Thomas Knight ESC-350 supercharger and water injection

[zerodefects]

I have a Thomas Knight ESC-350 electric supercharger. This is the only real working electric supercharger that I know of. It is a centrifugal compressor hooked up to an 8hp electric motor (instead of the engine). One of the cool benefits of it is the ability to achieve its full boost (about 5 psi) instantly at any rpm. The disadvantage is that I can only run boost at WOT and only for a few 15 second spirts every hour (depending on batteries used and the alternator).
Since I won't be on boost all the time I'd like to run 87 octane fuel, then use the water/methonal when the supercharger turns on in order to prevent detonation with the added intake cooling benefit. This I think is an excellent use of water injection.
From what my research has found as long as I keep my water to 10% of my fuel (I am assuming mass, not volume) I shouldn't have any risk detonation problems at all. Also if I keep my water below 30% of my fuel I shouldn't run into any engine bogging problems. I know every engine is different but these are the guidelines that I used.
According to my calculations injecting 6 liters of water per hour will achieve these boundaries. I have a whole spreadsheet where I did the calculations (cfm, lbs of air, lbs of fuel, and water to fuel ratios), but what I am asking if this sounds *about right*. That does seem like a small amount to me. The car is a 3.8L V6 Mustang, redline is 5200rpms, boost is around 5psi (lower rpms a bit more, higher a bit less).
Thank you.

[zerodefects]

No comments?

To rephrase I need enough methonal/water to drop down my octane requirements, while not injecting too much that it will bog down my engine at low rpms.

3.85L engine, 5psi of boost from 1500rpms to 5200rpms. What nossle should I use if I went with a 1s kit? Based on my calculations the 9 liters per hour the smallest nossle gives is 50% too much.

[JohnA]

6lts/hr is 100ml/min.

If you really do get 5psi boost on this engine, then you might want more water at higher rpm.
87octane is not a lot, so on hot days (depending on charge temps) you may want to dial in even more.

[zerodefects]

How much can I add without bogging the engine at low rpms? I know this is engine dependent, but what is the a generally acccepted safe limit for lower rpms and low boost in the ratio between W/M and fuel?

Unfortnately my car does not have a knock sensor, so I am going to try to get this right or as close as possible the first time instead of "working my way up" while detonating on my engine

[zerodefects]

Any tips at all?

I am kind of in the dark as to where I should start. Are my current thoughts on track or way off?

Based on my reading from multiple sources I've developed the following parameters:
10% of water/methonal to fuel minimum to reduce octane requirement.
25% maximum to stay out of combustion quench.

I've got one reply that says 10% may not be enough so I decided to check into things some more. One tuner for my car stated that an 11:1 fuel ratio should be able to run 4psi without detonation on 87 octane. Of course not as safe, but it would work. So I ran some numbers:

2260kJ of heat absorbed by water
1109kJ of heat absorbed by methanol
50/50 mix = 1685kJ

350kJ of heat absorbed by gasoline
1685/350 = about 4.8 times the latent heat aborbing ability

12.8 to 11 is a 14% increase in fuel
same results obtained through 3% increase in water/methonal

I'd say 10% is more than safe, if anything I should be able to go with less.

I am no expert though, I need to know if I am on the right track from the pros here.

[JohnA]

Do you really want to start flitring at the detonation threshold without a knock sensor of some sort? :?

You have got a wideband fitted at least, right?

In any case, I'd think that just a few psi boost for 15seconds max is not gonna melt pistons immediately. Most likely running a bit rich (10 or 11:1) will cover it.

[keithmac]

I think you may have your calcs wrong? I run 15psi though a 1.8l engine on a 0.8 or 1.0 jet to give aprrox 300cc/min, think I originally worked for a 20% water to fuel ratio.

Yopu need to work out you injector duty cycle, fuel used an go from there.

My 300cc`s come in at 2000 rpm and don`t bog the engine at all.

[zerodefects]

Originally Posted by keithmac

I think you may have your calcs wrong? I run 15psi though a 1.8l engine on a 0.8 or 1.0 jet to give approx 300cc/min, think I originally worked for a 20% water to fuel ratio.

You need to work out you injector duty cycle, fuel used an go from there.

My 300cc`s come in at 2000 rpm and don`t bog the engine at all.

Here are my calculations, it would be nice to have somebody else look them over:

First I calculate my cfm
CID * Pressure * RPM * VE / 3464
For 5200rpms (my redline), I expect to be making .3 bar boost. This is a 235 cubic inch engine, with about an 80% VE.
235*1.3*5200*.8/3464 = 366.88CFM

For 2000rpms I'll be making a touch more boost .34 bar
235*1.34*2000*.8/3464 = 145.45CFM

Convert CFM to lbs of air per hour:
CFM * lbs of air per cubic foot * 60
366.88 * .080645 * 60 = 1775.23 lbs of air per hour
145.45 * .080645 * 60 = 703.79 lbs of air per hour

My A/F on my current tune sits at about 12.8 at WOT, so to calculate the amount of fuel to burn the air:
lbs of air per hour / 12.8
1775.23 /12.8 = 138.69 lbs of fuel per hour
703.79 /12.8 = 54.98 lbs of fuel per hour

Using 1.74 gallons of 60% water/40%methanol per hour (2.3GPH nozzle on a 65psi pump) in lbs:
gallons of water * weight of a gallon of water + gallons of methanol * weight of gallons of methanol = lbs of water/methanol
(1.74*.6) * 8.33 + (1.74*.4)*6.63 = 13.31lbs per hour

Water to fuel percentage by mass:
lbs of water per hour/lbs of fuel per hour
13.31/138.69= .096
13.31/54.98= .0200

Based on those calculations 9.6% at redline and 20% at 2000rpms.