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Jlnance
| | Posted on Sunday, January 29, 2006 - 08:27 am: | 
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I'm facinated by water injection. I wish I'd stumbled upon this thread earlier.
I do believe that higher moisture content in the air will result in a higher effective compression ratio.
If you end up with liquid water entering the cylinder then it should. The pressure in the cylinder goes way up when the water boils.
And even if the air is just humid (rather than foggy), you might still end up with liquid water dropplets due to the chilling effects of injecting gasoline. |
Buellbozo
| | Posted on Sunday, January 29, 2006 - 09:14 am: |
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Again, Kevin Cameron,Cycle World July 03:
Quote-
"Some argue that showerhead injectors, by evaporatively cooling the air as it enters the intake tracts, act to increase it's density,thereby boosting engine airflow.
This debate dates back to at least WW2 period aircraft engines. U.S. and British engineers believed that by injecting fuel upstream from supercharger rotors, they gained a density increase from evaporative cooling,and so reduced the work required to compress the intake air. The Germans, who began developing gasoline direct cylinder injection in 1934,showed experimental results demonstrating that such up-stream fuel injection actually HEATED (italics K.C.) intake air rather than cooled it. The reason? Air,s low density makes it a good insulator, so it picks up only moderate heat by itself. If fuel is added,part of it forms a liquid film on interior manifold surfaces where the denser liquid's excellent heat conduction picks up much more heat. As this fuel evaporates, its heat is transfered to the air, reducing its density and engine airflow somewhat.
Peak power occurs when intake air picks up just enough heat to evaporate the fuel- no more and no less."
Whew! Tough to type and tough to get the brain cells around, but I'm gonna go with Cameron. Best mc tech writer since Gordon Jennings IMHO. |
Panic
| | Posted on Monday, January 30, 2006 - 11:25 am: |
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"Even the most basic of FI systems, strive to maintain a 14.7: a/f ratio"
Except at idle.
Except on full power.
Except on trailing throttle.
Except on high-vacuum cruise. |
Panic
| | Posted on Monday, January 30, 2006 - 11:35 am: |
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"You have a 1 million Gallon water tank and a 100,000 gallon water tank, each tank has 50 ft of water, which tank has a higher water pressure"
Static pressure = head, and for the first second, they're equal.
After that, the larger tank will always have higher pressure after the same time interval if the outlets are identical. |
Reepicheep
| | Posted on Monday, January 30, 2006 - 11:40 am: |
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Excellent contributions Panic, thanks! |
Panic
| | Posted on Monday, January 30, 2006 - 12:05 pm: |
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"Peak power occurs when intake air picks up just enough heat to evaporate the fuel- no more and no less"
Mr. Cameron is simplifying it somewhat. Some droplet evaporation can occur inside the chamber after the valve closes as compression increases, but obviously any remaining droplets must be very small or they'll be exhausted without contribution.
In the intake manifold and runner complete evaporation only produces max power if the port size is at least sufficient to allow 100 VE. If below this, any gas vapor displaces air (droplet volume is less than 1% of vapor volume) and reduces VE. Typically, bad ports need higher droplet size than good ports. |
Panic
| | Posted on Monday, January 30, 2006 - 12:11 pm: |
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I'm guessing that an XB FI system is probably slightly rich of stoichiometric at idle due to the cams. Milder cams (older, or stock XL with less overlap) would need 14.7 or so, but as overlap goes up the percentage of residual or re-breathed exhaust gas also goes up, which means you must add fuel molecules to make sure that all the O2 finds some. Race motors will need closer to 13 at idle.
A liquid cooled motor (not as much affected by chamber temperature) can run FI as lean as 15 or 16-1 because the spark is advanced to match. This only works if monitored very closely, so it's not entirely the FI that's doing it but the linked ignition that tailors the spark position accurately.
Max power for air cooled is typically 12.5 to 12.7, liquid cooled 12.7 to 13, turbos sometimes run a bit richer for cooling but not much below 12.2. |
Bob_thompson
| | Posted on Monday, January 30, 2006 - 01:30 pm: |
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On this water injection for quelling detonation: when I ran a carb injection system on my turbocharged BMW at Bonneville a while back I was told by a reputable automotive engineer to use straight alcohol. It cools the combustion chamber even better than water to quell detonation and actually burns adding another small amount of power. Indy cars using straight alcohol, I understand, when they begin to run hot simply increase fuel ratio to cool engine from the cockpit. Another plus is when inspecting combustion chamber is a complete lack of carbon formation. How about some more thoughts on this. Bob |
Mr_grumpy
| | Posted on Monday, January 30, 2006 - 03:08 pm: |
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No no no no, you've got it all wrong!
The gas is for the engine.
The alcohol is for the driver.
However in the driver's case the intake ratio can be over a much wider range, with a far greater variation in fuel quality for a given result.
Hope this makes things clear, hic. |
Cochise
| | Posted on Monday, January 30, 2006 - 05:53 pm: |
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Static pressure = head, and for the first second, they're equal.
After that, the larger tank will always have higher pressure after the same time interval if the outlets are identical.
Yeah, if the larger tank water level is higher. The equation I am going on for the above mentioned fifty foot water volume in the water tak\nk.
