Talking Thermodynamics

[Kim]

Sorry for the rudimentary question here, but people keep talking about a "poker burner."  Can someone give a quick explanation of what that is?

Thanks,
Kim

[crueby]

Sure thing - the poker burners are a small butane fired burner, has a nozzle at the back end with a couple of air intake holes next to it, than the other end has a few rows of small holes where the mixed gasses come out and get burned. That end sits inside the firetube in a small boiler - this style is used in most of the comercially available G1 locomotives - simple, no moving parts, works fairly well. Sometimes the holes are replaced with cross slots, sometimes covered in metal mesh to give a more radiant effect and cut down on the 'howl' that they typically have. I've attached a picture that I found, shows one lit, but not really burning evenly. They usually burn better when they are in the firetube. Also a pic from Roundhouse's website showing the system.

[steam guy willy]

Hi MJM et al , more good info here and interesting that the fire doors were not completely closed allowing air above the fire with an explanation of how the fire burns etc etc.........

[Kim]

Thanks Chris, seems simple enough.  But why are they called a "poke" burner? Cause you poke holes in a tube to make the burner?  I kept reading it Porker burner the first several times I saw it and thought it was what Cletus uses to do his Barbecuing!

Kim

[crueby]

Thanks Chris, seems simple enough.  But why are they called a "poke" burner? Cause you poke holes in a tube to make the burner?  I kept reading it Pork burner the first several times I saw it and thought it was what Cletus uses to do his Barbecuing!

Kim

I believe its called a poker burner since it pokes into the firetube, but thats a guess. Yet another case of the English language being strange. We could do worse, call it a straight-line-ring-burner...      like whi is a fly a fly and an ant isn't a crawl? ... But, that could be a whole other thread!

[Gas_mantle]

I assume the term comes from the similarity with a domestic coal fire poker :-

http://www.retonthenet.co.uk/antique-vintage-ornate-brass-handled-coal-or-log-fire-poker-fireplace-hearth-tools-1920s-1930s-fireside-5891-p.asp

[steam guy willy]

I believe its called a poker burner since it pokes into the firetube, but thats a guess. Yet another case of the English language being strange. We could do worse, call it a straight-line-ring-burner...      like whi is a fly a fly and an ant isn't a crawl? ... But, that could be a whole other thread!


[/quote]

Hi Chris, ok yes ,l am allways threading on ants thats why they don't crawl any more !!  Oh , Right ..i see what you did there !!!!

[MJM460]

Hi Gas Mantle, that was a great video on coal burning, thank you, very informative.

Hi Chris, those sliding sleeves are a clever way to make the air flow easily adjustable.  There still seems to be a real skill in working out the correct adjustment, especially for a boiler where you need to adjust the flame outside the boiler for how it needs to be when in position.  Thank you for the description of the poker burner.  Interesting that you mentioned noise levels.  That Southern Steam Trains site that I found also mentioned noise, but also that the poker burner with the radiant mesh needed a lot less gas to provide sufficient steam raising.  He put the lower noise level down to the consequent lower gas flow.  I wonder if the silent spirit burners I have seen mentioned are similar.

Hi Kim, I also had to look up the poker burner.  I am sure I read somewhere that early modellers of small gauge locomotives used a bar of cast iron which they heated with a blow lamp, or in a fireplace then put it into the firebox to generate steam.  I can't imagine that it gave a long run, and I am not sure now where I read about it.

Hi Willy, you were obviously ahead of me on that secondary air for the coal burning.  I wonder what they would make of a modern power station boiler which fires pulverised coal.  But I guess the principle is still similar.  The issues with a gas burner are less obvious.  But even the gas turbines that power aircraft have primary then secondary air introduction, and sometimes even tertiary air, but that is entirely another subject.  Got to be something to do with making a flammable mixture for combustion then adding the necessary excess air, but I really don't know any more than that.

Thanks to everyone for inserting a bit of fun on the name of the burner.  This thread needs a little humour otherwise it will tend to get seriously boring.

I don't really have a lot to add to the burner conversation, but people with more knowledge on the subject are most welcome to come and join in.

I don't know if all that helps you Chris, with your larger burner for the Lombard.  I don't know if you are planning a larger jet, and adjusting the air holes, or a new larger burner, but we are all keen to hear how you get on.

A bit of a shorter post tonight.  Any suggestions for where to next?

Thanks to everyone for dropping in and especially to those contributing,

MJM460

[crueby]

I do have a larger jet, nbr 8 vs the original nbr 5, got to make up a new burner tube with the larger air intake holes and room for the sliding sleeve. Will update when that happens...

[MJM460]

Hi Chris, do you know the size of those jets?  I will check butane vapour pressures tomorrow, and can make a reasonable estimate of the change in flow and heat input from the sizes if you have them.  Even if not, the increase in flow with the necessary additional area should give much better capacity to maintain the steam pressure for you.  Certainly the quickest fix from the current position.

We have a house full of visitors for the next three days, so while I will check in and keep up with any posts, I will need to keep my input brief until they are gone.

Thanks to all for looking in.

MJM460

[crueby]

Hi Chris, do you know the size of those jets?  I will check butane vapour pressures tomorrow, and can make a reasonable estimate of the change in flow and heat input from the sizes if you have them.  Even if not, the increase in flow with the necessary additional area should give much better capacity to maintain the steam pressure for you.  Certainly the quickest fix from the current position.

