There’s a lot of heavy duty R&D going on these days to reinvent the engine or replace the engines we’re using altogether. The free piston engine, though invented in the 1920s, is getting more attention because it is less expensive than fuel cells for generating electricity while potentially just as efficient.
The free piston engine has a straight rod that moves back and forth with a piston and 2 stroke combustion chamber on either end. The central portion of the rod has magnets attached which move past stationary coils to generate electricity. This creates an opposed 2 stroke, every stroke is a power stroke generating electricity. Used in place of a fuel cell, you still power the wheels with an electric motor. The engine could approach 50% efficiency which is about twice as efficient as standard internal combustion engines.
The potential high efficiency of free-piston engines gives them an advantage over conventional generators, and their ability to use a variety of fuels is an advantage over hydrogen fuel cells. What’s more, free-piston engines don’t require expensive materials such as the platinum catalysts needed in fuel cells, so they could be cheaper too.
Besides being a cool idea and having high efficiency, since it is a combustion engine, it gets around the silent electric vehicle problem which some say is a problem for pedestrians. Neat!
Link: Next Big Future
Link: Technology Review
tom w. says
Interesting. That seems like it would be particularly suited to the Chevy Volt. I wonder if GM is looking into anything like that.
Azzy says
That thing has to rattle a lot.
I wonder once it gets going, if just supplied with fuel, it could keep going on just compression combustion alone (diesel)
Ogre says
The problem is that it still has to burn something, and that means pollution; even if used with alcohol or biodiesel.
Interesting idea though.
kim scholer says
One may wonder why an idea avaiable since the 1920’s hasn’t been looked upon until know, in spite of its supposed effeciency.
Still, the engine is interesting, and be having it just generate electricity you can avoid having a gearbox.
AxeMan says
If you used two of these in opposite motion of each other, you would virtually eliminate the heavy vibration that would be generated by just one of them running. Very good idea! Need an mech or tech? Get ahold of me, I’m on board with this one!
B*A*M*F says
A lot of engine concepts from back in the day were abandoned not because they didn’t work. Often they were abandoned because metallurgy, machining technology, and other practices were just not up to the task of making these items in quantity or at a reasonable cost.
A number of other alternate engines that were explored often also had drivability issues that made them not very desirable for automotive use. If you are running at two speeds (on and off) for power generation, then drivability becomes a non-issue.
With direct injection, a 2 stroke can be made quite clean. This particular idea looks extremely feasible, and like it could be done quite inexpensively and in a relatively compact package.
JR says
Does compression alone keep the piston from slamming into the cylinder head? What stops it?
My mind is boggled…
JC says
“Does compression alone keep the piston from slamming into the cylinder head? ”
That’s what I’m guessing is the case.
If you had valves that were electrically (soleniod?) or air actuated you could have a four stroke as well. I know that is being researched for other reasons, so might be plausible.
pghcyclist says
this is pretty cool but isnt a turbine connected to generator more efficient. Reciprocating vs rotary and all.
Alex says
“Does compression alone keep the piston from slamming into the cylinder head? What stops it?”
Why should that be insufficient?
Besides, it is pretty easy to apply a mechanical stopper, no? The drawing above is a scheme, not a construction plan…
Alex says
I wanted to say that in my opinion the stroke length can be designed in such a way, that the crash can be omitted.
The developers however use an electronic control system and the generator / motor for preventing this to happen.
Paul says
Would love to see this produced initially as a portable generator.
Jim says
To add to B*A*M*F comment. A lot of these alternative engine designs have no ability to idle, or have very small operating RPM ranges that make them poor choices for how automobiles and MC have deployed the power generated by the engine.
But powering a generator to charge a battery and/or an electric motor the design deficiencies are no longer a problem.
Steve says
Looks like a great generator for a plugin series hybrid. Also, a diesel application would be interesting and would seem to well suited.
While i am nostalgic for traditional internal combustion, I am excited that we are entering a period where lots of engine innovation is now likely.
JR says
That’s a lot of inertia to arrest by perfect combustion timing and compression alone. It just seems like you would run into impact issues…
Also, a stopper would be a really violent way to stop the piston assembly, maybe it would need a damped stopper, but those take away energy too..
Just some thoughts.
Hawk says
There are really two types of energy that we can use. One is fossil fuels which have all our known shortcomings – sustainability, pollution and so on. However, they are the most convenient for now. This engine, while is will be improved and refined, gives an almost doubling of efficiency in extracting the energy from its fuel. For this reason alone, it is worthy of continued R&D.
The second type of energy is nuclear. This is not only the nuclear power generation stations that send environmentalists into an apoplectic fit, but it covers solar, hydro-electric and wind generated energy as well. (Hey – The sun is a nuclear furnace, eh?) Consider what will happen to our already almost-overloaded national grid when a few million Volts are plugged into it each night. Burning more fossil fuels or even bio-diesel type fuel (which raises our food costs) to support the grid is not the answer either. It too, must be supported by “nuclear” sources.
Some, in this forum, question why this technology from the ’20s was not developed earlier. I’d suggest that the main hold-back was the lack of battery technology as much as anything else.
