New ramjet experiments

[Irvine.J]

The welds have the slag left on, for what it was worth I really wasn't hassled by banging it off. On the inside, its nice and smooth, my wirespeed was so low that it wouldn't penetrate into the middle in the centre section.

I think thus far I have proven the somewhat inadequate flameholder design should be scrapped from the record.

The steel in each section is pretty much the same, however I only cleaned, sanded etc the parts that were to be welded...the middle cans are just a bit rusty. Some of the white colourbond on the front and back is left on there, just cause :D

If I was to use a design, or lets say a similar nature, it would look something like this. For now, the rear baffle is going to go, then the PFH then I'll install a new one, I'll also toy with the inlet nozzle making it nice n flared a little.

[Irvine.J]

Summary of tests so far.

To re-cap.
My aim thus far has been to build a no-cost ramjet of physical low quality, starting with a physical design aspects that are completely unusual and not "to spec" so to speak. Then as we go along, we modify it in a variety of ways, running it each time and filming the results. In the hope that after many modifications, changes, trial and error, we may enable it to actually run in the designed manner. The flameholder design as you may note is also poor, as it blocks airflow around the outside of the CC...I should say now I had already read the PDF and I was aware of this, (My flame holder had critically poor design) but for the purpose of this post/thread from the start, (if you go back to the start page) I said we would be documenting everything, and starting out with poor design.

Initially...
Inlet area = 19.625cmsq
Exit area. = 7.06cmsq
SFH (baffle) area =63.585 -12.56 = 51.025 or 12.56cmsq hole in baffle.

Initially, the exit diffuser ratio was much higher (or smaller in area) then the inlet, there was a secondary flame holder or SFH (baffle) in the rear of the engine, and the flameholder was a quick trial "hot cross bun pattern".

In the first tests, we notice a few things. (Figure 1)
The flameholder was allowing flames to creep foward.
The volume the engine produced was very low.
The tailflame was yellow.
The heat pattern was confined to the rear of the engine.

In the second tests, (figure 2)
we cut a small area of the exit nozzle off and increased the area by 2.55sqcm. (total of 9.61cmsq) and tried another run.
The first thing that we should note about this run, is the sparkler insertion point is now at the front of the engine. We noticed an instant increase in volume, however, the flames were now starting to leap foward out of the engine a little more then what they should be. The exit flame was blue surrounded by yellow carrying small particles of the disintergrating engine. By increasing the area, we had our first semi successful run, however it was far from adequite. The flame inside the chamber was blue, however the increase in pressure, secondary flame holder and small exit nozzle presented the burning gasses with little room to escape, hence why flameholder stabilisation was not occuring properly.

Test run 3 (Figure 3)
This was quite interesting.
The inlet and exit ratio are now practically the same after cutting off 1 and 1/2 inches from the tailpipe. Initially, I believed we had good flame holder stabilisation as shown on the video. The internal combustion was blue, and the exhaust flame was blue. It was very loud also. However, I was not able to replicate that first run shown on the video. I am also considering the possibility the flames in that run did breach the PFH, however we just couldn't see them as it was during daylight hours. After several runs, we noticed the SFH had been bent back... which later thanks to the forum members was understood to be caused by artificially high pressures withing the CC caused by the addition of the SFH itself and heat. We also confirmed at this point the flaws in the Flameholder itself, which was good to do, confirming information stored on the PDF, and the problems assosiated with adding a breach infront of already accelerating airflow.
In this run however it was pointed out that the exit nozzle was getting very hot, and the exit flame was bluish white, though provided very little if any thrust at all.

Conclusions...
1.A flameholder can be many designs, all unique, some better then others. However on of the most critical rules is to not impede the airflow around the wall of CC, or it will not function properly. Flame stabilisation is hard to achieve with a setup such as mine.

2. A secondary baffle does restrict the acceleration of gas flow, and should be excluded unless you can calculate a way to make it effect the gasses in your favour. The exit nozzle is working for you in providing thrust, and to distabilise the combusting airflow before it reaches the nozzle has a negative effect on performance.

3. You can actually run a ramjet with much smaller exit dimentions then previously thought, which is nice to know. Though its thrust output would be small, it suggests that using a variable area nozzle for different airspeeds could be a way of making the ramjet perform better at varying airspeeds.

4. The design of your inlet nozzle is extremely important for getting proper flow right accross the flameholder. If this does not occure you instantly get flame stabilisation problems.

Unfortunately this ramjet is getting into such a bad state of repair it might be impossble to modify the PFH, though the SFH could be removed. I might just do 1 more run with no SFH, before the thing just turns into dust.

Thanks for replying and commenting on my engine and videos. I think when new ramjet enthusiasts who are looking for answers to problems they are having, can watch the films I have posted, and use them to find solutions to their issues. Thanks for all your input, questions and tips. I believe this might help a few beginner ramjet-eers in some way. I'll post the video's of the run with no SFH shortly.
Thanks again all, hope I have contributed something, some of the topics discussed here are very important factors and might be good for review for the new guys to see (ON FILM!!!) what small differences will make in each area. This ramjet has nearly fallen appart, what a pity though, but its done the hard slog, so even if it ran like poo, and sounded like it, atleast it did its job in providing useful video and topics of discussion.
Thanks again all, i'll upload the latest test shortly.

[thecheat]

keep working on it!

The flameholder, I assume it's a more standard, circle in the middle, with pylons attaching, correct? (could you shade the holder itself in a bit?)

hehe, I like your budget for this, about the same as mine! No cost, no pain, perhaps little gain... (thrustwise) but still fun to do!

