Jam jar failure

[metiz]

Hi

I have a big problem running jam jar pulse jets - read: I can't get them to work. I've used multiple sized jars and holes and multilpe fuels (spiritus, thinner, acetone). Experimented with all kinds of hole sizes, numbers. First I tried the instructions on this website and also those on the jetzilla site I belief. My best result as of yet was about 2 seconds of combustion. Can anyone give me a couple of pointers, tips, jam jar sizes etc?

thnx

[NickC]

have you tried methanol? :lol:

[metiz]

If I could find it I would've tried it yes.

[NickC]

do they have HEET in the netherlands? you should be able to get a hold of some automotive methanol for racing go-karts or for there should be some kind of removing water from gasoline type of product that is methanol.

[Mark]

If you can't find methanol, ethanol will sometimes work if you can find some 190 proof, (95%) or some denatured stuff. But methanol is the best. You haven't a prayer with acetone or gasoline, unless you were to devote a few months into solving the fuel/air ratio problem. Maybe even isoproply alcohol might buy you several seconds if pure.
But that's why I like methanol so much, it is ideal for jam jars and it has certain characteristics other fuels don't have.
Mar'

[Bruno Ogorelec]

Drag racing is pretty big in the Netherlands. Contact people from drag racing -- they must have a good line of supply; they burn tons of the stuff.

[Mark]

Jam jars are really a lot of fun, so you shouldn't give up. You will be amazed at how they run once you get some good fuel and an acceptable jar. The jar should have a tight sealing lid, and you should only put enough fuel in the bottom to cover the bottom of the jar. Too much will splash and kill the effect. The hole in the lid should be neat and about 1/5th the diameter of the lid, perhaps a bit smaller. The jar should not be too tall and narrow or too short and fat, just a typical jelly jar works fine as long as the lid seals.
Shake the jar once with your finger over the lid. THEN... it is important to dry the top of the lid, there is a little bit of alcohol that will be left when you remove your finger. The top of the lid should be dry when you go to light it.
You can tell if your lid is sealing tight, when you remove your finger, there will be a little poof from the vapor pressure. And again this poof with your now wet finger will leave a little alcohol on the top of the lid. The lid should be then wiped dry. This is what Reynst says, he's the guy back in the 30's or 40's who wrote up the starting technique. Somehow the little bit of fuel dampens the first impulse, the one that gets the jar going.
Just get an ordinary jar, drill a centimeter hole or slightly larger in a lid and toy with that. Acetone for example, won't even let the flame advance into the jar it is so not the fuel to try. Surely you can find methanol somewhere or denatured alcohol as a second best fuel to try.
When I first got a jar running, I played with jam jars for several days it was so much fun. I tried all kinds of jars.
Mark

[mk]

IMO, you can just forget about running through the Netherlands for a few cL of methanol.

Normally, usual spirit (with some 98% ethanol in it) works just fine. At least if it is not some decades old. Acetone, to say the least, would not work nicely for jam jars, as would any other, so called "heavier" fuels.

So, for following experiments, please get a bottle of such ethanol-based spirit (eventually not much older than a year or so), a normal, working cigarette lighter (a long one for BBQ if preferred) and one or two jam jars. Those schould be rather cylindrical, and rather be longer than their inner diameter. Additionally, the lid should be in best conditions besides the hole in it, of course.

Before setting up a new one, or a new lid for a non-cracked jar, please answer the following questions (to yourself).

(a) How did you get single the hole in the lid? With a drill (press), a hammer and e.g. a screwdriver, or something different? -- You want it as round as possible.

(b) Which ratio of inner glass diameter D to hole diameter d did you use? -- For cylindrical glass jars with a length to inner diameter ratio inbetween 2:1 to 1:1, try a D:d ratio of about 5:1.

(c) Was the rim of the hole in the lid cleaned from defrormed material, which stands/stood up probably? -- You don't want any remaining material, around the hole. Therefore use a larger drill with your hands on each side a few times. Sandpaper will do just as good.

(d) Was the hole centered sufficiently? -- You want it as best in the center as you can get it there. Eyeballing might be sufficient.

(e) How much did you fasten the lid? -- Make sure it sits properly on the jar without allowing for by-pass air, but do not tighten it as much as you could.

(f) How much spirit did you pour in the jar? -- Usually some 2...4 mm (measured from the bottom) are more then sufficient. Rather, you would want as few as possible in the glass.

(g) Did you use a cool jar? -- Most often, using a cool jar and cool spirits (room temperature) works best.

(h) Did you shake the jar once or twice before lighting it at the hole? (hole plugged) -- If not, try it.

(i) Did you puff briefly into the hole of the unlighted(!) glass jar, which was treated like described in (h), also just prior to enlighting it? -- If not, try it.

Warning!
Do not puff into a glass jar, which you did not make sure any oxidizing reaction was stopped (e.g. by plugging the hole a while)!
Also, do not run the glass longer than a a few (maybe ten) seconds! It may crack and cause you or others injuries due to pieces of glass flying around, besides the risk of setting up a fire. To avoid the latter, always toy with those jar far from any material which may start to burn easily.

[NickC]

what about wrapping the jars in clear packaging tape? so if/when it breaks the little pieces will be stuck to the tape.

[Johansson]

The tape would probably melt...

//Anders

[NickC]

it'd still help some though.

[metiz]

thanks for the advice. I'll be trying this again tommorow :D

[alex]

All my jam jar jets have cracked into two parts, no smaller pieces at all.

[Mike Spike]

Try using fuel for RC cars, it works great for me, I prefere fuel with 10% Nitromethan but aslong as there are methanol in it it will work, unfortunately there will be some sticky oil left in it after running, but maybe that keeps it cool? (ideas?). The RC fuel is quite cheep and can be found in a hobby store or on the internet.


Mike

[metiz]

Well that worked, trashed 4 jars already :P