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Updating the Steam Engine: the Cyclone

An application of the Cyclone.

Cyclone Technologies LLP, developer of the Cyclone external combustion engine, received an Automotive Engineering International (SAE’s publication) Tech Award at the SAE World Congress in Detroit.

The Cyclone modifies the traditional Rankin cycle steam engine to deliver the use of super-critical pressure (3,200 psi) and super-heated steam (1,200° F)—normally found in high-efficiency electrical power plants—in an efficient, compact package suitable for a vehicle.

A sketch of the engine from the patent application.

The Cyclone. The engine, which uses water as both working fluid and lubricant,  consists primarily of a condenser, a steam generator and a main engine section having valves, cylinders, pistons, pushrods, a main bearing, cams and a camshaft.

Air pre-heated in a heat exchanger is mixed with fuel. An igniter burns the fuel charge as the flames and heat are directed in a centrifuge within the combustion chamber.

The combustion chamber heats the steam generator to produce high-pressure, super-heated steam.

A rocker and cam design which serves to open and close a needle type valve in the engine head controls the speed and torque of the engine. When the valve is opened, high-pressure, high-temperature steam is injected into the cylinder and allowed to expand as an explosion on the top of the piston.

Exhaust steam is directed through a condenser, in a centrifugal system of compressive condensation, consisting of a stacked arrangement of flat plates. Cooling air circulates through the flat plates, is heated in an exhaust heat exchanger and exits into the furnace. This reheat cycle of air greatly adds to the efficiency and compactness of the engine.

Efficiency. The efficiency of the Cyclone is based primary on three factors:

  • Heat Regeneration. Numerous design innovations significantly reduce the heat losses, cumulatively increasing the efficiency of the engine.

  • Super-Critical Liquid. Pressures in the range of 3,200 psi with temperatures of about 1,200° F cause super-critical vapor to act as a fluid. Maintaining the super-critical pressure, in the centrifuge process, eliminates the turbulence, backpressure events, and heat spikes that can occur during other less efficient types of super-critical processes. At these higher temperatures and pressures, the super-critical fluid carries more heat energy to the motor it powers. The Cyclone Engine is a piston engine with a special valve mechanism allowing it to operate at fluid pressures, thereby gaining multi-advantages: greater simplicity, reliability and enhanced power.

  • High compression. The Cyclone Engine is an external combustion/internal expansion engine, using variable timing, variable compression ratios and multiple heat exchangers to increases in engine efficiency. A reheat stage is included at lower compression ratios.

Cyclones can use almost any liquid or gaseous fuel. Power produced we be based on the energy content of the fuel in use. The design of the engine obviates the need for a separate cooling system.

The basic Cyclone engine is a compact, one-piece unit that can develop 3 hp per cubic inch of displacement, compared to a ballpark one horsepower per 1.5 cubic inches of displacement for a gasoline engine.

A Cyclone with three or more cylinders is self-starting—i.e., no flywheel needs to be turned by a starter.  Pulling the throttle lever activates flow through individual needle valves situated at each cylinder. From a dead stop, the engine attains its highest torque within less than one crankshaft revolution and transitions to engine horsepower at 5,250 rpm giving the Cyclone a remarkably robust power band.

The Cyclone Engine exhausts into the condenser, where the vapor is totally contained, not into the atmosphere. As a result, it requires no exhaust system muffler or catalytic converter.

Vibration is controlled because the crankshaft is counter weighted and the pulsations are balanced by equal offsetting pressures, thus requiring no harmonic dampener.

The Cyclone Engine is smaller than four-stroke internal combustion engines, with fewer parts. However, the materials handling the high operating temperatures and pressures are more expensive. At similar economies of scale, the two types of engines should be comparable in cost.

Applications. Harry Schoell, the inventor of the Cyclone, forsees a large range of applications for his engine, from small electrical generators in the 1 kW range up through medium-size cyclones for light-duty vehicles, large Cyclones of up to 1,000 hp for the heavy-duty diesel market and beyond to larger ships and generators.




any word about rough fuel efficiency ratings, warm-up period, life-cycle reliability, unloaded engine acceleration?


