buliding a vaccum engine and need some help

[chizz]

hi there

i am building a vacuum engine for a college project and have almost got it free running the flywheel assembly sits on bronze bushes, and the cylinder is made from stainless and the piston is ali bronze.

the engine turns over freely but does not look like it wants to run, ive been told balancing the flywheels is not important but to my thinking i cant help thinking it needs a counter weight to get it over the top stroke, this to be done by adding weight to the opposite side to the crank or drill hole in the flywheels on the crank side. is this wrong?

also i have been told meths burners are a no go as they contain to much water and will stop engine.

any help at all in any area would be very helpfull to me this is a new area for me.

i will add some pictures soon of my engine so far.

 

[NickG]

Hi, is the engine horizontal or vertical? If it's vertical balancing may be required as it will have a heavy piston.

Cast iron is probably the best material to make the piston and cylinder from, self lubricating properties and same rate of expansion. Most engines of this type have ball bearings to reduce friction to an absolute minimum but depending on the size could work with bronze bushes.

How freely does the engine turn over? Without the valve on it should do probably in excess of 20 revolutions with a flick of the flywheel.

Mine and most others run on meths so that advice is wrong, however, it does sometimes cause products of combustion to adhere to surfaces increasing friction. In my experience, either oil, or regular cleaning can prevent this.

The other thing you need is a very good fit between piston and cylinder, no leakage is acceptable but it still needs to be extremely low friction. Also make sure the valve is not leaking and the timing is right.

While we're waiting for pictures tell us some more details about the engine, how is the valve actuated and what are the sizes, bore, stroke, flywheel etc?

Good luck.

Nick

 

[chizz]

hi there thanks for the reply it is a horazontal engine and the design says it will run from a candel the valve is on the end and is activated by a cam on a spring this link is the engine i have built i have built it as an improvement engine. so bronze bushes are an improvement. it has a good seal because if i turn in the wrong direction it creates a good vacuum.

if it needs to do 20 rev with one flick of the flywheel then mine is not free enough yet.

http://www.scribd.com/doc/14511456/Candle-Powered-Engine

 

[NickG]

I've seen those plans before and can't believe anybody has got one to run, although they must have or there wouldn't be an article! The valve mechanism doesn't look great to me and how on earth a candle has enough heat and a clean enough flame is beyond me.

If you say it creates a good seal though, that's promising, I think you must be battling with friction.

here is a link to the version I made, the valve arrangement is somewhat different and gives little control so mine was a very difficult arrangement to get to run and is very tempremental. However, there is a good section on trouble shooting and a lot of it focuses on friction. It has some good guidelines, mine wasn't quite as good as suggested on the website but close and it still runs.

http://heetgasmodelbouw.ridders.nu/Webpaginas/pagina_happer_inw_schuif/inw_schuif_frameset.htm

Have a look at the trouble shooting checklist and watch the video to get an idea of how friction free these engines should be - I think you'll be shocked.

nick

 

[kcmillin]

Chizz, timing is also important.

The valve should close BEFORE the piston reaches bottom dead center. This is to allow time for the gas to cool and pull the piston forward.

How is this engine timed? I have also seen these plans and wondered about its ability, but like Nick said, they did create an article for it, so it must do something.

Kel

 

[Stan]

What is referred to as meths is denatured alcohol which has no water in it. Products like rubbing alcohol do contain water.
A good lubricant for your piston is powdered graphite, available from your local locksmith.
The location of the flame in front of the port is critical. It not only determines whether it will run but also the speed.
My experience has been that the wick has to be below the port,so that on the piston downstroke, the tip (hottest part of the flame) is sucked into the port.

 

[shred]

FWIW, don't be so sure about some of those old articles. Somebody told me a long while ago that a number of articles were knocked out and quickly mocked up for photos with an "I think this'll work... print it" attitude from the authors. I have no idea if this is one of those or not.

 

[chizz]

Hi all thanks for all your helpful comments I am taking all the information on board, i did speak to one bloke who had built this engine and got it running it does 300 rpm but not of a candle as with mine the exhaust blows the candle out as soon as you try to run it.

here are the pictures of my engine i said i would put on.

 

[DOC123]

Fabulous looking engine. I hope you get it going.

 

[NickG]

Chizz,

absolutely beautiful workmanship - it be a great shame if it didn't run, good luck.

How does the valve get shut? Is there a spring? It sounds like you've got a good seal between valve and face on the head, you must have lapped it in? I'm sure I've seen one of these with a flap type valve running before or at least a pic of one when I was researching it. Will have a look ....

What some people do to avoid the pressure build up / flame blowing out problem is include a supplimentary relief valve that vents as the piston gets near tdc.

