Lighter, Cleaner, More Efficient Diesel Engine: Too Good To Be True?

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LiquidPiston rotary diesel engine [Image: LiquidPiston]

LiquidPiston rotary diesel engine [Image: LiquidPiston]

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Clatter, grumble, shudder, belch.

Sound familiar? Not if you drive one of the modern breed of diesel-engined cars, which have virtually banished all sign of their clattery, tractor-like forebears.

A modern Volkswagen TDI, for example, isn't just efficient and quiet--it even approaches fun, if you get your thrills from effortless low-down torque.

Not that it can't be made better, and a company called LiquidPiston (via GigaOM) is promising just that with its latest engine design.

It offers greater benefits even than current diesel engines--lighter weight, smaller size, greater efficiency and less noise. It's also simpler, and so the theory goes--cheaper.

The prototype X2 engine is based on a rotary design, which is immediately beneficial in terms of smoothness next to typical reciprocating designs.

It works on a patent-pending "High-Efficiency Hybrid Cycle" combustion method, which uses elements of Otto, Diesel, Atkinson and Rankine cycles. And impressively, it isn't restricted to diesel--gasoline, natural gas, biofuels and others can all be potentially used.

LiquidPiston claims the engine operates at more than 50 percent thermodynamic efficiency, next to figures of less than 20 percent in regular piston engines. And contrary to current rotary engines, which have a bit of a gas-guzzling reputation, the engine should also be fuel-efficient.

The first engines are unlikely to be seen as the main powerplants in passenger vehicles, but use as range-extending engines in plug-in vehicles is more likely. Defense, industry and other niche markets are other likely avenues.

The company has raised $12.3 million to develop its engine so far, and hopes to find another $20 million soon.


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Comments (13)
  1. 50% efficiency? That would be "awesome"!

    But I will reserve my judgement until I see it.

  2. I just read about it in more details from its website and popular mechanics.

    It seems like the engine gains its effciciency from high compression ratio, constant volume combustion and over expansion. (Water injection is cool too).

    I think over expansion is the main reason it has gained so much more efficiency. However, with this, how much "torque" will this engine have in comparison with traditional ICE? I imagine this will be a high RPM engine similar to rotary design, but with much better emssion and less fuel consumption due to the higher compression ratio and over expansion.

    It sounds like a good fit for "range extender" in EREV application (or series hybrid).

  3. Agreed, I've noticed others suggest it may be light on torque too - but could well be suitable as a range-extender.

  4. It has to be since it tries to suck out every bit of pressure and heat out of its combustion. (similar to additional stages of gas turbines).

    I would be really interested to find out about its hp and torque curves. I imagine this will be a 10,000+ RPM spinner...

    Can you update us as soon as you have any torque or HP vs. RPM information?

  5. The design of this is >nearly perfect< for range extension. The "flaw" with the Volt and all EREVs today is they don't nearly go far enough in simplifying the gas powertrain. So you basically wind up with a nearly complete gasoline powertrain and an electric powertrain.

    A 100hp version of this coupled with a good link to your navigation system would be able to operate quite intelligently vis a vis battery recharging and allow for a greatly simplified liquid-fuel powertrain. If eventually one version can run on diesel or gasoline or E85, all the better.

  6. Not to mention that this 100hp version will be extremely "light" in weight and super efficient. Plus, its flex fuel capability will also help with extra long range travel.

    It is probably even a better engine for SUV and pickup trucks since it lacks torque but have super high efficiency... Perfect for a series hybrid configuration.

  7. Very interesting article. Diesel hybrids are definitely coming, and if this engine works it wound be a great offering. VW is already headed in that direction.

  8. VW is behind Peugeot on this, however. See the Peugeot 308 diesel hybrid as an example. Not many sales, but PSA has beat VW to the market here. It will be good to have VW & others join the diesel/hybrid group, assuming they can bring the price down sufficiently to justify the additional cost.

    I would not expect to see any diesel hybrids in NAFTA, however. The extra cost of the combined diesel and hybrid systems may make the base price too high, even if total cost of ownership makes up for the difference. But I'm not sure what the 308 hybrid sells for, so perhaps there has been progress on the cost side.

  9. If this "engine" is truly capable of 50% efficiency, then it can easily be "upgraded" to power large electricity generation with natural gas.

    If it is truly "that efficient", it would have investors flooding in instead of still looking for additional $20 Million in funding...

  10. Whatever happened to "suck, bang, blow?" We're gonna have to fit "spin" in there somehow.

  11. Well, turbine engines are "suck, push, spread, bang, blow, and they have been powering aircraft using "spin" for well over 50 years. We have room to add to the lexicon

  12. There are a number of companies that have experimental engines running. Each of them is trying to gain publicity so they can get additional capital to pay their salaries and fund the additional investment it would take to develop a product that meets the promises they are making. Then to develop that product into one that would make sense to manufacture affordably in large volumes. Very tough challenge.

    I have a general rule of thumb. When I see a touted innovation, whether it is a new battery chemistry, a new engine, or the latest medical breakthrough, I assume that there is less than a 10% chance of that product actually getting to market. And if it does, it likely will take around 8-10 years.

  13. look in the felix vankel's brilliant book about rotor engines ever-
    -nothing new under the sun
    i do not really see any liquid in this piston

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