Gas on the boat - silly question,of the day

[[2574]]

Why doesn’t the flame at the cooker burning element reverse up the supply pipe and eventually get back to the bottle?

 

[[194224]]

Not enough oxygen in the pipe?

 

[pyrojames]

No oxygen in the pipe! Also the laminar flame speed of butane is quite low, so even if you had the right mix, I suspect the flow rate out of the pipe would be too high for the flame to go back up it. I might give it go and see! (dont try this at home...)

 

[jac]

No oxygen in the pipe! Also the laminar flame speed of butane is quite low, so even if you had the right mix, I suspect the flow rate out of the pipe would be too high for the flame to go back up it. I might give it go and see! (dont try this at home...)

Is this experiment in anyway connected to you choosing "pyro" as part of your forum name??????

 

[Refueler]

Why doesn’t the flame at the cooker burning element reverse up the supply pipe and eventually get back to the bottle?

If you look at the setup at the flame end ..... its designed to 'spread' the gas to mix with a large amount of air to enable it to burn. as you move back along the supply - once you leave the actual burner - the gas to air mix is far too rich to burn ... there just is not enough air (oxygen) to allow ignition.

The average ratio Butane to Air is about 2 : 13 .... that is 2 parts Butane, 13 parts Air.

In my work - we regard LEL and UEL as % .... that is 2.5% as Lower Explosive Limit and 9.5% as Upper Explosive Limit ..... these are of course different numbers to your hob ... but gives an idea of the large amount of air (oxygen) required.

You can see the effect of increasing the Gas to Air mix as you "turn up the heat" .... the flames actually separate further out from the burner ring as it needs to get MORE air to sustain the ratio ... turn it down and the flames then close back in towards the ring.

 

[superheat6k]

The regulator would anyway act as an effective non return valve, not that any burning could occur sans air / oxygen.

 

[pyrojames]

Is this experiment in anyway connected to you choosing "pyro" as part of your forum name??????

I used to burn things for fun, then as my profession, now I just work out how other people have set fire to things!

 

[[2574]]

Thanks all, I shall sleep easier!

 

[Spirit (of Glenans)]

In Dublin, during the 1939-1945 Emergency (WW2 to you), the city's gas supply was periodically restricted due to the shortage of coal. There was a fear that, due to people using gas "on the glimmer" when pressure was reduced, that flames would travel back up the pipes to the gasworks and cause explosions
As a result inspectors, pejoratively known as Glimmermen, were appointed, with powers to enter homes in order to check on people's use of gas at unauthorised times, which had been made a criminal offence. Needless to say, it was subsequently proven that such a phenomenon could not happen.

 

[Ian_Edwards]

This property of gas, probably coal gas at the time, was spectacularly demonstrated by a science teacher when I was at school.
A golden syrup tin, with a press on lid, and holes in the base and lid was placed on a tripod stand with a bunsen burner under it. The gas was turned on, to allow the gas to flow through the tin, then lit at the top of the tin.
When the flame was stable the gas was turned off. The flame above tin continued for while, until the gas air ratio reached the Upper Explosion Limit, then the gas air mixture exploded within the tin and blew the lid off the tin with a loud BANG.
Probably against all the rules now, but very effective, I still remember it 60 years on.

 

[Birdseye]

In Dublin, during the 1939-1945 Emergency (WW2 to you), the city's gas supply was periodically restricted due to the shortage of coal. There was a fear that, due to people using gas "on the glimmer" when pressure was reduced, that flames would travel back up the pipes to the gasworks and cause explosions
As a result inspectors, pejoratively known as Glimmermen, were appointed, with powers to enter homes in order to check on people's use of gas at unauthorised times, which had been made a criminal offence. Needless to say, it was subsequently proven that such a phenomenon could not happen.

Interesting bit of history.

 

[Refueler]

Interesting bit of history.

Gary Glimmer ????

I'll get me coat !!

 

[AngusMcDoon]

Why doesn’t the flame at the cooker burning element reverse up the supply pipe and eventually get back to the bottle?

Even if there was sufficient oxygen mixed in the gas in the pipe to support combustion the flame would still not go up the pipe. Flames cannot pass through small holes which is the principle behind the Davy safety lamp. In your gas burner you have 2 sets of small holes between the flame and the pipe - the nozzle under the burner, and the holes round the burner circumference - which act as flame arresters.

Read all about it here...Flame arrester - Wikipedia

The lack of oxygen to support combustion is the main reason, but the flame arrester effect is why the flame above the burner does not ignite gas between the nozzle and the burner. You can see the same effect on those hob top toasters that have a mesh in. The mesh gets red hot, but the flame does not pass through.

 

[AngusMcDoon]

You can see the effect of increasing the Gas to Air mix as you "turn up the heat" .... the flames actually separate further out from the burner ring as it needs to get MORE air to sustain the ratio ... turn it down and the flames then close back in towards the ring.

In a standard gas burner the air supply is the opening between the nozzle and the burner. The high speed jet of gas entrains air as it moves. By the time the gas leaves the burner it is fully supplied and mixed with oxygen and it's both the flame arrester effect and the slow propagation speed of the flame that is stopping the flame propagating upstream. If it wasn't supplied and mixed with air, you would see a bright yellow flame. Remember school chemistry lessons and Bunsen burners - when the air opening just above the nozzle is closed off the flame becomes fully yellow. I expect pyrojames has pressed the button and lit the jet of gas coming out of a can of lighter fuel - same fully yellow flame as a closed Bunsen burner. I expect that the effect you are seeing is caused by the slow flame propagation speed.

