Another steam engine shaped object

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DJoksch

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This is the very first time it has seen steam. I need to tighten up the gland packings. Needs a boiler feed pump and a water preheater as pointed out. You have to watch the water level. Back to the larger boiler project.

 

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Doug, While I love the rhythm of the clicking and clacking.... but wonder what bits are making the noise?
I noted the shortage of steam, so I guess that if it were a single cylinder it would be OK...? Does that inspire you to convert it to a compound?
The limitations of your current boiler (from what I remember? - must check what we said when you were building the boiler) are simply in the burner.... The circle of ceramic won't last long if you increase the jet size - if it can draw the extra air - and the limitations of vertical boilers, that are fired from beneath with a ceramic, is really one of surface area. Then when you try a "bigger" burner (Alternative design), you simply get a limit of the restriction of the flue tubes, as they cannot cope with much extra exhaust gas. I must connect my compound engine to my 3inch vertical and see if it can cope? - as a comparison. (It will have a similar sized burner).
I have checked my notes on what I figured for your engine running at 150rpm... with bore 1.2" and stroke 2.25". Needs 2.0kW burner (min.).
The jet at
The burner at 3" dia has 7sq.in. = 45.6sq.cm. => 0.55kW at "industrial" power (for longevity) rated at 120kW/sq.m. (12W/sq.cm., or 77w/sq.in.). But I rate the burners at more like 200W/sq.in. (based on jet sizes and gas tables) - which seems OK for the lifetime I get for use in my boilers. So your 3" diameter ceramic should produce about 1.5kW of heat... so maybe just shy of the need of the engine? (Remind me of the jet size you are using, and the air-intake tube bore?).
Cheers.
K2
 

DJoksch

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Rear piston contacts the head on back stroke. The burner jet is .25 and I was using 5lbs of pressure. The first engine has a 1.5” bore and a 1.5” stroke and the boiler seems to keep up. This was the thought when I decided to build a larger boiler. I am also thinking it needs to be a compound engine. The simple solution is to sleeve the outer cylinder. I also have a nice piece of smaller hex bar stock for a new cylinder. I was not sure of the calculations. If I want a 3 to 1 cylinder ratio, a .7” bore high pressure would feed a 1.2” cylinder at 2” stroke. I also read that I need to account for an early cutoff to allow complete steam expansion.
 
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Hi Doug. Just a couple of thoughts.
Obviously, you need to adjust things to get rid of the contact between piston and cylinder cover. That will quickly knacker the big-end bearing, or cross-head bearing, or both. To put it simply. Been there, fixed it.
I like the idea of the compound engine, as I have seen a few in England. Trencherfield Mill engine, etc.
To sleeve the high pressure cylinder is a good idea. But the sleeve needs to be parallel, a press fit in the existing bore, and don't forget the ports will need to be machined in the liner. And a new piston, of course.
If you need to adjust the valve timing cut-off, then you will need to draw a diagram of the timing you have, the timing you need, and probably make new steam valves to give the new timing. I doubt you can simply reset the eccentric to achieve what is needed? What is the text you have been reading on this? I can help if you need a "number cruncher". Probably worth a direct communication if you want to send drawings of what you have, to avoid cluttering-up this thread?
The 0.7"bore HP will be about OK for 3:1 required for the 1.2" dia. LP. cylinder.
Thanks for including me, I am enjoying your project!
K2
 
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Hi again Doug. When you say "The burner jet is .25 and I was using 5lbs of pressure." - I assume the "5lbs of pressure" was steam pressure? - Or did you mean gas pressure on the 0.25" jet?
Ta,
K2
 
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Aha! You could run up to 20psi propane on that jet on your burner, if I remember your boiler development?
that could be 3 or 4 times the steam? Try 10 or 15 psi propane and you'lloyds probably have plenty of steam, compared to the video where you were short of steam for continuous running.
Enjoy,
K2
 

DJoksch

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I now have two sets of pipes. In a compound configuration, it runs better on steam. It definitely has more power in non-compound mode. Time to work on the boiler.

