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Free Piston Engines have existed for a while now in Stirling engines it's a novel idea to try and use them in ICE. I wonder how well it will stand up to the heat of an ICE.

I understand that NASA nearly used the first Stirling engine on Mars curiosity, instead of the standard Thermocouple RTG, but they hadn't quite finished testing in time.

Sun Power are also using free piston Stirling engines in solar applications with good results, and in some cases better efficiency than Pv. (parabolic mirror to focus heat to the hot end of the Stirling engine)
 

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But the jet engine would be cool! Bit noisy perhaps?
 
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They say how efficient it is in the video :)

30% more efficient than an ICE, they say around 50% efficiency.
I've not had chance to watch it yet (I'm at 'work'), I recall the TREV being around 40%? If it's efficient it shouldn't be noisy as such. I expect there will be less vibration than any reciprocating engine. I'll certainly be following both technologies with interest.

On a completely different tangent for anyone wanting an interesting read... Take a look at:

SABRE | Reaction Engines

Cheers,
Jim (working hard)
 

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Free piston engines are now being developed specifically for PHEVs and offers true integration between the ICE component and the electrical components. I love this design...

Hmm, their pressure-volume diagram is v suspicious! Seems to claim expansion to V large volume to allow pressure in cylinder to decrease to atmospheric. This won't work, for obvious reasons. Secondly, they claim that conventional rotary ICE using conventional Genny is bad, and their linear arrangement is better as goes straight to leccy avoiding crankshaft & eccentric. Sadly, 100 % of their motion energy has to go to Genny, then to leccy motor & back to motion, losing some efficiency every conversion. Ampera can feed the ICE motion straight into the wheels via single gear (maybe two) reduction, and is more efficient. Their linear Conrods also give zero flywheel effect, so expect a jerky motion .vs. rotary Genny acting as V useful smoothing flywheel. So I do not expect to see this being a winner.
 

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How rocky would that ride be?? ... I am certain an engine cannot be mount horizontal as then the car will be rocking right to left etc.. or front to back ... so it will have to be mounted vertical in the same way a typical I4 engine would have been ... but then there is a problem with height?
Not sure how can this be implemented and balance it self.
 

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Flat fours balance about as well as straight fours. The proposed linear flat 4 will have a problem keeping each of the 2 Conrods in sync, a job normally done for free by the crankshaft. But flat & straight 4s will both have a rocking imbalance. A straight 6 is the minimum number of cylinders to get perfect balance with no rocking, I was taught. A 5 cylinder should get pretty close, and V12 is fine as is 2x6. V8 s probably rock.
 

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But here we have no "pistons" in theory... although. If they put a shaft to balance it out ... wouldn't the middle part of the engine then be 2 pistons? Am I seeing the whole thing in the wrong way?
 

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Each cylinder has two pistons + 1 Conrod + magnets connected rigidly. When the left end is at max compression & spark fires, the resulting force pushes pistons etc to the right, and pushes crankcase to the left. So to balance this, we want the other cylinder to be firing its piston at the right side. But seen from above, because the cylinders are separated in space fore & aft, there's a bit of twisting about a vertical axis, our line of sight looking down on the middle. That's the rocking torque. We could add 2 more cylinders and cancel that, giving perfect balance with no rocking in a flat 8.
 

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Subaru's have used flat fours for quite a while. Gives a nice low Centre of Gravity apparently. Didn't Porsche use flat fours or flat sixes?
 

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How did we move the subject from Free piston engines to the Boxer flat engines? lol :)


OK got my answer regarding the "rocking balance"

"Toyota says this mechanically simple engine achieves a claimed thermal-efficiency rating of 42 percent in continuous use. Only the best, most complicated, and most expensive of today's gas engines can come close to that number, and only in specific circumstances. Even better, a two-cylinder FPEG is inherently balanced and would measure roughly 8 inches around and 2 feet long. An engine of that size and type could generate 15 hp, enough to move a compact electric vehicle at highway speed after its main drive battery has been depleted."

No crankshaft, no problem: Toyota's free piston engine is brilliant
 

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15hp? That's about 12kW... that would just about keep an Ampera at 60mph on the totally flat with no rain. Lots of work to do to make something that generates 100hp... Interesting technology though.
 

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A diagram of a prototype? Sorry, that's not a prototype, that's a first design. A prototype is a thing you build to the first design (sometimes called 'CV' [concept validation], or 'Sample A').

15 years of work on this. I trust they realise the whole automobile industry was invented in that time, at the turn of the 19th century, going from steam and electric to gas engines.

Sounds like it's designed more to pump Government grants to make money, rather than to pump air and fuel to make energy.

Colour me cynical...
 

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Blame Handy Andy, I think we will see a more conventional approach for the next gen EREV probably 3 cylinder with a 30Kw battery in the floor and a revised VOLTEC type tranmission motor generator with a 200hp motor nicked from the Bolt.
The orginal volt prototype had a 3 cylinder diesel engine as Ford has shown 3 cylinders can be made to work very well, in a light and compact package.
 
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