Avoided the house burning down!

[-steves-]

OK, heart still beating, still have a house but I think I can safely say that adrenaline is definately brown!

I build a little steam engine over the last couple of months, my first one and it now runs like a dream and doesn't look all that bad either. I made the burner for it and was always aware the wicks were a touch too small for it and the flames were too bigand it always had a little "pop" when you lit it. I thought I would fix that tonight, so I added some more wick into each hole and shortened each wick to a better size. Added just half a container of meths as it was only for test, and the lit it...........

WOW!..........BIG POP, all 3 wicks shot out the burner within a few seconds and set light to my shoes and the carpet, fortunately no major damage done as we had sufficient things to hand to put it all out very quickly.

My question is, what the hell happened and why????????


Below is a picture of the burner....

[John Rudd]

I'd hazard a guess and say that the meths started to boil from the heat....You know the rest...

[-steves-]

I'd hazard a guess and say that the meths started to boil from the heat....You know the rest...

It had only been lit a couple of seconds? It has been run from a full pot, with thinner wicks and longer wicks, obviously something I changed made it happen. The problem I have is I don't know why it would do that as I have never seen or even heard of it happening before. It was most definately dengerous and until I can eliminate it happening again, I dare not run it or any other home made burner again. Is the air hole too big and the flames managed to get inside the burner and blew it all out, is the hole too small and it quickly built up pressure somehow, are the wicks too tight causing some sort of pressure build up? I just don't know, my personal best guess is the meths must have some how managed to get a flame from the breather hole in the middle and cause the explosion, but will a smaller hole stop this happening again??

[John Swift]

Hi Steves ,
 

are the wicks fitted into tubes that nearly reach the bottom of the container ?

if the the fuel container is not all  filled with a heat resistant wadding , filling all the space above the fuel,

 fuel vapour   escaping out of the central hole or past a loose fitting  wick could ignite and burn back into the container

     John


PS - could you fit a fine wire gaze over the breather hole

[-steves-]

Hi Steves ,
 

are the wicks fitted into tubes that nearly reach the bottom of the container ?

if the the fuel container is not all  filled with a heat resistant wadding , filling all the space above the fuel,

 fuel vapour   escaping out of the central hole or past a loose fitting  wick could ignite and burn back into the container

     John


PS - could you fit a fine wire gaze over the breather hole

Hi John

The wick tubes are not all that long, they certainly dont reach anywhere near the botton of the burner, maybe half way down, could this be the issue and if so what is the reasons please?

The container is just neat meths, no wadding inside it, would this help and if so what should I use?

How fine would the gauze need to be as I don't have any at all so will need to purchase some if that will fix it.

Many thanks

[John Swift]

Hi Steve ,

I've not seen a Davy lamp but I guess the fine wire mesh they use has holes about 1/32"(0.8mm)
my be someone has the information

with mesh added to the breather hole and tight fitting wicks it should be OK
 the tubes going almost to the bottom of the tank
it should make it  more difficult for a flame to travel down the wick
 
but having the inside of the burner filled with wadding will give you a second line of defence and prevent you having a large open space filled with explosive methylated spirit / air mix 

with the small amount of mesh you require you could make your own
or just drill half a dozen 1mm holes in a piece of the brass you made the burner out off 

    John
 

[hopefuldave]

Quote:
The container is just neat meths, no wadding inside it, would this help and if so what should I use?

How fine would the gauze need to be as I don't have any at all so will need to purchase some if that will fix it.
Unquote

For the wadding, I'd experiment a bit - possibly glassfibre household insulation, mineral fibre wool?

For the gauze, visit your local "head shop" / drugs den, they keep fine brass woven mesh as "bong screens" among the smokers' paraphernalia in little packets (5 or so, about 3/4" diameter) for a Local Currency Unit or two! Good stuff, I've used it as a first-line filter on my spraygun to stop lumps clogging the nozzle (honest, officer...)

Dave H. (the other one)

[andyf]

A tea strainer might provide suitable mesh. There's a pic of a big one here
< http://en.wikipedia.org/wiki/Tea_strainer >
but the stainless steel one in my kitchen drawer is much smaller, the sieve part being about 50mm diameter. I don't know if SS mesh would work as well as brass, though.

Andy

[Pete49]

I think the air hole is the problem. I have a bottle type meths burner with a screw type lid for melting wax for dopping stones on when faceting and never had a problem with it. It shouldn't need a vent and I think that was the cause as the flame got inside the burner and caused the explosion.
Just my thoughts Though I've been wrong before
Pete

[Divided he ad]

I've had this happen... luckily my workshop is out the back and has concrete floors.

I came to the conclusion it was a vapour issue. It does get much worse as the meths boils!


The best way I know of is to make a tank and a long (2-3") feed tube to a wick holder well away from the tank. This is on a small burner with a single wick. Basically, keep the flame away from the vent and associated gasses.

Interesting note about burners you get with chemistry sets etc... Pete's right, you don't see a vent in them?
Maybe we're over engineering them?


Outdoor testing required... Stand well clear and face shield eh!? 


Best of luck...!





Ralph.

[andyf]

I reckon it's the vent, drawing air in, and letting a bit of ethanol vapour out. The external vapour acts as a fuse; the burner flame ignites it, the flame flashes back to the vapour/air mix inside the tank, and POP!

Tricky stuff, ethanol (the main component of meths). A pharmacist next door to my offices was decanting surgical spirit from a carboy into little bottles for retail. The coroner's verdict was that the vapour reached the pilot light on his central heating boiler in an adjacent room, the flame flashed over to the bench where he was doing the bottling, ignited the lot and started the fire which killed him.

Andy