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Cyclone Power to Showcase External Combustion Engine at SAE Event

20 September 2007

Cyclone Power Technologies will showcase two automotive applications of its external combustion Green Revolution Engine (earlier post) at the upcoming SAE Commercial Vehicle Convention in Chicago. The company will display a 100 hp Automotive Engine and a 330 hp Truck Engine, which will be installed in a full truck chassis for the first time.

Cyclone’s engine is a multi-fuel capable engine that uses an external combustion chamber to heat a separate working fluid, de-ionized water, which expands to create mechanical energy by moving pistons or a turbine.

The engine’s combustion chamber creates a rotating flow that facilitates complete air and fuel mixing and complete combustion. Less heat is also released. Exhausted gases run through a heat exchanger before leaving the engine, lowering the temperature at release.

The company proposes a number of configurations of the engine, including small single-cylinder units; a two-cylinder opposed piston engine; and three-, four- and six-cylinder radial engines.

The company most recently concluded its testing with low octane gasoline. The design of Cyclone’s fuel injector, which works with a primary and secondary air source, maintained a low temperature flame front with an extremely clean burn, according to the company.

As a result of the low temperature burn of the gasoline, the Cyclone engine produced little or no NOx, and kept carbon monoxide levels at a minimum. Additionally, the cylindrical design of the engine’s combustion chamber effectively eliminated much of the unburnt hydrocarbons from the fuel source, according to the company.

Cyclone has also tested a bio-fuel, d-Limonene, made from orange peels; biodiesels produced from palm oil, cotton seed oil and chicken fat; and three grades of ethanol produced from corn.

September 20, 2007 in Brief | Permalink | Comments (30) | TrackBack (0)


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So... it's a closed-loop steam engine?

"Cyclone’s engine ... uses ... combustion ... to heat a separate ... water, which expands to create mechanical energy ..."

Bring back the Stanley Steamer. My father, of blessed memory, loved them. He loved to tell me about how quite they were and how much torque they could generate at zero speed.

First, Grandma's Baker electric, now the Stanley Steamer. Everything old is new again.

But you had to wait for that Stanley Steamer to head up to boiling point to build up steam pressure before you could go anywhere. I doubt you'd see many of these engines in the average car for just that reason. This is why ICEs won out in the first place.

Unlike old steam locomotives (and the Stanley Steamer) which had to heat a lot of water before starting off, these engines have flash steam boilers which only heat a small amount of water at a time and can warm up in a matter of seconds.

Cool to see that this initiative is still alive and kicking.

So the cyclone engine has high specific power, can run on many different fuels, and has clean(er) emissions.

But the inevitable question is how efficient it is in terms of what percent of the fuel's potential energy is actually realized into mechanical work? Also - how is the engine lubricated, and how does one avoid the oxidation and corrosion caused by the water?

They're using de-ionized water - so no corrosion and oxidation - and I remember reading that its lubricated by water as well.

Upon reviewing of website, it appears that the Cyclone steam engine is of sound design principle and ingenious execution, far more advance than previous steam engines of antiquity.

However, only one thing that remain unproven: How good is lubrication by water? At such high power concentration per displacement (3hp/cid) and at 3200 psi peak pressure, surely the frictional stress on the metal surfaces is much stronger than that of an ICE with peak pressure of ~1000 psi and BMEP ~120psi range. And yet, the ICE piston, cylinder and bearing are supported by a much thicker layer of oil with much higher lubricity. If this water lubrication works, it will open up the way for more efficient ICE with less heat loss to coolant, since the engine (ICE) now with water lubrication can run at much higher temperature and needs much less cooling if at all. Air cooling will be more than sufficient if much less cooling is required, leading to lighter and lower cost ICE.

Thermodynamically speaking, with peak super-heated steam temperature of 1200 F, or 648 C and with a single stage adiabatic expansion, one can expect no more than ~35% thermal efficiency, even with minimum friction loss and heat regeneration. Even the best power plant steam turbines operating at comparable super-heated steam temperature with multiple reheating stages and meticulous attention to heat recycling can achieve ~40-45% thermal efficiency. This, in comparison to a simple truck diesel engine at 42% efficiency, or a power-generating diesel engine at nearly 50% efficiency.

This is perhaps the reason why no listing of thermal efficiency at the website.


I found a mention of thermal efficiency at the back end of Cyclone's PDF:

"Burning a gaseous fuel which is pre-expanded loses a lot of power where as using hydrogen in a cyclone is a plus.

Assume JP-8 @ 6.819 lbs per gal fuel burn at .06 gal per hp per hr
19,810 fuel BTU per lb
.06 X 6.819 =.40914 X 19,810 = 8105.063
2545 / 8105.063 = .314 or 31.4% thermal efficiency ±10%

Whereas, diesel is about 30% to 35% and gasoline is 20% to 25% after a hundred years of development."


I'm a bit confused about thermal efficiency and its importance in regard to the Cyclone. It'll run on many combustible things, so in the event that it gets the same mileage as a current ICE, the ability to use cheaper fuel would be advantageous. It pollutes a very miniscule amount, and it makes 2.5 hp/ cubic inch. So where does thermal efficiency come in? And how unorthodox is the water lubrication? Is there any precedent?

