You are going to have your hands full with this one. A couple of points if you will. A positive displacement pump (compressor) is a vapor pump and only a vapor pump. Any attempt to pump a liquid will end with catastrophic results, liquid always wins. In your case an atomizing nozzle should be used such as a 'oil burner nozzle'. In order to atomize the water(vapor), prior to compressing, the water will have to be pressurized to be forced through the nozzle. Here you will have to use a 'rotary' pump.

  The drawing is incorrect. Your exhaust gas, as shown, are already at a 'low pressure/low temperature' state. By the time the piston reaches B.D.C (Bottom Dead Center) a pressure drop and a resulting temperature drop has been created. In order to achieve a 'High' pressure/High temperature output the exhaust valve must open when the piston is at T.D.C. It should be noted that combustion should take place a few degree's prior to T.D.C on the flywheel.

  By no means am I discrediting your idea. OU devices come in two flavors mechanical and electrical. I am of the frame of mind that mechanical devices require greater skills. Others may disagree with that statement.

  Some ideas for you. There is a lot of power to be had when a liquid under pressure is Violently introduced to a low pressure area. An example of this power can be seen when a boiler explodes. Boiler explosions have nothing to do with gas. Boilers explode when high pressure water meets with atmospheric pressure. Water at sea level with boil at 212 Deg. F. When a liquid is pressurized its boiling temperature increases. So water under 200 psig will not boil at 212 Deg. F but higher, much higher. When this water, at high pressure/high temperature comes in contact with atmospheric pressure Low Temperature/low pressure the water will try to BOIL off instantaneously.

  So your device should be centered around the phase change of a liquid. The density of a liquid is greater then the density of its vapor state. Its volume is the reciprocal of its density. In a boiler the vessel size(its volume) is a fixed value. When the water rapidly boils off its volume increases, the vessel expands to the breaking point until rupture. This typically sends a boiler weighing many tons flying through the air like a missile.

   So if you can harness this raw power you will win. Be very careful you do not want to be anywhere near an exploding vessel regardless of its size. Good Luck I will try to help the best I can.

Respectfully,

Core     

Thanks for yout input. It will be taken into consideration. Hot water under great pressure is dangerous.

 Let us assume there is 1milligram water fog injected into the cylinder. The piston is at T.D.C, so there is great pressure inside. Also the cylinder is very hot, so even if the pressure would stop the water from vaporizing, the high temperature would allow it to. Then those milligrams of water that turn into vapor will require much greater space, and it will push the piston down to B.D.C.

If your point made sense to me, you say that the water will not vaporize anyways. It will also require great force to inject water into a high pressure chamber. Or am I totaly mistaking your point You want me to feed the cylinder with vapor, just as an ordinary steam engine, right? So the exhaust should exit at T.D.C?

I was thinking that the engine would need help the first few thousand cycles, but after those cycles the temperature in the engine would be very high. The water pressure between the pump and the nozzle would be greater than the pressure inside the cylinder. Else there would not be possible to pump water inside. However, the injection part takes maybe just a few micro seconds, so there is minimal of energy applied to inject the water. I would also use a pump which is pulsating and not be a pump which maintained this high water pressure all the time. How to find or make such a pump, I don't know.
A one way valve is used to prevent the pressure inside the cylinder to escape through the water nozzle.

Regarding the drawing, it would sertanly need some modifications, but I did not fully understood how the design should be changed, and for what reason. Even if the vapor has lower pressure right before it exits the exhaust outlet, its required space should be grater than the maximum cylinder volume. The cylinder walls and the piston is still warm (>100 deg.C) so the vapor will be vapor untill the pressure fully releases when the piston is at B.D.C?

I also know that I am a noob when it comes to steam engines in general even if I know the principals of an old fashion steam engine.
I have not the total understanding of the relationship between temperature, pressure, vaporation, condensation, and how these factors plays with eachother.

I don't get it, do I?

Vidar

 Let us assume there is 1milligram water fog injected into the cylinder. The piston is at T.D.C, so there is great pressure inside. Also the cylinder is very hot, so even if the pressure would stop the water from vaporizing, the high temperature would allow it to. Then those milligrams of water that turn into vapor will require much greater space, and it will push the piston down to B.D.C.

  Well that may not be 100% correct. Lets assume that the piston at T.D.C creates an environment in the cylinder that is at 200 psi. We know that water at atmospheric pressure (14.69 psi / 1 Bar) will boil at 212 Deg.F / 100 Deg. C. With the cylinder at 200 psi (14 Bar) our water will boil at 382 Deg.F / 192 Deg. C. If the the cylinder / chamber is below this temperature obviously no boiling can occur. We would need the friction of the piston and cylinder to create large amounts of heat or in other words have major losses. Can the engine overcome these losses? That's part of the design challenge because you will not get this heat for free.

If your point made sense to me, you say that the water will not vaporize anyways. It will also require great force to inject water into a high pressure chamber. Or am I totaly mistaking your point You want me to feed the cylinder with vapor, just as an ordinary steam engine, right? So the exhaust should exit at T.D.C?

  Correct, in order to boil off the water to create steam you would need to verify/operate at a temperature that is above the boiling temperature with respect to the cylinder pressure. Also if T.D.C equals 200 psi water vapor would have to be injected at a pressure greater then 200 psi to enter the cylinder. I think you already know this.

I would also use a pump which is pulsating and not be a pump which maintained this high water pressure all the time. How to find or make such a pump, I don't know.
A one way valve is used to prevent the pressure inside the cylinder to escape through the water nozzle.

  I think I can help you here. I have spent the last four weeks hammering out a design for a mechanical OU device that I will be building. There was a plethora of engineering issues to work out prior to building and I believe I solved 90% of them.
  One issue was creating a 'thrust' valve. My system will be oil driven and a periodic 'burst' of high pressure oil will be required. To achieve this a rotary oil pump will be coupled to a shaft via a specific gear ratio. In order to create a burst of high pressure oil rhythmically with the system I settled on creating a rotating valve utilizing a ball valve.
 If you remove the handle on a ball valve the ball of the valve spins freely. From the stem of the valve I will attach a small gear combination that will be driven by a variable speed DC motor. A spinning ball valve will create On/Off bursts in my system not harming my rotary oil pump.

Regarding the drawing, it would sertanly need some modifications, but I did not fully understood how the design should be changed, and for what reason. Even if the vapor has lower pressure right before it exits the exhaust outlet, its required space should be grater than the maximum cylinder volume. The cylinder walls and the piston is still warm (>100 deg.C) so the vapor will be vapor untill the pressure fully releases when the piston is at B.D.C?

  My question is 'Do you think that allowing the exhaust to release to atmosphere is wasting precious energy'? Also running the engine 'Red' hot how are you going to overcome lubrication issues?

Respectfully,

Core 

Lubrication is not the problem. Maybe its not needed at all. The flywheel will need it but that do not need to be that hot. The heat will hopefully rise because the relationship between the processes low-to-high pressure and high-to-low pressure is not linear. Try to block the nozzle of a bicycle pump and start pumping rapidly. It gets quite hot even if the decompression should cause in a full recovery of the initial  temperature at low pressure. I will keep thinking. Do some more research. Obviously i'm a noob at this area:)