Senft "Poppin" engine

[Brian Rupnow]

Some of the flame eaters I seen on you-tube (Big Nick for example) have exhaust stacks on the cylinder. What's that about? Has anyone knowledge of why. Obviously it must help from blowing out the flame, but I would like some more information. Thank you in advance, Brian

[Jasonb]

Having an exhaust valve makes for a better running engine as anything left in the cylinder after the gasses have cooled can be removed via the exhaust valve rather than getting compressed by the piston at the end of its stroke. You don't have to have a stack but any heat still left in the gas will create a draft and draw more exhaust out on the next stroke. the Chuky I did has an exhaust valve and chimney

[Brian Rupnow]

Thanks Jason--so is the exhaust simply a one way poppet valve?

[Jasonb]

On that one it is a large diaphragm valve, think of it like the atmospheric inlet valve on a hit and miss engine but rather than letting air in it lets it out. If you look at Graham's "Nettie" thread you will see he has one in the form of a simple flap valve rather than the sprung one on Chuky

[Zephyrin]

a valve like the breathing valve of IC engines is often present, a simple foil of metal above a hole with sharp edging.
to be operative, the opening of this setup must be lighter than the intake valve, and is expected to be active on slowly running engines with a "mechanical" valve, not on a "poppin" with a light and springy valve.
In my own vacuum engines, such valve did not affect running, nothing but the noise, even the frequent blowing of the flame was not modified as hoped !

[Jasonb]

In my own vacuum engines, such valve did not affect running, nothing but the noise, even the frequent blowing of the flame was not modified as hoped !

That got me thinking about what would happen with Chuky if it did not have an exhaust valve. Easiest way to test things was to block the exhaust, easy to see that on this design the exhaust does affect things and is needed.

[youtube1]https://www.youtube.com/watch?v=BeSdwzwrFoU[/youtube1]

[Zephyrin]

Wow, the effect of blocking the exhaust valve is absolutely dramatic !
But in your design with the sliding shutter, there is no other route for the exhaust, as the raising pressure in the cylinder on the back stroke of the piston cannot lift and open the intake valve, contrary to what it happens on many other designs as in "poppin"...where such pressure relieving valve would be useless.
You may see here that I put such a valve on the cylinder head of my engine, expecting that it would improve the flow of the exhaust and stops blowing the flame, but it was not so, alas, nothing different with or without the valve !
http://www.modelenginemaker.com/index.php/topic,7946.msg168473.html#msg168473

[Brian Rupnow]

 If anyone liked my sexy cylinder, here is the drawing of it.--Brian

[NickG]

Zeph, I agree with what you are saying but i wonder if the exhaust valve is easier to lift than the inlet then it may help divert the pressure away from disturbing the flame. It would also make cam closed duration less critical I presume, it’s like an automatic exhaust valve.


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[Alyn Foundry]

Hello All.

Attached is a picture of four of my own design " flame gulper " engines.

They ALL have a secondary exhaust relief valve.

Cheers Graham.

PS. Second from the left CHUK 2, Jason's Chuky is a slightly smaller version. Has just returned from a museum exhibition where it ran for 4 hours straight! So hot it actually burned another exhibitor who foolishly touched the cylinder.

A very short glimpse of CHUK 2 at the museum, surrounded by several of my models on display there.

<a href="https://www.youtube.com/watch?v=e1SwR0SugeA" target="_blank">http://www.youtube.com/watch?v=e1SwR0SugeA</a>

[Brian Rupnow]

What a lovely little engine this is. The more it runs, the better it runs. I fire it up a couple of times a day when I'm setting at my computer and it makes me smile. No need for a battery or an air compressor. This engine is pure fun!!!

[b.lindsey]

I agree Brian. It always amazes me how fast that heating/cooling cycle can be. It is a fun engine though for sure.

Bill

[NickG]

That’s what I’ve always loved about these too Brian, just a self contained engine with plenty of character!


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[Craig DeShong]

Brian.  Looks great and runs good too.  If a novice may ask, HOW did you form those beautifully shaped fins.  Mine look like crap compared to yours?

[Brian Rupnow]

Craig--I have a cheap old HSS parting off tool with a 1/16" wide parting off blade. I had enough of the 1/16" blade projecting so that the holder wouldn't touch the part. Ran the lathe at about 275 rpm, clenched my cheeks (at both ends) and hand fed the tool in. I had preset the maximum depth I wanted the tool to go on my DRO. It was just a matter of watch the DRO and crank the handle, and hope to God that it didn't catch and break the blade. The cylinder hadn't been parted off from the parent piece at this time. The part was cast iron, which I have never had problems cutting fins into.---Brian