Half a croissant, on a plate, with a sign in front of it saying '50c'
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HCCI Steam Hybrid

Better than the Crower 6-stroke
  [vote for,

Firstly, this design requires positive displacement, high pressure, forced induction. This would probably be accomplished with a layout similar to the Scuderi split cycle engine... but with a very different phase difference.

The compression piston would work almost exactly like that of a Scuderi split cycle engine, except that it reaches top dead center while the power piston is about halfway through it's upstroke. Also, the compression piston will be about half the size of a comparable Scuderi engine's compression piston, since there will be two compression strokes for every combustion power stroke.

The power piston head would contain three valves (or sets of valves): a crossover valve, an air exhaust valve, and a steam exhaust valve.

The first stroke is the steam expansion stroke. With all the valves closed, water is injected into the cylinder. The water hits the piston, and turns to steam. The pressure of the steam against the piston produces mechanical power as the piston descends.

The second stroke is more complex; at bottom dead center, the steam exhaust valve opens. When the piston is about halfway up (coinciding with when the compression piston is approaching top dead center), the crossover valve opens (with the steam exhast valve still open). Hot, high pressure recirculated exhast gas, that was previously forced into the crossover tube, rushes out of the crossover, forcing the steam out the open exhaust valve. Before too much exhast gas goes out the steam exhaust valve, it closes.

A short time after this, after all of the recirculated exhaust that had been forced into the crossover tube has reentered the chamber, and after the desired amount of fuel/air mix has entered the chamber, the crossover valve closes. The piston continues to rise, compressing the mixture of air, fuel, and recirculated exhaust gas, until autoignition occurs (as close as possible to TDC).

The third stroke is the power stroke -- mostly. After the piston has descended enough that the pressure in the chamber is only a little above the pressure in the crossover tube, the crossover valve opens, allowing some exhaust gas to go into the crossover tube. After the desired quantity of exhaust gas has gone into the crossover tube, the crossover valve is closed. The remaining exhast gas is then expanded conventionally.

The fourth stroke is a conventional exhaust stroke. The air exhast valve opens at bottom dead center, and closes at top dead center.

The steam exhast valves would lead to a steam exhast manifold, which would go to a condensor. A certain amount of entrained air is inevitable, so an air/water seperator would be needed to vent that air to the atmosphere.

goldbb, May 05 2009

Crower six stroke http://en.wikipedia...i/Crower_six_stroke
[goldbb, May 05 2009]


       Interesting, but seems to overestimate the heat present in the cylinder to evapourate the steam.
Skrewloose, May 07 2009

       If we don't run coolant through the engine block, there will be more than enough heat in the cylinder to make the desired quantity of steam.   

       We only need to turn a sufficient quantity of water to steam so that, after the steam expands, it will be at the same pressure pressure as the interior of the steam condensor. Assuming that the steam condensor's interior is at atmospheric pressure, that means the amount of water we need to boil is 1/1600th of the cylinder's displacement. Of course, we could boil more water (if there's available heat), but that would mean a higher steam exhaust pressure (prior to opening the steam exhaust valve), which would inevitably raise the pressure in the steam condensor... reducing thermodynamic efficiency (and also requiring a stronger, heavier steam condensor).   

       Before anyone objects to not cooling the engine with coolant, consider that we can remove *all* of the engine block's waste heat by means of the water/steam conversion.
goldbb, May 07 2009

       There are many high effeciency engine designs around and have been for many years. Most of them are limited by material technology.   

       Whist the thermodynamics of squirting water onto a very hot piston are attractive, I am at a loss to guess what material will put up with that kind of thermal shock cycling without falling apart very quickly. My best guess would be a ceramic disc fixed to the piston crown.   

       One of the design criteria for an IC engine piston is low mass. Low mass = low heat capacity.   

       I guess what you need is a massive version of the hot spot found in the heads of older diesel engines.   

       Have you considered how big your condensor needs to be?
Twizz, May 08 2009

       Although much of the heat will come from the piston, a large portion must also come from the cylinder walls.   

       As for the condensor size... I don't precisely know -- I only know that it needs to send into the atmosphere exactly as much heat as it absorbs from the engine :).   

       Since the water/steam conversion is effectively replacing the coolant loop through the engine, I suppose we'd either have a small condensor, cooled by coolant coming from the same size of radiator as would cool the conventional version of the engine, or have an air cooled condensor (and no radiator), which would be the same size as the radiator system it replaces.
goldbb, May 10 2009


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