Steam engine cant start to run

[Dark KnightParticipant @darkknight31337]

Hi,

today I finished model, pressure tested boiler with air, no leaks, so I tried to run it on steam. I heated boiler which produced maximum 0.7bar steam (boiler volume 34000 cubic mm; max filling volume 28200 cubic mm) which is quite a lot and cylinder (max volume 400 cubic mm) was trying really hard to run but couldnt turn flywheel around, I made oscilating cylinder engine, are maybe the holes not in perfectly aligned position, because piston only pushes when in maximum height position (intake only starts on highest position) or is the flywheel to heavy? Any ideas appreciated. Also added model image for reference, sorry for bad quality and my english.

Martin

[JasonBModerator @jasonb]

It would be worth testing the engine on air first which takes the boiler out of the possible list of problems. Just remove the plug on the right and feed air in through that hole. See what pressure it needs to run.

It is not easy to see on your engine where the cylinder ends and the piston starts, are you running the rod straight into the cylinder and using that as the piston?

The engine will not self start you need to flick it round to get it started.

[JasonBModerator @jasonb]

Can you post a sketch of the port block with size and position of the holes relative to the pivot and also what size hole is in the cylinder

[Dark KnightParticipant @darkknight31337]

Here this are my cad drawings, I hope this help, I suspect that the holes alignment is bad. Maximum cylinder angle off center line on valve block is 5 degrees

[JasonBModerator @jasonb]

No image in your post

[Dark KnightParticipant @darkknight31337]

I apologize 

[JasonBModerator @jasonb]

What is the distance from pivot to hole? and is it the same on both parts

Your main problem looks to be that the two holes are not equally spaced above and below the pivot height but need that dimension to plot it out.

 

[WearyParticipant @weary]

Scaling off your drawings (yea, yea, I know, but in the absence of dimensions …..!!) it looks suspiciously as if the arc of the port in the cylinder coincides poorly with the ‘arc’ of the ports on the block-face.

(Plus that piston-face surface-area is very small and will not help.)

Phil

 

 

[Martin ConnellyParticipant @martinconnelly55370]

By my estimates the two holes, inlet and exhaust, are too far apart for a single hole to act as both inlet and exhaust on the cylinder. The crank looks to be about 18mm between TDC and BDC and from the drawing looks like 4.5mm between the holes. That means the ratio of the holes to the distance between the pivot and flywheel centre should be about 4:1 and it looks more like 10:1

Change the exhaust on the block into a slightly larger hole and you may get it working but it needs proper analysis in the CAD model.

Martin C

[JasonBModerator @jasonb]

I scale the cylinder hole as 8.5mm from pivot and the block holes 6.5mm from pivot. Plotting those to the 5degree movement stated then it’s never going to see any steam into the cylinder. Green dotted circles are the cylinder ports at their max movement

[Dark KnightParticipant @darkknight31337]

Hole of cylinder is 2.5, also did you make hole on cylinder a little bit further back then 25mm because its at angle of 10 degrees (around 2mm). Maybe my drawing measures are little off than actual ones on model. I will remeasure… I tried to run it again now boiler got to 0.4bar and i figured why it ran before on 0.7bar, my valve had small ball bearing for ensuring tight seal on regulation valve, that ball bearing got stuck in hole in valve. I had to fix it today and remove ball-bearing. Now I soldered it on threaded rod of valve (image). Today I tested it again on air and it starts running on around 0.4-0.5bar. In this boiler I can achieve steam pressure of about 0.4bar, so conclusion is that boiler is a little bit to small. Should I make brass insert in cylinder, that it will require less steam, or should I make another smaller boiler and connect it with original boiler, that way I can produce higher pressure steam?

[Dark KnightParticipant @darkknight31337]

I can only enlarge intake hole for 0.5mm. I will remake Cad model. I now think the problem lies in boiler and pressure within it. Also is there any literature about steam engine model ratios, I have been looking everywhere on Internet and I can’t find any PDFs. Do you know for any literature about this ratios (boiler/cylinder ration, flywheel ration, ect.), or do you get this ratios with experience?

[Dark KnightParticipant @darkknight31337]

Distance between center of holes is 4.5mm if you still need.

Martin

[Dark KnightParticipant @darkknight31337]

My drawing are way off, im almost certain now XD ;(

Martin

[Chris GunnParticipant @chrisgunn36534]

I think Jason has probably solved the problem, but it looks to me that the spring holding the cylinder to the face is quite tight, maybe this could be eased a bit when the ports are sorted out.

Chris Gunn

[JasonBModerator @jasonb]

Yes I did allow for the angle of the cylinder hole but have now enlarged it to 2.5mm.

I think the best thing is to forget about steam for now and just get it to run on air, once you know it runs then try it on steam.

