WI quantity calculations

[TAZ]

Hi,

Is there a guide or some calculations to do in order to size the nozzle capacity?
The engine is a 1.8T (VAG group) 4 cyl transversal with the std equipped K03sport turbo (KKK ...053).
The goal is to be able to advance the timing.

The WI system is a Shurflo pump (543226 P/N) factory set at 60PSI (internal switch??) , a shurflo accumulator, a std solenoid 12V 250PSI and i'm thinking a suitable nozzle system from spraying systems (probaply the small capacity LND type..).

As i checked the site i spotted some info from hotrod but now it's difficult to find it again... :? :cry:

Thank you in advance,

[Forum Admin]

generally w/f ratio is between 10-15%. It you add up all the fuel injector's cflow rate and multiply it with the IDC tyiou wil come up with a figure something in the region of 1.5-2 litre/min. work the WI out from thre.

Not sure what nozzle you will be using, but you can also measure it by emptying the contents into a measuring glass for iminute.

I am afraid thart is the best way to do it.

[TAZ]

Thanks for the answer.

I have already data (Block 002 using Vag-Com) and the DC value (calculated) varies from 30% at 2400rpm (where boost is 0,96bar actual) to 86,5% at 6640rpm where boost is 0,87bar (actual).
The std injectors are 317cc/min@3bar FPR but i use 4bar FPR ....so the value calculated for all injectors are 1464,16cc/min (for Fuel).

If i calculate now the DC (using highest number?) will come to 1266,5cc/min.

Now the 10-15% of this should be ad-on water?
----> 126cc/min to 190cc/min (for 10 to 15%).

Is the above calculations correct??

To calculate the orrifice needed i need to check the WI preassure produced by the pump....(on a working condition where 10PSI or more for example boost exists in the intake manifold).
This is the (as per specs) 60PSI max pump preassure minus the 10 or more (max 22PSI) boost in the intake manifold?

Now for 38PSI pump effective preassure (2,6bar) i can see in specs the proper nozzle - orifice... (I'm right up to this point?).

Last is it possible to uprate the surflo pump to be able for 100PSI for example??
Is there any replacable preassure switch for this (P/N is on first post).

Thanks again...

[Richard L]

The calculation is pretty close, w/f is by volume only. Water is 25% heavier than fuel. so at present you are injecting between 12.5 to 18% mass. Not really a problem.

My concern would be your water pressure, if you could get teh 100psi pumpm it will be much better and don't have to worry about differential pressure loss.

Not shure if the pump's pressure governed by the pressure switch.

[hotrod]

On the 8000-543-238 shurflo 100 psi pump there is an adjustment screw visible at the top of the pressure switch. I "believe" that is the pressure set point adjustment for the pump pressure switch. I have personally never fiddled with mine, so cannot say with certainty, but you might give it a try and see if it will allow you to crank up the pump pressure switch shut off pressure.

I've read that the factory setting on that switch is the only difference between different pressure pumps of the same part number family.

It would be good to know if that works, but I just have not had the time to mess with it.

Larry

[TAZ]

Thank you guys,

Larry,

The P/N of the pump is actually (8009-543-236) and is factory set at 60PSI.
Yes there is a small allen type screw in top of the pump which can be adjusted....

I'll try that ......and see.

[b_boy]

The big picture--One way to do the calculation is to assert a maximum quantity of water that the air can hold (it's saturation point, beyond which water remains a liquid). For moderately warm air of 30 C (~85 F) this is about 25 grams water per kilogram.

At 300 hp, my engine is ingesting ~200 g/s of air (mass air flow readings). So, it's water capacity at 85 F is about 60s/min X 200g/s = 12 kg/ min => 25 g x 12 =300 g/min.

Now your air is not dry even if you live in a desert. If you live in an average climate you will have 50-60 % water saturation if it's not raining, and closed to 100% when it is raining. Hopefully, you don't live in the tropics, so you dont have to worry about 90% saturation at 85 F too often. For the sake of simplicity, lets assume 50% saturation. That gives you 300/2 = 150 g/min of water per kg that you can inject.

