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Old 10-17-2006, 05:52 PM   #1
Aquamist
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Default water or alcohol injection, which one makes more power?

I thought the forum has been pretty quiet lately, so a topic as "titled" may warm it up a little. Any contribution will be useful to this myth.
After reading many posts on this forum, I would like to contribute something that may help clarify some myth on water and alcohol injection. Please also note that it is only my view. In some areas, I can be completely wrong, I am very willing to take in any comments to correct it so hopefully this thread becomes more meaningful as it progresses. Water and methanol injection does the same job in different ways, they both perform in-cylinder cooling and knock suppression well. Since water has a higher latent heat value than methanol, you need to inject twice the amount of methanol by mass to extract the same amount of heat during combustion. This is why all pure alcohol injection systems require a bigger jet, you need to inject 2.5 times by volume more than water. This makes little difference in practice except you need to find a bigger container.


Effect on knock suppression is totally different:
Water suppresses knock by quenching peak flame front temperatures hence regulating the frame propagation speed – (too fast burn promotes knock). In-perfect charge distribution produces lean and rich pockets. Lean pockets burn at a higher temperature (oxygen-rich = faster) compared to fuel-rich pockets (excess CO slows down burn speed).

Alcohol suppresses detonation by increasing the knock threshold value of a given fuel grade. Since large amount of alcohol is required to control in-cylinder temperatures, air/fuel ratio will be affected significantly. Some fuel has to be removed to avoid over-rich mixture.[/font]

Power producing potentials:
In theory, more power will be produced if more charge is jammed into the combustion chamber, resulting in higher cylinder pressure and temperature. In practice, the associated components such as pistons, turbo turbine, etc has a finite operating temperature constraint. This is normally reflected by the EGT. The general accepted EGT figure is about 900C.
Power is basically a force exerted onto the piston per unit of time. Force (pressure) is generated with heated air in a confined space. If cylinder pressure can continue to increase without temperature rise, we have the ultimate power plant. Water injection and alcohol injection will be a good tool to perform this work, lets examine this in more details how each concept can help achieving this.

POWER TUNING:
(Assuming we have a powerful ignition system, a strong engine and unlimited supply of air and fuel).

For water: the task is relatively simple. First generate as much heat as possible by adding more boost and fuel. Water is then injected to absorb the excess heat until EGT is within a permitted safe level. Overall BMEP (Brake Mean Effective Pressure) is now increased due to the vaporized water. The amount of BMEP increase will depend on the mechanical strength of the engine structure. Water’s ability to push the power capability is almost unlimited.

For methanol: First consider using methanol as a fuel instead of Gasoline. Methanol’s ability to increase power is confined to the knock threshold, and available heat to increase the BMEP of an engine. Methanol has only about half of the energy content of gasoline, so twice as much methanol has to be injected to produce the same power. As twice the amount of liquid has to be injected, the cooling effect is huge, resulting in over-cooled combustion chamber, limiting the BMEP. A 100% methanol engine has to use multi-spark ignition system to ensure the mixture is constantly being re-ignited due to the cold combustion chamber. Within those constraints, there is still huge potential of power increase.

A good compromise to inject a percentage of methanol into a gasoline engine. This will ensure good inlet and in-cylinder cooling effect, but how much? From reading many results form various forums, it appeared to be between 10-30% to fuel. Unfortunately, the results were not consistent, some got excellent power increase, some experienced engine knock, some misfires and some with very low EGT. Why?

4-5 years ago, AI system was very basic, at a certain manifold pressure, the pump starts and deliver a fixed amount of alcohol into the engine. In those days, results have always been very consistent and yield excellent power increase. But for the past few years, the results have been a mix bag. I could only put this down on the availability of the 2-dimensional AI controller. They are termed as an electronic progressive AI controller. Method of delivery is very similar to the mechanical rising-rate fuel pressure regulator. The flow is governed by the pump speed, the controller reads the manifold pressure via a MAP sensor, translates to a PWM drive signal to the delivery pump

Lucky for some, the availability of stand-alone, piggyback type of engine controllers give user a high degree of control, changing fuel and ignition timing is a merely rapping a few keys on the laptop. In my view, I think this is the reason for the inconsistent result – user’s interpretation of quite a complex ratio of methanol and fuel. Taking fuel out of the factory ECU to accommodate a methanol delivery system that has no reference to RPM, is a tall order. There are a few guys on this forum have managed it, I take my hat off to them.

My personal view on this relatively new concept requires a great deal of patience, dyno result means very little compared to logged data. Dyno-graphs always cause argument. I would really hope to see more logged graphs with AFR, Methanol flow rate, and EGT. If possibly include a second to fourth gear run-up so we can spot the afr change due to Methanol. For those who has just embarked on the WAI, tune with W50:M50 first - 100% methanol and lastly 100% for ultimate power.
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Last edited by Aquamist; 10-18-2006 at 06:50 AM. Reason: font change
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Old 10-17-2006, 06:01 PM   #2
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excellent info thanks
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Old 10-17-2006, 06:04 PM   #3
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...that font is VERY difficult to read.......a revision would be nice
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Old 10-17-2006, 06:44 PM   #4
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Quote:
Originally Posted by Uncle Scotty View Post
...that font is VERY difficult to read.......a revision would be nice
I took all the Bill Gates tag off.
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Old 10-17-2006, 06:48 PM   #5
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Moderator, could you edit my title - to

"water or alcohol injection, which one makes more power? "
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Old 10-17-2006, 06:48 PM   #6
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great read. thx!
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Old 10-17-2006, 08:19 PM   #7
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great as always...
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Old 10-18-2006, 04:19 AM   #8
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good info. learned something new today...
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Old 10-18-2006, 04:42 AM   #9
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Say for a 50:50 mix @ ~15% fuel delivery ratio, would be better if we *increase* this ratio [of the 50:50 mixture] in order to gain benefits over a single agent eg water OR methanol?

My reason is being that if we injected either water OR methanol at a ~7.5% ratio we are would probably see better results if we increased it.
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Old 10-18-2006, 07:46 AM   #10
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Yes, you might see better results when running a given amount of injection with a 50/50 mix then if you ran the same amount of 100% water(or possibly the other way around depending on the situation), but more injection does not always equal more power. Imagine hearing a tuner say, "We're running an a/f ratio of 1 to 1. I know it sounds like a lot of liquid, but we're trying for the most power we can get." Long story short, sometimes less is more, sometimes more is more, and sometimes you can be close enough to where you wanna be that neither is more.

peace

Last edited by hippy; 10-18-2006 at 08:52 AM.
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Old 10-18-2006, 04:21 PM   #11
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Quote:
Originally Posted by Aquamist View Post
Moderator, could you edit my title - to

"water or alcohol injection, which one makes more power? "
Done. Good thread.
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Old 10-18-2006, 05:01 PM   #12
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Thank you very much AaronB
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Old 10-18-2006, 05:10 PM   #13
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In case someone who wants to go a bit crazy with boost and static compression ratio. I am referring to having a 10:1+ CR and 4 bar boost (absolute).

Here is an example of such a car. Using water injection only, alcohol is not permitted due to regulation. It is an old thread but good practical guide.

http://www.i-club.com/forums/showthr...ght=subaru+wrc

Last edited by Aquamist; 10-18-2006 at 05:58 PM.
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