Crower six stroke

The Crower six-stroke engine is a concept under development by Bruce Crower, known for the invention and manufacture of many devices now used in automotive acceleration racing (see National Hot Rod Association and drag racing).

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 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 ( 200oC ), 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 engines 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.


Positive aspects:

Crower claims a 40% reduction in fuel consumption and reduced exhaust emissions.

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.

The cooler piston top and reduced combustion chamber temperature (heat is extracted in the conversion of injected water to steam) 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. (Very high compression ratios are used in racing engines as a means to increase power.)

The weight of most conventional cooling system parts can be eliminated.

The power loss to operate fans and pumps is eliminated.

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.

The modification to water injection could be done simultaneous to the use of all liquid and gaseous fuels now in widespread use (diesel, gasoline, ethanol, methanol, LP gas, natural gas as well as all plant-derived oils) in the conventional four-stroke portion of the engine.

Physical engine size reduction is possible as one-third of the engine strokes produce power (in the Crower six-stroke), instead of one-quarter (in the Otto cycle).

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 system is ideal for heavy industrial applications and electric utility peaking plants where "dirty" internal combustion plants are commonly used for stand-by generation.

This is the only "steam engine" that does not require a certified pressure boiler and related hardware complexities, dangers, and weight penalties.


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.

Water is more dense than all motor fuels.

Oil adulteration, from the water/steam cycle, is an obstacle to be dealt with, though additional piston/cylinder sealing rings can be added easily.

The weight of an oil separator and a water condenser are likely additions.

Current anti-air pollution legislation does not allow for experimental use status on public roadways.