Hi PD's,
Interesting observation DEREK,
and it may well have a small effect, however, don't forget that whilst isolated, then the whole steam feed from poiler to regulator will be cold, and when the steam is first turned on (via the stop valve) it will more than likely condense out and pass through to the engine.... yer can't win....not only that, but the engine itself will condense a fair amount of steam until it gets up to temperature.
GREBO.... I meant to tell you....CATS DON'T LIKE STEAM WHISTLES....
.....
it might pay you, since your oiltrap/condenser is quite small (volume wise)...I think Derek has the same size also, so it may also apply...... is to warm up the engine with the oil trap disconnected (just be sure SWMBO aint around, especially if in the bathroom
) this will prevent it filling up with start up condensate, which could also be part of your problem.
Once warmed up thoroughly, reconnect the condenser/oil trap and away you go.
Moritz asks: -
Why should it condense properly at all?
In my understanding, its purpose is more a mechanical trap for oil and water already condensed in the engine, than an actual condenser.
If it condenses too much steam, it could overflow (and then you get serious spitting...). Therefore I think insulating it wouldn't be a bad idea at all! So it stays warm and catches only the already existing droplets out of the exhaust steam.
In my own setup with selfmade (in my case unlagged) condenser, after evaportating one full boiler, I found only as little as 20 ml water and oil.
Why should I want to condense more steam? I like the plume out of the funnel...
Good question, however, the answer is not as straight forward as first appears…….
Agreed… the primary objective of the oil trap/condenser is to capture the waste steam oil and any water droplets, how this occurs is the issue……
First off… what we are talking about is NOT the CONDENSING of the steam, but rather the condensing of the fatty compounds contained within the steam oil, and the trapping of oil itself. SO we are not really talking about a steam condenser in the true sense of the word…..
Steam oil contains a compound of animal fats and other fatty materials in order that the oil can become more easily miscible with the water vapour (steam), which in turn makes the resulting emulsion spread more easily over the surface of the moving parts of the engine, carrying the oils molecules with it, thus giving a better, and more evenly distributed, lubrication layer.
These fatty compounds remain in vapour form at a temperature above about 110deg C (approx temperature of steam at around 6psig), therefore, in order to eliminate these from the exhaust steam the temperature if the steam must be reduced to below 110deg C, however, the water vapour (steam) will still be vapour, albeit quite wet.
The exhaust steam directly from the engine will be at a somewhat higher temperature.
The actual exhaust temperature (and pressure for that matter) will be determined by many factors of engine design, valve gear timing etc, and operational layout.
If you consider that, in the majority of small model engines, the actual amount of RESTRICTED EXPANSION inside the engine is quite low (probably no more than 20%) then the pressure at the exhaust port will only be around 20% lower than the inlet pressure.
E.G 40psi inlet pressure (141.5deg C) …32psi exhaust pressure (135deg C).
This exhaust steam is then met with a, shortish, length of small-bore pipe (between engine and OIL TRAP), which restricts its further expansion and in order to escape it’s velocity increases as it is forced through the pipe by the pressure behind it……
Suddenly the steam arrives at a large void area (the OIL TRAP CHAMBER) where it can more easily expand (UNRESTRICTED) to a lower pressure (not atmospheric…YET)…. Result, it slows down, its pressure drops, and some of the oil, and water, droplets can fall free from the stream….. but hold on a minute…..
UNRESTRICTED expansion has another side effect…… SUPERHEATING.
When steam, at a given pressure/temperature is suddenly allowed to expand ,down to the lower pressure within the condenser vessel, the result will be steam which is SUPERHEATED for the new, lower pressure.
This can make some of the water droplets carried over from the engine return to steam, and the fatty materials contained in the oil will become more vapourised.
The temperature rise is a direct result of the LATENT HEAT stored in the high pressure steam…. It must go somewhere, or do something……. The initial response is to increase the heat of the steam, relative to the new pressure (SUPERHEATED)……. The only way to overcome this is for the heat to be dissipated via the walls of the container……. HENCE LAGGING WILL interfere with this process.
Some may suggest that the OIL TRAP (condenser) is open to atmosphere, and hence no pressure can be involved……WRONG.
Whilst I agree that the oil trap/condenser is not a true pressure vessel (in as much as it is not a sealed container) it is in fact connected to the TRUE atmosphere by a length (variable) of pipe, which in turn (depending upon length and bore) will impose a restriction on the free expansion of the steam down to final atmospheric pressure, therefore, whilst in operation, the contents of the oil trap/condenser vessel will be at some pressure above that of the atmosphere.
If the pressure, in the vessel, can be reduced to below 5psi (steam temperature 108deg C) and the excess LATENT HEAT of expansion can be expelled via the walls of the vessel, then all should work just fine, the fatty part will condense out and only clean steam vapour will exit from the final outlet to atmosphere.
This is a tricky balancing act, and is very specific to each and every installation….. get the OIL TRAP/condenser vessel TO SMALL and the pressure and steam temperature will remain to high (heat exchange via vessel walls will be a much bigger problem, especially if lagged), and some of the fatty deposits will be expelled rather than condensed out and trapped.
Get the VESSEL to big and the exhaust steam can become far to superheated, which in turn will keep the fatty deposits in vapour form and again expelled with the steam unless the LATENT HEAT can be extracted via surface conduction.
Again, lagging will not help, but hinder.
Moritz….. I am very impressed with your steam plant layout and the trouble you have gone to in order to get it set up as closely as possible prior to installation.
I look forward to seeing the final build of the model.
From your description of your testing, and the residue recovered after on boiler full of water had been evaporated, (which on the face of it is a very remarkable achievement) I wonder, how much of the 20ml was actual oil? And how much oil went in to the engine from the lubricator?
I understand that it is difficult to be precise about the amount of recovered oil, however, if e.g.5 ml was the estimated recovery, and 6 ml was taken from the lubricator….. where has the remaining 1 ml gone…….. this could be the amount of fatty material lost with the steam via the funnel…… I.E not condensed out.
If, on the other hand, the recovered amount was exactly what was taken from the lubricator, then you have got the MAGIC balance, however, lagging the oil trap/condenser could actually ruin the results by interfering with the heat transfer.
I think you will agree, on balance, that perhaps it is better to over-condense a little, and be sure of getting all the oily deposits out, rather then under-condense, and allow some fatty/oil deposits to escape into the surrounding environment.
After all, it is no big hardship to stop and empty the condenser at suitable intervals, and if you don't use automatic boiler water level control, you will need to stop and re-fill the boiler anyway, and possibly the gas supply tank,...so why not empty the condenser whilst waiting for pressure to come back up again.
One thing is for sure..... this is a tricky and fascinating subject, and not one there are always easy answers to.
Ok, enough already!!
Keep steaming,
Best regards.
Sandy
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