NRDC Challenges Toyota on Fuel Economy Stance
ABAT to Supply Polymer Li-Ion Batteries to Wuxi Angell Autocycle

Cyclone Power Technologies Develops Waste Heat Engine Offshoot of External Combustion Engine

Cyclone Power Technologies Inc. has developed and has filed a patent application on a Waste Heat Engine (WHE), a technology off-shoot of its external combustion Green Revolution Engine. (Earlier post.) 

Like the Green Revolution Engine (GRE), the WHE is an external combustion engine. Unlike its more powerful counterpart, however, the WHE operates in a low-pressure, low-temperature range. By contrast, the GRE employs super-critical pressure (3,200 psi) and super-heated steam (1,200°F). The low-pressure design opens new commercial possibilities, according to inventor and Cyclone CEO Harry Schoell.

This feature allows the engine to run on waste heat emanating from an external source, such as the exhaust from an internal (or external) combustion engine, or the direct burning of biomass (i.e., processing garbage into methane would not be required). The WHE is also designed to run efficiently on solar heat without the installation of costly photovoltaic panels.

Such commercial applications for the WHE include boosting the power and efficiency of large gasoline or diesel-powered generators. When installed to the exhaust system of such an engine, the WHE could materially increase overall horsepower and reduce fuel consumption. Additionally, once installed, the WHE could serve as a stand-by generator should the primary system shut down.

Another major commercial application includes solar-power generators for homes or businesses. By attaching as little as 500 sq. ft. of inexpensive poly-carbonate panels to a roof, enough heat can be produced to run the WHE, according to Cyclone Power. The company believes that such a system could be installed in a home at 1/5 the price of comparable photovoltaic panel systems, while also providing home owners with a back-up power supply that current solar options do not.

The company will be testing the WHE over the following months and commencing discussions with potential licensees in the commercial truck, large generator and home builder markets. The company believes that the WHE could be in commercial production by the end of 2008.

Cyclone Power will showcase a 100 hp Automotive Engine and a 330 hp Truck Engine applications of its modified Rankin cycle Green Revolution Engine at the upcoming SAE Commercial Vehicles event. (Earlier post.)



I've been thinking about flat-panel solar thermal to electricity for years as a very cheap alternative to PV (although based on organic rankine cycle). Could be easily scaleable for cheap, storeable, on-demand electricity.

daniel billinton

It has alwasy been the holy grail of any heat engine to maximise the thermal efficiency.

Sadly most internal combustion engines used in cars rarely achieve more than 30% thermal efficiency (some turbo diesels can reach 40% or so)

the rest is lost as heat.

it's amazing that this has not been done before but it is notoriously difficult to harness thermal energy and rveret it back into meaningful amounts of power.

Mind you, even if it's a only a small proportion that is converted successfully then that could raise the overlal efficiency of the engine to 50% and imporving fuel economy and helping manufacyurers reach CO" targets.


But for solar thermal to electricity, it doesn't really matter if it's only 10% efficient. Plastic panels are cheap!

Michael McMillan

This sounds like a stirling engine to me. The main problems here are the need for maintainance, high mechanical complexity and low power to weight ratio.

It needs to be maintained so can't opperate without maintaince. It has many many parts and no trained mechanics, and is difficult to repair an abnormal problem, and when run at high tempratures, the parts rub and wear out faster.

however for waste heat, it is an option as it does in fact work with higher efficiency than a peltier juction, but a turbine is much better if given the option.


Rafael Seidl

@ Michael McMillan -

the company's GRE is a steam engine, which is fine for stationary applications if the pressure can be controlled - i.e. safely bled off in case things go haywire. The IP is really in the combustion chamber.

Since the WHE is derived from the GRE, I expect it's a smaller, less efficient but also less expensive steam engine. Less dangerous, too.

Automotive history buffs will recall that very early on, steam power competed against both ICEs and electric motors. Steam offers constant power at any engine speed, subject only to a maximum torque rating. No clutches, not even a transmission to worry about.

Unfortunately, it takes a long time for a boiler to work up a head of steam, i.e. system dynamics are unacceptable for the prime mover in an automobile. Plus, boilers explode violently in a crash. Another obstacle is weight, as thermodynamic efficiency is poor at low temperature differentials and pressures are high at high ones. Finally, you need a large radiator to shed the heat of a Rankine cycle in a mobile application, unless you blow off the waste steam and frequently take on additional water.

BMW is working on a long-term research project called turbosteamer to leverage waste heat using a rankine cycle based on ethanol as the working medium. Also, VW had IAV in Berlin develop a demonstration steam engine with reciprocating pistons but it ran smack into the weight-vs-efficiency issue.

Personally, I think hermetically sealed Stirling gensets with four free pistons and linear alternators are the way to go for those mobile applications that need the efficiency and have sufficient space to fit one. To keep pressure and weight within reason, the working medium would be hydrogen, even though that means using special materials to avoid hydrogen embrittling. The output would be electric rather than shaft power.


How does one use waste heat as a fuel? I could understand the GRE, but unless you're burning off unburned fuel, like some sort of awesome, power producing catalytic converter, I just don't get it. Plus how does this feed the power made into an ICE engine?

John Schreiber

Elliot, you need to change your frame of reference. Waste heat is not fuel, it is energy that has not been harnessed. These products aim to harness the heat energy from fuel that was previously used to push a piston down inside an ICE. Generally you would feed this recovered energy into an accessory like an A/C compressor for instance.