If you've got some 14oz empty propane torch bottles, you could try making one like mine... different flameholder design... I tell you what, mine is REALLY sturdy, I was very pleased with that aspect! Also, it seems like it wants to work... I hope to get mine working correctly soon...

[Irvine.J]

Ahh mate I'm not too worried I basically invested no money, no time, and very little effort, if I want a good one I'd just take my time and measure and cut everything perfectly. Work out the ratios etc etc. This was more just an attempt to video document as much as I could in the interests of contributing to the forum, which I hope I have accomplished. I'm going to run the the jet with no SFH which I've just finished cutting out.

If I wanted a good one, i'd build something like this I finished up a week or so ago. The 3D program has got all the dimensions so I can print them out and get cutting with a conemaker... But i'm saving this one for a bit later. I just have to finish up calculating one or two things :D

[Zippiot]

I'm testing how a cone in the intake affects performance.

8 finger flameholder with cone (badly rolled by me, all I had was a hammer...) bolted on. Slightly sticks out the intake.

Big pic is looking down the exhaust at the flameholder

[Zippiot]

Soon to come:
carbon fiber cone and intake sections.
Internal vortex inducer (little fins that spin the air around) hopefully mixes fuel and air better
Solid fuel tests

[Irvine.J]

Ok ok ok... so here we go.

I removed the secondary baffle for the final test run..."snicker snicker snicker"... Now I also cheated a little bit and drilled a hole in each of the 4 arms in my hot cross bun...however it was going to be the last time I lit this baby up... check it out!

I'm very happy with it, especially with how it looks inside the CC, I guess in conclusion it just goes to show with a few tins, and some modification, going through the process...you will get results! Enjoy the final video of this thread, I certainly enjoy presenting it... CAN YOU FEEL THE BURN!

Thanks for your comments and suggestions... as more and more people visit the forums, your posts offer good ideas and tips, and I'm glad more then anything I could be a part of it... come to think of it...it wont be my last run... 1 more thing... Zippiot... I'll put a divergent nozzle on "Just for you"...do you feel privileged?! HAHAHA!

The final video is here.

http://mangyjet.freewebpage.org/rj.html

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Zippiot.
Lol sweet, hahah
Thats should be an interesting run... I would however make your asterix a little smaller, and maybe drill a hole in each arm. Maybe V angle them towards the CC walls so they don't distabilise the airflow too much. I hope it goes well for you, I look foward to your results. That front cone is well formed, what cone calc /sheet did you use?
Mate good luck with that engine. With something new and experimental like that, you should start a new thread.

Best regards to all...enjoy the final video...(though there might be a divergent cone one later.

ALSO: I nearly forgot. I got my hands on a new metal today called zincalum. Its mild steel 55% and the rest in unknown quantities of zinc and aluminum. I rang the company who make it, they tell me it should not exceed 400*C...but its light, and VERY easy to form cones etc out of that don't get too much heat. I am going to use it for my inlet nozzle. I also got a 1800x900 piece of 1.6 mm mild steel for the combustion chamber, it will be VERY hard to roll, but its going to get extremely hot, liquid gas like, so it should last a while.

Thanks to all who contributed to this post, larry, zippiot the cheat and najim, and anyone else who posted. The final video I hope you agree is what your "after".

http://mangyjet.freewebpage.org/rj.html

Give it a minute it will be available shortly, it will be worth it.

[larry cottrill]

James -

Yes, sir - that's the ticket!

Congratulations on that, and thanks for a wonderful series of off-beat experimentation! Great stuff!

L Cottrill

[Irvine.J]

Thanks Larry, glad you like it!
I was also going to say I just banged a small flare all the way around the inlet with a metal bar, it was pretty smooth in the end, and I'm sure it did make alot of difference, it really seemed to make combustion in the chamber more uniform.
Rock'n roll!
James.

[thecheat]

GAHHH! Can't... see... vid...

Anyways... that's a big cone! Methinks smaller would be better...

Also, 1.6mm isn't hard to roll, that's about 20gauge (what I used)

However, things are a heck of a lot simpler if you have a pipe or something to roll them on.. (steel/iron pipe) Also, I've found a nice big pair of channel lock pliers are really useful for bending pieces around a form. Never would have gotten those intakes done for the PJ without 'em.

PS: go ahead and send me the vid (latest one) to my email, big or no, I'd like to see it!

[Zippiot]

BEAUTIFUL RUN!!!

Doesn't matter if it makes thrust that was excellent! Nice cone of pretty blue and purple, well formed and very consistant. Great job!

Congrats, you have built a jet engine!

-and yes I feel Special :)
I think it might benefit from a divergent section, the flame expands to much larger than the exhaust exit very quickly, a small angle (10 or 12 degrees maybe) might give it more punch.

[Zippiot]

Cone calc, I used a compass and calc like a real man!!!

It worked fine, I guess...just very hard to roll a cone from a flat piece of metal.

CUTS ON ALL OF MY FINGERS!!!!!

[Mr.B]

Looks to me that your flameholder is bending by the force of the blower. Remember it is very hot during a run. Perhaps try a more heat resistent steel as well as different shapes. Nice work!

[Najm]

Good run.
And congrats on getting an engine to run properly. (with noise)

P.S. Pause the video and set the seeker on 1:32

[Irvine.J]

What you mean this...muahahah yeah how cool is that vortex out the front...