I’ve drawn it out again and as far as I can teel the cylinder hole is further away from the pivot than the holes in the port face so does not connect.

rather than making complete new parts it would be possible if you have a milling machine to cut two 1mm deep slot 2mm wide which will extend the holes too where they are able to connect with the cylinder.

It is not ideal but worth a try before remaking other parts.

[Roger WoollettParticipant @rogerwoollett53105]

I think you would be better off if the cylinder were closer to the crankshaft. That would increase the swing and hence increase the distance btween the port holes. I try to get the two as close as possible. I also tend to make the stroke twice the bore (longer strokes increase the swing) but I doubt if that is critical. 0.4 mm seems very small for a steam passage and that can also be inreased if you can get a bigger swing.

The distance between the port holes should be slightly more than twice the diameter of the port holes which should all be the same. For instance if the inlet and exhaust ports are 2.1mm apart you could have 1mm diameter holes.

Spring pressure should be a small as possible. Make sure the cylinder is flat on the port face – hold it up to the light and look closely. A very small gap will stop it working. It may be worth while to slacken the crankpin and pivot bearings slightly to make sure the cylinder settles firmly onto the port face.

[Dark KnightParticipant @darkknight31337]

Currently I don’t have a milling machine. I could enlarge hole of cylinder along Z axis with drill bit, if that doesnt work i will have to dump valve block completely.

[Dark KnightParticipant @darkknight31337]

Ok I fixed it today by enlarging hole on face of cylinder, here is a link to compressed air test run:

https://files.fm/u/8bh36a8jq2

Than I tried to run it on steam, engine ran for about 2 seconds on 0.5bar steam by itself and then it stopped. Is the boiler volume to small? I have ratio of cylinder : boiler = 1: 67 (80% filled with water). Should I smaller piston’s diameter in cylinder or enlarge boiler volume?

[SillyOldDufferModerator @sillyoldduffer]

As the engine is struggling to run I wouldn’t reduce the size of the cylinder.  It needs more power, not less.

A few things to try before making a bigger boiler.

Insulate the boiler and pipework.  The pressure in the cylinder depends on keeping the steam hot, and, at the moment, the pipes will be losing lots of heat.

The conrod is very heavy.  Try reducing the weight, perhaps:

The flywheel diameter looks too small to me, and it is too solid.  A flywheel’s weight should be concentrated at the rim, done by removing metal in the middle, like:

Dave

[WearyParticipant @weary]

And when you start the engine with max boiler pressure of 0.7 bar what happens??

Does boiler lose pressure rapidly/slowly until engine stalls?   Over what time-period?  Does engine run and boiler maintain pressure above 0.6 bar, 0.5 bar, etc., etc.?

If you load/slow the engine with a brake (friction against flywheel) does the boiler maintain pressure better??

The answers to these questions may assist in starting to diagnose if your boiler can generate enough steam to run that engine.

I note that from your ‘running on air’ video the stall pressure appears to be around 0.4bar (5.5 lbs sq in), so perilously close to the pressure you are trying to run at.  Can you confirm the ‘stall air pressure’ perhaps as engine appears to run on 5 bar (7 lbs sq in)?

Interesting to know what fuel you are using for heating the boiler too …… gas, flammable liquid, solid (i.e. ‘meta’ blocks), or ……??  And how, if at all, can you vary the heat input?

Phil

 

[JasonBModerator @jasonb]

It’s not running very well on air, unless you have a tiny compressor then unrestricted 0.5 bar should see several 100rpm if not 1000, as I said sort the engine on air then look at the steam supply.

If the holes are in the right place a wobbler does not need much air or steam to run. That was one breath of air.

[Dark KnightParticipant @darkknight31337]

I did not run it on compressor, I ran it on hand pump which is meant for bike tires. This engine is not built for 1000rpm, probably maximum 200-140rpm.

 

[Dark KnightParticipant @darkknight31337]

Thanks for advice, I will fix flywheel and I will see what can I do about conrod.

Martin

[Dark KnightParticipant @darkknight31337]

Engine runs for about 2 seconds then stalls and pressure in boiler is always steady around 0.5-0.6bar (steam)

If you load/slow the engine with a brake (friction against flywheel) does the boiler maintain pressure better??

It maintains it the same. If i put it on inlet position presure rises a little bit.

I note that from your ‘running on air’ video the stall pressure appears to be around 0.4bar (5.5 lbs sq in), so perilously close to the pressure you are trying to run at.  Can you confirm the ‘stall air pressure’ perhaps as engine appears to run on 5 bar (7 lbs sq in)?

Stall pressure is about 0.4bar yes and it varys betwen 0.35-0.45 on how much I tighten thread on conrod connected to brass connector to flywheel.

Interesting to know what fuel you are using for heating the boiler too …… gas, flammable liquid, solid (i.e. ‘meta’ blocks), or ……??  And how, if at all, can you vary the heat input?

For fuel I use small butane gas burner (T = 400 °C). I can regulate amount of gas burnt.

I hope this answers your questions.

Martin

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