View Full Version : Calculate your correct injection Percentage !

TurboGTi

11-06-2004, 07:06 PM

As the topic says please can someone post the information on how to calculate

fuel injector flow in cc/min

and also

WI flow in cc/min

along with all the necessary calculations to obtain optimum Water injection percentage

thanks

Richard L

11-06-2004, 10:51 PM

Are you referring how much water is needed to replacing excessive fuel injected based on stoichimetric air/fuel mixture?

For example, if an engine is running with rich air furl mixture to maintain resonable egt level and and knock free - 10-10.5:1 is normally considered as a safe tune by most tuners now a days and manufacturers.

TurboGTi

12-06-2004, 07:23 PM

Are you referring how much water is needed to replacing excessive fuel injected based on stoichimetric air/fuel mixture?

For example, if an engine is running with rich air furl mixture to maintain resonable egt level and and knock free - 10-10.5:1 is normally considered as a safe tune by most tuners now a days and manufacturers.

Well its more of calculating how much CC/min of water must be injected .

I've previously seen some guys in here calculating their cc/min for both the fuel injectors and their water injection.

I'm not certain if this is foe AFR tuning or just general injection amounts.

Currently i'm running water injection on my 1300cc but i have 380cc fuel injectors. My WI jet that i'm using is a 0.5mm on the race pump.

My WI is active at 10 psi full boost is 15psi.

What i want to know is if the 0.5mm jet is enough.

I've seen people make reffeerence to the chart that you have richard with the various Jet flow rate at xxxpsi !

You understand what i'm saying... i'm a bit confused myself :(

Richard L

13-06-2004, 10:44 AM

The quantity of water will largely depending on the following factors:

1. effective cmpressure ratio

2. fuel grade

3. egt

4. knock tendency

5. ambient temperature

6. final charge temperature

7. a/f ratio

8. how close you run your engine towards MBT timing

Most factory produced car will have all the above variables under control. As soon as you start to modify your engine - you will notice a few of the above variables will change - but if it is inside the safe-operating area of the ECU, minor adjustment to the fuel, timing etc will keep the engine safe.

Most factory fitted ECU employs the following procedure strategy to keep the engine alive with the following balancing act:

1) retard timing with mild knock (knock sensor)

2) Increase air/fuel and timimng with heavy knock.

It normally works very well until you iincease the boost pressure, the excess fuel used to cool the engine is now being uswed for power.

Under this circumstances - you must replenish the engine's cooling capability by either using bigger injectors or water injection. Since water has six times the latent heat of fuel, you need to dump six litres of fuel per litre of water!

Since un-burnt fuel has huge impact on the combustion process, it robs huge amount of power if it is used as a coolant rather than as a fuel. In comparison, the OH radicals within water enhances the burn process.

(please read turboice's WI paper)

At last you question as to how mush water to inject ? the sweeping conclusion and simplied - around 10-15% w/f ratio when you are running a few psi over the stock boost.

Quite easy to calculate: add all your injectors flowrate together and multiple it by 10% or 15% - look at the aquamist jet size/flow, that is it!

http://www.aquamist.co.uk/forum/flowrate4.gif

It is clear that WI injectionf

honki24

06-05-2005, 09:15 PM

dont think I get it... so I've got an evo8, w/ 550cc injectors. so all added up thats 2200cc. I have a nozzle that @ 100 psi pump pressure injects 3.9 gal/min. how do I figure out if that is enough?

honki24

06-05-2005, 09:22 PM

k... lets see... 3.9 gal = 14763 cc ...therefore... 3.9gal/min WI should mean I am injecting 14763cc/min. In one rotation there is 4 ignitions, meaning 2200cc per rotation. if I'm at say 6K rpm... then I have 13,200,000cc per minute of fuel. and 14763cc per minute of water. that means I am running .1118% water to fuel? did I do that right?

hotrod

06-05-2005, 10:12 PM

I think you need to throw out that math and start over your numbers are WAY out of the ball park!

then I have 13,200,000cc per minute of fuel

That is 13,200 kilograms of water or about 29,040 lbs of fuel ---- I don't think so ;)

At max rpm, WOT the injectors are nearly running continuously. Forget how many times the engine fires, ( a 4 cycle engine only fires each cylinder once every 2 revs anyway ).

