Crower six stroke

The Crower six-stroke engine is a claimed high-efficiency variant of an internal combustion engine under development by Bruce Crower.
Two extra strokes are added to the customary internal combustion engine four stroke Otto cycle, which makes a six stroke engine. A third down-stroke is a "steam stroke" and a third up-stroke exhausts the expanded steam while venting heat from the engine.
The engine cold starts on the Otto cycle, coasting through the fifth and sixth strokes for a short period. After the combustion chamber temperature reaches approximately 400 degrees Fahrenheit (200 °C), a mechanical operation phases in the fifth and sixth strokes. Just before the fifth stroke, water is injected directly into the hot combustion chamber via the engine's fuel injector pump, creating steam and another . The phase change from liquid to steam removes the excess heat of the combustion stroke forcing the piston down (a second power stroke). As a substantial portion of engine heat now leaves the cylinder in the form of steam, no cooling system radiator is required. A proportion of the energy that is dissipated in conventional arrangements by the radiator in a water-based cooling system has been converted into additional power strokes.
In Crower's prototype, the water for the steam portion of the cycle is consumed at a rate approximately equal to that of the fuel, but in production models, the steam will be recaptured in a condenser for re-use. Heat will be available from the condenser to provide interior heating of the vehicle, much as a conventional heater core works in cars and trucks today.
Positive aspects
Crower claims a 40% reduction in fuel consumption and reduced exhaust emissions per a given power range.
The principal advantage of the six-stroke design is its ability to extract work from heat that is ordinarily lost through the cooling system of a conventional engine. Since the steam strokes have the side-effect of cooling the engine internally, this will allow the use of much higher compression ratios, allowing the full potential of a fuel to be extracted. This internal cooling allows high compression ratios once usable for only short term applications (such as race engines) to be used in regular, long-running time scenarios without environmentally harmful anti-knock chemicals. Ultra-lean air/fuel mixtures, desirable for low emissions and high efficiency, may be used since excess heat, undesirable in other engine architectures, can likewise be harnessed in six-stroke applications.
The weight and power loss of most conventional cooling system parts, such as the fan, radiator, and coolant pump, can be eliminated. On a large diesel truck, these parts make up approximately a quarter of the engine's weight. At least a portion of this advantage is lost if water is recovered from the exhaust through a condenser.
The mechanical modifications needed to "six-stroke" a small air-cooled industrial diesel already being manufactured are far less complicated than any hybrid system. Many maintenance features of this engine would be parallel or identical to the knowledge base of mechanics well-versed with gasoline, diesel, and racing engines.
Physical engine size reduction (per a designated power rating) is possible as one third of the engine strokes produce power (in the Crower six-stroke), instead of one quarter (in the Otto cycle). This, and the extra power stroke being provided by using water instead of fuel, means there is a significant improvement to the fuel efficiency and pollution within a given power range, and this is in a field where small improvements create great interest.
The higher percentage of power strokes may allow lower working speeds, with higher torque output at lower and broader rpm ranges. Lower working speed might allow designs with greater crankshaft diameter, for engine dimensions with inherently more torque potential.
As a high pressure steam engine that does not need a certified pressure boiler, the related hardware complexities, dangers, and weight penalties and certification requirements are removed.
Obstacles and problems
A warm-up period would be needed in all automotive applications. Power and efficiency is reduced during the warm-up period due to the coasting 5th and 6th stroke.
Injecting relatively cold water onto a hot metal piston can damage it over time from thermal expansion and contraction, especially if the heat of combustion is significantly increased compared to a four-stroke engine. Depending on the actual temperature of the steam compared to exhaust gasses, this could also potentially apply to the engine block, exhaust headers, and any turbochargers.
A steam-free cool down period is needed to clear water/steam from the engine.
Cold climate anti-freezing measures would be needed in the water reservoir.
Oil contamination, from the water/steam portion of the cycle, is an obstacle to be dealt with, though additional piston/cylinder sealing rings can be easily added and special oils used. Also, data from lubrication oil engineering systems for steam turbines is readily available to help identify likely concerns and possible "well-researched" remedies.
The weight of an oil separator and a water condenser are likely additions, although these will be far smaller and lighter than a conventional cooling system.
A condenser would likely be a major exhaust restriction, while a separate water tank would have significant weight and space penalties (roughly the same as carrying twice as much fuel). Potential solutions include a dedicated steam-exhaust port, with the steam sent to a condenser and the fuel exhaust sent down its usual path. A turbocharged engine could have a post-turbo valve timed to do the same thing, but allowing both steam and the exhaust to spool the turbo.
Endurance testing will likely identify components that may need to have upgraded materials designated, such as possibly using stainless steel for the valves, cylinders, and rings.
Prior art exist to Crower's invention, but no preexisting six-stroke patents were mentioned in his patent application.
As of July 2009, no patent has been awarded.
Possible engine configurations and applications
The Crower six-stroke is not the same technology as water injection, where water is added to the incoming air/fuel mixture to allow higher power output through increased pressure.
The "steam" power stroke and the "burning hydrocarbon" stroke may not produce the same amount of force as each other. A one-cylinder engine would run much smoother with a relatively heavy flywheel to smooth pulsations, much like the early large one-cylinder diesel industrial factory engines.
One down-stroke does not provide any power, and, as mentioned above, the other two down-strokes may each provide different levels of power. This suggests the most compact configuration that will provide an inherently smooth running operation is an in-line three-cylinder engine. Of course, many other configurations and cylinder quantities may work - a boxer engine would remain balanced regardless of the number of strokes in its operation cycle.
Although the Crower cycle could be made functional with a variety of fuels and RPM ranges, steam theory suggests it would be very useful when coupled with a diesel cycle, which performs well in low-rpm long-stroke applications and at high compression ratios.
A Crower cycle engine may prove to be useful as a passenger vehicle power plant. If meeting automobile emissions standards proves troublesome, the design may prove useful in heavy engine applications such as transport diesel trucks, heavy equipment (bulldozers, etc.), buses, and stationary power generators.
Related US Patents
*1339176 Internal combustion engine May 4, 1920. Leonard H. Dyer invented the first 6-stroke internal combustion/water-injection engine in 1915.
*3964263 Six cycle combustion and fluid vaporization engine Jun 22, 1976
*4143518 Internal combustion and steam engine Mar 13, 1979
*4301655 Combination internal combustion and steam engine Nov 24, 1981
*4433548 Combination internal combustion and steam engine Feb 28, 1984
*4489558 Compound internal combustion engine and method for its use Dec 25, 1984
*4489560 Compound internal combustion engine and method for its use Dec 25, 1984
*4736715 Engine with a six-stroke cycle, variable compression ratio, and constant stroke Apr 12, 1988
*4917054 Six-stroke internal combustion engine Apr 17, 1990
*4924823 Six stroke internal combustion engine May 15, 1990
*6253745 Multiple stroke engine having fuel and vapor charges Jul 3, 2001
*6311651 Computer controlled six stroke internal combustion engine and its method of operation Nov 6, 2001
*6571749 Computer controlled six stroke cycle internal combustion engine and its method of operation Jun 3, 2003
*7021272 Computer controlled multi-stroke cycle power generating assembly and method of operation Apr 4, 2006

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