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[Geoff]

I have a question – I have a Cheddar Models Puffin steam plant which has sailed for many years in my Victorian Battleship, Canopus, 1899.
In the very early years, I had trouble with the burner going out after about 10 mins or so. I tracked this down to oxygen starvation as the installation is completely enclosed and therefor opened up the deck and side gunports to provide more ventilation and the problem was completely cured. I sailed it many times and years in this condition in virtually any wind and weather conditions- and it worked every time. The only time I experienced any issues was with indoor sailing at the Model Engineer exhibition, years ago, which I put down to the humid atmosphere.
Of late the burner keeps going out again after about 10/15 mins. On checking I found some residue around the jet screw thread and cleaned it out – same result. On further checking some brown stuff came out the gas tank, a build-up of debris of some kind. I cleaned this all up and the gas pipe to the jet. Same result burner keeps going out, but the gas keeps coming out okay and relights fine with a very good stable flame. At one point the debris was so bad I could not get the gas to exit the tank, but full cleaning cured this. Each time I check the jet its clean and on burning it’s a very stable flame.
I had also decided to try some modifications by using a small PC fan to provide additional air to the burner, same result as the burner goes out after about 10/15 mins! I even ducted the fan towards the burner, same result!!
The boiler heats up fine and holds pressure okay so I’m certain there are no leaks, there are no strange plumes of steam anywhere either.
The installation has remained completely unchanged for many years so I’m puzzled as to why I’m now having these problems.
The symptoms seem to mirror the early oxygen starvation, but I can’t see what has changed as nothing has.
Does anybody have any ideas?
Thanks
 
Geoff

[Bunkerbarge]

Does your gas tank get very cold after ten minutes of burning?  If so it could be over cooling and affecting evaporation of the gas.  This could be as a result of erosion of the nozzle with age which causes gas to be used at a much greater rate as well as giving you poorer combustion.  Try a new nozzle and measure the temperature of the gas tank when you start and after ten minutes running, or when the burner shuts off.

[Geoff]

Thank you for the suggestion which is appreciated, this shouldn't be an issue as I have sighted the gas tank so it touches the oil separator such that typically at the end of a run the gas tank is hand warm to the touch to keep the gas pressure up.


I just can't figure out what's wrong on a system I've been using for years. If there was a blockage in the jet then the gas wouldn't be coming out properly so this could put the flame out but on retrieval I light the gas and the flame burns perfectly!


[size=78%]The only thing I can think of is that by installing a PC fan despite it working it may actually have reduced the air flow in some way. Initially I was running it on 6.4 volts (or thereabouts) but it was noisy so used resistors to reduce the voltage down to 5.5 volts which is better but I'm still getting the same problem albeit since then I've added some ducting to direct it to the burner.[/size]


All very odd.


Cheers


Geoff

[Bunkerbarge]

Erosion of the orifice is still a possibility and worth changing just to eliminate it from the equation.

[KNO3]

I have heard of impurities in tanks before and they can cause the jet to clog. Cleaning everything and installing a gas filter should help (it can be easily made at home or bought).

[KBIO]

Hello !
The BuPro cans contain tar, debris of rust, sand and others coming from the well bore as well  as the installations. Whatever the precautions , there is more or less depending on the country it is coming from and we sometime have to buy another bottle to get away from this problem.
Depending on the stock , it may take some time to have it clean !
If you leave the gas tank full, in the worst case, this "paste" may accumulate in the bottom and flow back with the gas then. It may plug the jet (more or less after a while.
Cleaning from time to time may solve the problem.


I do not think that the high velocity of the gas through the jet has enough wash out effect  to enlarge the jet bore ; modifying the air/gas ratio.
The humidity has no effect on the combustion , but eventually cools down ( a tiny bit) the temp of the flare. Not our concern !
A 2" x 2" opening in the deck above the burner is plenty enough to supply the burner with air. Easy to calculate for a N°5 (+/- 60gr/h) jet as the one, you probably have on your Cheddar plant.
I stopped to install PC fans in close boats. No interest !


Instead , I think that a weak wind on the top of the chimney can disturb and shut off the burner. Ventury effect ?? Back pressure ??
See below that it is not easy to switch off a burner.
(Sorry, it is in French but I know that some of you are fluent in it.)

https://youtu.be/k2nU-FcaKtM
https://youtu.be/vrZ63BRI9IM


At the end, I can tell you that I have no solution , not even one ounce of one ,I live with it . This "phenomena" is another steam  mystery of the witch!


Have a good day !

[Bunkerbarge]

I do not think that the high velocity of the gas through the jet has enough wash out effect  to enlarge the jet bore ; modifying the air/gas ratio.

Yes it does, this is a well known effect, accelerated by the inclusion of the impurities you mention.


Just out of interest a ceramic insert was used in nozzles at one point, as the ceramic is harder than brass, to specifically deal with the erosion concern.  They fell out of favour though as a result of the cost, which could not be justified when erosion was only an issue in nozzles with very high usage and poor quality gas.

[Geoff]

Thank you all for your feedback which is appreciated. Hmm, ultimately I may need to make some kind of blood sacrifice to the boiler gods to get it working!! Are there any well known chants that work!! 


I quite understand about the debris in the gas as the plant had not been used for a few years so its possible its collected or worked loose in the tank so I can see that being an issue but I have cleaned it out best I can and the burner immediately re-lights with a perfect flame which is what's puzzling me!


I may try to run it in the bath and see what happens but as before nothing has changed in the set up since it was installed and it all worked perfectly fine for years, Mr reliable in fact!


I'll report back in due course


Cheers


Geoff

[Geoff]

I think I have found the solution. Firstly since I cleaned the tank the jet has remained clear and I have a good clean burn. As I haven't used the model in years I think I forgot some of the things I automatically did and that was causing the problem of burner going out.


The set up puts the oil separator in direct contact with the gas can so once all is running this passes gentle heat to the gas tank and keeps it at about warm hand temperature thus ensuring a constant gas pressure.


So in practice what I was doing was: from cold having the burner quite high to raise steam and off goes the model. It takes a while for the heat to transfer to the oil separator and hence the gas tank, so as the tank warms up the burner gets fiercer until a point is reached where there is a blow back as the flame and heat cannot pass through the boiler with the result the blow back puts the burner out.


So now I use a high flame to get the pressure up then turn it down, so off goes the model albeit initially with a full head of steam and then a little a little slower than before and as the heat works its way through the flame increases but not to the point the hot flux gets trapped in the boiler and blows back putting the burner out. Last couple of sailings I got two runs at 30 mins and one at 25 mins which is acceptable. Time will tell if I have found the solution but its looking positive.


Cheers


Geoff

[CliffW]

Thank you for posting your solution Geoff...it was good to follow along in your thread and then finally see the problem stated and solution