 

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Hi again Doug.
I found a picture of the compound twin that I hold - belongs to the local model engineering club and I run it on show days. I only have a picture of it away from the boiler, so must make a video of it "next time" it runs...
Re-watching both your videos, the "clanking and knocking" present in the earlier "twin-steamed" video has greatly improved in the "compound" run... Testament to you fettling and tuning I think.
Very good to watch (or am I a bit "sad" in the head?). How do you feel about the ability (limitation?) of the boiler to run it as a compound compared to the Twin configuration? - e.g. at "full fire", what actual speed difference is there (at the crank) between the 2 configurations? (at higher pressure, the compound "effect" will increase).
Ken
 

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DJoksch

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As a compound engine the boiler seems to keep up although it still requires a lot of water pumping to keep up. You can definitely see a pressure drop as water is added. I will run it with the boiler at full fire next time and alternate compound and non-compound configuration. I saw an interesting oil trap condenser and water preheater which might be the solution. I built another eccentric which could run a water pump.

Oh yes,.. I was given another box. In this case, I need to work from the steam ports back to the required stroke and slide valve. I just put it back in the box for later.
 

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Superb! Another twin, this time a marine vertical. You can either make it a Generator engine, with just a simple eccentric at either end, or a reversing (marine) engine with pairs of eccentrics at either end and some fancy linkages to the valves. Either way, an extra drive for a boiler feed water pump is a good idea.
Enjoy!
K2
 

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I now have two sets of pipes. In a compound configuration, it runs better on steam. It definitely has more power in non-compound mode. Time to work on the boiler.



Run Great .
Congratulations !
 
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Hi Doug,
On the " I built another eccentric which could run a water pump."... Feed pumps need to be sized to the engine, and steam usage, so the "feed-water" balances the "used steam". If you send me the following data (I have some, but worth a re-check) then I can let you know the displacement, bore and stroke, of the pump for feeding continuously from your crank eccentric.
Engine Bore (1.2"?);
Engine stroke (2.25"?) = double acting;
Cylinders being fed with steam (1 = compound, 2 = twin-feed)
Crank speed: ( max - guessed from video of twin, post #82) = (250rpm?);
This gives me 1272 cu-in of steam per minute... which equates to 3.14cu.in. of water per min. (at steam NWP = 50psi). This also proposes a need for 2.3kW of heat developed into steam. (at 60% efficiency, because the boiler loses heat to the room, heat is lost up the chimney, etc.) you need a 3.8kW burner. Maybe your burner is smaller than that, so maybe the engine is actually running at lower pressure than 50psi...?
Of course, change any of these parameters changes the (Simple) calculation. e.g. at 20psi it would be 1272cu.i. steam, 1.75 cu.in water and 1.3kW of heat transferred to steam (needing a 2.2kW burner?). (Possibly this is what I can see on the gauge in post #82?).
Now translating the 1.75cu.in/min. of water:
a pump at 250rpm would need a displacement of 0.007cu.i. per REV.
So a single-acting pump, stroke = 1/2", would be 0.1335in bore... Just over 1/8". ~3.4mm?
I am sure you can plug-in your actual numbers - (or I can?) to get a more accurate design of pump.
Hope this is useful?
K2
 
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Hi Doug, reply to post #91: here is a similar twin for when you decide to start on your twin compound in the box...
Cheers!
K2
 

DJoksch

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Here is the engine info.
Bore: 1.2”
Stroke: 2”
Eccentric stroke: .5” (easy enough to change)
Compound running configuration.

It runs smoothly as a compound engine. Speeds over 300 rpm starts to demonstrate the need for counter balancing. At about 250 rpm, it seems very happy and I can watch the Rube Goldberg action. I was thinking about using casting clay and pouring lead between flywheel spokes once I decide how much weight is needed. The counter balancing should actually go on the crank. I came across a lucky counter weighted flywheel allowing for high speeds for the previous engine project with no vibration.

The Stuart twin looks real close to the engine in the box. The boxed twin has the crank at 180 degrees so compound operation would be pretty straight forward. There are no screw holes drilled in the head or the valve chest so I don’t have any non-symmetric drilling issues. The big blue engine cylinder caps were randomly drilled and the cylinders were not bored straight. In fact, when it arrived, the cylinders and cross slide were glued to the base. It was pretty hysterical, but there was no drag. I do have a nice aluminum crank, eccentric, and crank rod bearing left over that will likely never use.
 
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Hi Doug: Here goes:
As compound running means you are only filling 1 cylinder from the boiler, and I was using a longer stroke, the numbers now work out at:
- Bore: 1.2”
- Stroke: 2” = double acting;
- Compound running configuration.
- Crank speed: 300rpm.
- Steam pressure 20psi (guessed from what I think I can see on the pressure gauge?).

