water injection = Higher Efficiency?

[drmiller100]

Originally Posted by t vago

You really have no idea how a turbine works, do you? Tell me what happens to the pressure of a gas, when it forced through a nozzle. Then, tell me what happens to that gas's temperature.

efficiency.

Oldmech recently reminded me, in an oh so friendly way, we are here to HELP each other.

When we are unsure of something, it is pretty easy to come across as rude and abrasive.

If we are TRULY knowledgeable of something, it is pretty easy to TEACH and HELP each other in a friendly way.

Perhaps rather then asking Serial in a rude way to explain how it works, you could nicely ask.

Or, if you think you know more, you could NICELY discuss the topic in question.

Thank you.

[drmiller100]

Originally Posted by IamIan

... where did you account for the expansion effect of the % of liquid water that is converted to steam in the system ...

Please clarify... thanks

He skipped it. The math is pretty tough - beyond all of our skill levels. I keep hoping someone more skilled will come along and help us out.

Interestingly enough, steam engines use this effect with great success.

The Rankine cycle uses this effect pretty effectively, albeit usually with freon or alcohol.

Adiabatic would be "better", but getting a gas engine to run at 50:1 air/fuel ratios is beyond us.

[IamIan]

Originally Posted by drmiller100

He skipped it. The math is pretty tough - beyond all of our skill levels.

Maybe ... maybe not ... I saw some things that didn't add up for me ... so I figured the best option was just to ask ... that way he can tell me what step I missed or detail I missed , to get his final system pressure numbers.

Originally Posted by drmiller100

Interestingly enough, steam engines use this effect with great success.

All the previous points made do still stand ... it takes energy to raise room temperature water up to the phase transition point ... and it takes more energy to actually do the phase transition.

All that energy has to come from somewhere ... it isn't free and there are pros and cons ... the pros are fine , but one should be aware of the cons as well , in order to form as accurate and balanced an understanding as possible.

Yes a steam engine works well with the expansion from the phase change of the water ... but that is significantly different than just injecting liquid room temperature water into a ICE that was not designed for it.

[t vago]

Originally Posted by IamIan

#1> You can't inject the liquid water into that system without the application of the liquid water being at a higher pressure than the system was before you added the water... unless that was ignored for simplicity?

Yes, that was ignored for simplicity. I did ask drmiller100 how he proposed to inject water into a 150 psia pressure vessel, while ensuring that that same pressure vessel at 2500 psia would not leak back, but he chose to ignore my question.

Originally Posted by IamIan

#2> Even before the temperature change takes effect ... displacing the volume of the added liquid water itself in a fixed volume will increase the pressure of the system ... plus the additional pressure ( energy ) added to the system that was needed to inject the water in the first place... unless that was ignored for simplicity?

That was also ignored for simplicity. However, I'll go over the math of how pressure and temperature would rise by injecting 1 gram of water into a 40 cc vessel.

It's true that the liquid water volume will displace the gas, effectively shrinking the gas to 39 cc. This is due to the fact that 1 gram of water has a volume of 1 mL, or 1 cc. Using the ideal gas law (P1 * V1 = P2 * V2), that should raise the gas pressure from 150 psia to 154 psia, which is negligible.

The adiabatic compression of the exhaust by the injected water will cause the exhaust gas temperature to increase as its pressure increases. Using T2 = T1 * (V2 / V1) ^ (k - 1), we find that the final temperature is 807 F instead of 800 F. Again, negligible. They do not change the final outcome, as discussed below.

Originally Posted by IamIan

#3> The end system result you gave looks like it is just the effect of the initial gas in the fixed volume ... which contracts as it cools from the transfer of energy to the liquid water ... where did you account for the expansion effect of the % of liquid water that is converted to steam in the system ... that liquid to steam expansion counters the initial gas contraction you showed

No, it doesn't. Look, the water that flashed into steam is saturated steam. It's right at the boiling point temperature. Assuming a temperature of 100 C for the steam, that means that its corresponding pressure is 101 kPa, or 14.7 psia. The 1700:1 so-called expansion factor that drmiller100 keeps bandying about is misleading in this, because it is for standard atmospheric conditions. In other words, it doesn't apply to exhaust gas at 800 F and 150 psia stuck in a little 40 cc volume.

Let's look at that 0.04 grams of water that flashed into steam. It formerly occupied 0.04 cc of volume, but now it occupies the entire 39.04 cc of volume occupied by the gas, because it is itself a gas now. For that tiny amount of liquid, we just saw a 975:1 expansion factor, which is not 1700:1. However, that water sucked out all of the available heat energy from the exhaust gas to do so, and it would have sucked out even more heat had the water been below 100 C when it was introduced into the pressure vessel. The end result is that the exhaust gas, steam from the liquid water that flashed, and the remaining liquid water all have the same temperature, which is the temperature of the introduced water.