Any modern automotive steam concepts I've seen use flash boilers which heat only a small bit of working fluid (water) at a time, obviating the need for a teakettle-like boiler and building a 'head of steam' in seconds from a cold start.


I find thi to be very interesting. I live in SC, and I have had a solar hot water system installed (pressurized glycol type). That sucker gets HOT, and produces much more hot water than my family needs with 2 collectors (4x8 ft).

Supposedly, the he panels can collect 40,000 BTU each in a day under optimal conditions. What is that, just under 12 kwh?

I'm not sure what the efficiency of a sterling engine can achieve, but if it decent, then collecting 6 kwh per panel per day seems reasonable.

Not sure how real world performance would compare to PV or a direct solar concentrator-sterling setup. PV may do better in overcast situations.


Oh. Hmmm. Thanks John, you're right on the frame of reference, I get it now. I think I'm going to need to see a video of it in action before I'm sold on it, but at least now I understand it. Thanks.

Roger Pham


I agree with you that a hermetically-sealed free-piston Stirling with built-in linear generator is more practical than a Rankine-cycle engine for converting low-grade heat to electricity.

For low-grade heat, an organic Rankine in a closed cycle would invariably be the case, and this is subjected to the use of potentially flammable or toxic organic solvents such as Toluene, or Florinal, or Acetone, etc. and would be more bulky, since condensation at lower temperature than steam at 1 atm would require a rather bulky heat exchanger, with plenty of change for leakage eventually with time. Plus, more complication including pumps and a lot of valves, crankcase, bearing etc...
whereas in a free-piston Stirling, a linear generator designed to harness power directly from a reciprocating piston has almost no mechanical loss, and much lower piston friction due to the lack of side force on the piston skirt in the absence of the crank mechanism. An organic Rankine cycle cannot utilize high heat because the working fluid will decompose, while the Hydrogen-Stirling can use much higher temperature for higher thermal efficiency.

A solar heat collector powering a free-piston Stirling would be real neat, since you can use natural gas to generate electricity during sun-down period, and use the waste heat for your hot water storage tank, or use the waste heat to heat your house in the winter while selling the excess electricity back to the grid to charge up someone else's BEV's. Combined solar electricity and distributed generation with combined heat and power generation (CHP) all in one system and one investment much lower than a PV panel system with inverters of equivalent output.

A hermetically-sealed Stirling engine can be built to last for tens of thousands of hours with minimum maintenance, if properly designed, and not subjected to too high temperatures.

Rafael Seidl

@ Roger -

solar-powered free-piston Stirlings already exist, albeit at low power ratings.

A German company has developed a system for storing solar heat energy using magnesium hydride. This permits solar-powered operation of a medium-temperature stirling engine at any time, even at night. The thermochemical store eliminates the need for a bank of batteries.


3M makes HFE fluids with low boiling point, non flammable and not as harmful for the environment as CFCs. BMW uses ethanol, which is cheap, but flammable. But them again, automobile fuel is flammable and direct injection pressures are high. I guess it is all in how you look at the safety of the fluid you use.

Roger Pham

Thanks, Rafael, for the link to BSR solar technologies. Their ideas appear quite promising, though not much details are released. Their claim of 36% efficiency for a 300-C Stirling is very good, and if everything works out reliability and cost wise, Stirling Solar thermal electricity with thermal energy storage will make a big contribution toward renewable energy future, greatly displacing coal and nuclear electricity in areas of good sunlight irradiation.

Mark Goodson


The automotive cyclone engine is a 100 hp, 6 cylinder, 618 cc, uniflow, radial piston engine with 700 ft lbs of starting torque. Engine starts in only 15 seconds from cold and is fully warmed up in only one minute (faster than Diesels). The entire system weighs less than half that of conventional automotive systems of equal power. The condenser is full contained in the compact unit and is extremely compact. There is ZERO danger of a boiler explosion. The thermal efficiency of the Cyclone is in the Diesel range and peak effiency was measured at 36%. The water/steam system is fully contained with ZERO need to add water. Power is controlled by steam inlet valve timing and moderating compression ratio. The steam pressure is not throttled but remains constant at 3200 psi with temperature of 1200F.

Email me if you want more info, but please do not make further comments on this technology until you understand it.



You may have succeeded in alienating about half of the people that visit this site. Way to go. I can see diplomacy is your strong point.

Roger Pham

I certainly can sympathize with your frustration at times.

However, these "unprepared" responses from this forum, or responses by less-than-experts, to put it politely, can give you valuable feedback on how to go about preparing for the promotion of your project. Many potential investors have little technological background, and therefore, the advantages of new ideas must be hammered on and on relentlessly in layman's terms and approaches before they will sink in.

It is only human nature to have pre-conceived notions or biases, especially against new and revolutional ideas. Howver, through patience and persistence, these unfavorable notions will [sometimes] slowly change.

Mark Goodson

My comments should have been directed at Rafael and not Michael, so sorry for the misunderstanding Michael. But my comments stand.

I am not associated with Cyclone Power Technologies in any way. I am only aware of what they've done.

Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Your comment could not be posted. Error type:
Your comment has been posted. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.


Post a comment

Your Information

(Name is required. Email address will not be displayed with the comment.)