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  #1  
Old 23-11-2014, 12:05 AM
HYDE16 HYDE16 is offline
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Default JET PLACEMENT FOR AIR FLOW (POST-MAF)

I've read here that pre-turbo jets which, based on OEM turbo housings, can only be installed further upstream (post-MAF) and not at the compressor should be installed to spray against the direction of oncoming air post MAF to atomize most effectively (basically spraying at the back of the MAF housing).

Based on my VW GTI's engine layout and more specifically the intake layout, I've been studying the air velocity in a 90 degree bend (the bend leading to the horizontal intake pipe running across the back of the engine (from the MAF to the beginning of the long straight).

Intake layout:


This video shows in yellow the highest velocity stream which would help atomize any water meth spraying inside of this intake pipe:
https://www.youtube.com/watch?v=OvprEu-yH-A

Based on the video example alone, should I install the jet at the top of the horizontal pipe to spray against (into) the yellow stream? Or at the bottom of the pipe to spray into (with) the yellow stream?

When people place jets within the intake tract, are they accounting for flow diagrams or streams?
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  #2  
Old 18-12-2015, 10:21 PM
jondee86 jondee86 is offline
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Question Re: JET PLACEMENT FOR AIR FLOW (POST-MAF)

Interested in this question as I will be looking to implement a water injection
system myself. Because the intake manifold that I will be using (4AGZE) has
unequal runners, getting even water distribution to the cylinders will be a
challenge.

The flow simulation that you have used as an example is a rectangular
ventilation duct. A smaller tube operating at higher velocity will get much
more flow separation on the inside radius of the bend, and this will create a
lot of turbulence immediately after the bend. I would suggest that placing
the injector on the engine side of the duct immediately after the MAF would
give the most effective mixing of mist and air.

As far as the orientation of the nozzle to airflow is concerned, I suspect
that angling the jet into the oncoming airstream is unnecessary. However,
I have read that recessing the tip of the nozzle out of the airstream helps
to achieve superior atomisation. This is something I will be researching
before I decide on how/where to mount my post blower nozzle.

Cheers... jondee86
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  #3  
Old 19-12-2015, 10:56 PM
jondee86 jondee86 is offline
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Exclamation Re: JET PLACEMENT FOR AIR FLOW (POST-MAF)

This picture purports to illustrate the benefits of a recessed tip nozzle...


http://www.alcoholinjectionsystems.c...rticles_id=100

... and is lifted from a competitors site strictly for discussion purposes

The spray is always going to be "sheared" by the high velocity airstream
passing the nozzle tip. However it seems logical to me that if the spray can
be more finely divided prior to entry, it will diffuse more quickly into the
airstream.

Probably not an issue if there is a resonable length of intake duct between
the injection point and the intake runners. But in my case the duct will most
likely be very short and getting the mist well mixed with the intake air for
equal distribution to all cylinders not so easy.

Cheers... jondee86
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  #4  
Old 19-12-2015, 11:38 PM
jondee86 jondee86 is offline
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Question Re: JET PLACEMENT FOR AIR FLOW (POST-MAF)

This is a view of (underside) the 4AGZE intake manifold...



I have to use this manifold as I will be mounting my supercharger in the
same position as the stock GZE charger, but with a custom mounting plate.
Individual nozzles in each runner would be possible, although I would prefer
to use a single post charger nozzle for simplicity.

If anyone has implemented water injection on an engine using this manifold
I would appreciate some advice on how you did it and how effective it was ?

Cheers... jondee86
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  #5  
Old 23-12-2015, 09:11 PM
rotrex rotrex is offline
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Default Re: JET PLACEMENT FOR AIR FLOW (POST-MAF)

just go direct port. works really well. I have recently upgraded to 0.4mm c nozzles with a nominal flow rate of 150 cc / min.
To get the most spray into the cylinder, I mounted them on the top side of my plenum right behind the fuel injectors.
Make sure the spray does not have to take any turns. Mount them in a straight section leading straight to the cylinder head and have them spray from the top down (for a upright mounted motor) This way most of the spray will end up flowing over the rear half of the intake valves into the main "volume" of the cylinder. It will spread nicely and swirl around.
if you mount them on the bottom, most of the spray will flow over the first half of the intake valve into the frontal section of the cylinder. Most water will end up in the frontal section of the cylinder and collide with the cylinder wall.
This picture gives you an idea of what I mean.