2.31 ft of head = 1 p.s.i. no matter what size tank or piece of pipe. If I have a 1 MG water tank filled to fifty feet of water and a fifty foot piece of pipe standing up will have the same pressure at the bottom. |
Panic
| | Posted on Monday, January 30, 2006 - 06:12 pm: |
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One more time: after the first second, the larger tank will always have higher pressure after the same time interval if the outlets are identical.} |
Blake
| | Posted on Monday, January 30, 2006 - 06:35 pm: |
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Panic got the comprehensively entirely accurate answer, except for the cases where the water is frozen, or in vapor form. ![: ]](http://www.badweatherbikers.com/buell/clipart/proud.gif)
Water absorbs a lot more heat when it vaporizes than alcohol. So no, alcohol will not cool the combustion chamber as well as the same quantity of water. I did mix alcolhol with the water though, mainly to keep it from freezing during cold Winter days. |
Buellbozo
| | Posted on Monday, January 30, 2006 - 07:18 pm: |
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I believe Indy cars run methanol...
I believe alcohol fuel burns cooler than gas.
Allows massively greater quantities to be used to generate same or greater power at less destructive chamber temps.
Usual disclaimer applies... |
Mr_grumpy
| | Posted on Tuesday, January 31, 2006 - 03:40 am: |
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Scuse me, but did I not say sometime ago it depends on spigot size?
It also depends on atmospheric pressure,
I mean are these tanks at the same height above sea level?
Are we doing this test on the same day at the same time in the same place with identical weather conditions?
How picky are we gonna be here?
This is pool tech not rocket science! |
Mr_grumpy
| | Posted on Tuesday, January 31, 2006 - 03:42 am: |
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Doh, shouldn't of said that, someone will now endeavour to prove to me that you can launch an olympic sized swimming pool into space using a gas & alcohol powered rubber band.  |
Cochise
| | Posted on Tuesday, January 31, 2006 - 07:55 am: |
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One more time: after the first second, the larger tank will always have higher pressure after the same time interval if the outlets are identical.
I guess I don't get it. How will it have more pressure later? One ft of head is one ft of head no matter what length of time is spent. |
Jprovo
| | Posted on Tuesday, January 31, 2006 - 08:43 am: |
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Cochise-
one 50 gallon tank, one 500 gallon tank.
Both have the same water level when you open the valve (10 ft).
Flow out of the valve remains relatively constant at 5 gpm for both tanks. After 1 minuite you shut off the valve.
The smaller tank is now ~45 gallons, and is now only ~9 ft tall.
The larger tank is now ~495 gallons, and is ~9.9 ft tall.
The larger tank has more pressure after a given time period with equal flow leaving the tank. |
Mr_grumpy
| | Posted on Tuesday, January 31, 2006 - 01:33 pm: |
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Yup, depends on spigot size.
haven't I read that somewhere before? |
Mr_grumpy
| | Posted on Tuesday, January 31, 2006 - 01:40 pm: |
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OK now if I get this right,
If I have one tank with 10 times the capacity of the other, but of equal height,to maintain the the same water pressures on both tanks, I will need 10 spigots of the same size as on the smaller tanks.
A spigot, or valve if you prefer, 10 times larger won't do it due to flow rate differences.
Am I wrong?  |
Newfie_buell
| | Posted on Tuesday, January 31, 2006 - 01:40 pm: |
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Do they have the same spigot size?
What do I know "I'm only a COOK!!" |
Mr_grumpy
| | Posted on Tuesday, January 31, 2006 - 03:19 pm: |
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Ask your missus, she'll tell you that spigot size matters!
Except in relation to Muffins of course. |
Blake
| | Posted on Tuesday, January 31, 2006 - 05:40 pm: |
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Joe,
What he's trying to say is that once the valves are open, assuming they are identical and each located at the bottom of the tanks, the water level in the smaller tank will drop more quickly, thus it's head/pressure decreases more rapidly too.
Imagine a 5 ft tall 20 gallon bucket next to a 5 ft tall above ground 10,000 gallon swimming pool, each filled to the brim. Poke a one inch hole in the side near the bottom of each. Plug each hole when the bucket has lost half it's water. Compare the relative water levels in bucket and pool. Which is higher and thus has more head/pressure? |
Oldog
| | Posted on Tuesday, January 31, 2006 - 05:54 pm: |
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in that wood treating plants are just tanks, pipes, pumps, and valves I think I can explain [ if needed ]
in the analogy the larger tank was dramiticaly larger,
because of that the rate of level change between the two would be greater for the smaller tank, the level in the tank effects the pressure of the water passing through the spigot
in the end its not the size of the spigot but rather the size of the pipe it's attached to, that counts |
Cochise
| | Posted on Tuesday, January 31, 2006 - 06:30 pm: |
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Blake, that's fine and dandy, but I never said anything about moving water. Obviously 50 ft of water will empty out of a smaller container faster than a bigger one because there is more volume in a larger tank. Well, that was fun.
(Message edited by cochise on January 31, 2006) |
Crusty
| | Posted on Tuesday, January 31, 2006 - 09:28 pm: |
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Mr. Grumpy, is that an Egg McPuffin? Or a Puffin muffin? Or maybe a Puffin Egg McMuffin? |
Newfie_buell
| | Posted on Tuesday, January 31, 2006 - 09:33 pm: |
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A good english muffin would go over nice now?!? |
Iamike
| | Posted on Tuesday, January 31, 2006 - 09:33 pm: |
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He's more familiar with stuffin a puffin muffin! |
Prior
| | Posted on Tuesday, January 31, 2006 - 10:03 pm: |
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Or puffin muffin stuffin. Depends on the time of the day! |
Mr_grumpy
| | Posted on Wednesday, February 01, 2006 - 11:31 am: |
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Ah, Happy memories, 
Those of you that weren't there may be wondering what this is all about, well..............keep wondering. |
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How Engineering Types Talk About Engines
