Razor: Formula or Method for Estimating Alky/Water Injection?

[dsagers]

Saw in one of your posts that you have your alky injection comes on at 3 lbs of boost.

Wondering how you decide how much alky to inject. Is your estimate a percentage of what your gasoline injectors flow? This would make sense, and would allow your progressive system to be used on engines from 1.6L to a 572 cu BBC.

Reason for my question is that I enjoy driving on the streets and freeways, haven’t taken the car to a race track in years.

I’m looking for a way to estimate the alky injection needed when I’m just cruising along with 4 or 8 lbs of boost, almost never use wide open throttle for more than a few seconds. I like the idea of having the alky injection start at 2 or 3 lbs of boost, and have the amount of alky increase based on boost and RPM.

 

[Razor]

Man what a loaded question

My own playing around.. the bigger the motor, the more alky. And the initial alcohol amount is pretty much used to offset detonation from happening. In other words, getting some alcohol into the motor heads off the detonation monster from appearing. See if the motor detonates at X psi, and you spray rite at X psi in a perfect world, you would still get detonation, becuase the boost rising vs time to get alcohol into the cylinders. If you have some alcohol in the air stream before the detonation... then the added fueling, and cooling calms the motor from knocking.

And the reality is one tunes the progressive around WOT not the initial. If you can get your metering dialed in at WOT... the bottom stuff is meaningless.

Now as to your question.. cruising at 4-8 PSI of boost.. well if your application is a turbo buick, and you typically can run lets say 20 PSI boost, then the need at 4-8 PSI is negligible. If you have a supercharger, and it pings at 6 PSI boost.. then you really cant cruise at 4-8..whereby you need X amount of alcohol to control detonation at 6 PSI. And will be spraying heavily. Only circumstance I can see this is in a boat with a supercharger where boost is constant for an extended period of time.

Now lets make this complicated, you introduce water. Water is overly sprayed will steam, while the same amount of alcohol will burn nice and clean. look at nozzles used for water vs alcohol. the alcohol nozzles are many times the orfice size as the water nozzles are. If you look at an aquamist system, they use an M1 nozzle. Thing is minute. And with water.. typical power application you spray 250 CC per min., on Alcohol.. expect 900 CC per min. How much on water/alcohol.... ahhh I hope you see the point. Probably 450-500 on a 4 liter motor approx.

now add heads, camshaft, breathing.. you can spray even more alcohol and the motor will respond to it. If you get tricky, then you limit the fueling by clamping down the injector DC and then adding a lot of alcohol to offset the missing fuel. Result is pretty much unlimited octane potential.

So i'm sorry I cant say a 1.6 liter motor need "X" amount of alcohol at 5 PSI. I will say that tho it is possible to replace 10-15 % of your fueling with alcohol at high demand levels. Probably even more...

 

[bruce]

Originally posted by dsagers

Wondering how you decide how much alky to inject. Is your estimate a percentage of what your gasoline injectors flow?

I’m looking for a way to estimate the alky injection needed when I’m just cruising along with 4 or 8 lbs of boost, almost never use wide open throttle for more than a few seconds. I like the idea of having the alky injection start at 2 or 3 lbs of boost, and have the amount of alky increase based on boost and RPM.

Goggling for NACA, and reading the paper about In Cylinder cooling is an interesting read.
Ricardo mentions 10-30% of the total fuel load being replaced with water.

It might be worth while to install an actual MAT temp guage and see where you with the tune you have now. Actually a MAT and EGT will best track what you have now. Then you can add the injection and see what settings give what results.