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Author Topic: Calculating Water Injection and placement  (Read 38882 times)
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landracing
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« on: May 11, 2007, 02:31:43 AM »

So we know you have a system and different nozzle sizes from Snow Performance. But what is a rule of thumb or a calculation estimate on the amount that is needed.

Just curious to know how it is calculated, and if its calculated on a single nozzle system. What happens when you want to run four individual nozzles on a 4 cyl FI motor?

I'm thinking of a system but using a fuel rail setup for the nozzles. Which leads to placement of nozzles. Before or after the fuel injector or will it not matter?. I know this will open a can of worms, but im pretty unfamiliar on the setup or the possibilities.

Jon
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« Reply #1 on: May 11, 2007, 10:26:49 AM »

So we know you have a system and different nozzle sizes from Snow Performance. But what is a rule of thumb or a calculation estimate on the amount that is needed.

Just curious to know how it is calculated, and if its calculated on a single nozzle system. What happens when you want to run four individual nozzles on a 4 cyl FI motor?

I'm thinking of a system but using a fuel rail setup for the nozzles. Which leads to placement of nozzles. Before or after the fuel injector or will it not matter?. I know this will open a can of worms, but I'm pretty unfamiliar on the setup or the possibilities.

Jon


Jon is there a reason you want to run 4 nozzles???  Because my memory is so bad I can't remember if you are running an intercooler now or not??  I looked at a picture I have of your bike, is the aluminum box just an air box that goes to the intake runners or is it also an intercooler??

On the side of it there appears to be a single throttle body.  I don't know what Nate is going to say, but if you look on page 130 of Dec. 2006 HOT ROD (I could send you a copy) they used Snow's system on a blown vette and the injection point was after two air/air intercoolers and ahead of the throttle body.  They used two injectors there, but I think Nate told me they could have used just one.

I would think the further you get away from the combustion chamber the more the water will mix with the air and cool it, but I could be wrong.  Their nozzles so finely atomize the water or water/meth mix that you will get complete mixing injecting down stream and it will be equal to all cylinders.

Nate would help you pick the right nozzle size.  It might also be on their site.  I remember one of the sites that sells these had a place that helps you size, but I think they all have their proprietary nozzles and they probably would not cross reference.

I'm wondering if they would have a small enough nozzle to run 4 in your application??

I'll bet Nate answers some of these questions.  Hooley picked up our stuff at their facility yesterday and he was very impressed with their operation and Nate's knowledge along with Matt Snow's, the owner.  We look forward to working with their system this summer.

c ya,

Sum
« Last Edit: May 11, 2007, 10:29:43 AM by Sumner » Logged

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« Reply #2 on: May 11, 2007, 11:36:36 AM »

The intake charge begins to heat up at inlet  point where it is compressed and that is where it can begin to do some good.
If your system allowes it to fall out of suspension and puddle , it is a bad design to start.  wink
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« Reply #3 on: May 11, 2007, 02:30:04 PM »

Like Sum had mentioned our nozzles are proprietary and our nozzle selection process is slightly guarded as it's the product of years of r&d and testing. 

I can tell you this: we base our nozzle selection on a number of reference points.  Depending on your horsepower output, which is indicative of airflow and fuel consumption, and boost level, which is indicative of heat, we inject a percentage of your primary fuel flow rate. 

So long as you have an idea as to how much power and boost your making we can get you accurately sized with the nozzle that will work best for your application.  We find the the required flow rate and select an appropriately sized nozzle (two nozzles are included in every kit to cover a wide range of flow requirements).  If the required flow rate is more than what our largest nozzle can support we simply add in another nozzle.

There really isn't much of an advantage to running multiple nozzles if one nozzle will support the required flow rate.  It just complicates the system.  Our nozzles do a great job of atomizing the fluid that there are little to no concerns of distribution.  When the fluid is being injected it's in a very very fine mist.

In your instance Jon, if we used four of our smallest nozzles you'd have way too much flow.  To reduce flow you'd have to reduce system pressure.  With reduced pressures comes reduced atomization.  It's better to have one large nozzle at max pressure than four small nozzles at reduced pressure.

