The Crower six-stroke engine or Crower Cycle is a concept under development by Bruce Crower.

Two extra strokes are added to the customary internal combustion engine four stroke Otto cycle. A fifth down-stroke is a "steam stroke" and the sixth is to exhaust the expanded steam while venting heat from the engine. The four-stroke cycle of an internal combustion engine is the cycle most commonly used for automotive and industrial purposes today ( cars and trucks, generators, etc). ...

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 (204 °C), a mechanical operation phases in the fifth and sixth cycles. Just prior to the fifth-cycle, water is injected directly into the heated combustion chamber via the converted diesel engine's fuel injector pump, creating steam and another power stroke. 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. Energy that is dissipated in conventional arrangements by the radiation cooling system has been converted into additional power strokes. A combustion chamber is part of an engine in which fuel is burned. ... A power stroke is, in general, the stroke of a cyclic motor which generates force. ...

Crower has indicated that the volume of water used by the initial prototype configuration is at approximately the same rate as the amount of gasoline consumed. The water is a "total loss" and is not recaptured from the exhaust. Thus the water storage tank should be the same size as the fuel tank and should be refilled at the same time as the fuel, although the engine would still function without water. (This is evidenced by its ability to run without steam during its "warm-up" phase. However, it would overheat quickly running this way.) He has also indicated that water of a high level of purity is required.

Positive aspects:

Crower claims a 40% reduction in fuel consumption and reduced exhaust emissions per a given power range. Fuel efficiency relates the efficiency of converting energy contained in a carrier fuel to kinetic energy or work. ...

The base engine for modification uses a high compression ratio which is essential for compression ignition. This high ratio is useful in extracting the full potential of ethanol (one of many fuels that this engine may use). These high ratios are a dramatic alteration over present multi-fuel engines which typically use a 10:1 compression ratio, similar to gasoline engines.^{[citation needed]} Bold text The compression ratio is a single number that can be used to predict the performance of any engine (such as an internal-combustion engine or a Stirling Engine). ... This article does not cite any references or sources. ... Ethanol, also known as ethyl alcohol, drinking alcohol or grain alcohol, is a flammable, colorless, slightly toxic chemical compound, and is best known as the alcohol found in alcoholic beverages. ...

The cooler piston top and reduced combustion chamber temperature may allow gasoline to be used at very high compression ratios or without environmentally harmful anti-knock chemicals, which are now in universal use with conventional automobile gasoline engine applications. Under these circumstances, far more energy from the gasoline fuel could be converted to horsepower output.^{[citation needed]}

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 may weigh as much as a thousand pounds.

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, coupled with the fact that the extra power stroke is provided by using water instead of fuel means there is a significant improvement to the fuel efficiency and pollution per a given power range, and this is in a field where small improvements create great interest.^{[citation needed]}

The higher percentage of power strokes may allow lower operational speeds, with higher torque output at lower and broader rpm ranges. Lower operational speed might allow designs with greater crankshaft diameter, for the use of engine dimensions with inherently more torque potential.

This is the only steam engine that does not require a certified pressure boiler and related hardware complexities, dangers, and weight penalties. ^{[citation needed]}

Obstacles or problems:

A warm up period of at least several minutes would be required in all automotive applications. Power is reduced during the warm-up period.

A steam-free cool down period is required to clear water/steam from the engine.

Cold climate anti-freezing electrical resistance heating systems would be required in the mobile water supply.

Oil adulteration, from the water/steam 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 lube 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.

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.

Possible Engine Configurations and Applications

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 the other two down-strokes may each provide slightly 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 can be made to work.

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.

A Crower Cycle engine may eventually prove to be useful as a passenger vehicle power plant, but even if its implementation in that field proves troublesome, there are several less-regulated fields in which it should prove to be immediately successful, including transport diesel trucks, heavy equipment (bulldozers, etc), busses, and stationary power generators, among others. ^{[citation needed]}

A large number of municipalities are beginning to generate electricity by burning the methane gas that is emitted by the decaying trash in landfills. Doing this consumes a greenhouse gas, and reduces the amount of electricity that needs to be produced by burning coal. This type of methane is often described as too "wet" and "dirty" to burn in the preferred gas turbine generator, so it is often burned in large V-12 locomotive diesel engines that have had a sparking system added. The Crower Cycle would improve the fuel consumption and emmissions per a given amount of power generated, which is significant considering today's stringent environmental concerns over increasing electrical generation needs.^{[citation needed]}

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External links

• Autoweek article, Feb. 23, 2006
• Another six stroke engine concept