Poppin vacuum engine cylinder head

[nearnexus]

Hi all,

I'm building a Poppin vacuum engine.

The flame inlet valve (hole) is in the centre of the head.

The barrel is air cooled aluminum with a thin bronze liner.

Looking at the thermal efficiency of the various metals I was wondering if it would be better to use ordinary low carbon steel for the head rather than aluminum or brass, as it would have much less heat transfer.

My reasoning is that the head is mainly to feed the flame and is exposed to the heat source continually so a poor thermal conductor should be better.

The cylinder will have the main cooling effect and if the head is a high heat conductor then the head will transfer heat from the flame throughout the full engine cycle, which you don't really want.

Steel on the other hand would not as it has poor thermal transfer ability.

The plans I am working from are for a totally cast iron engine, but I'm not going that way as I'm only using materials I have to hand.

The downside is that the steel will go rusty if not oiled over after use, but it would be more durable for wear from the flap valve.

What do you recon?

 

[mklotz]

My Poppin has an aluminum cylinder and steel head, just as you suggest, and it works very nicely.

A high conductivity head might quench the flame before it could reach the interior of the cylinder. At least, that's my take on the physics.

 

[zeeprogrammer]

Welcome to the forum nearnexus.
There's a Welcome thread where you can make a thread and tell us a little about yourself.
Looking forward to seeing Poppin build. Pics please! We love pics! ;D

 

[MikeR C]

I built a poppin', and corresponded with Mr. Senft as I was building it, he recommended stainless steel for heat conduction and corrosion reasons. He also reiterated the need for the sharp edges around the hole to stop turbulence as the flame is drawn into the cylinder.
I made my head in stainless and it has not given me any problems and the engine actually runs!

Thx
MikeR C

 

[nearnexus]

Thanks for the replies on this.

I have never tried my hand at this before. as I've always been too busy.

I'm using these plans - see down page a bit.

http://www.john-tom.com/html/SteamPlans3.html

So from the comments, I will go with steel for the head and I also take it that the inlet port should taper to a sharp edge with a cone effect on the inside of the head - does this give a venturi effect?

I notice the plans look to do this.

Yes when I finish it I will put up some pictures - everyone likes pictures

 

[Longboy]

..........Its 6 of one, half dozen of the other. High conduction or low conduction your engine isn't gonna care even if you run it an hour at a time. Checking with an infared thermometer it will be hot and running with either steel or aluminum. The radiator is back from the head and will dissipate the heat at a rate quick enough to maintain its operational zone. Lots of fins on the Poppin. Another way to look at it is this question: If steel has a lower rate of heat migration, does the steel radiator fining have a slower rate of heat rejection? And conversely, aluminum. Quicker rate of heat absorbsion balanced by a quicker rate of heat rejection. There are brass head/ radiator flame suckers out there too. Material choice is builders preference. Dave.

 

[nearnexus]

OK you wanted photos, here's a couple down the page a bit.

http://users.picknowl.com.au/~gloaming_agnet/cq9325rev-a.html

I just put em on my lathe page for a quick look.

Later when it's complete I will put up a bit of a blog on it - maybe.