Engine for Electrical Power Generation" Qingfeng Li, Jin Xiao, Zhen Huang, Shanghai Jiaotong University, China et al.

2008 China, flat alternator
2008 China, flat alternator
2008 China: Flat type alternator

Source: "Flat-type permanent magnet linear alternator: A suitable device for a free piston linear alternator", Qingfeng Li, Jin Xiao, Zhen Huang, Shanghai Jiaotong University, China et al.

2012 General Motors
2012 General Motors
1962 Stirling A. Colgate, USA
1962 Stirling A. Colgate, USA

2012 General Motors

This picture looks very familiar, showing an opposed poston engine with an integrated linear alternator. 50 years ago, a patent for this principle was already filed in 1962 by Stirling A. Colgate.

The work of GM is based on the Pescara-SIGMA free-piston engine and the history as GM ordered the "Hyprex" engine for their XP500 Firebird at S.I.G.M.A. back in 1955. A first intention to reactivate the name "Hyprex" was dropped. 

freikolben.ch was cited with text and pictures in the following extensive dissertation:

Download "TURBINE-COMPOUND FREE-PISTON LINEAR ALTERNATOR ENGINE" 


2012 Toyota
2012 Toyota
2012 Toyota
2012 Toyota
2012 TOYOTA CENTRAL R&D LABS INC

Toyota works obviously on hardware: Single-acting recoil-operated engine.

2012 Toyota
2012 Toyota
2012 Toyota
2012 TOYOTA CENTRAL R&D LABS INC

Some proposals show two conected engines to eliminate the vibrations.
2014 BEETRON, Switzerland

Unlike most other approaches, BEETRON concentrates on smart grid and off-grid power generation. As a highly efficient multifuel engine, BEETRON converts not only fossil fuels but enables the transition to sustainable power generation, with solar and renewable fuels. 

BEETRON Homepage

The Far East interest in these engines is growing rapidly. Most of the recent work comes from the Asian region.