Now, if we could only figure out how to capture and re-use the energy in heat loss …..
(BTW – There is a joint engineering project between, I think, Peugeot and BMW to work on doing just that – capturing the heat loss energy.)
chaz says
It should not be necessary to stop the pistons. The power generated by combustion would be used to push the magnets on the rod through the coils. The resistance will slow the rod, and the kinetic energy is converted into electrical energy.
Peter Argiros says
HOW IS BURNING FUEL ON EVERY STROKE MORE EFFICIENT
THAN EVERY 2 OR 4 STROKES. ITS NOT MORE EFFICIENT JUST MORE POWERFUL.
Wave says
This looks like a very interesting concept, but I can see why it would have been abandoned in the 1920s. With modern power electronics and control equipment this could probably run quite nicely, however the noise would be very annoying in a car. I imagine that this type of engine would need to run at constant rpm to generate power at peak efficiency, which would be far more irritating then the nice sound of a conventional engine which rises and falls in pitch. Also, well done to the kneeslider for covering interesting technology which is extremely unlikely to ever be used on a motorcycle! This is the kind of stuff that I like to see.
Wave says
Oops, it doesn’t spin so it doesn’t have any rpm! Constant frequency then.
B*A*M*F says
Peter Argiros:
More power means you can use a smaller, lower capacity engine. Therefore, you should be able to use less fuel, at least in theory. Coupled with a generator, a powerful and compact engine could be run for a very short time to recharge batteries.
Wave:
There are many advantages to running an engine at a constant speed. Being able to really work on emissions is one of them. Without having to deal with a huge range of engine speeds, it’s much easier. The same goes for better sound attenuation at the muffler.
MAX says
B*A*M*F
Yes, a smaller engine of the same power would be
more economical, but only if we’re talking smaller displacement. This “free piston” design, is basically a “two stroke boxer engine” without the crankshaft. Rotary engines fire three times per rev and their mileage sucks.I think ita alot of hype but I appreciate their efforts working on the future
P.S I would’nt want a misfire in that engine, could give a whole new meaning to GIVING HEAD. LOL
Simon says
A similar generator is under development by:
http://peec-power.com/
Some pictures of the design principle:
http://www.groenopweg.nl/fotovenster.php?id=9371&d=1&p=2
If we’re going this direction why not dust off the old Stirling engine?
MAX says
I dont think you can harness all the power of a single combustion cycle within a few inches of piston stroke without the benefit of carryover energy as with a crankshaft, There would be too much wasted energy. The amount of field coil windings needed would probably weigh more than the car.
Simon says
@Max
I think this depends on displacement, length of stroke and strenght of electro-magnetic field. One should be able to find a working mix of these variables. Perhaps better not start with a set of big-block pistons 😉
WRXr says
“Consider what will happen to our already almost-overloaded national grid when a few million Volts are plugged into it each night.”
Actually nothing would happen.
Night time is low power usage, yet the reactors are not shut down, the water doesn’t stop going over the dam and the coal fires are not put out.
Essentially, the power output of the fuel source during these hours is wasted, which is why power companies are generally OK with the idea of plug-in hybrid vehicles.
Insideous says
I agree with Simon. When you view this engine as a variation of a solenoid, the bar in the middle (armature) will want to stay in the middle just as if it were on springs so there is carry-over energy combined with the previously mentioned air compression of the non-used piston. Then it would be a matter of timing with the appropriate displacement and length of stroke.
The stability of frequency of the resulting wave form would be interesting to see.
coho says
Perhaps opposed-pole magnets in the heads and the ends of the piston to arrest the stroke and give it a little push back the other way?
Hawk, you mean this one?
http://www.autoblog.com/2005/12/09/bmw-turbosteamer-gets-hot-and-goes/
Warren says
This looks like the Stelzer motor that I saw in various mags back in the 80s. I’m glad the concept hasn’t died, but I’m getting anxious to see some real-world applications.
Nick says
How does the Free-piston engines transmit the power to the wheels? In a internal combution engines the crankshaft does the job but in this case…???
Charles says
Seems to be a lot of misunderstanding in the comments.
One, this device produces electricity which in turn sends power to an electric motor which turns the wheels of a car, if that is what it is being used for.
Two, the pistons will not slap the head because in the chamber there is air. When the piston moves into the chamber this air becomes compressed which acts like an air cushion…or spring.
This is a very simple concept which was demonstated by Nikola Tesla and his reciprocating engine design. This motor can also run on compressed air or steam. It doesn’t have to use combustion.
The real benefit seems to be missed by the designers of this device. This motor can produce a consistent frequency. What this means is that a certain resonating frequency can be established. Harnessing the extra power resulting from the resonance benifit of this device could do more than the simple current it generates as shown.
Ben says
The engine in the diagram appears to be a two stroke engine, but I don’t see any component to force air in through the intake. Does this mean that it can operate without forced induction, or was that ommited to simplify the diagram?
If I were going to design a car powered by a free piston engine, I’d go for something closer to the original Stelzer motor design, which has supercharging built in… plus, if it’s to be used for electrical generation, the linear alternator can be placed further away from the hot components of the engine.