This whole thing seems almost too good to be true. The idea of an "external combustion engine," that runs on anything and can be tied perspectively to steam engines, is more marketable than an electric one. Especially in the US and double especially when it looks like it's straight out of the 60's.


This engine could perhaps be interesting as a range extender for series plug-in electric vehicles. Its characteristics of multi-fuel, low emission and low noise are important for such an application. Instant torque is not important for a range extender. If it also is efficient and can be produced at low cost it will be really interesting. Once the batteries are ready for plug-in vehicles the development of chemical fuel engines will be mostly about creating good range extenders. When these batteries are made it should be quite possible that the ICE will get really tough competition from engines such as the Stirling engine, see I am not an engine expert so I could be wrong on this matter.

Uhhhh, Stirling cycle anyone? I can't see anything novel here other than using water with a phase change to steam....

it is not stirling cycle, it is a modified Rankine cycle.

I just learned that sterling engines have very low specific power so unless that can be dramatically improved that will disqualify them as range extenders for future plug-in vehicles.

Organic rankine cycle is going to be one of the big, big things this century.

"This engine could perhaps be interesting as a range extender for series plug-in electric vehicles"

I was thinking the same thing myself. If this is a truly "direct drive" engine that doesn't require a gear reduction, it would be efficient for mounting directly to a generator, similar to how power plant steam turbines are mounted.

You could probably use it in parallel hybrids as well, but it would have to run through the power split device.

AES, Elliot, et al,

Thanks to the info on thermal efficiency. Indeed, I should have mentioned also that thermal efficiency in the 30's % is quite good, considering that steam engine does not need a transmission, hence no loss via the transmission internal friction.
Steam engine develops huge amount of torque even at very low rpms, and since this engine is capable of above 5,000 rpms with low internal friction, no transmission would be needed. No need for engine idling, either, at traffic stop. These are more advangages of this engine in comparison to more expensive and heavier HEV drive train with comparable overall thermal efficiency.

I wish that the Cyclone company would publish some data on engine wear characteristic while using water as lubricant. For example, piston mass measured in 1/10 of a gram before and after 100-500 hours of endurance testing. This would go a long way in convincing potential investor as to the viability of this concept.

AES, the Cyclone operates in the efficiency range of automotive Diesel engines... 15-20% more efficient than gasoline 4 stroke internal combustion engines.

The peak efficiency of the Mark V 100 hp 6 cylinder radial Cyclone was measured at THIRTY SIX PERCENT (36%). Advantages of the Cyclone in automotive use include the fact that the Cyclone is more efficient at part load. Also, as Roger pointed out there are fewer losses in power transmission (more work generated at the shaft is transmitted to the wheels in the Cyclone system vs. conventional systems). The Cyclone engine does not idle. When the vehicle stops, the engine stops.

The Cyclone engine powered vehicle will see greater mpg than an identical vehicle powered by a conventional gasoline engine. The Cyclone power plant will also be lighter. There will be no transmission, no drive shaft, no radiator, no flywheel, no oil pump, no oil, no starter motor, no computer, no catalytic converter, no other expensive emissions controls equipment (half the cost of current automotive power plants). The emissions of a Cyclone pass CA smog standards for the year 2020... with no emissions controls at all. The cyclone has been fueled so far with gasoline, acetone, methanol, ethanol, E-85, E-10, fuel oil, kerosene, orange oil, propane, butane, diesel, biodiesel, vegetable oil, coal dust, wood flour, and can even operate on concentrated solar energy.

Sorry, but I'm not done yet plugging the Cyclone ;-). I want to point out that the physics of steam power make it the superior choice for automotive propulsion. The problem has been an engineering deficiency. The Cyclone is still in its infancy and already it is superior to conventional automotive power plants.

There are two primary problems that caused the IC engine to win over steam for automotive applications. The first is the problem with lubrication. Oil was required and this greatly limited the temperatures at which the steam systems could operate, and efficiency suffered greatly. Second, and perhaps even more important, is the fact that the condensing systems were very bulky and inefficient. The Cyclone has solved both problems elegantly. The working fluid system is fully closed with no oil lubrication. The consenser is a centrifugal system of spinning aluminum discs that raise the saturation temperature and allow for more efficient heat transfer. Also, efficiency is boosted further by transferring heat from the steam cylinder exhaust to the air entering the combustion chamber and the water before it enters the steam generating tubes.

NOTE: The slow starting characteristic of automotive steam systems was solved by the Doble steam car which could start from cold in less than a minute. But it still suffered from relatively low thermal efficiency and a bulky condensing system. Still one hell of a machine though.

@ Mark -

"Advantages of the Cyclone in automotive use include the fact that the Cyclone is more efficient at part load"

At what point in the power band does that peak efficiency occur, though? Is it merely more efficent at part load than a conventional ICE, or is it that it's optimum efficiency PERIOD is at part load?