So:
This gives me 636 cu-in of steam per minute... which equates to 0.88 cu.in. of water per min. (at steam NWP = 20psi). This also proposes a need for 0.6kW of heat developed into steam. (at 60% efficiency, because the boiler loses heat to the room, heat is lost up the chimney, etc. you need a 1.1kW burner).
Now translating the 0.88cu.in/min. of water:
a pump at 250rpm would need a displacement of 0.0035cu.in. per REV.
So a single-acting pump, stroke = 1/2", would be 0.095in bore... IF I have crunched the numbers correctyly! (I can't even type correctilly!).
The way many manage this is not with a direct acting eccentric/pump, but with a geared shaft that has the pump attached. The tiny bore (~3/32"?) will have some dead spaces at "TDC" (due to valves etc.) that will cause it to not function if they have any entrained air. The draw-back then is that the engine can appear to speed-up in the "intake" stoke, and slow on the "pressure" pumping stroke when it is working against boiler pressure. I compensated for this with a weird eccentric drive motion that gave the pumping time approx. 3 x the inlet time... and evened out the pressure variation somewhat.
I'll have to strip the system to show you with picture and video.
K2
 

DJoksch

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Hi Doug: Here goes:
As compound running means you are only filling 1 cylinder from the boiler, and I was using a longer stroke, the numbers now work out at:
- Bore: 1.2”
- Stroke: 2” = double acting;
- Compound running configuration.
- Crank speed: 300rpm.
- Steam pressure 20psi (guessed from what I think I can see on the pressure gauge?).

So:
This gives me 636 cu-in of steam per minute... which equates to 0.88 cu.in. of water per min. (at steam NWP = 20psi). This also proposes a need for 0.6kW of heat developed into steam. (at 60% efficiency, because the boiler loses heat to the room, heat is lost up the chimney, etc. you need a 1.1kW burner).
Now translating the 0.88cu.in/min. of water:
a pump at 250rpm would need a displacement of 0.0035cu.in. per REV.
So a single-acting pump, stroke = 1/2", would be 0.095in bore... IF I have crunched the numbers correctyly! (I can't even type correctilly!).
The way many manage this is not with a direct acting eccentric/pump, but with a geared shaft that has the pump attached. The tiny bore (~3/32"?) will have some dead spaces at "TDC" (due to valves etc.) that will cause it to not function if they have any entrained air. The draw-back then is that the engine can appear to speed-up in the "intake" stoke, and slow on the "pressure" pumping stroke when it is working against boiler pressure. I compensated for this with a weird eccentric drive motion that gave the pumping time approx. 3 x the inlet time... and evened out the pressure variation somewhat.
I'll have to strip the system to show you with picture and video.
K2
Good point. Did not consider the speed imbalance due to pumping. I have some nice indexing tools for cutting gears. Old clocks can wind up storing the power of a garage door spring. I’ve had to make a gear or two.
 
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Hi Doug (and watchers all!).
Just a quick post as I am off out with my beloved lady to enjoy the sun!
Here is a VERY quick sketch (NO CAD!) to indicate how a simply wheel driven lever can vary between one stroke and the other for the pump.
Rotate the pin clockwise in your mind (or YOUR CAD model!). When the drive pin approaches l1, it has a good velocity ratio for quick priming of the pump, sucking against atmospheric pressure.
As it approaches L2 it has a very good mechanical advantage to push against the pressure in the boiler.
Hope this makes sense?
K2
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DJoksch

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Hi Doug (and watchers all!).
Just a quick post as I am off out with my beloved lady to enjoy the sun!
Here is a VERY quick sketch (NO CAD!) to indicate how a simply wheel driven lever can vary between one stroke and the other for the pump.
Rotate the pin clockwise in your mind (or YOUR CAD model!). When the drive pin approaches l1, it has a good velocity ratio for quick priming of the pump, sucking against atmospheric pressure.
As it approaches L2 it has a very good mechanical advantage to push against the pressure in the boiler.
Hope this makes sense?
K2
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I like the concept. That’s exactly what this engine needs. I would have responded sooner, but I was asked to play in a pit orchestra for a show opening this weekend. The proceeds of course go directly into my projects.
 

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