The longer the fluid is present in the air intake tract the longer it has to pull heat from the air charge.  This is great for reducing IATs but this limits how much fluid gets into the combustion chamber where it acts as a fuel and detonation suppresant.  We generically recommend that the nozzle be placed before the throttle body or throttle plate that way it has some time to reduce IATs and still act as a fuel. 

Thanks,

Nate

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« Reply #4 on: May 11, 2007, 02:31:09 PM »

There are several rules of thumb used for picking a WI spray rate.

Most assume a 50/50 mix of water and methanol, on straight water you can get away with less spray due to its higher cooling power than the methanol. It will also typically requires a slight change in ignition timing going to straight water vs water methanol. Something like an additional 2 degrees of timing seems to be common.

Most folks start off running a spray rate of approximately 15% - 25% of the fuel as a starting point.
In the unlimited Air racing world, Unlimited Hydroplanes and the WWII military aircraft, they used a 50% to fuel injection rate on a 50/50 mix of water and methanol. (ie 1 lb of ADI fluid for each 2 lbs of fuel  ---- ADI is the term used by the military for water injection stands for Anti-Detonation Injection)


That should get you in the ball park then you need to dial it in to run the least injection you can and still be safe, to avoid over cooling the combustion process.

At least that's my experience.

Larry
« Last Edit: May 11, 2007, 02:32:46 PM by hotrod » Logged

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« Reply #5 on: May 11, 2007, 04:33:02 PM »

The intake charge begins to heat up at inlet  point where it is compressed and that is where it can begin to do some good.
If your system allowes it to fall out of suspension and puddle , it is a bad design to start.  wink


One point - if you have a centrifugal-type compressor, you really don't want to inject any fluid before it or into it.  You can, and people do, with draw-through carbed turbo setups and low-pressure water injection setups, except it isn't a good idea for a couple reasons.  One, is that it will erode the impellor blades - even our tiny droplets hitting something spinning 60,000-150,000rpm is going to deform the leading edges of those blades.  We have tractor pullers do this - but they replace their turbos very often regardless, so it is less of an issue.  Two, a turbo or centrifugal supercharger compresses air with centrifugal force - air, that weighs very little (in comparison to water/methanol).  Think what will happen to the tiny droplets as they go through and get slammed into the outer compressor housing wall - recollect into larger droplets and we get much less benefit than with smaller droplets. 
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« Reply #6 on: May 11, 2007, 08:29:30 PM »

We are speaking primarily of racing here and draw - through has been very effective even with the fluid volumes seen with NOS over Alky.
I have a 6 cyl. Honda for example that has been setup with a draw-through gas system and about 40k miles with no erosion to the inlet blades.
The gate is set for 25lbs. and the manifold supplies the pressure for the water injection.
We use a selection of commonly available Mikuni pilot jets.

"There is more than one solution as there is more than one problem, but they often share the same objective with simular results." (me) wink 
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« Reply #7 on: May 12, 2007, 12:02:49 AM »

Pre-compressor injection on turbocharges can be made to work but it is not suitable for most people.
It can significantly improve the efficiency of the compressor due to the thermal effects it has on the air under compression.

It takes very little water injection to achieve these gains (only a couple percent of the air flow by mass).
I used it on the street for over a year with only minor erosion of the impeller, and with a different design on the system it does not necessarily erode the impellers.

It generally is only appropriate for users that cannot get a big enough turbocharger to meet their needs. The result of the WI pre-compressor makes the turbo act like it is bigger than it really is.

(oh by the way the military aircraft ADI systems used in WWII on the Pratt and Whitney 2800 and other engines use pre-compressor injection of both fuel and ADI fluid)

Larry
« Last Edit: May 12, 2007, 12:07:21 AM by hotrod » Logged

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« Reply #8 on: May 15, 2007, 06:53:56 AM »

There is some interesting info here http://www.rbracing-rsr.com/waterinjection.html, including an online calculator .
Hope i'm not stepping on Snows toes.