You will find that the WI nozzle is probably rated in gallons / HOUR

For a gallon/hr nozzle just multiply the gal/hr by 63 and you have cc/min flow. In your case your spray nozzle flows about 246 cc/min

Your fuel injectors flow 550cc/min MAXIMUM at 100% duty cycle. So the max fuel you can flow under any conditions is 2200 cc/min. If you car runs a max injector duty cycle of 85% ( that's typical max on a factory set up) your max fuel flow is 2200 x .85 = 1870 cc/min. 15% of that is 280.5 cc/min.

Your 3.9 gal/hr nozzle will give you about 13% water to fuel at max fuel injector duty cycle and the WI spray wide open.

Larry

Roverdose

07-05-2005, 09:09 AM

ok then...

i have 4x 750cc injectors = 3000cc/min max flow

lets say i have a max of 80% duty cycle on the injectors

80% of 3000 = 2400cc/min

15% of 2400 = 360cc/min

looking on the above flow chart id need 2x 0.4 jets (350cc) or 2x 0.5 jets (440cc)

Drew

honki24

09-05-2005, 01:09 PM

I think you need to throw out that math and start over your numbers are WAY out of the ball park!

then I have 13,200,000cc per minute of fuel

That is 13,200 kilograms of water or about 29,040 lbs of fuel ---- I don't think so ;)

At max rpm, WOT the injectors are nearly running continuously. Forget how many times the engine fires, ( a 4 cycle engine only fires each cylinder once every 2 revs anyway ).

You will find that the WI nozzle is probably rated in gallons / HOUR

For a gallon/hr nozzle just multiply the gal/hr by 63 and you have cc/min flow. In your case your spray nozzle flows about 246 cc/min

Your fuel injectors flow 550cc/min MAXIMUM at 100% duty cycle. So the max fuel you can flow under any conditions is 2200 cc/min. If you car runs a max injector duty cycle of 85% ( that's typical max on a factory set up) your max fuel flow is 2200 x .85 = 1870 cc/min. 15% of that is 280.5 cc/min.

Your 3.9 gal/hr nozzle will give you about 13% water to fuel at max fuel injector duty cycle and the WI spray wide open.

Larry

thanks for helpin me there! The math really helps...however I am pretty modded, and so I definately run 90-95% duty cycle. question though... why do you just neglect the rpm?

dsmtuned

09-05-2005, 01:45 PM

Larry[/quote]

thanks for helpin me there! The math really helps...however I am pretty modded, and so I definately run 90-95% duty cycle. question though... why do you just neglect the rpm?[/quote]

RPM is one of the factors that determines injector duty cycles. :wink:

Craig

Gert_

09-05-2005, 04:06 PM

For example, if an engine is running with rich air fuel mixture to maintain resonable egt level and and knock free - 10-10.5:1 is normally considered as a safe tune by most tuners now a days and manufacturers.

Are you serious?? Resonable egt level and knock free level with 10-10.5:1?? This is a power free level too, I suppose :?

Gert

Gert_

09-05-2005, 04:16 PM

RPM is one of the factors that determines injector duty cycles. :wink:

Craig

To calculate duty cycle:

(60 / (RPM / 2)) * 1000 = Msec ( maximum injector time available at this rpm)

To find duty cycle:

(Inj time / Msec) * 100 = Injector Duty.

If you want to know exact duty cycle at any rpm, you have to know the exact injection time, so you must have some logging tool.

Now, if you have logging files, you can make an excel sheet, and calculate what fuel is injected, and how much water is needed at any * percentage.

That is not an garantue that it is working correct right away, at least, not at my car. After the math, there are some adjustments needed, based on knock, and intake temps.

