3 inlets

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hinote
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Re: 3 inlets

Post by hinote » Wed Mar 09, 2011 1:12 am

Jutte wrote:Hi Pryo,
Do you have fuel going into each seperate intake.
That is main fuel line split into three - or do you place the fuel
directely into the combustion chamber?
FWIW ("for what it's worth") I thought I would relate to you the fueling (on propane) which I used quite successfully--and some other observations based on this general type of VPJ (flat head plate, like the Escopeta, etc.).

I was very fortunate in many ways with the Kentfield project (which was also my first successful pulsejet project); in addition to finding a design which was accurately proportioned in the documentation I could access, I made several fortunate assumptions which turned out to be correct, or at least pretty nearly so.

One of the most important was my assumption of the location and proportions of the so-called "fuel injector"; in this case, I chose a simplified injector consisting of a centralized tube (between the 4 intakes) which had radial holes drilled into it and aligned closely with the centerlines of the intakes. This turned out to be quite adequate and even moderately optimal.

Further experience with the general design type reinforced a location for the fuel injector which appeared to focus on the "optimum" location. This seems to be the conjunction of the intake centerline with the inner face of the head plate. My best engines used an injector which faced forward from its mount point on the side of the combustion chamber at an angle of about 45 degrees--but which had its output end immersed in the intake airflow and which was geometrically aligned with the intersecting point described above.

IMO you could do a lot worse than to duplicate this location.

The testing required to find this location involves the construction of a lot of engines, with various experimental injector locations. Don't underestimate the importance of the fueling system and its installation in your engine.

I hope this post saves somebody a lot of time and effort in finding a good location for your fueling system.

Bill

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Re: 3 inlets

Post by Jutte » Wed Mar 09, 2011 9:30 am

Thanks Bill.

PyroJoe
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Re: 3 inlets

Post by PyroJoe » Wed Mar 09, 2011 3:04 pm

Thanks Bill,
I am trying to visualize that injector location. If i understand it correctly the injector is near the plane of the head plate on the inlet centerlines, pointing into the inlet with the holes 22.5 degrees off the intake centerline? I attached a sketch of how I think you described it.

Jutte,
I fueled with a split 3 pipe injector, one in each intake.
At the moment I am less concerned about intake drag as the inlets become shorter as more are used. It is a little revealing about how the valved engines are able to mix their fuel to a great degree. This three inlet represents 3 engines blended from the head plate to the tail. When I look at the DynaJet it has close to 3 blended bodies, but 10 inlet ports. That gives it about 3.33 inlets per body. It should be obvious to see the advantages in mixing liquid fuels when using 3 inlets per body.

I never really understood how engines with a low containment ratio could run. The blended body idea shows how it is feasible.

Single inlet valveless engines tend to be long and thin, as inlets/bodies are added they become shorter and fatter in cross section ratio. But... the blended body is only as good as the sub bodies within it. If you combine 3 thermojet bodies, you will get thermo jet efficiency, if you combine three Escopettes, you will get Escopette performance

I still to this day think Mikes combined 3 pocket jet should have made near 7.5 pounds with a fresh propane tank. Everything was in place, he had the same tail pump, the same aerodynamic valving, the same recompression times from the tail and intake. Even the same frequency as the single duct, which pretty much speeks to whats occurring with the resonator volume. Last I read the combustor failed.

The combustor volumes I use suit me very well, I have for about the last year been very impressed with the Dynajet combustor, even more so now with a review of how blended bodies work.

When I have used combustors of a certain volume, the injector position becomes less important. These combustor volumes combined with specific tail lengths that function outside what would be considered "normal" valveless.
I have produced engines that the injector can be completely pulled outside the flare and placed 90 degrees across the intake and still run in good form.(even at high flow rates from the injector)

There is more, but I have to do more testing to confirm.
Attachments
inject1.JPG
inject1.JPG (11.24 KiB) Viewed 2357 times

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Re: 3 inlets

Post by hinote » Thu Mar 10, 2011 4:19 am

PyroJoe wrote:Thanks Bill,
I am trying to visualize that injector location. If i understand it correctly the injector is near the plane of the head plate on the inlet centerlines, pointing into the inlet with the holes 22.5 degrees off the intake centerline? I attached a sketch of how I think you described it.
Sorry, that's not quite right. I've attached a simple drawing to try and illustrate my version.

Note how the C/L of the intake tube and the C/L of the injector intersect where the intake intersects the inner face of the head plate. Also, the injector angle is at 45 degrees to the flow through the intake tube.

Less obvious is how the injector inner tip barely touches an extension of the flowpath established by the intake.

My belief is this arrangement provides an intersection of the fuel with the incoming air, just where it begins its transition from high velocity/low pressure to lower velocity/higher pressure. Thank you, Bernoulli!!

I hope this helps.

Bill
Attachments
multi intake injector orientation.JPG

PyroJoe
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Re: 3 inlets

Post by PyroJoe » Thu Mar 10, 2011 2:11 pm

Excellent, that helps a great deal!

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