Mini oscillator question

[retailer]

I had a brilliant idea to make mini steam engine similar toJenny Wren for my father in law for Xmas, it’s mostly finished bar thepolishing and safety valve. It runs well on compressed air at about 5-10psi andalso steams if I use a mini butane burner as the heat source. It will not steamif I use the metho burner, it's quite frustrating, to be so near and yet so far. I feel that the problem is mainly due to insufficient volume of steam which points to the metho burner. Even though it runs on 5-10psi my compressor is well able to supply the volume of air needed.

if any one is able to able to offer me any tips or advice it wouldbe much appreciated.

I did not have Jenny Wren drawings, I designed it my self,the engine was drawn up with a cad program and the boiler was done fromsketches as I went.

Cheers
Zenon

 

[gus]

Please post fotos. And from here we can offer good advice.

I made several Oscillating Engines together with steam plants too. I suspect water level too high.
Try 1/4-----1/2 level. Using very hot water to top up helps cut steam time.You also need a very high head room for the spirit burner flames to be effective.Too low head room means poor heating.Tubal Cain's plans read at 3/4" height from floor to boiler bottom. Burner torch height from floor is 5/16 with wick sticking out at 3/32. Jenny Wren is a miniature boiler/engine plant which looks very deceivingly easy to built and hard to get it up and running. Boiler plate thickness 26g. Parafin wax fuel is not a good alternative.

Foto shows a bigger version. Due to low head room in the fire chamber,the spirit burner took too long to fire up.I put in a horizontal DIY gas burner and engine ran well.

 

[retailer]

Thanks for the prompt reply it's much appreciated.

The boiler is just over 1in high and the fire box is also just over 1 in high. The fire box opening is 0.7in x 0.9 in. At around .030 in thick the boiler would be approx 22gauge, it was salvaged from an industrial mop bucket and formed the rollers that squeezed the mop dry.
The burner height is 0.5in and I've tried various lengths of wick which is cotton rope from the hardware store. It may well be too high, but the fire box was initially higher and I cut about 0.6in off the bottom and resoldered it to the base, didn't make any difference.
Looking at my design I see that I have a 0.16in bore but a 0.33in stroke, I'm guessing that this would be a long stroke, common sense tells me that a long stroke uses more steam per revolution than a short stroke which would compound the problem. If I shorten the stroke I'll need to shorten the distance between the cylinder pivot and the crankshaft so that the port holes won't overlap. I'm not an expert here and maybe the picture I have in my mind is wrong. Is it back to the drawing board, or will a revised burner help ?

Cheers Zenon

 

[modelman1838]

Hi
Jenny wren was the first model engine that I built about thirty years ago and which started me into model engineering. At first mine would not run but I traced it down to the strength of the spring which must be as light as possible but achieve steam tightness.
As it so happens I still have the engine and have measured the spring which is made of .006" dia wire .40" long and has 14 active coils. I hope this will get you going.

Hugh

 

[SandyC]

Hi Guy's

Ok... having spent 20 mins trying to log in ( using my old site password) . I eventually remembered that I had to change it when the site changed servers ( silly old s*d ):wall: so I had to search for my new one which I had written down in a SAFE place... Why is it they are always so safe, even you can't find them?

Anyways...

Zenon... It is probable that most of the heat from your single burner flame is passing straight up the centre chimney flue with that type of boiler... hence most of the heat is wasted.
I attach a rough sketch of a couple of possible alternatives which you may find work much better for your small boiler, since they place the flame/s around the centre flue.. not directly under it.

The drawings are not to scale but should give you the general idea.

The ring type uses flat type wick usually available, in various sizes, at camping equipment suppliers.

The three point one uses straight wicks approx 1/4" in dia( make from your cotton rope by pulling it apart and removing some strands, if necessary) and the 3 holders are joined together using brass or copper tubing the same as the fuel supply tube.

In either case make the burner body approx. 1/2" high and have approx 3/16" wick showing.

Take note of the max fuel level in the main fuel tank in relation to the burner head/s or you will get overspill... which could/can lead to a fire which can be difficult to see especially when used in bright lighting conditions.

NOTE... this applies to ALL meths type burners.

I hope they are of some help.

Best regards.

SandyC.

View attachment Multi point and ring burners.pdf

 

[gus]

Hi Sandy.

You are right.Heat escape.
I used single wick burner too.Took ages to steam.Hot water priming did help. I went over to a short DIY horizontal gas burner and it ran like crazy. The burner flame was spreaded out and hence minimal heat escape thru the flue.
May go back using your plans to make meth burners.
Tubal Cain has some plans for very simple engines.Will go back to build these engines.

 

[retailer]

Thanks all for the replies.

Modelman1838- I'd already worked that one out about the spring, mine is made from 10 thou wire 9 turns, I originally tried a stiffer spring and found it was critical in it's adjustment. The present spring is much more tolerent and an extra turn or so on the nut doesn't matter.

Sandy- there is not much room inside the fire box for multiple wick assemblies, but possibly the annulus type burner may work better. The present burner is 1/2 in high and I founf that I could get it to just steam if I spread out the cotton rope to about 0.7 in in dia.

Talking of meths burners, an elderly chap gave me his Stuart Turner Mill engine along with the steam plant he had made. The burner consisted of a regluar spirit burner that heated what looked like a small coffee tin that was filled with metho, a tube ran from this tin to the burner proper under the boiler. The idea was that the meths in the coffee tin boiled and resulting vapour travelled down the tube to the burner under the boiler producing a hotter flame than was possible with a straight wick type burner. The bolier in this case is a good size being about 5ins in diam and about 8 inches long. I have yet to try it as I'm not sure about the boiling meths part, doesn't seem entirely safe. The old chap assured me it was prefectly safe- maybe one day.

I'll work through the ideas here and I know that eventually it will work.

Cheers Zenon

 

[thayer]

Boiling off the meths should be okay. The extreme example I've seen is folks putting resealed beer bottles full of gasoline in a bonfire after using an icepick to place a small hole in the cap. Obviously not something you are going to think is a good idea until you have emptied a good supply of bottles, but I must say, the resulting effect is quite dramatic. The gas vaporizes and is ejected from the bottle in a pulsing plume of flame that can reach 15 feet or so above the source. I'm told, having only witnessed this once and never wanting to again, that the main risk is doing it in the rain. Apparently then the shock cooling on the bottle can cause it to crack with the expected effect. The night I saw it had a dense fog and a bit of mist. I didn't stick around for long.

And just to be clear, I am in no way advocating that anyone give this a try.

 

[fcheslop]

Hi Zenon, As with any small engine friction and steam leaks kill them
The burner on Jenny Wren can be positioned away from the flue
A one inch gap between the the flame and boiler is to large an easy way to see the hieght needed is to place a bit of wire above the flame and lower it into the flame till you see the hotest part a bit rough arsed but it works