Bingo ... look about half way down the page at a post from Zephyrin, he made one of the same type of engine as you are (same article) he said it required some experimentation and a gas burner to get it to run, and slowly but it ran! He included an exhaust valve as he says in his words.

Hopefully this will help and give you some inspiration and trouble shooting ideas if needed.

Best of luck.

Nick

 

[NickG]

Chizz, forgot to mention that a bit further up on that page there is a picture of an oscillating type - because I had built so many oscillating steam engines at the time, I had that idea even before I had seen it! I thought I had come up with a new idea but somebody had beaten me to it years before!!!

Now, there is a u tube video of one such sort running, impressive stuff.

Nick

 

[chizz]

thanks nick

thats the guy i have spoken to he gave me lots of useful information as well.

as to your question about the valve it is ativated but a spring the design to bend the spring into shape, but i machined the profile up and then added an insert out of spring steel still has the same function. thes is then deflected by a cam on the crank assembly.

 

[NickG]

Ah I see! nice idea

As kel said, check your valve timing, the valve should close just before BDC and will open naturally (if cam allows) before TDC.

Ensure you have a good seal piston to cylinder but no tight spots, very low friction and low friction on the crank too (would be better with ball bearings if possible although the workmanship on your bearings is outstanding.

Finally, make sure the flame is large and covers the whole port, if it draws any cooler air in, it will not run and make sure the flame is positioned such that it isn't blown about too much. If this is causing a big problem, it might be an idea to include that relief valve somewhere.

Nick

 

[Stan]

My experience is that flame blowout is caused by the flame being too high in relation to the port. The flame will not blow out if the exhaust air is only hitting the top part of the flame. Your current setup with an alcohol burner is low enough unless something is directing the exhaust air downward.

Be advised that having the flame centered under the port is not necessarily the best position.

 

[Gedeon Spilett]

hi Chizz,
As I told you, I have extracted my engine from the depth of my garage and I did a few run last sunday and take some videos of my engine running and looking carefully to a few point that could be of some interest to you. I will try to post a video on YouTube but it is a première for me... I will post here also some comments .
it took me a while to get my engine running...
Zephyrin

 

[chizz]

thanks Zephyrin

I am trying to get mine going when I turn it over should I feel a slight vacuum when as the valve shuts just before the top of the stroke, this pressure is much greater when the heat is added.

but it just seems the pressure is to much when it trys to get over the stroke

 

[NickG]

Hi Zephyrin

welcome to the forum, good to hear from you. You gave me a lot of help over on CNC zone, I finally got my first flame licker built about this time last year!

Looking forward to seeing your videos.

Chizz,

The valve should be shutting just before the bottom of the stroke i.e. piston furthest away from the flame, not the top of the stroke

Nick

 

[chizz]

ah that's what I meant nick me just wording it wrong, i can now see why these engines are tricky built a low temperature hot air engine which I thought was quite challenging but i think this is more difficult so many different factors to consider. Still I will not let it beat me!

thanks again for your advise.

 

[Gedeon Spilett]

Chizz,
I don't get the point about the pressure you feel, there is something wrong in the valve diagram or I have missed something in you question.
Running forward you should not feel any resistance, nothing, the more free running you may achieve is the best. on the opposite, backwards, the vacuum strongly resists, and you cannot pass the top dead centre.
I have estimated (with a plastic angle gauge) the actual setting of the valve of my own engine :
the flap start to open 44° and is 100% open 7° before TDC.
the closure starts 52° and is fully closed 16° before BDC. I guess that it is important that the gas start to contract before BDC allowing the maximum vacuum during the return stroke.
the post by NickG underlined this vital point too.

ha ha for the video
look at
[ame]http://www.youtube.com/watch?v=yEWOO2XyF20[/ame]
[ame]http://www.youtube.com/watch?v=LoAEWeycAwI[/ame]
I have tested these engines, they worked not too bad after a 2 years rest.

cheers all,

I really enjoy this forum

 

[chizz]

Hi Zephyrin

The videos are great well done for getting them on here I found it have to get pictures on here not to good on computers.

I may have confused you when talking about the pressure I feel my valve shuts just before BDC but as it shuts I can feel the vacuum starting and when I run it by hand with the burner as it gets to the same point when the valve shuts just before BDC the vacuum seems alot more than it did before, so when I flick the flywheel over to start it is does about 2 turns of the flywheels and then bounces back from this point almost like the pressure is to much.

one last thing I wanted to ask you is on your model you went for one flywheel and did you use ball bearings on the crank as you can see from my pictures I have made bronze bushes wondering if this is what I am battling with.