Originally Posted by IamIan

... even just 0.04 grams of liquid water to steam is a significant increase in pressure for a fixed volume ... the if not contained in the fixed volume the initial 1cc of liquid water would be 0.96cc of liquid water + about ~64cc of steam..

Nope. Here, though, you'll find that I made a mistake in neglecting to show the exhaust gas final pressure. It turns out that, due to the ideal gas law, the final exhaust gas pressure is 82 psia, or 55% of the original pressure.

Using the law of partial pressures, we add the new steam at 14.7 psia to the existing exhaust gas at 82 psia. We come up with 96.7 psia total for the system final pressure, which is roughly 2/3 of the original exhaust gas pressure.

Like I said, this idea of spraying water into exhaust gas is merely a novel way to cool off said gas.

Originally Posted by IamIan

confined by the 40cc fixed volume and the other contents in that volume ... I don't see how you got the 0.04 grams of steam being that low of a final system pressure.

That's because I wasn't clear, and I apologize for the resulting confusion.

This just goes to show how complicated an ideal example is. Real-world modelling is even more complicated. There are steam tables that must be consulted. There are gas tables that must be consulted. The example here has been ridiculously simplified in order to make it as understandable as possible.

[t vago]

Originally Posted by drmiller100

Oldmech recently reminded me, in an oh so friendly way, we are here to HELP each other.

When we are unsure of something, it is pretty easy to come across as rude and abrasive.

If we are TRULY knowledgeable of something, it is pretty easy to TEACH and HELP each other in a friendly way.

Perhaps rather then asking Serial in a rude way to explain how it works, you could nicely ask.

Or, if you think you know more, you could NICELY discuss the topic in question.

Thank you.

Get off your high horse! I have been trying to help, but you keep stubbornly refusing to even try to understand. 1700:1! 1700:1! Awk! At least IamIan made the effort.

You're just as bad as those snake-oil peddlers that come here from time to time. Worse, even, since not only do you not understand the necessary theory behind the things you propose, you take some sort of arrogant pride in your ignorance, and you only encourage others to leap without thinking. "Oooo! Look at me! I have no idea about real-world considerations, but I'm going to push this idea I had because I think I can make it work when every-bloody-else in the last 100 years couldn't!"

By the way, my questions to serialk11r still stand, even if I've offended your precious little sensibilities.

[maxc]

Interesting points at 2:39 and 4:57. Development and Testing of Water injection for Internal combustion design - YouTube

[IamIan]

Originally Posted by t vago

Using the law of partial pressures, we add the new steam at 14.7 psia to the existing exhaust gas at 82 psia. We come up with 96.7 psia total for the system final pressure, which is roughly 2/3 of the original exhaust gas pressure.

Thanks ... that result makes more sense to me... than the original post with just 14.7

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one other minor thing.
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Originally Posted by t vago

The 1700:1 so-called expansion factor that drmiller100 keeps bandying about is misleading in this, because it is for standard atmospheric conditions

For that tiny amount of liquid, we just saw a 975:1 expansion factor, which is not 1700:1

correct ... but doesn't that just mean we need to compensate for that with the ideal gas law ... to prevent the steam from expanding with a fixed volume container , the lack of expansion is compensated for with greater than standard atmospheric partial pressure from the steam.

So wouldn't the steams partial pressure when confined to 39.04cc be around ~26 psi.

Which brings the system up to ~108 psi.... which is still about ~28% less than initial pressure at the 100C.

It works in a steam engine because there is more energy available from the cylinder walls due to the heat of what ever is being burned ... than the energy just from the hot air.

Originally Posted by t vago

Like I said, this idea of spraying water into exhaust gas is merely a novel way to cool off said gas.

I didn't have a problem with the concept / point itself ... I just didn't see how you were getting such low 14.7 psi figure ... thanks for the corrections.

Three side notes:

#1> In a different engine designed to take advantage of it ... the timing of the piston being exhausted could be set equal to the power stroke of an opposed piston ... lower pressure on the second part from cooler temperature exhaust gasses creates a larger pressure difference to move the power stroke piston with.

#2> If the water is inside a confined heat exchanger pipe ... the water will expand in the pipe which could drive a turbine or other piston... thus extracting some useful energy / work from the otherwise exhaust gas.

#3> The biggest thing from my perspective often missed in a lot of the water injection type of discussions is the weight penalty of the additional device and the additional water ... even if a system does manage to increase real time efficiency from one mechanism or another ... it won't be a net benefit unless the pro is bigger than all the cons added together.

