how does a vacuum engine work

[chizz]

hi all

I am currently making a vacuum engine and have already got loads of useful information from a few of you, but i just want to ask one more question my engine is nearly running i can see it wants to go but it is held back by something. the vacuum is formed and pulls back quite hard but then the energy seems to be taken away I'm not sure whether the valve is not opening in time at TDC or the flame is not hot enough and is not causing a big enough vacuum.

is this how it is meant to work "the valve closes just before BDC and the vaccum is created pulling the piston back is the valve meant to open at that point to allow that power stroke to continue with the kinetic energy already in action" think maybe my valve does not open in time meaning the piston then is slowed down abit by the slight resistance before the valve opens.

thanks

Chizz

 

[Omnimill]

Which engine is it? th_wwp then perhaps folk that have built your particular engine can help!

Vic.

 

[b.lindsey]

Chizz, if you have that much suction the it shouldn't be a piston to cylinder fit problem which leaves the valve timing as the most likely culprit assuming there aren't any other friction/binding problems. From what you say it sounds like the valve may not be opening quite soon enough which could create some suction, thus slowing the piston down as you said. It should be easy enough to play with the timing and/or flame intensity until its running ...just stay after it

Bill

 

[chizz]

hi Vic

its the candle engine from the attached doc i have posted pictures of it under the Thread "building a vacuum engine and need some help" and some of you guys have really helped and i have adjusted accordingly. but just wanted i more general overview of how an vacuum engine is meant to work, but from what you are saying it sounds like they are all different.

thanks bill i thought that is what it might be the design for the cam on this engine is very vague making the engine timing tricky, i have had help from others on this but it seems every engine is slightly different depending on how you have built it.

Chizz

View attachment Candle_Engine.pdf

 

[b.lindsey]

Another thought Chizz after looking at the pdf file. Could it be that the spring if too stiff and therefore slowing the whole thing down as it tries to open the valve? It shouldn't take much spring tension at all to close the valve.

Bill

 

[chizz]

OK thanks bill i will look into that one.

 

[Longboy]

hi Vic

its the candle engine from the attached doc i have posted pictures of it under the Thread "building a vacuum engine and need some help" and some of you guys have really helped and i have adjusted accordingly. but just wanted i more general overview of how an vacuum engine is meant to work, but from what you are saying it sounds like they are all different.



Chizz

The science around the vacuum engine is the same with individual designs being different. It is outside atmospheric pressure pushing the piston back up the bore as the heated air drawn into the cylinder is cooled, its pressure drops to below outside atmospheric pressure. You may be "running out" of this pressure differential as the piston returns to TDC before the next cycle starts. Some engines use a check valve to exhaust internal air where as the flapper valve does the same thing and can be vissualized as the flame wavers back and forth from the piston motion in the bore. Your candle engine does not specify a check valve so the flapper valve may be openning a few degrees too late. If this is so you may be generating a compression stalling the cycle, or in other words.............a mechanical paperweight w/ candle! ;D

 

[Fingers]

Hi
I have just finished building a vacuum engine vertical type. For me one of the most critical factors in getting mine to run was first off the timing of the valve the valve must only just close at tdc or maybe even the very slightest opening of .001 or .002, I think this helps to relieve pressure in the cylinder as the piston reaches the top of the stroke, also the try adjusting the timing in small increments trying it each time without touching the burner, This will eliminate various flame positions while testing the timing. I find mine works best when the flame burns about 5mm from the valve.
Jamie