Quote:
Originally Posted by Air-Hybrid
IIRC, I'm pretty certain that what you are describing can not be compared to (or claimed to be) a Rankine cycle. Further, adding a turbo (a Brayton cycle) still won't allow the energy in the additional quantity of dry-steam (coming from your method, as you've described it) to generate any further work (aka an efficiency gain).
The reason for this is that by transferring a portion of the exhaust heat to the inlet heat (forget what your method of doing this is for now, ie. ignore the water/steam) you are moving heat from the hot reservoir to the cold reservoir BUT without doing any useful (mechanical) work. This cannot be at all ideal!
You describe the water/steam as moderating the cylinder temperature, but, if by this you mean lowering, then this is presciently the opposite of what provides highest Thermal efficiency - ie. The Maximum differential between hot and cold reservoirs. In a way you are diluting this very effect.
If alternatively by moderation you mean limiting the in-cylinder peak-pressure then, yes agreed, but plain old water would do this even better, plus it has no negative impact on the thermal efficiency.
If there was some (unexplained) validity to your design then it would undoubtedly be an extra win to produce steam from the block. Remember block cooling is a totally parasitic effect in piston engines (unlike the exhaust temp which is inherent to the heat-engine's workings). Further the cylinder walls are by nature incredibly hot and, though perhaps not an easy modification for the backyard tinkerer, a heatpipe will happily transfer superheating temps all day long (and at a rapid rate too!). ... Imagine the possibilities to completely delete the cooling circuit!
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The "work" done when using exhaust or coolant heat to create steam or hot water vapor is just that to create steam or turn the water more easily into vapor. Instead of using high pressure pumps and injecting nozzles which require moderate electrical energy we are using waste heat to our advantage to tip the tables in our favor. Thats why I mentioned using coolant heat and ultrasonic device together with the throttle vacuum to more easily create water vapor. With a 195 deg F thermostat quite a bit of heat is rejected through the radiator. When using that same coolant heat to heat up the water in a container that has an immersed ultrasonic vaporizer in it, and under partial vacuum conditions from the intake that same heat that would have been wasted through the radiator can now be used to promote water vaporization for us without the use of pumps/fuel injector nozzles. The electrical demand of the ultrasonic vaporizer coupled with the sub boiling water really lowers the energy input required to get that water into the intake stream. Even if experimentally we found that the coolant temps drop too much with this approach, then we can just use exhaust heat through a heat pipe to accomplish the same effect. I have made heat pipes myself really easily that worked extremely well FWIW.
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