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LiquidPiston Closes $1.25M Venture Seed Round; Funding to Develop HEHC-Cycle Engine

27 July 2007

Lp2
The Liquid Piston engine. A) full housing. B) Transparent housing showing principle components. Click to enlarge.

LiquidPiston, developers of a new engine architecture they claim will achieve 50% fuel efficiency (compared to the ~30% of existing engines) and drastically reduce pollutant emissions (earlier post), closed a $1.25 million seed investment round with Adams Capital Management and Northwater Capital.

The architecture is based on a “High-Efficiency Hybrid Cycle” (HEHC) thermodynamic cycle, which borrows elements from Otto, Diesel, Atkinson and Rankine cycles. The HEHC cycle can be implemented in a variety of ways; LiquidPiston is developing an implementation that uses a separate rotary compressor, two isolated combustion chambers, and a separate rotary expander.

Hehc
The HEHC cycle. Click to enlarge.

In the HEHC cycle (diagram at right), air (with no fuel) is compressed to a high ratio (> 18) in a compressor cylinder of the engine. The air is directed into an isolated combustion chamber. Fuel is injected into the combustion chamber and auto ignites. Combustion occurs under truly isochoric conditions and is allowed to complete until all fuel is fully combusted. The combustion products expand into an expander cylinder, which has larger volume than the intake volume.  A small amount of water (an optional component) may be used in the system. Water may facilitate the cooling, lubricating, and sealing of combustion chamber and pistons.

Earlier this year, the company announced a $70,000 Phase I grant from the Army Small Business Innovation Research (SBIR) program. The father-son team led by immigrant physicist Nikolay and his son Alexander Shkolnik, a graduate student in MIT’s department of Electrical Engineering & Computer Science, will use this latest $1.25 million seed round of venture capital to build and test a working prototype.

Aside from significant improvements in fuel efficiency, LiquidPiston’s approach to ICE design has the potential to result in a substantially higher power-to-weight ratio, fewer moving parts leading to higher reliability and lower maintenance costs, and significantly lower emissions. The company expects to demonstrate a working prototype in the next 18 to 24 months.

The potential of this technology is tremendous, and the interest we are seeing from both the public and private sectors is very encouraging. With this latest round of investment, LiquidPiston is on its way to achieving its goal of revolutionizing the $250 billion market for internal combustion engines.

—Dr. Ed Crow, retired senior vice president of Pratt & Whitney and an advisor to LiquidPiston

July 27, 2007 in Concept Engines, Engines, Fuel Efficiency | Permalink | Comments (20) | TrackBack (0)

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Comments

The true isochoric combustion sounds promising- isn't that the goal of HCCI engines?

However, wouldn't there be significant losses associated with directing 18:1 compressed air into an isolated combustion chamber- and then directing them again into a separate expansion area?

Raphael... others... would you please weigh in.

I'll wait until 3rd parties try out there prototypes before I believe it. People have been trying new engine designs for over a century and have had little success: the basic engine architecture has not change much since it was forged.

Offtopic,

did not see this posted, new solar breakthru...

Solar efficiency of 42.8% at University of Delaware in collaboration with DARPA, DuPont and other universities.

"As a result of the consortium’s technical performance, DARPA is initiating the next phase of the program by funding the newly formed DuPont-University of Delaware VHESC Consortium to transition the lab-scale work to an engineering and manufacturing prototype model. This three-year effort could be worth as much as $100 million, including industry cost-share."

They intend to reach 50% goal set by DARPA utilizing the new designs and wide collaboration with private and public sector.

link to news comment above:
http://www.physorg.com/news104501218.html

@ DieselHybrid -

this is essentially a type of single-stage gas turbine but crucially, with near-isochoric rather than isobaric combustion. If you look at the thermodynamic diagram, you'll see the claimed peak pressures far exceed those of conventional engines.

The big question is, how do you ensure a tight seal between the rotating combustion chamber and the pipe it's located in? The inlet and outlet of the chamber are simple holes, so how do you avoid massive blow-by into both the turbine chamber and the compressor? As Felix Wankel pointed out, you cannot achieve a perfect seal without a thin oil film.

The problem is quite similar to that of the various rotary valve designs (Aspin, Cross, Lotus, Coates etc.), none of which ever made it into mass production. Sealing and lubrication problem have been the bane of many an interesting mechanism.

A second issue with this particular design is that both the combustion chamber and the turbine rotor are never exposed to cool air. In a regular (large) gas turbine, you can bleed off air from the compressor, route it through the shaft and turbine vanes to create a protective shroud of cooler gas around them. I don't see how that could be achieved here, given that neither rotor is fixed to the driveshaft.