I was thinking of putting 4 jets after my plenum mounted intercooler and trying to size the droplets to be small enough to be dispersed in the cyl but large enough to not vaporise before combustion, intending that the intercooler do its job and water inj be for detonation suppression without occupying too much combustion chamber space ....comments welcome!



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« Reply #9 on: May 15, 2007, 04:17:20 PM »

The WRC folks are having good results as I understand it, going to direct port injection for the WI setup. This allows them to tune by cylinder to be absolutely sure they get uniform mixture. The down side of that setup is if you lose a jet due to it plugging you have a fatal lean out in that one cylinder where a manifold type injection will suffer less if a single jet in a multi-jet setup  plugs up.

WRC is one of the few racing catagories that still allows WI and also has a sustained high power environment so it would probably be worth while for folks to investigate how they do things.

Larry
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« Reply #10 on: May 17, 2007, 03:45:39 PM »

Multiple nozzle systems can definitely be used however we've seen that because our nozzles atomize fluid so well that distribution typically isn't an issue.  You can run individual nozzles per cylinder if you've got the horsepower/heat/airflow to support it.  We typically try to make things as simple as possible and provide a system that is more or less "bolt on".  Obviously we can do whatever is needed to support different applications and horsepower levels. 

In regards to the nozzle placement for cooling versus consumption as a fuel:  We have a generic recommendation that the nozzle be placed before the throttle body.  This usually provides a "happy medium" that allows for IAT reductions and increased detonation control.  The closer you are to the combustion chamber the more the fluid acts as a fuel and the farther away from the combustion chamber the more the fluid acts as an intercooler.  Data logging and tuning are normally the best way to determine optimal nozzle placement for your specific application.

In regards to nozzle selection: it is correct in that we base the injection quantity off of a percentage of primary fuel flow.  Our nozzle selection guide (and any other guide) is exactly that: a guide.  There is nothing absolute in the information we provide regarding nozzle selection because there are so many variable at play on different applications.  We can get you close but final tuning is up to the end user.

I hope this helps.

Nate
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« Reply #11 on: May 19, 2007, 06:54:22 PM »

:  We have a generic recommendation that the nozzle be placed before the throttle body. 
Nate

Thanks Nate

Re: quote , does your recommendation vary in relation to throttlebody placement ? single throttlebody car engines would be fairly different to a multiple TB bike in there needs ??
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« Reply #12 on: May 22, 2007, 01:03:49 PM »

:  We have a generic recommendation that the nozzle be placed before the throttle body. 
Nate

Thanks Nate

Re: quote , does your recommendation vary in relation to throttlebody placement ? single throttlebody car engines would be fairly different to a multiple TB bike in there needs ??

Because four of our smallest nozzles would more than likely be too much flow for your bike engine we would recommend using one larger nozzle and mounting it in a common plenum or airbox.  If this isn't an option we could look into possible solutions.

Nate
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« Reply #13 on: May 30, 2007, 04:18:48 PM »

Good news Jon.  We might be stocking a new nozzle that's flows half as much as our smallest nozzle.  Maybe your four nozzle setup will work after all.

Nate
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« Reply #14 on: July 09, 2007, 12:58:24 AM »

The intake charge begins to heat up at inlet  point where it is compressed and that is where it can begin to do some good.
If your system allowes it to fall out of suspension and puddle , it is a bad design to start.  wink


One point - if you have a centrifugal-type compressor, you really don't want to inject any fluid before it or into it.  You can, and people do, with draw-through carbed turbo setups and low-pressure water injection setups, except it isn't a good idea for a couple reasons.  One, is that it will erode the impellor blades - even our tiny droplets hitting something spinning 60,000-150,000rpm is going to deform the leading edges of those blades.  We have tractor pullers do this - but they replace their turbos very often regardless, so it is less of an issue.  Two, a turbo or centrifugal supercharger compresses air with centrifugal force - air, that weighs very little (in comparison to water/methanol).  Think what will happen to the tiny droplets as they go through and get slammed into the outer compressor housing wall - recollect into larger droplets and we get much less benefit than with smaller droplets. 


Not so sure on turbos, but the WW2 air craft water injected before the centrifugal compressor and made huge gains in power.  They also use methanol to keep the water from freezing.
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