Or if we look at it from the engine's point of view 2.5 g/s of WI at 300 hp of an engine ingesting 200g/s. Let's stick with g/min because 150g/min is the same as 150 ml/min (1 ml of water = 1 gram).

So for my engine, I could inject a maximum of 150 ml/min at maximum RPM and horsepower (we are making some assumptions here).

Let's make it easy, and assume your are running very rich air to fuel ratio of 10:1 AFR (it's really 9 parts air to 1 part fuel). At 12 kg/min air that is 120 g/min of fuel. Thus theoretically you could inject more water than fuel: 150 g water (in 50% sat air) plus 1200 g of fuel. This corresponds to more that 100% WI as most people view it, as percentage of fuel. Most people would not inject more that 25% of fuel.

So, here come's the simple approach I: Figure out your maximum amount of fuel that you inject in gram/min like Ed said. Multiply times 0.25. Voila, 25% water injection. In the example above, that is 300 g/ min or 300 ml per min.

300 ml/min would be the maximum amount I would inject. I would need a jet or jets that could dispense 300 ml/min of water. I look at the nozzle chart of Aquamist and find that two 0.5 mm jets, running at 10 bar and 85% high speed valve duty would do it.

If you are running 25 psi of boost, I might run 5% WI at 5 psi, 10% at 10psi, and so on.

Don't like 25% WI as a maximum rate, substitute 15% instead.
Now it's 180 ml/min maximum.
One 0.7 mm jet at 90% HSV duty.
3% at 5 psi (or 18% HSV duty)
6% at 10 psi (or 36% HSV duty) and so on.

Don't use Aquamist, but like McMaster Carr nozzles, convert from gallons/ hour to grams/min at a specified water pressure by multiplying times 29.6 ml/ounce times 128 oz/ gallon, and divide by 60 min/hour. For at 6 gal/hr at 80 psi nozzle, that's 378 ml/min. Ooohh..... your pump runs 100 psi, not 80 psi, either use the Aquamist graph to convert your nozzle rate to one of theirs (or in between Aquamist jets), or do some pretty fancy math with Poiselle's Law (I don't recommend this).

Another simple approach II: when you don't know how much air you are ingesting or how much fuel you are injecting is to just use horsepower or your fuel injector flow rating. You have a four cylinder engine and your injectors are running at maximum duty (IDC) of 80%. Each injector is 350 cc/min = 25% water injection (one cc equals one ml). This is too simple, as to be inaccurate (boost and fuel pressure can change injector ratings), but it gets you in the ball park, and that is all that matters for WI.

Play around with this calculator and see if you can get any better info, if you know your horsepower at the crank:

http://www.stealth316.com/2-air-fuel-flow.htm

Fuel Flow is the one your want.

[Richard L]

I wonder if you can do the same calculation how much water can the air hold after compressor. Two factors need to be considered: pressure increase and temperature increase.

The percentage between saturated air and suspended water droplet will depend on the final temperarture after the air has been cooled.

I think the calculation will be a great deal more involved.

[Richard L]

Over the year I have often heard that the amount of water is unlimied until the engine start showe signs of bogging down. Very often with good results.

I would like to know the theory behind this application, just try to put this practice in a manner that makes sense for engineers - in either thermal dynamic terms or any scientific explaination.

any ideas?

[cosator]

Over the year I have often heard that the amount of water is unlimied until the engine start showe signs of bogging down. Very often with good results.

what are these signs of bogging down ? can you list them/some of them, please ?

thanks.


cosator

[hotrod]

The engine bogging down shows up mostly as a subjective evaluation by the driver. In its usual usage the engine might stumble or hesitate a moment or just have a brief period where power seems to be down a bit. In severe cases bogging is very obvious, its like the cars ignition was turned off for a fraction of a second, or the car acts like it suddenly got much heavier and the engine had to work much harder than normal for a second or so.

