Sounds like what you want for future serial PHEVs and BEV range extenders.

Either way, there is no need for a small generator to have the same characteristics as a traction motor, so it should be possible to make them very efficient, cheap and small. It is a matter of enough research getting done and tested.
Let a thousand gensets bloom.

Ummm Sweet. An unbalanced two stroke.
This sounds like a good fit for the new German Retro-Trabant hybrid.

@ Harvey:
Very interesting and original idea, to use the genset e-motor as a drive motor, on demand.
Some mechanical device would be required to do the switch, some sort of transmission.
It would allow either the use of a smaller main drive e-motor for 2WD, or one e-motor less for part-time 4WD setup. The price to pay would be an extra transmission.

As for the use of a light weight rotary engine in genset - there are advantages and disadvantages.
If you look at the rotary engine used in Mazda RX-8 (I think it is the only rotary currently sold outside Japan), it is about 20% less fuel efficient then comparable (in power terms) in-line ICE designs. Plus reports say it also burns oil too much, even when new.
It's true it offers higher power output per kg, then conventional ICE's. But in terms of total car weight it might not make big difference.

Some transmission expert could comment on complexity (and cost) of a mechanical switch required for your proposed solution.

... but would be complex and expensive to the extreme.

The free-piston arrangement lends itself to HCCI without the control problems of having to manage the moment of ignition, but free-piston engines have historically been extremely difficult to control and can't operate over a wide speed range. The latter is not a problem for some specific applications (e.g. a constant-load generator).

The HCCI self-ignition and extremely fast combustion process should lead to lower thermal losses than a standard engine. The direct actuation of the alternator eliminates a lot of sources of friction. Theoretically, this potentially has a better fuel-to-electricity efficiency than a standard diesel engine, and the HCCI operation should give low emissions if correctly implemented. Also, this arrangement keeps the number of moving parts to the absolute minimum.

Vibration is a big problem with the layout shown.

Piston ring lubrication is an issue with all piston-ported two-stroke engines (including diesels). The lack of side thrust on the pistons should help a little, but it can't be ignored. There are some emission-related implications of this because a little of the lube oil unavoidably gets out the exhaust ports.

Also remember that since the compression ratio can be freely varied almost instantaeously, the FPLA engine can run on almost any liquid or gaseous fuel, and almost any mixture of fuels. Also, it is less than half the size of a comparable standard four stroke engine.
The range extender of a PHEV needs to be only about 10 to 20 kW, so the vibration of such a tiny engine is probably manageable with special engine mounts.
For these reasons, the FPLA engine is also my current favorite for this purpose.
However, if any of the technical problems already mentioned above prove to be unsolveable then it will be out of the running.
I second the notion of getting some prototypes running as soon as possible to see if the practical problems can be solved, because the basic concept is excellent and ideal for PHEVs.

I’m sure some type of synchronous liner generator could be developed and applied to this to get away from the heat effects on the permanent magnets. I would like to see a diesel version made with electronic fuel injection and turbo charged.

I am never sure of anything, but an inductive linear alternator might be constructed. You may need to excite the motion to get the whole thing started in the first place, so the alternator could become an actuator as well.

If ever a free piston generator were comercialized, Peter Van would lose some lunch money. The Pescara free piston machines and especially the Junkers were made in large numbers. The Pescara had a turbine output and the Junkers was an aircompressor. The NOAX machine can be converted into a four-cycle machine if necessary, and it should be made as a balanced dual piston device. It is the logical succesor to the Pescara and computer control makes it a winner. It should be used in series hydraulic hybrids, but if you want electricity, use a turgo wheel and standard alternator. Efficient linear alternators are hard to build in large sizes. ..HG..

Yes mahonj you are right. Why not then use compressed air to drive the piston? Easy, cheap, no heat :)

It is good to see free piston engines starting to be looked at hard again. They have been shown to have much better fuel conversion efficiency due largely to combustion at higher pressures, and this was proven about 50 years ago. The major issue was how to extract power out of these engines. The linear alternator is a good option to investigate, but as indicated in this blog, there are vibration issues with this linear design. There are other designs that eliminate this vibration, and operate in the 4-stroke mode. These charateristics are new to FPE develop, and some of the benefits haven't surface yet.