Free piston petrol range extender?

[RoverP6B]

This makes for very interesting reading.

http://www.roadandtrack.com/car-culture/a6326/out-...

I wonder if this could be applied to conventional piston engines and thus do away with the alternator, use all electric ancillaries rather than sapping engine power?

[TooMany2cvs]

RoverP6B said:

I wonder if this could be applied to conventional piston engines and thus do away with the alternator, use all electric ancillaries rather than sapping engine power?

It's still going to sap power - there's a lot of resistance to motion in the magnetic fields, same as the load required to rotate a generator. Then there's the gas spring - where's the pressure from that coming from? Sure, there's probably efficiencies, but it's certainly not "free" power.

[2Btoo]

Interesting indeed, thanks for the link. I wonder how they return the piston at the end of the stroke if there is no crankshaft and rotational mass to push it back.

[TooMany2cvs]

2Btoo said:

I wonder how they return the piston at the end of the stroke if there is no crankshaft and rotational mass to push it back.

That's the gas spring.

[2Btoo]

Oh, thanks. I didn't spot that bit.

[anonymous-user]

The issue with the free piston linear engine is that it's Patented up to the hilt, and the owners of said Patents want a LOT of money for a licence to make it.

[AER]

There are plenty of issues with free-piston generators!

Seems simple at first. Then you need to attempt to balance them, convert the single-phase AC to DC, control the valves (why not a loop-scavenged 2-stroke...?) and probably a ton more issues.

Don't hold your breath.

[RoverP6B]

Hmm, right... it seems such a simple concept that it's a wonder it wasn't around a century ago...

[OldGermanHeaps]

If lubrication could be sorted you cold have a spark plug and valves at either end of the stroke

[anonymous-user]

The problem with all these "new engine concepts" is that they are now 50 years too late!

Right now, no one is going to spend hundreds of millions of pounds on developing technology that is going to be really pretty obsolete in a few short years!

Not for nothing has every current RE-EV had a pretty normal(and pre-existing) reciprocating ICE doing the RE bit.............

[RoverP6B]

Double-acting piston engines were the norm in the steam era...

I don't understand why conventional single-acting petrol/diesel piston engines would be used as range extenders. They're much too complex, heavy and inefficient. A gas turbine or wankel makes much more sense. Jaguar obviously showed the CX-75 with the former, and although it was shelved, I think they've retained their shareholding in Bladon Jets, while Audi showed off a 50cc wankel range-extended A1 EV.

[TooMany2cvs]

RoverP6B said:

I don't understand why conventional single-acting petrol/diesel piston engines would be used as range extenders. They're much too complex, heavy and inefficient.

Because they're cheap and not scary to the average dealer mechanic.

The REx in the i3 is a BMW bike engine. Where are they going to get a nice easy off-the-shelf gas turbine that can be serviced at any dealer?

Edited by TooMany2cvs on Sunday 18th October 15:10

[RoverP6B]

Well, a microturbine shouldn't actually need servicing, the battery pack will go first.

I wonder if they could stick the 1.6 litre straight six bike engine in the i3? Or, better still, in the 1/2/maybe 3-series as the -16i engine?

[AER]

A microturbine will drink like a fish and completely destroy the fuel efficiency ideals of a RE-EV.

They can be made to moderate their drinking habits, but not without very expensive and complex recuperators

[RoverP6B]

Even a tiny little thing like a hairdryer?

The whole reason turboprops/turboshafts replaced pistons was their greater efficiency.

[AER]

Yes - gas turbines scale very badly. A good small piston engine will be sub-300g/kWh whereas a gas turbine of a similar size will be into the kg range

The reason they work well on jets is that they are generally very large and they operate most of the time at high altitudes which will double or triple the pressure ratio they operate at. Pressure ratio is the gas turbine equivalent of compression ratio and is one of the large influencing factors in efficiency.

Gas turbines also have an unbeatable power density so in some applications you can trade fuel consumption potential (and thus the need to carry fuel) for a very low powerplant mass.

[callmedave]

Just seen this thread, interesting concept, but why not do away with the gas spring and replicate the piston on t'other end?

Some energy is lost in compressing the spring, with another 'bang' on the opposing end, this will return the piston to its starting position and reduce wasted energy, meaning the magnets can be stronger and produce more power with each stroke?

any thoughts?

[amstrange1]

callmedave said:

Just seen this thread, interesting concept, but why not do away with the gas spring and replicate the piston on t'other end?

Some energy is lost in compressing the spring, with another 'bang' on the opposing end, this will return the piston to its starting position and reduce wasted energy, meaning the magnets can be stronger and produce more power with each stroke?

any thoughts?

Controlling it is challenging. You've got no flywheel keeping the thing moving, so it's an unforgiving system. I believe that twin-piston linear engine concepts often end up using the electrical machine as a motor for very brief periods to keep it all moving.

There's some info on the concept you're talking about here:
http://www3.fs.cvut.cz/web/fileadmin/documents/122...

Edited to add a better link:
http://www.lceproject.org/en/

[98elise]

RoverP6B said:

This makes for very interesting reading.

http://www.roadandtrack.com/car-culture/a6326/out-...

I wonder if this could be applied to conventional piston engines and thus do away with the alternator, use all electric ancillaries rather than sapping engine power?

Power (or energy) always has to come from somewhere.

[RoverP6B]

I know that, but running the ancillaries with electric power rather than pulleys is more efficient.