An ideal engine, properly tuned, has good throttle response and seems eager to pull. When you blip the throttle for a down shift for example, the engine has a very sharp crisp response. It revs immedialtly and willingly. Under hard acceleration you get the feeling the engine "wants to rev -- it wants to pull".

On an engine that has a bad tune ( could be too much water injection or other things like improper timing etc.) the engine is not as crisp, there is a small but detectable lag between when you change the throttle setting and when the engine responds. It simply feels a bit flat. On an engine that you can hear the intake sounds it sometimes sounds like its strangling or choking on the excess water. A lot of tuners will say the engine sounds "soggy" it feels and sounds water logged.

In severe cases there may be an obvious loss in power when the WI first engages as the excess water actually reduces power output, then as the engine revs it gets the power back plus a small improvement at the top end. This might indicate a turn on poiint that is too early or the jet is too big until the engine gets higher up the power curve.

All very subjective, but one of those things you'll usually recognize when you see it.

Its like the driver who comes in for service and tells the service manager the car runs fine but just doesn't feel right, its a bit sluggish etc.
On examination the shop might find something like bad plugs. The symptoms were noticable to someone familiar with the car but a total stranger might think the car was running normally.

Larry

[TAZ]

Larry,

Managed to get the service bulletin from shurflo for adjusting my pump for up to 100PSI (from the 60).
It describes the procedure to do it....
(if you want it i can sent it via an email....).

Now i'm fixing a distribution manifold to connect the pump, accumulator, solenoid (drives the nozzle system) a preassure gauge, a preassure switch for the manifold and some spare ports for future use.
The order for the ingector nozzle has been set (spraying systems nozzle system) and the steel pipe replacement of the feed to intake manifold is planned to support the nozzle and future additions ... :twisted:

Just an info....
Any schematic for converting my setup with preasure regulator will be much appreciated???

[Slump]

The engine bogging down shows up mostly as a subjective evaluation by the driver. In its usual usage the engine might stumble or hesitate a moment or just have a brief period where power seems to be down a bit. In severe cases bogging is very obvious, its like the cars ignition was turned off for a fraction of a second, or the car acts like it suddenly got much heavier and the engine had to work much harder than normal for a second or so.

Larry

Here's a dyno chart showing "too much water".

The blue curves had far, far too much water.

The difference between the blue and red curves where simply turning down the amount of water.

http://cobweb.ibsys.com/~smith/miataweb/tuning/dyno2.gif

[hotrod]

Hey very good dyno plots, those very clearly show the "fluttering" effect some folks report when you get too much water.


It also points out how easy it is for a vendor who doesn't like WI to make it look bad, all he has to do is over inject the water and you get an instant 20 hp drop in power output.

Larry

[b_boy]

Bogging most often occurs in most peoples cars when they leave the car in a high gear, and when trying to accelrate the car "bogs". It kind of chugs. I think it's a series of misfires.

Pressure will tend to slightly raise saturation point, increased temperature tends to greatly raise it. Hence rain when air cools, and lower pressure signals rain. Also, you can see that warm air can hold a great deal more water. At 50 F, air will hold about 4 g per cubic foot, and at 90 F, about 14 g per cubic foot.

At 30 psi, 50 F holds the same 4 g per cu ft. At 90F, 30 psi, sat. air holds 15 g per cu ft.

Good calculator:

http://www.engineeringtoolbox.com/8_240qframed.html

dry=wet bulb temp equals 100% saturation of air.

[SaabTuner]

Many WWII aircraft injected as much as 50% water to fuel even at A/F ratios richer than 11:1, often leaner than 20:1 as well.

I think that's more a problem with the ignition system. The Aquamist WI setup shouldn't even be capable of drowning the engine.

The water in the air might be making it too easy for the spark to jump the stock gap. I wonder if a larger gap would be appropriate when running high water/air ratios.

Also remember that, by the time your cyllinder fires, the temperature of the air in the cyllinder is well over 350F.

Adrian~