metal jam jar experiments

[Bruno Ogorelec]

Bruno, I'd have to cut it in two halves to do that. I just TLARed the combustor more or less and forgot to write down the measurments.

But you can get an idea of the whole assembly by measuring the things in the picture, can't you?

OK! :o)

[steve]

You guys have any tips on getting the gasoline fueled reynsts to fire? I've made several attempts with a new sacrificial reynst (that I won't mind accidentally destroying in the name of science) and have had no sucesses yet. would kerosine be easier to light? should I still shake it up with my thumb over the hole? I'm obviously doing something wrong.

I graduated from high school yesterday so I now have some free time to start experimenting with reynsts again!

[Mark]

Here's all the windows of opportunity.
Mark
http://www.engineeringtoolbox.com/explo ... 2_423.html

[larry cottrill]

Steve, let me be the first to congratulate you on graduating! I hope that will be a moment fondly remembered with satisfaction.

Now, a question. You guys are spending all this time and effort at building your Reynsts of all sizes, and have achieved some success. On the other hand, some results are pretty iffy. It still seems to me that most of the time, the little cone just gets built TLAR and thrown in there. I just wish SOMEBODY that wants to build one of these things would consider looking once again at my 'Secrets of the Dead' post and try building JUST ONE based on that method of locating the nodes. I'd be willing to bet that the exact shape and diameter of the little 'cone' aren't nearly as important as getting the length and location right, taking the end corrections into account as described there. Of course, I can't offer any proof that what I speculated there is right, but I think anyone would be crazy to believe that the layout Reynst got just happened by coincidence. So, why not at least try it?

Of course, that doesn't help with the fueling problems of various kinds that you're apparently dealing with now. However, it might give you some added confidence that you're working with an engine that is acoustically "tuned up" so that you don't have any doubt where you stand in relation to more detail issues.

Just my two cents thrown into The Pot ... I don't really want to throw any steel into one ...

Secrets of the Dead:
http://www.pulse-jets.com/phpbb2/viewtopic.php?t=1572

L Cottrill

[mk]

Yeah, Steve! Jump in again.
Congratulations, too!


What size and shape is your combustor you are refering to?

If it is a pretty small one, you probably won't have much luck with gasolene.
At least 75mm/3" ID should be used, IMHO. A bit larger should not matter.


Does it already feature the internal cone or not?


What's the diameter of the hole?

For gasolene you'll have to enlarge it. Up to probably 1/4 of the combustor main ID, when not using a tuned pipe (and inner cone?).
Remember the two oval glass jars I posted earlier to this topic?


However, preheating on gasolene is a must. Perhaps you can try shaking the combustor, lighting, re-cherge, light it, re-charge, roll it, light it...while the combustor gets warmer, the initial "whuip" should then turn to a "woosh". I think you already know the typical behaviour or the indications for yourself. If you cnnot get the combustor to self sustain this way, despite it got really hot, try enlarging the hole or adding some bits of (m-)ethanol to the gasolene, to get a mixture that has a better cold-start ability and makes for better re-ignition for a jar style combustor.

----------------

Larry,
I still had the combustor laying around. It is probably older than one year or so. There has been taken place quite some knowledge gain over the time, but I don't plan to build a new one yet. A new one would look quite differently, of course. And I don't want to waste my time on cutting the more or less ugly thing apart. Getting an even better understanding by changing the fuel, the hole and the tuned pipe only is okay for me. At least for the moment.

[mk]

Okay, I tried to measure the internal cone structure.

It can be said that its smallest, upper diameter is definitely larger than 30mm or rather 35mm, due to copper pipe trials. If I can recall it it must be around 40 to 45mm.
Then the larger, lower ID must be about 50 to 55mm, maybe even 60mm, but I doubt that it wents beyond 55mm for now.

The upper edge is placed 70mm (-1mm) below the hole.

The lower edge is placed 110mm (-2mm) below the hole.

Nothing more to it.

-----

Today I was able to achive a rel. long run, about 20 seconds, on gasolene-two-stroke-oil mixture only.

After some warming up and pipe length reductions, I just put the combustor and the pipe into some water. So the pipe temperatures went to about 20°C. The combustor must have been still a bit hotter, especially inside, due to not filling it with water and a missing inner cooling assembly. So maybe it was about 30°C outside and about 50 to 60°C inside. Both were bit wet after cooling.

Then I just did the usual procedure, still having a "fuel-pool" covering the bottom:

- Layed the combustor on its side -- horizontal position.
- Rolled it one time (360°) over the table .
- Put it in a vertical position again.
- Blew one time into the hole.
- Attached the pipe about parallel to the combustorss center line and nearly concentric with the hole. The pipe protruded only slightly into the combustor. Optional it is possible to light the fire at the hole first and attach the pipe afterwards, trying to find a nice spot to start self-aspiration .
- After the pulsating and deeper into the combustor wandering flame blasts occured with a rising amplitude the pipe was slowly moved to the well known 1.0 to 1.5 times the pipe OD protruding point.
The pipe length to combustor length ratio was at 4:1.