Whats next? back to horse?


I've been looking for a modern buggy.


It burns fuel (to produce steam) so how can there be no exhaust?

Tim Russell

It said it exhausts to the condenser so I guess it condenses the combustion vapors but then what happens to the resulting condensate?


I wonder if this could be used as a generator for electricity. Depending on noise and fuel efficiency, this might be a good solution for remote places without electrical lines or damamged lines.

Mark A

Interesting development. Steam engines were highly developed for trains at the beginning of the twentieth century, having power strokes on the up and down (or forward and back) strokes. Their limitations back then were their size, and that eras limited metallurgical knowledge. I always thought steam could have been a major player in the automotive world, with developed corresponding advances over the years, had it not been for cheap gasoline at the birth of the automotive age.

So it is now interesting to see these types of developments. I, too, would like to see efficiency numbers. But again, another potential option in a market that will ultimately determine its own destinity. Just give us more options.


their website is brief, but to the point. the want to target every power market between 20 and 4,000+ hp.

sounds like it is time to talk to a businessman and find 1 market to start with.

multifuel generators for serial hybrid H1s for the military, perhaps?

Rafael Seidl

There have been numerous attempts to revisit the steam cycle for automobiles. Its combustion is continous and can therefore be much cleaner than that of any reciprocating engine design. Note that this is only true if the fuel is free of contaminants such as sulphur and the burner designed for it. Steam power provides high low-end torque and a hyperbolic drop-off beyond a certain corner point - ideal for a vehicle.

Packaging has apparently been addressed in this design. However, overrall weight and, especially, crash safety are always issues - steam explosions were the reason Stirling, Benz and Daimler focussed on gas engines.

One serious downside is that it takes significant time to build up a head of steam. Therefore, a steam motor responds poorly to load changes (acceleration and deceleration demand from the driver). It is therefore best suited to powering vehicles traveling mostly at constant speed, e.g. ships, locomotives or large trucks on the freeway.

You can mask the lag with a hybrid system, which can also recuperate during braking and soak up the residual enthalpy in the boiler after you park the vehicle. As a result, the steam boiler and motor can be far smaller. However, the expense and weight of the entire system will be substantial.

tom deplume

The biggest problem facing an automotive steam engine is the condensor which these guy's claim to have solved. Now show me doing the job in a Pheonix summer and I will be impressed.


As per Rafael, external combustion can be great for controlling emissions (except for CO2). If they've solved the condenser problem, then the remaining major questions are efficiency and cost. High efficiency means materials exposed to sustained high temperatures which necessitates expensive, exotic metals or ceramics, etc. The beauty of the ICE is that exposure to very high temperature gases is alternated with exposure to cool gas, allowing the use of cheap materials in a relatively fuel-efficient engine.

Since limiting GHG will increasingly become the prime consideration, efficiency vis-a-vis comparable ICE engines should determine the viability of this approach.

Rafael Seidl

Nick -

pls provide a link to a steam motor or turbine that requires ceramics. The temperatures involved in handling steam are far lower than those in ICEs or gas turbines.

Mark A

Heres an interesting link:

As far as waiting to build up steam pressure, I am not sure that would be much of a problem, considering even the cheapest automatic coffemaker can build up steam pressure/hot water, in as little as 5-10 seconds. Plus this engine, I would think, would inheritently stay warm overnight except in the extremest of cases. Perhaps if the efficiencies are there, they could run overnight in generator mode to connect to the grid somehow. Would be interesting to see this developed, promoted in some fashion.


Mike Mulligan & (Mary Ann ) His Steam Shovel

----Has Anybody Read This Book?

I Loved this book when I was 5.



If this engine is light and efficient enough, it could be used to extend the range of EVs. An efficiency of 20% would enable to make the car competitive even on highways...
It is a great hope, but the security issue is stil there.

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