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Old 04-30-2021, 11:31 PM   #10 (permalink)
Isaac Zachary
High Altitude Hybrid
 
Join Date: Dec 2020
Location: Gunnison, CO
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Avalon - '13 Toyota Avalon HV
90 day: 40.45 mpg (US)

Prius - '06 Toyota Prius
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Quote:
Originally Posted by serialk11r View Post
... you just pair it with a higher compression ratio, and the forces seen by the piston are more or less the same.
That's kind of what I'm saying. IF you don't increase the compression ratio, then the pressure will be lower, because you're taking a fluid that expands less and exerts less force when you inject the same amount of heat energy into it. The way to extract that lost energy is to increase the compression ratio.

This is definitely doable, especially with limited amounts of water injection. Water injection reduces the chances of knock, so therefore you can increase the compression ratio. But if you inject a whole lot of it you would need a very high compression ratio to get the same efficiency. So there's obviously going to be a point of diminishing returns is what I'm saying.

Quote:
Originally Posted by serialk11r View Post
Air is a desirable dilutant since it has oxygen to promote more complete combustion, but water can be useful too, e.g. at high load where you need to remove excess heat. Absolute heat capacity rather than heat capacity ratio can make a gas more useful for reducing temperatures and heat conduction losses, that's why cooled EGR is combined with lean burn in experimental high efficiency engines rather than just running even more lean
I don't understand how cooled EGR works better than air, but water I can understand since it changes phases and reduces temperatures that way. But that is interesting.
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