And voila, the combustor-pipe assembly just locked-up for the mentioned periode of time! Pretty cool!

But it was felt to further lowering the P/C ratio. So 3.85 will be the next attempt.

Two things to do next as well are increasing the hole ID a bit and putting a water jacket to the combustor.

[Doodlebug]

Hello everyone.

I have read through the forum, and I read this by Mark.

If you want to surprise yourself, get/prepare a 3 liter plastic Coke bottle and put a tiny amount of methanol in it and swirl it around. The lid should have a 1/4 inch hole or so. If you have a spark system, just snip a double strand wire such as speaker wire with a pair of snips, the spark will arc over fine.
Set your bottle down sideways and aim it in some interesting direction. Then just push the twin wire inside the bottle a few inches and spark it. The bottle will fly faster than your eye can follow it. It's fun for a rainy day, something I know about living in Salem and Corvallis from days gone by. Make sure your bottle is thoroughly dry after rinsing out the Coke and draining the remaining residual water. It usually takes a few days if you leave it sit to dry inverted.
Mark

Well there is another way to do this.

I have been doing it for ages.

Take a plastic bottle (500ml bottles work best). Drill a 1-3mm hole in the lid, and then stick some tape over the hole (Sellotape, sticky tape, etc, just make sure it is thin and melts under heat from a lighter). Use a very flammable liquid like petrol/gasoline or hair spray. I have found that hair spray works best. Using hair spray, spray it into the bottle until there is about 1/2 an inch in the bottom, and quickly put the lid on. put it on the graound or even mount the bottle on wheels if you want, and then just hold a lighter or match against the tape. When the tape starts to melt, get ready for a little missile! Just be careful! I have burnt my fingers many times, because some times the flame out of the hole can be several feet long!

There is also a small chance the bottle could explode, because the hole is too small.

Have fun!

I am going to try the jam jar jet and if it works to how I need, then I will make a metal one.

I havent ever made one before, so could you tell me, if a metal flask would work?

I thought it might because you could drill 2 holes into the outer layer (the vacuum) and then connect pipes for water cooling.

Please help.

Thanks

Doodlebug

[Zippiot]

it works much better if you drill 1 or 3 holes in the BOTTOM of the bottle. not only does it look more aerodynamic, we have achieved heights passing 30 vertical feet on 91% alcohol!

but we had a little help, a 4 inch pvc pipe connectoer, the bottle rests comfortably inside and all you gotta do is start a fire (lighter usually works) underneath. the bottle streaks skywards with a pretty bluish flame.

[steve]

see the soda bottle rocket threads in the rocket section of the forum

[Doodlebug]

I have tried that idea Zippiot.

I have got my version to heights of 50ft (and then it losess control).
If you make a basic fin structure around the bottle, comprising of 4-6 fins (6 is very stable), they can reach heights of over 100ft! using hair spray that is.

If you fit wheels, and a basic chassis, me and my friends have clocked them travelling at over 40mph.

I did try to get a rocket car to work from a small (1kg) propane tank, but the damn bottle melts in about 10 seconds! It did go VERY fast, infact it out accelerated a Suzuki Hayabusa 1300 Turbo, along a flat road.

It travelled a good distance (around 250 feet), but then the plastic bottle melted and the flame backed up the propane pipe, which was a bit annoying as we had to fill in a 50 foot crater!

Ahh well........all in the name of science!

Also, thanks steve, I will look in the soda bottle rocket section.

Doodlebug

[Zippiot]

i would definately revisit this experiment, but i had a bad accident with it. i was using nitromethane as fuel, it didnt combust, so i unscrewed the cap (i waited about 15 seconds) and it blew, straight down my throat. my lungs seriosuly collapsed for 20 seconds, i was in the hospital for a few hours...
hurt like hell

[thecheat]

I was just thinking about the renst jar, couldn't you make it so, during each pulsation a line connected to a fuel tank (with a one way valve to keep back wash from occuring) drip the correct amount of fuel into the renst jar to keep the pulsations going till the can busts or the large tank runs out?

[steve]

yeah, a few members have done that sucessfully. there is still the problem of overheating after long runs, but this can be solved with a water cooling system of some kind

[thecheat]

what's wrong with over heating in a metal can? :twisted:

[steve]

the excessive heat changes the way the reynst runs, usually causing the fuel to boil off to quickly and over-richening the mixture untill the point where it just stops running.