Dump Ramjet Design

[Rescyou]

Here's a nice little bit of info on properties of various fuel gases:

http://www.krona.srv.br/display05_engl.htm

The Good Stuff:
http://www.gichd.ch/pdf/TN_09_30__04__2 ... on%201.pdf


Good Info:

http://hypersonic2002.aaaf.asso.fr/received.html
http://www.popsci.com/popsci/aviation/a ... -3,00.html

s.

[Viv]

Well rereading your last post and sorry i did not read it properly the first time but I was a bit rushed.

From your remarks it sounds more like a traped vortex combustor than dump combustor.

If thats the case then there are some good results from google on the subject

Viv

[dwenger]

All,

Thanks for all of the information. The maximum fuel pressure that can be used will be 500 psia at room temperature. This will make the injected fuel gaseous which is desired.

As for the actual flow field, the flow will have total recirculation at the dump plane. Quoting my fluids book, "the kinetic energy per unit mass is completely didssipated by mixing when flow discharges from a duct into a large reservoir or plenum chamber." The flow may act like a jet into a reservoir, but at some point the flow must recirculate or at least slow down due to the choked nozzle.

The trapped vortex combustor is similar to this design. The diference is that there is no internal flameholder other than the dump plane. Looking at some of the pictures this seems to have some sort of internal flameholder in which flow recirculates around. Imagine the recirculating due to a disc in the flow. My hope is that this will be similar to the recirculating due to the sudden expansion at the dump plane.

My potential design now has a .125 in (3.175 mm) inlet diameter dumping into a .5 in (12.7 mm) combustion chamber and exiting a .125 in (3.175 mm) diameter choked nozzle. The first drawing posting on this topic is the design, but these diameters must be changed. What does everyone think of this???? Will this design run???? By run I simply mean hold a flame.

Again thanks to everyone for the interest in this!!!!

Dwenger

[Viv]

Transit time is an issue, the fuel has to be in the cc long enough to burn, if it jets then the centre of the jet will transit to fast.

Can you inject the fuel only in to the recirculation zone? allowing excess air to transit in the central jet.

Viv

[dwenger]

If the fuel is introduced into the recirculation zone the flame will be a diffussion type instead of premixed. The premixed flame is much hotter and stable. If the fuel is introduced into the recirculation,the air (at least some of it) will have to enter the recirculation or the rich limit will be exceeded. Also, if some of the air is entering the recirculation zone from the inlet then there is no reason that a mixture of fuel and air will not do the same.

The problem of the flow of a jet into a reservoir is a good analogy. However, the majority of the flow may simply flow out of the nozzle, but some of it will be mixed with the hot exhaust gasses and burned. My hope is that this will be enough to have a stable burn. If the chamber holds a flame I believe that the remaining "jet" of fuel and air will be burned simply by the shear heat inside the chamber or even outside the chamber. The auto-ignition temperature is 842 F (450 C). The temperature inside the chamber should easily exceed this and if the flow is too fast the temperature should still exceed this after the nozzle in which case the ramjet will have twocombustion regions. This assumes that the nozzle freezes the reaction.

How does this sound to everyone??? Will the ramjet hold a flame or will it blow itself out??? I hope I am not just talking myself into this design working!!! Please keep the questions coming and thanks for the interest!!!!!!

Dwenger

[Viv]

I don't seem to be able to get myself past this jet problem, I do think it may be a bit short and fast but this is purely from thinking about it not from actuel experiance.

So build it and see:-) and i will watch avidly to see what happens!

One more thing about the recirculation zone, do you think it worth making the chamber toridel shaped? (dougnut) it cant hurt and it would help to set up a smooth fast spinning recirculation zone.

Viv