Author Topic: Gas Firing the Scott Vacuum Engine..........  (Read 6812 times)

Offline Stilldrillin

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Gas Firing the Scott Vacuum Engine..........
« on: November 28, 2015, 08:58:45 PM »
Many of you, will remember my Scott build.
 For those who don't, but have plenty of time. It's here...... http://www.modelenginemaker.com/index.php?topic=4270.0





It has run, faultlessly, (so far), "straight out of the box". Two shows, at some 6 hours each. Plus, my own pleasure runs.

The only bugbear, has been refilling the meths burner, every 25 mins. The paint, doesn't like meths.......

Time to go, gas fired!

Bought a tank, from Forest Classics, at the last show.
 Mounted on 3mm thick aluminium x 50mm wide.
The wooden bearers are 47mm apart. I milled a rebate along the inner corners, allowing the alloy strip to slide underneath, like a drawer. The weight of the engine will, (probably), hold it in position.




It needs twin flames. So, it needs a T piece, as the burner base.

1/2" brass bar, with 5mm, (M6 tapping size), through holes. Slot drilled, to centre line......




Flux, only where it's needed. Silver solder........




Mount like so. Apply heat.......




Happy, with that........




The burner's main components.......




Further progress. As, and when.......

Thanks for looking in!

David.
David.
Still modifying bits of metal... Occasionally, making an improvement!
Still drilling holes... Sometimes, in the right place!

Offline b.lindsey

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Re: Gas Firing the Scott Vacuum Engine..........
« Reply #1 on: November 28, 2015, 09:54:53 PM »
Nice start on the conversion David. How long do you think it will run on the gas before having to refill the tank?

Bill

Offline Stilldrillin

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Re: Gas Firing the Scott Vacuum Engine..........
« Reply #2 on: November 28, 2015, 10:33:55 PM »
Nice start on the conversion David. How long do you think it will run on the gas before having to refill the tank?
Bill

Not too sure on that one, Bill.......

The Robinson, has passed 1½ hours. But, it was not a full tank! 





David.
David.
Still modifying bits of metal... Occasionally, making an improvement!
Still drilling holes... Sometimes, in the right place!

Offline Stilldrillin

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Re: Gas Firing the Scott Vacuum Engine..........
« Reply #3 on: November 29, 2015, 10:59:58 AM »
Today's instalment.

Assembled, and gas turned up. We've got twin bunsen burners.......




Add a couple of caps.......




Already, it's a rapid runner. I've now found the revs are limited, by the follower coming off the cam........




The uprights are too high, at the moment. I will experiment with packing under the engine, before reducing their height to suit.

I'm thinking of installing a small pilot light. As the engine still insists on blowing out the flame, when it's too close to the port.
 But, that might change, with a lower burner height.

David.
David.
Still modifying bits of metal... Occasionally, making an improvement!
Still drilling holes... Sometimes, in the right place!

Offline Stilldrillin

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Re: Gas Firing the Scott Vacuum Engine..........
« Reply #4 on: December 01, 2015, 04:50:11 PM »
I have tried pairs of jets, in vertical, horizontal, and 45* formats. Also, at different heights.

None of which worked any differently, to the others.  :-\





They all blew out, when the engine got going. VERY frustrating! :ShakeHead:



I've just had one of those moments......... An epiphany....... When you realise, you've had it all wrong. For so long........ 

Yesterday's workshop weather, bit me.
 Stayed indoors, today. Chance to test the various burner angles.......

Only place available, is on top of a wardrobe. At forehead level. Mrs. Drillin doesn't complain too much, about gas smells......  :(

All the various terminals performed, exactly the same as each other! Always, the blummin light, blew out!!!


Standing where I was. Looking up at the burner. Never observed from this angle before.......





The light's not being blown out....... It's being sucked out!!

Very difficult to photograph. But, obvious to the Mk1 eyeball. The intake velocity is greater than the gas velocity........

Puts a whole new slant on things, don't it?   :thinking:

Sheesh!

David.
David.
Still modifying bits of metal... Occasionally, making an improvement!
Still drilling holes... Sometimes, in the right place!

Offline Admiral_dk

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Re: Gas Firing the Scott Vacuum Engine..........
« Reply #5 on: December 01, 2015, 08:46:34 PM »
Never saw that one coming either  ;)

But it just shows (again) that things do change with perspective  ;D

Glad that you found out, since this could help you solve the problem.

Offline b.lindsey

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Re: Gas Firing the Scott Vacuum Engine..........
« Reply #6 on: December 02, 2015, 01:29:23 AM »
Still following along with interest David. Looks like it will be a nice set-up once you get the kinks and angles worked out. It certainly shouldn't suffer from a lack of heat with those twin Bunsen burners :)

Bill

Offline Steamer5

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Re: Gas Firing the Scott Vacuum Engine..........
« Reply #7 on: December 02, 2015, 07:26:20 AM »
Hi David,
 That's a great find! I guess when you think about a vacuum engine is going to do just that .....suck! Still wouldn't of thought it would be that great. As a thought & not know much ( read just about nothing) about these engines, how about a mesh screen between the flame & the engine, open enough to allow the flame though but maybe enough to prevent it sucking the flame off the burner. It may also get hot enough to either provide some more heat, or relight the burner......bit of a long shot but hay easy to try.

