--- Water injection VS Steam Injection ---

[t vago]

Originally Posted by drmiller100

but doesn't an air compressor look a WHOLE lot like a piston engine?

No. Piston engines typically use poppet valves to seal the cylinder, while air compressors use reed valves. As the piston travels up in an air compressor cylinder, the resultant buildup of pressure forces the inlet reed valve shut and the outlet reed valve open, forcing the air into a pressure vessel. Similarly, as the piston travels downward, the inlet reed valve is forced open by the partial vacuum formed, and the outlet reed valve is forced shut.

For this reason, an air compressor can be modeled most nearly as an isobaric process (constant pressure) for its cycle, which is different from an adiabatic (constant heat energy) process that occurs inside a combustion engine. The only real heat buildup in an air compressor is as a result of friction as the piston travels back and forth inside its cylinder. The temperature of the air doesn't really rise all that much because the heat energy has enough time to bleed out of the compressed air's pressure vessel.

So why does water condense inside the pressure vessel of an air compressor? Simple. Remember that the compressor is compressing the incoming air. That air, in turn, is composed of water vapor at some partial pressure (probably around 1 psig on a good, hot, humid summer day). If that hot summer air is being compressed to 100 psig, the water vapor present is also being compressed to about 7 psig partial pressure. Assuming that the compressed air does not appreciably rise in temperature, which it doesn't, the water vapor concentration increases to about 6 times what the air can support, and the excess water condenses out as a liquid.

Originally Posted by drmiller100

And doesn't a 10:1 compression ratio pretty much equal the final pressure in most compressers?

Please see above.

Originally Posted by drmiller100

And if you are arguing the gasoline gets boiled/vaporized, why wouldn't the water reach 100 percent relative humidity for the given pressure/ temperature and do the same?

Are you talking about what happens inside a combustion chamber? Or in an air compressor?

Originally Posted by drmiller100

And if the pressure is 150 psi, the ignition event happens, and the temperature sky rockets to, say, 1200 degrees or so, wouldn't the water turn to steam keeping the absolute pressure up nice and high for the entire piston stroke????

I am going to assume you're thinking of a piston engine here.

On the compression stroke, any entrained water or gasoline droplets will in fact enter their gaseous state. This is because, as the temperature of the air rises as a result of adiabatic compression, the temperature differential will increase between the air and the entrained droplets of liquid.

This, in turn, will cause heat energy to flow from the air being compressed to the entrained droplets of liquid, causing the temperature of the droplets to rise until the temperature inside the droplets reaches the boiling point of said droplets.

Once this happens, further heat energy transfer from the air to the droplets will not cause further temperature increase, but will force the droplets to change from a liquid state to a gaseous state.

Keep in mind, that as all of this happens, the temperature of the air will not rise as much as it would if the entrained droplets of liquid were not there.

Finally, combustion temperatures approach something closer to 6000 F than 1200 F.

[oil pan 4]

Originally Posted by Air-Hybrid

Harlan:
Dumping heat from the exhaust into the intake has (by Carnot) to lower the thermal efficiency of the cycle.

Redirecting as much heat as possible heat back into the thermodynamic cycles sounds like trying to get work from one heat reservoir.

My take on water injection, for a diesel, is that it promotes heat transfer from hot to cold by making the cold side colder.
Making the engine hotter is bad for the oil, seals, head gaskets and aluminum parts.


Gasoline engines seem to respond well to anything that can help reduce isentropic throttling losses while at light load cruise. Things such as warm air intake, egr, using a smaller engine and running it harder, regearing the final drive for lower cruise RPMs and maybe some form of steam injection cut down on these losses.

[t vago]

Originally Posted by oil pan 4

Gasoline engines seem to respond well to anything that can help reduce isentropic throttling losses while at light load cruise. Things such as warm air intake, egr, using a smaller engine and running it harder, regearing the final drive for lower cruise RPMs and maybe some form of steam injection cut down on these losses.

Steam injection might could work, given a large enough external heat source to make the large amounts of steam that would be necessary. There is the problem, though, of uneven steam mixing with the air. There is also the fact that steam would encounter cooler environments and immediately condense out. The sides of the intake manifold come to mind. As soon as this occurs, the water condensate would pool inside the intake manifold, and might could become a hydrolock concern at some point down the road.

For these reasons, I'd probably lean toward port water injection, along with leaning out the air/fuel mixture to around 17:1. The water injection by itself would, of course, lower peak cylinder pressure as it cooled off the combustion charge being compressed, and Carnot efficiency would go down as a result.

However, these two factors would be more than offset by the reduction in throttling and pumping losses that would result from leaning out the fuel/air mix. The engine would be able to safely run this lean due to said lowering of combustion chamber temperatures. Engine power output would obviously decrease, compared to a similar engine that was running at stoich. The driver would then have to open up the throttle to compensate, and it'd have the same effect as lowered gearing, EGR, or shifting to a smaller capacity engine.

[Air-Hybrid]

Originally Posted by Harlan

I am not violating the laws of thermodynamics nor Carnot's heat engine, I'm simply massaging an Otto cycle adding some Rankine elements and creating something slightly new.
....
Still need a turbo to get the biggest gains. Then it would be a true coexisting Rankine cycle.

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.

Originally Posted by Harlan

As for heating only with engine coolant. ... It drops coolant temperatures because it removes heat from the cycle because it's wet steam. Using the coolant is self limiting because the steam acts as internal coolant.

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!

[oil pan 4]

Originally Posted by t vago

There is also the fact that steam would encounter cooler environments and immediately condense out. The sides of the intake manifold come to mind.

Thats where the design gets interesting. Anyone wanting to do this will need to create a boiler and superheater that runs off waste heat a steam hybrid maybe?
The superheater would be the easy part.
You would have steam bleeders, blow down valves it would be kind of scary to see it in operation.

There are 2 kinds of intake manifolds to watch out for. Carbed and throttle body injection style intake manifolds are designed so fuel (or any other liquid) wont pool in them. That type of design is good for these kinds of things, some times you get lucky with direct port designs to where they are all down hill wont allow pooling, but there are a lot out there that will pool liquid.
On my diesel, I plan to run water methanol injection soon and lucky for me its intake is a carb design copy.

[gone-ot]

...the only difference(s) between water VAPOR and STEAM are their HEAT content and VAPOR pressures.

...that's what 'steam tables' are for.

[drmiller100]

Originally Posted by Old Tele man

...the only difference(s) between water VAPOR and STEAM are their HEAT content and VAPOR pressures.

...that's what 'steam tables' are for.

I just learned the name of what I don't know. (Smiles!!)

So, now I want to learn to read it.

Please.

So, lets say I take a given volume (say 1 liter) of saturated steam at 80 degrees F. and at 1 Bar.

Now I compress that volume 10:1. So now it is 100cc's. My temp from compressing the air says the temp will be 750 degrees or so.

Do I STILL have 100 percent saturated steam at the 10 Bar pressure?

Is the amount of water held as vapor more or less then it was at 1 bar?

How do I read the tables to let me know this? Mol's? Grams?

Please?

[Josh8loop]

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!

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.



..

[maxc]

Development and Testing of Water injection for Internal combustion design - YouTube

[gone-ot]

...the Wankel was "revolutionary" once too, but it never lived up to it's hype either.