Originally Posted by t vago

That's because I wasn't clear, and I apologize for the resulting confusion.

Thanks for the clarification and correction.

Originally Posted by t vago

This just goes to show how complicated an ideal example is. Real-world modelling is even more complicated. There are steam tables that must be consulted. There are gas tables that must be consulted. The example here has been ridiculously simplified in order to make it as understandable as possible.

agreed.
yeah computer models.

[ProDarwin]

Originally Posted by IamIan

It works in a steam engine because there is more energy available from the cylinder walls due to the heat of what ever is being burned ... than the energy just from the hot air.

Well, a piston steam engine is a different animal. Steam is not created in the cylinder, it is let into the cylinder. Water is heated in a pressurized vessel to well above 100C. When a valve is opened to release/inject/whatever the water it instantly converts to steam and will drive the piston down.

Originally Posted by IamIan

#1> In a different engine designed to take advantage of it ... the timing of the piston being exhausted could be set equal to the power stroke of an opposed piston ... lower pressure on the second part from cooler temperature exhaust gasses creates a larger pressure difference to move the power stroke piston with.

On any inline 4, the power stroke of 1 cylinder will always be opposite the exhaust of another. The effect you are describing is similar to what a tuned header does... only without the need for any complex water injection system.

Originally Posted by IamIan

#2> If the water is inside a confined heat exchanger pipe ... the water will expand in the pipe which could drive a turbine or other piston... thus extracting some useful energy / work from the otherwise exhaust gas.

And this is what BMW's gas turbine concept is.

[drmiller100]

>>
Let's look at that 0.04 grams of water that flashed into steam. It formerly occupied 0.04 cc of volume, but now it occupies the entire 39.04 cc of volume occupied by the gas, because it is itself a gas now. For that tiny amount of liquid, we just saw a 975:1 expansion factor, which is not 1700:1.
>>


i'm kind of slow. we had a bit of liquid water which is now steam. we had a bunch of exhaust gasses occupying the 40 cc's.

Where did the exhaust gasses go? Do they now occupy .06 cc's????

are you saying the exhaust gasses and the water are all occupying the same space at the same time????

[IamIan]

Originally Posted by ProDarwin

Well, a piston steam engine is a different animal. Steam is not created in the cylinder, it is let into the cylinder. Water is heated in a pressurized vessel to well above 100C. When a valve is opened to release/inject/whatever the water it instantly converts to steam and will drive the piston down.

agreed ... sorry for my less than accurate simplification.

Originally Posted by ProDarwin

On any inline 4, the power stroke of 1 cylinder will always be opposite the exhaust of another. The effect you are describing is similar to what a tuned header does... only without the need for any complex water injection system.

agreed.

The difference is that the tuned header doesn't lower the pressures of the other side.

Past a certain point of converting engine heat to steam ... it would be increasing the pressure ... which gets back to the 6 stroke version.

Originally Posted by ProDarwin

And this is what BMW's gas turbine concept is.

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Originally Posted by drmiller100

>>
Where did the exhaust gasses go? Do they now occupy .06 cc's????

are you saying the exhaust gasses and the water are all occupying the same space at the same time????

Not to step on t-vago's toes... but I'm here so I thought I would try and help explain.

In this simplified example.
All the gasses share the 39.04cc of space ... the liquid water is only occupying the 0.96 cc of space.

The original hot gasses contracted when their temperature dropped ... causing their contribution to become the 82 t-vago wrote last time... this contraction happens to all gases in a fixed volume as they cool.

That drop in temperature was the heat energy transfer to the liquid water ... that heat energy transfer was what enabled the liquid water to phase change ~0.04g to steam ... the phase change itself does not change the temperature ... to change the temperature first you add the heat energy to get to the phase change point ... then you add more energy to do the phase change itself ... then you can add more energy to increase the temperature of the material in it's new phase... but you can't increase the temperature of the phase change material until you have added enough energy to phase change all the rest of the ~0.96g that is still liquid water just bellow the phase change point.

That water phase changed to steam ... expanded to fill the volume of the container ~39.04cc ... as any gas will do ... because there was not room for the full ~1700:1 expansion that would result at a lower ~14.7psi pressures the steam contributes a bit more than ~14.7psi ... I'm estimating ~26 psi.

Both gas forces ~26psi + ~82psi combine to make the total system ~108psi of gas in the ~39.04cc of volume... which with the still liquid water is now all the same temperature just bellow the phase change point.

If there was more thermal energy in the system more water would get converted to steam ... but to have more thermal energy without also having the same hot air contracts as it cools effect of giving up that thermal energy you need something with more thermal mass that doesn't change as much as a gas would.