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Thanks Alberto and George!
Quote from: Karen W. on 30/10/2007 15:49:53Thanks Alberto and George! Thanks Karen, but this time it was eric I to answer you! By the way, in a recent antifire course (I hope to have translated correctly) they said a curious thing: exploiting the fact gas needs air to ignite, technicians who repairs big gas pipes can weld them electrically while the high pressure gas comes out of the broken pipe!Sincerely, I wouldn't advise anyone to try doing it!(Can someone please tell me if the phrase I've written in blue is grammatically correct?Thank you.)
Thanks Alberto and George! Hamza It is not a foolish Question! I being crazy over my gas appliances have often wondered about that and would never thought to have put the question in here, but what a great question!
but pyrotechically risky.
There are a number of reasons, and this list will probably quite incomplete.a fuel can only burn when it is mixed with air in a ratio between definte values (depending on the fuel), a mixture that is either too rich or to lean (in fuel) does not burnthe gas comes from the pipe through a nozzle, only after which it is mixed with air; the gas in the pipe does not contain enough oxygen to burnthere is also the speed of the flame front, if the speed of the mixture of gas and air is higher than this speed of the flamefront, the flame can not travel back to the nozzlethe flame is formed on the gas ring, a perforated tube. The perforations make sure that the speed of the mixture remains high and the metal acts as a kind of heat sink so that the mixture inside remains cooler than the "flash point" (http://en.wikipedia.org/wiki/Flash_point)See also :- http://en.wikipedia.org/wiki/Bunsen_burner- http://en.wikipedia.org/wiki/Gas_burner- http://home.howstuffworks.com/how-to-repair-an-oven.htm
Eric, The wiki links were great about telling how the air to gas ratio burns and the bunsen burner one helped a great deal but somehow I still don't get or see that it answered why the fire once lit does not travel back down the tube and just blow everything to bits! How is the flame only burning the gas coming out the end? WAS THIS TO DO WITH THE GAS AIR RATIO COMING OUT OF THE TUBE???I am confused because I still don't get it.. what is to prevent the flame from traveling down the tube? Is it because the tube is narrow and maybe the gas heavy enough to prevent oxygen mix sufficient for ignition or what...OH......Dear wait.. Thats where Alberto comes in Gas needs air to ignite so the tube allows so much gas though to the opening where it is mixed further with the air making it igniteable.... whats in the tube will not ignite because of lack air...Air mix with gas + ignition sourse + flame on exit but not down tube as gas coming through has no air yet! Is that correct?? Is that right???
It was possible to get a 'blow-back' on bunsens at school; you could make it happen, sometimes, by punching the rubber rube and interrupting the gas supply. Or you can light it at the air inlet hole and get a flame, sometimes.
Bunsens are quite different from domestic gas fires because bunsens introduce air ahead of the flame front, through a hole in the base of the bunsen,
The shape of the flame front, at the top of the Bunsen tube, is conical.If it starts to burn quicker, the cone gets smaller and, so, the area of burning gets less - this slows the rate at which gas can be burned and then tend to make the cone bigger - this produces a stable situation in which the flame is advancing downwards at the same rate as the gas/air mixture is blowing it upwards and produces a steady flame (usually - although you can get a 'guttering flame' when the pressure is too low for the burner design. There is a maximum size of Bunsen 'chimney' tube for which this can work and the flame will just travel down a wide enough bore tube and burn at the mouth of the gas jet, which is called a blowback.It was possible to get a 'blow-back' on bunsens at school; you could make it happen, sometimes, by punching the rubber rube and interrupting the gas supply. Or you can light it at the air inlet hole and get a flame, sometimes.I haven't actually added anything to the previous posts but I've tried to put it more simply.