Cheers Kerrin
Get excited and make something!

Offline Jo

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Re: Gas Firing the Scott Vacuum Engine..........
« Reply #8 on: December 02, 2015, 10:54:41 PM »
Hi David,

I have just had an orphan follow me home:  One of the members at my club's father started this engine in his mid eighties. I was told to expect a few challenges  :-\

So I am watching with even greater interest than I was before  :drinking-41:

Jo
Usus est optimum magister

Offline AOG

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Re: Gas Firing the Scott Vacuum Engine..........
« Reply #9 on: December 02, 2015, 11:16:00 PM »
Have you considered a gas mantle like they used to use to use for a gas light? You can still get them for the Colman lamps.

Tony

Offline Stilldrillin

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Re: Gas Firing the Scott Vacuum Engine..........
« Reply #10 on: December 03, 2015, 01:27:44 PM »
Admiral, Bill.
 Thanks for the comments, and support.

Kerrin, Tony.
 Thanks for your thoughts. I was also thinking, of a tea strainer's, stainless mesh.  :thinking:
Also. An alloy shroud, immediately above the terminal. A little short, of the flames.

Jo.
Wishing you, good luck, Lass!
 I'll be watching.......  ;)


My thoughts, then started running along the lines of a soap bubble. Easily taken from it's ring. Mod the orifice, to make it less ring like.

Milled a 4mm slot, in the 5mm bore terminal.......




Burns well.......




Cam follower bounce, at full blast.......




But. That's not what we're here for! I need it to run reliably at around 150rpm. And, wind up, as necessary. 

Sleeved down, to a 3mm orifice.......




No! ...... Not enough gas! Needs a larger bore terminal.

The one thing this has proved. It works perfectly well, when the burner is outside the shroud. The vacuum kills the flame, when under the shroud.

I'm now steeling myself, to remove the sides, (or all) of the shroud. Without any collateral damage to the polished cyl head......   :help:

David.
David.
Still modifying bits of metal... Occasionally, making an improvement!
Still drilling holes... Sometimes, in the right place!

Offline Stilldrillin

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Re: Gas Firing the Scott Vacuum Engine..........
« Reply #11 on: December 03, 2015, 08:02:37 PM »
This afternoon, I did a bit of sawing. (Not, the finger)........




And made this racy little, cut down number.........




Will probably, make some longer horizontals. From stainless steel...... 

David.
David.
Still modifying bits of metal... Occasionally, making an improvement!
Still drilling holes... Sometimes, in the right place!

Offline Ian S C

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Re: Gas Firing the Scott Vacuum Engine..........
« Reply #12 on: December 04, 2015, 10:18:51 AM »
David, your motor has two holes in the cylinder head, I wonder if the hole was enlarged to a slot whether the intake velocity be reduced.
On my motor, I changed from one 1/4" diameter hole at the side of the head, to a slot3/8" x 1/4", it still blows out the flame until it warms up (spirit burner), but I think it is improved over the small hole.
For a gas flame I can't decide if the flame should be a soft one, or a hard one(as in a gas torch), I suspect it may be the former, with the top of the burner well below the intake. :thinking:
Ian S C
« Last Edit: December 05, 2015, 10:46:00 AM by Ian S C »

Offline b.lindsey

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Re: Gas Firing the Scott Vacuum Engine..........
« Reply #13 on: December 05, 2015, 12:40:33 AM »
So how did the cut down shroud work out David? I hope better than your finger made out!!

Bill

Offline Stilldrillin

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Re: Gas Firing the Scott Vacuum Engine..........
« Reply #14 on: December 05, 2015, 08:51:47 PM »
David, your motor has two holes in the cylinder head, I wonder if the hole was enlarged to a slot whether the intake velocity be reduced.
On my motor, I changed from one 1/4" diameter hole at the side of the head, to a slot3/8" x 1/4", it still blows out the flame until it warms up (spirit burner), but I think it is improved over the small hole.
For a gas flame I can't decide if the flame should be a soft one, or a hard one(as in a gas torch), I suspect it may be the former, with the top of the burner well below the intake. :thinking:
Ian S C

Ian.
 They were my thoughts too!  ;)
A larger port would make a big difference.

Unfortunately, the 5thou shim was occasionally sucked into the original slot. It needs support, in it's centre area.
 Guess I could file, to square corners, the outer lower sections of the ports. But, I'm happy with it's performance, as is.......  :)

A little more fiddling should make it more manageable.  :ThumbsUp:

David.
David.
Still modifying bits of metal... Occasionally, making an improvement!
Still drilling holes... Sometimes, in the right place!