The Great Ramjet Challenge!!!

[Eric]

Those metal anti-bug screens are oftly restrictive, instead of just drilling holes in it which will cause it to fray like crazy, try cutting them and then curling the edges and pounding them flat with a hammer.

Heres a short video clip of the monster on very low throttle.

Eric

[Jim Berquist]

Eric: I can try that placing tabs on the edges. The metal gets so soft after red hot you look at it and it bends.

Jim

[redneck]

i am making a fuel sprayer and am using a # 60 drill bit, is that to large a bit to get a good spray? i am presurizing my fuel system with a propane bottle made for a torch. can a bottle of propane presurize fuel enough to get a good spray out of 4 # 60 drill bit holes???

[thecheat]

James, actually... I was thinking of that very thing. I was looking at one of those strainers you put in your sink so nothing goes down the drain and thought- "gee, I wonder if that would work?" The only thing that bothered me was that there would be no "still" spot for a flame to find refuge.

However, I already have my flameholder in place! unfortunately the metal was just so hard to bend I couldn't get it past an asterisk flameholder design with twisted fingers... Ah well... And besides the welds turning out REALLY ugly, and blasted hard to weld... I got it in. Couldn't attach all of the eight fingers, but, I've got atleast 5 attached and one on every side.

The "pyroid" spike has minimal work until it's welded into place. Learning from my issues welding the struts onto the pyramid, I just cut some slots with the hacksaw on the body of the jet and will just slide the legs into them, and weld, then grind. MUCH easier. After that, weld the reducer on the rear, weld, and attach to scale! Oh, and attach the diffuser...

All in all, Boxy has been a very useful welding project... I've learned quite a bit, like welding inside a corner is really blasted hard.

Eric... you are tricky! trying to build hype with an abnormally short video! *drools*

PS: Eric... what's the speed of the air coming from the PJ? Also, how long are the pipes on the PJ? I've got an idea that may make the RJ a lot easier....

[Eric]

Well the other parts of the video I was zooming down inside the intake to get some video for studying how the engine is behaving, and then my battery died from the cold, and its not even that cold out :(

The engine is overall about the same duct length as the classic 55 lb lockwood, actually its a bit shorter, in the J configuration the overall length is longer.

Believe me its not as easy as it looks to get a ramjet to work on the intake of the pulsejet, especially so close. The pulsations are greater, the pulse velocity is higher, there is more combusted gas and less oxygen, and a whole bunch of other things that make it a pain in the ass to make one that will run even when the engine is at max throttle, on a big engine no less.

Smaller engines run at a higher frequency so the pulsations are much easier to dampen, or not even neccessary to dampen, and the flow is much more smooth and uniform a short distance back. The big engine is blasting around 90 herts with each pulse extremely strong, much stronger per htz than a tiny engine.

Eric

[redneck]

my jet uses a sink strainer as a flame holder and it does great as you can see. i stopped up the center large hole, where the handle goes, with my fuel injector. the fuel sprays out of that in 4 directions. i have no problems with the sink strainer idea, only think is when it gets a little to lean the flame wants to blow out, but then, that is to be expected.

to show you what i mean about the kitchin drain stopper here are some pics. i know they are repeats but it is easier than looking back over the pages.

[Jim Berquist]

Eric:

Here is what I ended up with. The small cone will need to be re fabricated as it got so hot it tweaked out of shape..

Jim

[Jim Berquist]

Eric: This is what was left!

[redneck]

ok here is the thing, i have spent the past few days modifieng my jet and came out with quiet a few variations that require just unscrewing things and 0 cuts on the actual jet. i think that is kinda kool. first mod is i put the fuel intake on the side of the jet out of the way of the air stream so i have less drag now. i also rebuilt my fuel nozel and made 4 tiny holes, i had 6 but that was too much. instead of changing the diameter of my exhaust pipe, i slid a bolt through the center of it and screw on washers of random sizes to change the area of it.all this didnt hurt the way it ran, but didnt help either, except the fuel nozzel, i get a good fuel coverage now. i thought that was kinda weird. i actually got frustrated, id like to see results from changing thigs to my jet. good or bad, at least i am learning, but nothing, and 0 thrust. then i tried one last thing for the night. i put a huge restriction right after my burner, to help build up pressure and maybe get a better burn. i also switched to liquid fuel for the first time with this configuration. i couldnt believe the difference!!!! that restriction i placed did alot of what i had hoped it would do, but i think i need to make it a bit smaller. when i went to liquid, it ran way better than on gas. also, its noise got much much louder!. the bolt i had running down the center, got cherry red. first time i ever had any heat show up on my jet. i also put the blower nozzel right up to and touching the jet, the flame didnt go out, as it would have in the past. also the outside edge of the exhaust casing started glowing red also, and when i got the blower into the right poition, the flame crept almost all the way inside the jet. im stoked! finally results, and i think good ones at that. here are pics of my current configuration. oh and dont worry guys i have vids of it all i just dont have a way to load them all right now, so tomorrow i am going to work to use the computer there. i hope that will work if so i have a load of vids to show yall. anyway here are the pics, the first is a pic with a large washer in the rear, made no difference on how it ran, kinda made me wonder. the rest are of the last mods i did. i wish i had takin pics with my cell to post so yall can see, but i was to bussy with everything else, tomorrow i will run again and have more pics to show. by the way, the run was 5 min long and ate 1 litre of paint thinner, alot was wasted by a still not quiet good enough fuel sprayer, but im still working on that. there is alot of soot in the inside of the what i am going for now call the secondary flame holder, though it is nothing of the sort. its sole porpose is to build up pressure and slow the oncoming gasses enough to allow my rear difuser to do its job. however im not sure how well it does that, ffmy read hot spots were forming a ring around where the edges of the secondary are. however it only formed on one side of the motor, making me think it is out of alignment. i will try to make it more center then try again, im also going to try k1 as a fuel, and if i get bold enough, maybe even gassoline. however, im not going to presurize that with propane, im going to use a fuel pump for it. i just have to figure out how to get a good misting out of my fuel sprayer.maybe if i wraped a small screen around it to atomize the fuel even more, because right now all it is is a small brass fitting with threads on both sides. i drilled 4 # 60 holes in it on the sides so it shoots cross the air stream. maybe that will work? yall got any ideas?