As proposed, the are also difficult to cool with oil or water. This means you either have to accept low peak temperatures and hence, low thermodynamic efficiency (especially in part load), or you have to resort to expensive exotic materials. Poor longevity at high load and temperature has been the other bane of many radical engine concepts.

For the moderate power levels required for cars and trucks, the reciprocating piston engine remains the worst possible powerplant - except for all the others.

HEHC cycle? Give me a break. It's just constant volume combustion. And the way that engine must transfer the working gas between various chambers, it will be a very inefficient engine due to pumping losses and leakage.

I have a patent on a recip piston, 4-stroke engine that produces a true constant volume combustion.

http://www.google.com/patents?id=s0IUAAAAEBAJ&printsec=abstract&zoom=4&dq=buelna#PPP1,M1

Why hasn't anyone given me $1.2 million in VC money? Maybe I need a better marketing guy?

"The company expects to demonstrate a working prototype in the next 18 to 24 months."

Uh oh--another engineering revolution on paper.

I'll be much more impressed with this breakthrough when they have on large enough to power a small car for tens of thousands of miles without seal problems.

I don't mean to sound negative, as I sincerely hope they can make this work. Something like this running the onboard generator in a plug-in series hybrid could be quite nice.

Agree with Rafael and Terry. Sealing, cooling, transfer losses, etc.

BTW, isochoric combustion produces high peak temperature, pressure, and hence a lot of NOx. Nothing to do about it in SI engine, where CR is limited by gasoline octane rating, but for diesel engines in order to reduce NOx modern engines prolong injection events to have piston descent and cool combustion gases a little bit before last injection event. Delayed and prolonged injection inefficiency is compensated (but not completely) by higher compression ratio. So they are moving further from most efficient isochoric combustion to reduce NOx (reduction of ignition noise is additional bonus).

Terry:
Your patent reminds me of couple of wobble/swashplate designs experimented with shortly after WW2 . Take a look at “Some unusual engines” by LJK Setright – magnificent book.

Agree with Rafael, Terry, and Andrey.

Prolonged isochoric combustion at the compression ratio of 18 is a no no with respect to NOx formation, that is, further assuming that your combustion chamber has not melted (ie. if made from ceramic materials). (Gas turbines' isobaric continous combustion at 1/2 the temperatures of that of Otto-cycle engines still facing high NOx emission problem).

In fact, a ceramic rotating combustion chamber would solve the tribology problem (friction & lubrication) since hot ceramic surface is slippery needing no lubrication, BUT, sealing of very hot combusted gas is still a big issue, and ceramic's brittle nature leading to catastrophic failures so far has prevented the use of this material in modern heat engines.

"For the moderate power levels required for cars and trucks, the reciprocating piston engine remains the worst possible powerplant - except for all the others."

Quite a clever and poignant yet realistic statement...that is, until the advent of the full hybrid HEV...which allows near-peak thermodynamic efficiency of the highly efficient Otto-cycle engine to be realized throughout the entire operating regime of the automobile.

The best of real-world Otto-cycle or Diesel-cycle engines can get up to 45-50% efficiency, and that's darn close to the ideal efficiency of 60-65% of the Otto-or Diesel cycles using practical compression ratio, given the fact that ideal cycle efficiency ignores friction and heat loss thru cyclinder head and wall. Friction and Heat loss is unavoidable, since your metal melts at a fraction of the peak combustion temperature, and your lubricant would burn at even much less temperatures, so you must really cool it down as much as you can.
Real-world Sterling cycle engines or other cycles such as Rankine (steam) cannot beat this efficiency and are more bulky.

The claim of "Liquid Piston engine at 50% peak efficiency does not offer higher than the best of possible real-world Otto-cycle engines (with HCCI, plus other tweaks such as variable compression ratio, variable valve opening and timing, etc) and has many aforementioned technical issues. In fact, you take a given 35% peak efficiency of a typical modern Otto engine and add to it the 40% improvement as in the latest DB DiesOtto engine, and you'll get 49% peak efficiency. Darn close!

@ Andrey -

good point. A three-way catalyst can only clean up enough NOx if there's enough HC and CO in the exhaust gas as well. There's no point in building a super-efficient automotive engine if it cannot pass emissions.

@ Roger -

except for plug-in concepts, I consider all types of hybrids to be energy management systems. They essentially permit the ICE to spend more of its time in areas of the engine map where thermodynamic efficiency is high and parasitic losses are low. That improves vehicle fuel economy, which is what really matters, but the ICE is still just and ICE.

