I can foresee high reciprocating mass, hence restriction in engine uh...rpm...uh...I mean engine cycles per minute (cpm?) and thus lower maximum power available. Also, higher vibration level will also be a problem at higher power output, unless a number of these cylinders are bundled together.

Engine crankcase splash lubrication is not possible, forcing a total-loss lubrication? This will also cause a higher exhaust emission level.

What is the calculated advantage of this engine vs. a two-stroke Orbital engine with similar air-fuel direct injection?

Makes a lot of sense to develop a high efficiency integrated engine-generator for series hybrids, the other route being toroid combustion chambers and a classic spinning generator. One would expect the same type of multi-cylinder balancing for this engine as is done with current engines with regard to vibration. HCCI or close to it is well suited for series hybrid applications where the engine is not required to change load suddenly.

Interesting! But can any magnet material withstand the high internal temperatures of a combustion engine?

These guys at Chalmers are fantasizing that their IC engine's piston and rings will function without lubrication. Van Blarigan (at SNL) tried the same thing years ago. He dropped the concept because it was inefficient and had high levels of vibration in a single cylinder.

Van Blarigan even proposed running his engine on anhydrous ammonia fuel at 40:1 CR.

http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/30535bf.pdf

This item and the resulting discussion illustrate how this web site stands above so many others. Thanks to all for constructive, reasoned comment.

The graph suggests the scavenging mode is either cross-flow or loop, not the more efficient uniflow mode. Note also that linear electric generators are harder to control and generally less efficient than rotary types.

Terry -

they'd have to add valves in the cylinder heads for that, and actuators for them. Major design change.

So now the race is on to figure out how to mass produce the super low-mass magnet or moving coil, then the super-hard low-friction coatings which work at high temperature in a moving vehicle, then the......probably not.

Aside from the vibration issues, wouldn't this thing generate AC rather than DC needed to charge batteries or run an electric motor?

With a frequency that varried as the RPMs changed?

Wouldn't that pose problems whose solutions would reduce overall systems efficiency substantially (this is not my area of expertise).

I attended the SAE Commercial Vehicle Engineering Congress and Exhibition this last week. I visited with Peter Achten who was instrumental in developing the Chiron free piston engine (SAE paper 2000-01-2545). The Chiron, a hydraulic pumping free piston engine was licensed to Caterpillar for more development, which according to one Cat engineer that development project has been stopped.
Peter is working with a car manufacture to make an electrical generating unit. One problem is reducing moving mass so permanent magnets are being used. They have had difficulties with the permanent magnets handing the start-stop shocks of operation.
I personally don’t think any 2 stroke will ever be more thermally efficient than a 4 stroke. First, the power stroke is the same length as the intake and compression (think Atkinson, or Miller cycle engines). This limits the time to convert the heat to work. Second, intake and exhaust must happen over a shorter time, and the intake air must be compressed and stored, then flowed at very high speeds with a pressure drop to complete intake and exhaust. Basic fluid power losses happen at high flow rates and with any pressure drop. Storing compressed air can have significant energy costs as heat is added to the air during compression.
Another problem with free piston or linear engines is the way the energy is made available for extraction. It starts out very high energy and fast moving, and becomes lower and slower as time increases. Converting ever changing levels of power to a high energy storage level efficiently seems to be the major problem for both, electric or hydraulic free piston engines.
The December 2002 thesis paper by Hans Thomas Aichlmayr, has some good background on the subject.

Ed Danzer,
Regarding thermal efficiency of 2 and 4 stroke engines, I would like to let you know this:
The efficiency attained in large 4-stroke (low speed) diesel engines is about 48.5 %
The efficiency attained in large 2-stroke (low speed) diesel engines has reached 52 % !!!

These machines can also operate using fuel oil instead of diesel.
The huge 2-stroke engines work at about 100 RPM or slightly lower.

Erick, Could you elaborate on this please? "On the graphic, notice the air assist fuel injector. One could have a diesel, w/variable cylinder compression, like the one Caterpillar is developing. The engine would compress the charge in the cyinder to 99.9-99.99% of HCCI pressure. Then a blast of high pressure air, maybe w/H2+O2 assist, would ignite the charge."

Is this the process using Orbital's OCP with EGR being mixed with injection air(fluids) to the OCP injector? Cat had a patent app. in for this recently?

Thanks Tom