[redneck]

well dang, whered everybody go off too? did the thread die all of a sudden?

[Irvine.J]

No redneck we are all here, chances are we are all off modifying our designs in a attempt to beat yours! :D Seriously though, thats a killer setup you have there. A secondary flameholder?! Sweet! haha, I tried that myself at one point. I made a jet I called the "Burninator" a while back, with a central impedance spike to attempt to do the same thing you did, after about 10 minutes it was completely disintergrated... turns out the disintergration was why as heat increased it got more and more yellow...crazy huh?

When you say 0 thrust, then I couldn't believe the difference, did you achieve thrust? How are you going to measure it, I'd love to see a video of your run, you certainly have one cool jet redneck.

I'm waiting for the sheet metal guy to open again...sheesh.
Oh by the way, make a cone down to a point for the secondary , it will help those gasses converge again. You know... if "|" is the secondary make another cone |> like that and give it a go. Know what i mean... Interesting stuff!

[redneck]

no thrust yet my friend but diffiniatly much more noise, and i got a pinpoint blue flame off of liquid fuel, paint thinner of all things! dont understand the no thrust thing though? im going to mod the secondary, maybe even make it the primary, i just dont think i am slowing down the intake winds enough, not enough pressure in the combustion chamber....

[Zippiot]

I am still trying to get stuff together...

And school is starting up soon and everyone is in town for the vacation, just busy most of the day.

In an attempt to save time I tried to design a triangular ramjet, but it is proving nearly impossible to bend the stuff into a triangle!!! I may just cut it all out roll it into cones and smoothe off the sharp edges...hope that works

On a side note I was at home depot today, saw some cool stuff that might prove fun in he future, tomorrow I head to the steel shop to find some cheap materials to further my experiments!!

How do you weld copper? I think I heard you can do it with a mig welder and some aluminum wire, or was it zinc wire...or was it thick steel wire? Anyone know how to mig/flux copper parts together? Home Depot has a wide variety of copper pipings and other funs parts to stick together, I am starting my liquid fueling system too!

Also I am on the verge of making a turbine and trying to design an r/c plane, so I have maybe 4 or 5 projects all at once!!! But dont worry, in a few days you will have at least 1/4 of my attention!

[redneck]

i believe i have a pressure problem in my jet. otherwise putting a blockage right infront of my exhaust difuser wouldnt have helped me any. i looked at the inside of my jet and it dont seem like the blockage is acting as a secondary flameholder at all. so here is the question. how do i slow down the air when it hits the combustion chamber? i have seen aerospike engines on this board and one fellow mentioned having a larger degree on the spike than the intake had to help build up pressure. however, if i am not mistaking, wont that decrease pressure, and increase velocity? the opposite of what he wants? as volume gets smaller, velocity increases and pressure drops, and vise versa? which is why the tail cone needs to get smaller and the intake needs to get larger? so why is he doing that and if it works, why? i can only figure you want the slowest moving air in the cc. however you need it to be just the right speed for the oncoming air so it doesnt flame out or travel up the intake. so you wouldnt want your flame holder to slow down the air too much, to build up pressure, but rather to provide a few dead spots of aair for the flame to live, if you make the flame holder to restrictive, it will build up pressure in your intake, and increase velocity as the air escapes the flame holders openings, making the flame go up into the intake difuser, right?so the only two ways i can figure to slow down the ar right after the flame holder is to restrict the tail pipe, which i think will alow the flame to combust through out the intire lenght of the pipe, instead of accelerating, and eventually out of it, or block the flame to allow for a better burn right aft of the cc, at the opening orfice of the exhaust. this way you are not inturupting accelerated air, the intake difuser is slowing down the air some for you, the flame holder creates a few dead spots for the flame to hide, and the blockage builds up pressure in the cc while the exhaust difuser accelerates the escaping gasses.

now all that was my understanding of a ram jet, i put it out there to be corrected, not to be as a factual statement. i have gathered this from experiments and other readings, so before i go and waste anymore precious propane/ paint thinner, ( its getting expinsive) please somebody give me a swift kick in the pants to get my head on straight.

[Zippiot]

Well if, for example, the entrance to the intake has a spike in it. There is .5 inches on each side of the intake between the cone and the shell, but at the exit of the intake there is .25 inch clearance. Even though the clearance is smaller, the air expands around the cone b/c the total diameter of the shell has increase, so lets say that the intake is 1.25 inches with a .25 inch spike, is a few inches long, and the exit of the intake is 3 inch diameter with .25 inch clearance, so the cone is 2.5 inches in diameter there. There is much more area at the exit of the intake than at the entrance, so the air is slowed in reality...

Hope that made sense and was correct I'm kinda tired