Btw, I feel micro- and perhaps mild hybrids make more financial and environmental sense than full hybrids, simply because they can be produced economically in much higher numbers. The only reason that isn't happening yet is that Toyota marketing has succeeded in persuading the US public that anything less than "full" just isn't a hybrid at all, which is rubbish.

Afaik, peak efficiencies for automotive gasoline engines are 35-38%, the latter for turbocharged variants. Diesel max out at 42-45%, though very large gensets and marine diesels can go as high as 52%. Your numbers appear a little too optimistic to me. In any case, LDV engines are rarely operated at peak efficiency.

Why doesn't someone add a second cycle to a ICE to use the compressed gas from the Otto cycle to turn the crank shaft ?

Hi Rafael,
Oh, I see the sarcasm in your statement! "...the reciprocating piston engine remains the worst possible power plant-except for all the other [ICE power plants]" implying that actually, piston engine remains the best...since "in the land of the blind, the one-eye man is king." he he he.

What I was thinking was that the synergy between the piston ICE and the electric motor as a second power plant would make it the best combination. The deficiency of the piston engine is vibration, noise, and high friction in proportion to engine output at low loads, therefore, many rotary ICE concepts were introduced to ameliorate the vibration and friction of the piston engine design. But, an "energy management system" allows the piston ICE to shutoff at low power regime and at a stop, therefore allowing the car to be quiet, vibration-free, and no energy lost from engine friction and poor combustion at idling or low loads.
Full-hybrid is still more expensive, but affordable, if people really care about fuel efficiency. The battery packs used are still relatively small in comparison to that of PHEV's, and is recyclable, such that there would not be problem in manufacturing hundreds of millions of HEV battery packs.

My number of ~50% efficiency is my projection for the latest DiesOtto engine, which is reported to improve 40% over a modern gasoline engine. In the back of my mind, I've suspected all along that 50% efficiency is possible for an ICE piston engine, and now, am glad that DB has supported it with actual data.

@ Bob H -

I'm not sure I fully understand what you are suggesting. An ICE works by exploiting the difference between the work required to compress air and that done by the expanding combustion gases.

The exhaust gases do, however, still have considerable amounts of heat. This is often more than the mechanical work done by the crankshaft. The waste heat can be used by secondary thermodynamic machines, of which the best known is the turbocharger. In effect, it is a small single-stage gas turbine whose work is transmitted to the crankshaft pneumatically. Put that way, every turbocharged ICE is actually a hybrid.

Other examples include multi-stage turbocharging, Swiss Auto Wenko's Hyprex pressure wave charger, variations on turbocompounding (Scania, Catarpillar), the TIGERS turbine genset project and BMW's turbosteamer R&D effort.

The exhaust heat of a large stationary genset can be used to power an absorption chiller. Some Danish fishing vessels do use Vuilleumier chillers instead to keep their catch cold. In an automotive context, cold from heat could in theory be used for cabin air conditioning, cargo refrigeration and/or the aggressive intercooling of the fresh and/or recirculated charge in boosted engines.

Bob H,
The compressed gas by the piston in the compression stroke is used up in the combustion that powers the power stroke. The residual pressure of this exhaust gas can be used to power a turbocharger or a turbo-compounding exhaust turbine to add more power to the engine, as in the piston-engine airliners of yesteryears, notably the Lockheed Constellation and the DC5, DC7 variants, and other piston-engine long-range bombers. This is impractical in automobile application because of additional cost, and for most of the time, the engine operates at very low loads in comparison to the engine's maximum output, so the residual exhaust pressure is quite low.
But, hey, for the GM Volt as a serial hybrid in which the engine would operates continously at a single most efficient speed to recharge the battery, exhaust turbo-compounding may be worth a try as an option, to improve mpg by a further 10-15%, if the buyers wanna shell out some extra bucks for the bragging rights of oneupmanship over mpg.
Now, that's priceless..."and for everything else, there's MasterCard."

Actually, all that is needed to more fully expand the (still) "compressed gas" from the end of a conventional Otto cycle, is to tinker with the valve timing so that the effective expansion ratio is greater than the effective compression ratio, and then make the combustion chamber smaller so that the effective compression ratio remains in a "normal" range. It can be done either by closing the intake valve early, or leaving it open really late so that the first part of the compression stroke pushes out some of the air that just went in.