Gert

honki24

10-05-2005, 10:10 PM

well, Its just nice to know I'm running in the 10-15% w/f ratio, rather than .11% :lol: now... how to figure out the afr I want w/o a piggyback or any means of knock detection...

Santo Fontana

13-05-2005, 08:41 AM

I think you need to throw out that math and start over your numbers are WAY out of the ball park!

then I have 13,200,000cc per minute of fuel

That is 13,200 kilograms of water or about 29,040 lbs of fuel ---- I don't think so ;)

At max rpm, WOT the injectors are nearly running continuously. Forget how many times the engine fires, ( a 4 cycle engine only fires each cylinder once every 2 revs anyway ).

You will find that the WI nozzle is probably rated in gallons / HOUR

For a gallon/hr nozzle just multiply the gal/hr by 63 and you have cc/min flow. In your case your spray nozzle flows about 246 cc/min

Your fuel injectors flow 550cc/min MAXIMUM at 100% duty cycle. So the max fuel you can flow under any conditions is 2200 cc/min. If you car runs a max injector duty cycle of 85% ( that's typical max on a factory set up) your max fuel flow is 2200 x .85 = 1870 cc/min. 15% of that is 280.5 cc/min.

Your 3.9 gal/hr nozzle will give you about 13% water to fuel at max fuel injector duty cycle and the WI spray wide open.

Larry

If you were using a simple single stage with a solenoid, wouldnt you want to take your IDC at your tourque peak, or whereever you plan on starting the spray, and figure out your fuel flow at that point? It seems to me if you if you size your nozzle at max idc, then you wouldnt want to turn it on until then.

RX-Heven

16-07-2005, 12:39 AM

Injector setup is 2x720cc primaries and 2x1600cc secondaries.

To run 15% water to fuel at 70% IDC, I calculate this way:

(IDC) x (Total fuel cc's) x (Target % water) =

(.70) x (1440 +3200) x (0.15) = 448 cc's of water

Then, also assuming the water nozzles operate at 70% DC and one 0.9 mm WI nozzle flows 315cc (max), I get:

(15% water to fuel) / [(WI flow rate) x (IDC)] =

(448) / [(315) x (.70)] = 2

So I would need two 0.9 mm nozzles to meet my 15%.

Alternatively,

The water (mixture)-to-fuel percentage is roughly 10% with one .8mm nozzle and one .5 mm nozzle in my setup.

Here is how to find that:

To run 10% water to fuel at 70% IDC (assuming), calculate this way:

(IDC) x (Total fuel injector cc's) x (Target % water) =

(.70) x (1440 +3200) x (0.10) = 325cc's of water

Then, knowing the water nozzles operate at 70% DC (from our assumption of IDC) and one 0.8 mm WI nozzle flows 280cc (max) and one 0.5 mm WI nozzleflows 180cc (max), I get:

(required cc's of water) / [(WI flow rate x IDC)] = 10%

(325) / [(280 x .70) + (180 x .70) ] = 10%

james-g40

05-01-2013, 08:36 PM

I know this is an old topic but this might be the answer im looking for.

Going by the math provided this should be correct:

4 x 250cc injectors = 1000cc

1000 x .85 = 850

15% of 850 = 127.5

Im planning on running the smallest injector my kit come with which was 0.5mm. Is this too much?

Richard L

05-01-2013, 08:44 PM

0.5mm injects aboiut 200cc/min. If you ad about 25% methanol as an antifreeze, You are not far off the ideal.

Since we have stopped the production of the 1s system six years ago. Look after it well as there are no more spares available.

james-g40

07-01-2013, 09:55 PM

Ok, i will make sure its well looked after.

Im going to be using a 50/50 mix.

Would a 0.4 be better? Or i can run 2 x 0.3's but that gets more expensive but will help if one injector gets blocked.

james-g40

07-01-2013, 10:41 PM

Richard, i spoke to my mapper as he logs/stores it all and he said that my 250cc injectors are running around 75-78% duty cycle on 1 bar boost above 2500rpm or so.

Richard L

07-01-2013, 11:05 PM

In this case, 0.4mm may be just about right.

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