(DEUTSCH) Since 1925, efforts were made using the theoretically simplest of all internal combustion engines - the free-piston engine - to generate electricity directly through an oscillating motion using magnets and coils. A very simple task - you should at least think - in which the longer the more renowned companies and research institutes are involved since some 15 years.
Any interested person who has graciously fought her/his way through the large amount of information on these pages, will now ask himself:
"Why the heck today - in the advanced 21st century - is no serial production of such engine in sight, having such allegedly outstanding advantages?"
Please allow me to turn around the above question, thus the explanation will be visible:
"What needs to be done to successfully construct a free-piston linear alternator?"
Fundraising, of course. Lots of money, what else. But for a safe investment, something else must be happening first:
1. DROP THE CRANK
An engine designer is used to work with a crankshaft. Opening and closing of the valves, timing of the ignition point: Everything is expressed in degrees of crankshaft rotation. Each designer learned it this way, and all software works with it this way. Now remove the crankshaft- the core of an engine, by which everything is derived, and the designer and his software are standing in the middle of nowhere. It's always temting to sit back and lean mentally against a well known crankshaft. Therefore, you have to think all over again from the very first beginning: It's not as simple as it seems, if you look at it from the wrong point of view.
2. DO NOT INVENT THE WHEEL TWICE
Thermodynamics is universally valid and never out of date. A commercial successful free-piston engine has been calculated in detail. These experiences should be incorporated into new developments. Before WW2, the Otto engine was already on today's standard- with the exception of advanced materials, fuel injection and electronic engine management. The engine per se has remained the same. Same too, for a freepiston engine - except that this one is even younger: So, why not benefit from decades of experience?
3. WORK WITH OTHERS
In a free-piston linear alternator engine, the two main components "engine" and "alternator" are not just coupled but melted together. Thus they cannot be developed separately, as is possible with conventional generators. It is therefore necessary that the thermodynamicist has electrical knowledge and vice versa: Allrounders wanted in a highly specialized world.
4. What kind of theoretical work is available
The linear engines and alternators have been calculated sufficiently in the theory. The benefits in general and the extremely high efficiency in particular has been documented in several ways.
As a reminder: An up to four times higher piston acceleration - compared with crank engines - will result in significantly less heat loss through the cylinder walls. This is the main reason of their high efficiency.
Source: "The Free Piston Engine for all Fuels: The World-Wide Sigma Experience", M. Maurice Barthalon, ASME publication 1962
In any work on the efficiency of free-piston engines, this high piston acceleration is mentioned.
Moreover - since no bearings are loaded - the engine can operate on much higher compression pressures. This fact was realized by Robert Huber and thus allowed him to develop an early high-efficiency combustion engine.
Source: "The Free Piston Engine for all Fuels: The World-Wide Sigma Experience", M. Maurice Barthalon, ASME publication 1962
The efficiency of these engines reached over 40% as early as in the 1950s.
Source: "The Free-Piston Gas-Generator Turbine as a Power Plant for Ship Propulsion", F.A.I. Muntz and R. Huber, The Institute of Marine Engneers Transactions, 1954
The outstanding efficiency of the free-piston engine has been reduced due to the limited efficiency of the turbine and the reduction gear. Efforts to convert the energy directly into electricity via a linear alternator will eventually lead to a higher overall efficiency.
Source: "FREE-PISTON GAS GENERATORS AND THEIR APPLICATIONS", E.S.L. Beale and P. Watson, Diesel Engineers and Users Association, 1956
Recalculations in the 90's revealed the true potential of these engines. The diagram shows the theoretically possible thermal efficiency of the free-piston engines under different conditions.
Preliminary project for the EU-funded research on free-piston engines with the involvement of various institutions and companies. Calculated efficiency: between 43 - 45%.
Engine designs that vibrate fall out of consideration from the outset
Opposed free- piston engines according to Jarret cannot provide a possibility for the heat-sensitive permanent magnets to be mounted in a cool place.
The proof of concept for Jarret engines has not been provided yet.
The engine does not have any means for scavenging, i.e. an additional apparatus has to be added to this machine to accomplish the gas exchange.
Development of an opposed free-piston linear generator according to the Pescara principle: We have thermodynamic formulas, know-how and experience.
A modern version of the Pescara engine with an enlarged engine cylinder and a customized gas exchange meets the requirements for a reliable and economic free-piston linear alternator.
The heat-sensitive permanent magnets can be mounted in a cool area. Furthermore, the windings of the linear alternator are not affected by the the combustion heat.
Thermodynamic formulas and plans as a base to design such modernized Pescara engine are available.
Assuming an efficiency of 43...48% as a basis and 5...15% electric power rectification loss, the result is a free-piston linear alternator with an efficiency of +/-40%. On HCCI mode, an even higher efficiency is exprected. However, 40% overall efficiency is an excellent value for a relatively small unit of about 5 - 50 kW.
A high efficiency and durability, the simple and compact design, and the suitability for various fuels from hydrogen and natural gas to diesel and palm oil: This engine configuration offers compelling advantages.
1. DROP THE CRANK
2. DO NOT INVENT THE WHEEL TWICE
3. WORK WITH OTHERS
4. What kind of theoretical work is available