And, it's already been done. It's variously called the Atkinson or Miller cycle. Mazda Millenia used it years ago (and Mazda seems to be bringing it back in the new Demio). Toyota Prius uses it now. The standard engine in the current Honda Civic uses the Atkinson cycle on the "low lift" cam of its i-VTEC system. Upcoming Honda A-VTEC will use it at part load.

Doing something like this, alone, does not work miracles (10 - 15% improvement), but multiple strategies working in unison are how improved efficiencies are being achieved.

On the subject of that Liquid Piston engine, speaking as someone who has actually spun wrenches on a number of engines, I don't hold much hope for it in the real world, for all the reasons that others have already explained.

This is nothing more than an Atkinson cycle with a separated combustion chamber. Apart from the massive gas exchange losses inherent in this concept they have forgotten the limitations of the Atkinson cycle. Indicated efficiency is proportional to engine load with max effiency occuring at max load. The best efficiency from the Atkinson cycle is achieved at low CR values.

In addition, the Atkinson cycle suffers from low imep by its very nature of operation. Therefore bmep is correspondingly poor. With two rotors doing the work of compression and expansion, the friction losses will be very high in achieving a reasonable bmep.

Has anyone considered how the combustion chamber will be scavenged? There is no gas flow through it so at the end of every expansion event the combustion chamber will still contain exhaust gas. There will be an enormous problem with thermal loading on the combustion chamber device which will make sealing a huge challenge. Naturally heat losses will be very high which will futher erode thermal ifficiency.

This in an interesting attempt to come up with something new but until it is proven with real prototypes it will be just an academic exercise like many other similar ideas. Nice mental exercise though.

extracomment,
Absolutely, Atkinson cycle engine is better suited for hybrids which require a narrow operting range and mediocre power output. At the low end near idle, there is concern that the combustion gas may have to expand below atmospheric pressure, thus robbing efficiency. At the high end of power, volumetric efficiency suffers due to incomplete filling of the intake stroke, hence poor power density,leading to higher engine friction if operates mostly at the low end of the power band.

Whereas, if turbocompounding is used, high efficiency is maintained at both ends, and if a turbo-supercharger is used, even higher power density is possible, allowing engine downsizing to maintain high efficiency at the low end.

Back to the Liquid Piston engine, the combustion chambers picks up compressed intake air on one end in communication with the compression side via a rotary intake valve into the combustion chamber, and when this valve is closed, fuel is sprayed and combustion takes place. Then, rotation of the combustion chamber opens up a rotary exhaust valve in communication with the expansion chamber, allowing combusted gas to pass on to the expansion chamber. I share the same concern with everyone here regarding how to seal this rotary valve that is exposed to extremely high temperature. Both the compression and expansion side will share the sealing problem inherent in the Wankel Rotary engine, and cooling of the expander may also be an issue, as Rafael pointed out. The designer is a physicist and his son is a graduate student from MIT, so may be they know something that we don't know. But, we shall see!

Folks,

You observations and concerns are well taken, it's nice to find a forum like this where people actually know what they are talking about. One of the reasons we held back investing in Liquid Piston until now is that the design described on the web site raised exactly the concerns that you raised. A new design based on the same thermodynamics, which is not yet public, addresses many though not all of these issues and has been thoroughly vetted by a number of experts we retained to help us with our due diligence. That being said, the company is looking to hire a senior engineer to help us turn Nik's designs into a reality. I would be very grateful if you could take a look at http://www.liquidpiston.com/seniormechanical.asp and recommend candidates that might be up to the task.

There is fame and fortune to be made here for all concerned if this works. :)

Best regards,

Bill Frezza
General Partner
Adams Capital Management

I agree this engine design cannot possibly work, and I don’t mean that it will work but work inefficiently but that it probably won’t work at all. It is like a poorer design of the
idolmotor first invented by a Turkish Engineering student. The effort does not seem to have worked out but a preview of the site can still be seen here. Can the liquid piston engine still claim originality in the light of this ? In fact if you stop and think about it even the Wankel Engine that has gained such fame, was just a modification of the eccentric rotary vacuum pump, that has been around for half a century! I have often thought that Wankel must have had a good laugh up his sleeve, thinking about the huge amounts of money that had been spent on his invention. One concept engine design that really does break new ground is the Rotary Pulse Jet Engine . This engine design does not use pistons at all, has very few moving parts, is a zero pollution engine and like the Wankel produces tremendous torque ( but does so efficiently), is very compact, consisting basically of only a rotor whose maximum diameter is 12”, and fuel efficient. Anyway, please do check out the site and let me know what you think. If Possible the design might even make it into the Green Car Congress web-site. D. James.

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