Peak efficiency in a steam engine with good insulation of its working cylinders occurs when the steam is allowed to fully expand to atmospheric temperature. Of course, when the steam condenser is below atmospheric pressure, let's say that the steam condenses at 60 C, then the steam vapor pressure at this temperature is only ~5 psi ( I have to look at the table for the exact number) the atmospheric pressure in the crankcase will push the piston upward to complete the exhaust stroke, imparting more power to the crankshaft even in the exhaust stroke. In an uniflow design, in which the steam goes in from the cylinder top and exit via the cylinder bottom into the crank case via a valve in the bottom of the piston, then, maximum expansion can be even below atmospheric pressure. IF you take into account friction, then your expansion ratio has to be less in order to counter the loss via internal friction. At any rate, I would predict that peak efficiency occurs at much lower power setting than in an ICE, since a steam engine does not lose heat via coolant, and the residual heat from exhaust steam is regenerated back into the water going into the boiler loop. Depending on power rating and peak pressure and peak temperature, I would predict that peak efficiency on the Cyclone engine occurs at 1/6 to 1/8th of maximum power setting.

From what little I’ve read about conventional steam engines, the maximum torque is attained by timing the admission valve for late cutoff (steam is admitted to the cylinder for much of the power stroke). This allows for greater torque without a transmission, but at the expense of efficiency. If the requirement is for less torque, the admission valve cuts off the steam earlier on the power stroke (say 10% of the stroke) allowing nearly full expansion and greater efficiency. Does the Cyclone’s engine accomplish maximum torque in this same way? If so, what efficiency penalty is there at peak torque and is the condenser sized for this greater load?

Great questions! Roger touched on the most important factor affecting efficiency in steam engines. It's all about expansion. However, I would like to add that a pressure differential between the cylinder and the crank case is required to ensure sufficient steam is exhausted. The expansion, therefore, must be limited to ensure sufficient steam pressure remains once the exhaust ports are uncovered by the piston.

Uniflow steam engines are more efficient than their counterflow cousins because the compression of residual steam in the cylinder raises the temperature at the cylinder head before the next charge of high pressure steam is admitted. A counterflow steam engine exhausts the low pressure steam through the cylinder head which cools it... when the new charge of steam enters on the next cycle the cooler cylinder head robs heat from the steam... this condenses some steam and more steam is needed to establish the same pressure... more steam (i.e. heat) for the same work = less efficiency by definition.

Highest efficiency is reached where the steam is allowed to expand the most, and this occurs where compression ratio is highest. This is also true with IC engines. However, the steam engine must also admit steam while the piston approaches the cylinder head, and this must be done very quickly. At higher rpms there is not much time to establish full pressure. Without maximum pressure established (when piston still remains at or near TDC) there cannot be maximum expansion... try to expand a low pressure charge too much and there won't be enough pressure to exhaust any steam. The best combination of both very high compression and very high steam pressure cannot be achieved where rpm is very high because the valve is not opened long enough. Hence, the greatest efficiency will be seen at lower speeds.

Now, wherever steam expansion is highest the mean effective pressure in the cylinder will be lower (steam pressure falls as it expands). The combination of high expansion/lower MEP/lower torque and lower rpm should put the most efficient output roughly where Roger places it. Incidentally, this output roughly corresponds to where an automobile operates on flat terrain at highway speeds... where most cars spend their time. Perfect for high real world mpg... and one of the reasons that I want to see the Cyclone in a car soon.

The Cyclone uses a steam generator (boiler) that is maintained at a constant pressure of 3200 psi and within a narrow temperature band of about 1150-1200F. The extremely high density of steam at this pressure allows high pressure to be established very quickly and also allows for very high steam expansion. These are the factors necessary to run a highly efficient steam engine that also sees high performance in a small package. Engine output is controlled primarily by varying the compression ratio through an auxiliary cylinder and piston that taps off the cylinder head... check out web site, there's great pic of this configuration.

Thomas, the cyclone cutoff is a function of rpm. There is no valve advance at very low speed (and at rest), and the cutoff is very long here. This ensures that when steam is admitted while at rest at least one cylinder will have steam admitted when steam is applied (self-starting). The cutoff rapidly changes and inlet valve timing is advanced with increasing rpm. This explains the monstrous starting torque of 700 ft lbs in a 620 cc engine (6 cylinder, 2" bore, 2" stroke)... 3200 psi steam admitted staight to the cylinder with very little expansion. Efficiency would be low under these conditions, but there is a reheat stage at these low speeds where compressed steam is readmitted to a section of the steam generator tube to pick up additional heat.

I just realized that I didn't quite answer AES's question directly. The Cyclone, and in general most steam engines, is most efficient at part load. That is, the thermal efficiency is actually highest at part load. Another significant benefit of the Cyclone and other steam engines is the fact that the engine does not idle. There are still a few Doble steam cars in operation today, and one owner (who happens to be an engineer) notes that his Doble sees higher mpg in city driving than conventional modern vehicles of similar weight. The thermal efficiency of the Doble power plant is roughly half that of the Cyclone, so do the math... it looks good!

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