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Fuel Injection and combustion chamber

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Old   April 12, 2017, 16:23
Default Fuel Injection and combustion chamber
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Ross
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Hey guys,

I am new to here however I have a question. I am currently trying to model fuel injection from a nozzle which contains 3 holes. I am creating multiple fuel injectors with different amount of orifices, and was wondering how I would simulate this in FLUENT.

I have created a combustion chamber of which the fuel injector tip mates to in solidworks however I am unsure as to how I should define the different fluid zones (combustion chamber will have very hot air and the injector will have diesel fuel being pumped through.

I am not very good at explaining this so I have attached a picture of the cross-section of my design in the hopes that this will convey what I am trying to say.

Many Thanks,
Ross
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File Type: png Combustion chamber cross-section.PNG (79.0 KB, 16 views)
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Old   April 12, 2017, 22:59
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Kumaresh
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As an overall gist, in Fluent, flow is defined by meshing, so the domain should be completely packed (solid form). If your domain is composed of more than one body, use Boolean operator such as Add, Remove or union for constructing your domain in better way.
I guess, in your case, try implementing Remove option for the multiple fuel injectors.
Hope it helps
Thank you
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Old   April 13, 2017, 05:43
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Does that mean that the nozzles should also be solid with no hollow hole?

It's been a while since I used this software so I've since forgotten a lot of what you have to do

What do you mean by implementing the remove option for the multiple fuel injectors? This bit has confused me a lot also

Many Thanks,

Ross
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Old   April 13, 2017, 09:24
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Thanks for the help btw, it's made my progress much quicker
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Old   April 13, 2017, 09:41
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Good luck
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Old   April 19, 2017, 10:16
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Hey so I've progressed to the next stage however I keep getting the following error:

Warning: zone of type interior found between different fluids!
Material of cell zone 10 is diesel-liquid, while material of cell zone 8 is air.
This will adversely affect the solution.

I've attached a picture also if it helps understand my problem more!

The green is a fluid zone which is the combustion chamber, the blue is the solid surrounding the injector tip and the grey is a fluid zone where the diesel is located

I am having a problem where the diesel and air zones combine!

If you could describe in as much detail as possible what is happening and how to fix it I would be extremely grateful!

Many Thanks,

Ross Evans
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Old   April 20, 2017, 02:40
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Hi Ross,

as kummi pointed out already, the only thing that should be meched in Fluent ist the fluid domain (diesel and air). All solid parts (the nozzle) should be "not existent" in the geometry. You create the fluid domain and leave out all solid parts.
-> this blue thing shouldn't be there at all.
-> the grey one and the green one should be meshed

perhaps one can define a part of the geomerty as solid and not mesh it... but that I don't know, the first version I described above will for sure work.

There is a Fluent Multiphase tutorial about an inkjet simulation that might be helpful further on... perhaps you have acces to the customer portal. I do not have it here.

Cheers
Martin
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Old   April 20, 2017, 06:20
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Hey Martin,

Thanks for the help, I've removed it from my geometry now!

I'll message here how it goes!

Many Thanks,

Ross
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Old   April 20, 2017, 16:44
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So the advice worked, I've got the majority of it to work now however I am on the final part!

I am using DPM Injection and I was wondering where I should place it as I don't think the face of the inlet will work sufficiently.

Many Thanks,

Ross
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Old   April 21, 2017, 12:01
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Hi Ross,

What do you mean by "face of the inlet" - so where is this thing you call inlet?

If you work with DPM you could have left out all the geometry part of the nozzle itself because with DPM you define the particle size distribution at the point where the fluid leaves the nozzle (where grey meets green)... you do not need to model the inner geometry of the nozzle, only the outer contour (if it affects your fluid region).

Well, there is an error by doing so because with DPM modeling you do not simulate the primary (and perhaps secondary breakup, depending on your definition of the spray), you typically model the final distribution, but that is up to you or your input data.

So, you will have to decide where to put the injection point, because in reality the size distribution you model will be present somehow downstream of the nozzle exit... but placing your injection downstream or not, you are simplyfying anyway because the heat and mass transfer in the sheet region is neglected and different from that of your final droplets... but I am not familiar if to put the injection right at the exit or a bit downstream for better results.

Easiest way to do from my point of view:
- delete the inner geometry of the nozzle
- decide where you would place the spray (see thoughts above) (for a first shot and testing, everything will work, just put it right after the nozzle exit)
- define/calculate the coordinates for the injection point and the direction and geometry of the spray (cone/flat/whatever)
- test it...
- ... and the look for/find out where to put the injection exactly.

I hope my description is fairly comprehensible...

Cheers
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