When I had a look at my cylinder head and pistons during a rebuild I was able to see where stress of water were flowing over the front part of the piston. This was wen I had my nozzles installed on top of a 180? curved intake plenum. The centrifugal forces were throwing the droplets against the plenum runner walls leading to streams of water on the bottom of the intake.
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  #6  
Old 24-12-2015, 06:32 AM
jondee86 jondee86 is offline
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Thumbs up Re: JET PLACEMENT FOR AIR FLOW (POST-MAF)

Very interesting !!!! I had been looking for some flow analysis more relevant
to the conditions in an intake manifold, but must have been looking in the
wrong places.

I had also been giving some thought to the reasons why fuel injectors are
aligned to spray with the airflow, whereas misting injectors are invariably
installed at right angles to the airflow. Your picture actually explains the
difference quite well. Fuel injectors have a narrow angle jet with a greater
mass (more concentrated), so the jet will penetrate the airflow and impinge
on the opposite wall. Misting jets have a wide angle jet with lower flow and
less mass, so the droplets are swept away by the airstream before there is
any (or little chance of) impingement on the opposite wall.



On the 4AGZE engine, once the wiring conduit under the fuel rail is removed,
there should be the opportunity to place port injection nozzles in the top of
the inlet runners. Some nice low-profile right-angle nozzle holders should
fit in there without getting in the way of anything. I would anticipate using
one other nozzle (after the throttle) in the inlet ducting before the charger.

The injectors are in the head which means equal fuel distribution is assured.
That only leaves the puzzle of how to obtain equal air distribution in the
rather unusual non-symetrical runner layout

Cheers... jondee86
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  #7  
Old 24-12-2015, 04:29 PM
rotrex rotrex is offline
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Default Re: JET PLACEMENT FOR AIR FLOW (POST-MAF)

Actually air distribution will be pretty uniform, too. Otherwise it won't pass emissions.
Dry manifolds, they only flow air, are usually pretty good and spread air within a few %.
Once you go forced induction, you need spend more time to get uniform airflow.

But for methanol water direct port injection, you don't have to bother with flow inequality.
Just install them close to the inlet port of the head, top side, straight section, behind the fuel injectors.
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  #8  
Old 24-12-2015, 04:37 PM
rotrex rotrex is offline
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Default Re: JET PLACEMENT FOR AIR FLOW (POST-MAF)

https://youtu.be/NtrkWNId0Ws?t=139

This gives you a nice idea of the gas flow. it shows that the majority of the fuel or mix shall enter via the top part of the port entering via the rear half of the valve.
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  #9  
Old 25-12-2015, 01:19 AM
jondee86 jondee86 is offline
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Smile Re: JET PLACEMENT FOR AIR FLOW (POST-MAF)

This picture shows the angle of the intake connection on the 4AGZE...



That intake usually connects to the intercooler outlet (the intercooler is
mounted on top of the cam covers). In my case I am installing in a RWD car
and the intake connection will be coming up from the charger mounted below
the manifold. I do not have enough clearance between the top of the engine
and the hood to go up high and then connect to the OEM intake pipe. So I
will have to fabricate an intake connection that comes from below and then
makes 2 x 90 degree bends to connect to the intake manifold.

Whatever I do it will mess with the factory airflow that probably was set up
to give reasonable distribution to all cylinders. I may well have to insert some
turning vanes or splitters, but that will have to wait until I have the charger
mounted to the engine, and can see how much room I have to work with
when fabricating the ducting.

Cheers... jondee86
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  #10  
Old 28-12-2015, 11:01 AM
rotrex rotrex is offline
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Default Re: JET PLACEMENT FOR AIR FLOW (POST-MAF)

This intake locks like a manifold designed for central injection. For forced induction, it is good for uniform distribution as there is no change in air velocity across a chamber like in a log style manifold. To correct velocity for these, the chamber gets smaller in cross section as you go away from the air inlet.

You manifold is also reasonable symmetrical left to right. For port injection, you should be fine injecting on the flat top part of the inlet runner before the fuel injector. If you use a single nozzle, you could mount the nozzle righ in the middle, maybe a bit up, of those 4 bolt holes on the flat front of the manifold as all air has to pass this opening and the droplets do not have to take any sharp bends anymore.
If you add two 90 deg bends, it will change the flow pattern. But if you keep it symmetrical it won't change left/right distribution too much.
You could also consider moving that inlet opening on the manifold from the top to the bottom or the front as visible in the picture saving you a bend or two.
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