New Internal Combustion Tech Could Improve Range-Extended Electric Cars

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As any Chevrolet Volt owner will tell you, the range-extended electric car concept is very well adapted to the average car ownership experience.

The majority of your daily driving can be accomplished on electricity alone, but there's always that engine there waiting to back you up should a longer journey be needed--or those occasions where you've been unable to recharge the car's battery pack.

So far, the range-extending engine is usually based on a production automobile engine--but bigger gains in efficiency could be found with units like the Free Piston Linear Generator (FPLG), reports Fox News.

Essentially, any regular automobile engine is a bit of a compromise for a range-extended vehicle.

It's often heavier than it needs to be, larger than it needs to be, and while optimized for use at constant engine speeds, it's really compromised by its original purpose of working over a large power band.

Developed by engineers at the German Aerospace Center’s (DLR) Institute of Vehicle Concepts, the FPLG doesn't have any of these issues.

As the name suggests, the engine is linear, in that the pistons aren't connected to a crankshaft, where their linear motion is converted into rotational motion.

The engine uses two pistons, facing each other in a single combustion chamber. The pistons are mounted on air springs, which generate electricity as they move back and forth. Combustion happens right at the center of the engine, using the traditional 'Otto cycle'--induction, compression, expansion and exhaust.

Because of the unique design, the engine can also run on all sorts of fuels, including gasoline, diesel, natural gas and hydrogen.

At the moment, the team's prototype is a large laboratory unit, but they say it could be reduced in size to a 125-pound unit putting out around 40 horsepower. Due to its size and shape, several could be mounted side-by-side for larger, more power-intensive applications.

A spokesman for DLR says a production version could be on the road in four to five years--provided they can find an industrial partner to help develop and finance the technology.


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Comments (15)
  1. Why does fuel have to go through an engine, with all of its complexity, to generate electricity?

    I'm sure there's technology out there that converts fuel (gasoline, hydrogen, etc) directly into electricity. It would be perfect for supporting a low battery, not make noise, and be small. ICE's are looking more and more like fossils.

  2. They are being worked on to use gas/diesel for fuel cells. The problem, though, is that while it is more efficient to use fuel cells, we still have the problem of our oil addiction. We just trade one engine for another and not really solving the problem of energy independence.

  3. DEFC - Direct Ethanol Fuel Cell.

    People who bash ethanol always assume it will try to replace 100% of our gasoline.

    Cellulosic ethanol can replace up to 35% of current gasoline consumption without any affect on food supply. Cellulosic ethanol is made from things we currently throw away (forest mill waste, corn stalks and leaves, municipal waste, etc). Cellulosic ethanol also comes from energy crops which will grow on land unsuitable for farming. These non-food sources can replace 35% of gasoline consumption. In other words, cellulosic ethanol only affects food supply when you try to scale it beyond 35%.

    EREVs can replace 80% of our gasoline consumption. 80% + 35% = 115%, more than enough to completely replace gasoline.

  4. How far away is cellulosic ethanol from that 35%? I thought it wasnt viable yet. Still trying to get it right.

    Also, that seems like fuzzy math there. Sure EREVs can replace 80% of gasoline, but they still need gasoline to run long distance. The other 20% of gasoline use can't be replaced with ethonal. Unless it can run ethonoal, you dont make sense.

  5. Few issues I see:
    1) this is a two-stroke cycle & is traditionally less efficient. It can't completely burn fuel as exhaust gas needs to be expelled the last half of power stroke & mixes with incoming mixture.
    2) no clear in-take/exhaust shown; no details of valves & timing?
    3) synchronizing two pistons is critical; since no flywheel. Energy needed to to adjust in real time (+ compressed air heat loss)
    4) electrical power will be non-linear unlike rotational generator… a spike of max power with each ignition with exponential ramp down to near zero as pistons travel away from the center point. In modern ICE the flywheel averages out the power spikes through conserving angular momentum (& reducing vibrations)
    5) lubrication mixed with fuel?

  6. 1) It's a four stroke, not a two stroke.
    2) Since there isn't anything rotating, there will be no cam shaft. I would guess they are using solenoids to drive the valves. That would also allow them to infinitely adjust timing and compression, allowing them to run on a variety of fuels.
    4) Since this is just generating electricity, maybe the battery or a capacitor is evening out the power. This would be a very smooth running engine though because the only motion is two pistons that counter-act each other. There are no additional rotating masses to cause vibration.
    5) Again, this is a four cycle, not a two cycle.

  7. Yes, but the FPLG is still an internal combustion engine. The popping inside the cylinder still causes noise. You'll still need an exhaust system with a muffler.

    Compare that with a Sterling engine, which uses a relatively constant external source of combustion. Since the combustion is constant, as opposed to the popping explosions of an internal combustion engine, the efficiency can be much greater, and the noise is dramatically lower, so the exhaust system can be much simpler and less expensive.

  8. They don't show any valves or air intake or exhaust - it is not clear how these could work right in the cylinder wall? They would be side valves by definition, so flow patterns and flame spread could be issues. There would seem to be a small pocket next to the valves, since their diameter has to be bigger than the TDC gap between the pistons.


  9. With that kind of design, it's close to nonsense to start comparing actual 2strokes or 4strokes engines properties. If you refer to the minimal definitions, it's closer to a 2 strokes piston cycle : exhaust and intake are made in the same time, via transfer from lower to upper chamber (external to internal here). In 4 strokes, these are seperated. This linear engine can hardly be transfered to a 4strokes-like cycle, because the inertia acquired from the explosion is here immediately absorbed by linear generators, instead of a temporaty tranfer to crankshaft/flywheel rotating mass. 2 strokes engine is not known for his thermodynamic efficiency but more for power/weight ratio , and here is an injector improving the combustion.

  10. these have been around for 50 yrs as this and free pistion engines for 80+ yrs. The weight/hp ratio and eff is worse than present engines.

    Fact is it's hard to beat modern car ICE on eff when run steady state as a generator.

  11. Perhaps the RadMax / RandCam engine would be a good fit for this usage once it's commercially available - any day now?

  12. It look very efficient. Im interrested to buy. Can't wait to see this.

  13. I would think that a rotary engine that drives a spinning generator would be a lot more efficient? Oscillating pistons have to be stopped and started wasting a lot of energy. Air springs have to have seals = more friction. A spinning generator would have a constant output; rather than pulses from this design.


  14. Agreed. I think the saving comes from the combustion portion of the design. It is far more compact than the traditional design.

    I am still NOT sure about its reliability and durability.

  15. A spinning generator also has pulses which are smoothed electronically, Your household electric has pulses 60 cycles or 50 in the UK. This is down to the design constraints of the generator and not the rotation of the prime mover.

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