We have a house full of visitors for the next three days, so while I will check in and keep up with any posts, I will need to keep my input brief until they are gone.

Thanks to all for looking in.

MJM460

The listings I have seen show nbr 5 is .2mm and nbr 8 is .25mm diameter. The air holes in the side of the burner for nbr 5 is .25", am guessing that the hole for the nbr 8 must go up by at least the same proportions as the areas of the nozzle hole, if not more since the gas is a pressured flow and the air is not.

[MJM460]

Hi Chris,

Butane is usually a mixture of normal butane and isobutane.  I will talk about what the terms mean later in the week.  Isobutane has a bit higher vapour pressure than normal butane, so the vapour pressure depends on how much of each.  But a 50% mixture would be about 450 kPa at 40 deg C.  Even pure normal butane would be about 377 kPa, while pure isobutane would be 528 kPa at 40 C, but the purification requires a lot of energy, and I suspect you have about 30% of one, I am just not sure which for the moment.

The camping gas we get here in throwaway containers also has a good percentage of propane which boosts the pressure considerably.  I don't know what you have. 

However I would estimate that the fuel tank would initially have high enough vapour pressure to give sonic velocity in the jet if you have reasonable temperatures.  If you basically have a butane mix, as you boil off gas, it will cool and probably the pressure will be too low for sonic.  If you have some propane, it will stay sonic.  Because the nozzle does not have the diverging outlet, you never get above sonic velocity.

The important thing is that for constant presssure on the boiler side and near sonic velocity in the jet, mass flow proportional to upstream pressure and jet area is a good estimate.  Because of the uptstream pressure component, the flow drops off as the pressure falls, and it will drop more when you boil off more gas with the bigger jet.  The momentum (mass times velocity) of the gas jet gives energy to induce the air flow, and increasing the air holes in the same proportion by area would, I think, give you a similar air/fuel ratio, and nearly 50% more flow.  Thus 50% more heat.  Should be a great place to start on seeing if you can maintain the pressure.  If you are providing the adjustable sleeve, it may be worth making the holes a bit bigger as you can reduce the air flow if required, but the adjusting the sleeve also shifts the position of the air intake relative to the gas jet, so may also have an effect on combustion.

Still keeping posts short for a few days, but I hope that is enough to keep you thinking while you scale those  Marion drawings.

Thanks for dropping in,

MJM460

[Admiral_dk]

But even the gas turbines that power aircraft have primary then secondary air introduction, and sometimes even tertiary air, but that is entirely another subject.

The extra air inlets in an aircraft gas turbine has everything to do with cooling - as they create a boundary layer between the very hot combustion gasses and the metal of the engine. Getting the more than 1700 degree centigrade combustion gasses separated from the metal is vital for engine life 

The first two (or more) turbine wheels has hollow blades that are air cooled from the inside + holes for letting some of the cooling air out to form yet another boundary layer around the blades.

A certain percentage of the incoming air is use for cooling the engine parts at different locations. The first is use to cool the last compressor stages, then maybe 40% is feed to the combustion chamber for power production. The next is use to cool the outside of the chamber and enters as secondary air as cooling (some might be used to burn too). Now some is used to cool the turbine housing and stator blades.

There is more than one airflow in a modern engine :
One going through the inner parts and out through the last rotating compressor blades and out through the first rotating turbine blades.
Next layer goes through the power section and is burned.
Third layer is used to cool stator + turbine blades and combustion chamber + turbine chamber.
All modern Jet engines has a bypass fourth layer created from the big fan in the inlet - this is the main thrust and also cools the outside of the engine (not the part we see outside) - you will not see the fourth layer in a gas turbine for helicopters for instance.

I probably shouldn't have answered this - but I could not help myself 

[crueby]

The extra air inlets in an aircraft gas turbine has everything to do with cooling - as they create a boundary layer between the very hot combustion gasses and the metal of the engine. Getting the more than 1700 degree centigrade combustion gasses separated from the metal is vital for engine life 

The first two (or more) turbine wheels has hollow blades that are air cooled from the inside + holes for letting some of the cooling air out to form yet another boundary layer around the blades.

A certain percentage of the incoming air is use for cooling the engine parts at different locations. The first is use to cool the last compressor stages, then maybe 40% is feed to the combustion chamber for power production. The next is use to cool the outside of the chamber and enters as secondary air as cooling (some might be used to burn too). Now some is used to cool the turbine housing and stator blades.

There is more than one airflow in a modern engine :
One going through the inner parts and out through the last rotating compressor blades and out through the first rotating turbine blades.
Next layer goes through the power section and is burned.
Third layer is used to cool stator + turbine blades and combustion chamber + turbine chamber.
All modern Jet engines has a bypass fourth layer created from the big fan in the inlet - this is the main thrust and also cools the outside of the engine (not the part we see outside) - you will not see the fourth layer in a gas turbine for helicopters for instance.

Wow - thats a very different kind of 'jet' - I was referring to the tiny gas nozzle jet in the poker burner. Sounds like you have some experience with the big kind - built any working models of jet turbines?

[Admiral_dk]

Sorry - I got carried away with MJM460's comment about aircraft turbines 

No - I'm just interested in engines  in my childhood it was steam engines, in my preteens it became IC engines and this interest has never stopped and like you I like to research my subject