There are stoves that do without the burner and use just the propagation speed of the flame being less than the speed of the jet of gas to keep it is place (but see * below), but these are unusual and are noisy. The MSR XGK mountaineer's stove is one, and the old style Primus is another. Although the fuel is liquid it is gas by the time it leaves the nozzle. The flame cannot move upstream of the nozzle because of the lack of oxygen, but it also does not move up to the nozzle, but remains a few cm above it. I don't know why this arrangement is noisy, but it certainly roars. You can hear across a mountainside when someone fires one up.

XGK™ EX Multi-Liquid Fuel Backpacking Stove | MSR®

* Also the jet entrains air as it leaves the nozzle, so immediately above the nozzle it won't have sufficient oxygen to burn. You want it to have the correct fuel/air mixture ratio when it does burn, so the nozzle size is calibrated to cause the jet to leave at the correct speed compared to the flame propagation speed so that when the slowing jet speed matches the flame propagation speed (and the flame starts) the correct amount of air has been entrained. That's why you have to change nozzle if you change fuel from, for example, petrol to paraffin. Note here that 'jet' is the stream of gas, and 'nozzle' is the thing with the hole in. In carburettors the latter is often incorrectly called the former.

 

[pyrojames]

This property of gas, probably coal gas at the time, was spectacularly demonstrated by a science teacher when I was at school.
A golden syrup tin, with a press on lid, and holes in the base and lid was placed on a tripod stand with a bunsen burner under it. The gas was turned on, to allow the gas to flow through the tin, then lit at the top of the tin.
When the flame was stable the gas was turned off. The flame above tin continued for while, until the gas air ratio reached the Upper Explosion Limit, then the gas air mixture exploded within the tin and blew the lid off the tin with a loud BANG.
Probably against all the rules now, but very effective, I still remember it 60 years on.

I still do that trick when I give CPD lecturers to the insurance industry. It certainly wakes the class up!

 

[Jim@sea]

I had a 26ft Cabin Cruiser where the gas bottle was in a locker in the stern. One day out at sea I went into the cabin and lit the gas hob and put the kettle on the hob. A few moments later there was a loud band , a flash and the cooker was on fire, I rushed up the steps and into the cockpit, (My crew had heard the bang and seen the flash and thought I was jumping overboard)
I was rushing to the gas bottle to turn the gas off.
The boat today would be 40 years old, in those days perhaps requirements were not so stringent. The boat manufacturer had plumbed in the cooker just using copper piping. In hindsight this boat had often travelled at 20 knots plus going bash, bash hitting the waves. A simple flexible rubber pipe should have been fitted, So anyone with a 40 year old boat should check if their cooker is connected with copper fixings.

 

[fisherman]

I saw some film of far eastern rioters, one holding the valve of a large upside down gas bottle , the other lighting the gas. About 20-30 feet of flame.
In re science teachers, ours held a match over the bunsen, a thin stream of water extinguished it. We had discovered the water pressure was much greater than the gas pressure, flexible pipe to connect. The cookers in domestic science downstairs gushed as well.

 

[AntarcticPilot]

I still do that trick when I give CPD lecturers to the insurance industry. It certainly wakes the class up!

Something similar occurs when I turn my Weed Wand off! A Weed Wand is a can of LPG connected via a long pipe to a burner at the bottom end, with a sparker to light it. The pipe is quite a wide bore - maybe 15-20mm. Lighting it is undramatic - you turn the gas on, press the sparker button, and it lights at the bottom with a nice roaring flame (this is for outdoor use only!). Very handy for killing patio weeds and lighting BBQs! But when you turn it off at the gas cylinder, the flame retreats up the pipe with a squealing noise that increases in frequency as it goes up the pipe, and then finally dies with a tiny "pop"!

 

[mattonthesea]

This property of gas, probably coal gas at the time, was spectacularly demonstrated by a science teacher when I was at school.
A golden syrup tin, with a press on lid, and holes in the base and lid was placed on a tripod stand with a bunsen burner under it. The gas was turned on, to allow the gas to flow through the tin, then lit at the top of the tin.
When the flame was stable the gas was turned off. The flame above tin continued for while, until the gas air ratio reached the Upper Explosion Limit, then the gas air mixture exploded within the tin and blew the lid off the tin with a loud BANG.
Probably against all the rules now, but very effective, I still remember it 60 years on.

We did this one too. As teenagers, we spent time on Norfolk Broads yachts, mostly with cockpit cookers. One evening we were drinking tea and feeding the swans at Reedham when the oven door flapped down with a moderate bang. A little investigation revealed that we'd turned the oven tap on as well as the kettle burner.
A gentle but salutary lesson.

 

[DownWest]

This property of gas, probably coal gas at the time, was spectacularly demonstrated by a science teacher when I was at school.
A golden syrup tin, with a press on lid, and holes in the base and lid was placed on a tripod stand with a bunsen burner under it. The gas was turned on, to allow the gas to flow through the tin, then lit at the top of the tin.
When the flame was stable the gas was turned off. The flame above tin continued for while, until the gas air ratio reached the Upper Explosion Limit, then the gas air mixture exploded within the tin and blew the lid off the tin with a loud BANG.
Probably against all the rules now, but very effective, I still remember it 60 years on.

I was given a book by American friends when young . Dr Wizard's Science Secrets, spin off from his TV show. The tin with gas was one of the experiments, as was a similar one with flour...

I can tell you, it works a lot better with a dustbin!