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Old 04-17-2012, 12:13 PM   #20 (permalink)
t vago
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Originally Posted by drmiller100 View Post
imagine the combustion chamber at 600C full of hot gasses at a pressure of 500 psi.

Add excess liquid water. My GUESS is the pressure will go up slightly, the temperature will go down significantly.
Points are not awarded for guessing. If you add even a small amount of low temperature water (low temperature meaning that the water temperature is such that it's still a liquid) to a set amount of high temperature gas, the temperature of the gas will drop. Because the temperature of the gas drops, so does its pressure. Since water needs much more heat energy to raise its temperature by 1 degree C, as compared to the gas in question, it's going to lower the gas temperature that much more. Finally, that water has to absorb even more heat energy from the gas if it's going to vaporize (latent heat of vaporization, right?), which is going to further drop the temperature of the gas. The gas temperature will drop significantly. You're not going to get the results you've envisioned.

You apparently are making the mistake that exhaust gas has the same specific heat capacity as water. This is not true.

Originally Posted by drmiller100 View Post
Now expand the volume by letting the piston go down. As the piston goes down, the pressure normally would go down, but the liquid water is rapidly turning to steam.
You really need to work the math out yourself. This statement is factually incorrect.

Originally Posted by drmiller100 View Post
Will the average pressure be higher or lower with water?
With water? Lower. Much lower.

Originally Posted by drmiller100 View Post
Thought experiment two. Imagine a 4 or 2 stroke engine, except it has superheated piston, and we have direct injection of liquid water. We inject the water at TDC.

Will this engine "run"????
Not nearly as well as the standalone engine without direct water injection, if it runs at all.

I'll construct a graph later on, that graphically shows what happens when water is added to exhaust gas.
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