freshly delivered household gas
A cylinder holds about 14.2 kg of liquefied petroleum gas ( LPG ) at an internal pressure of about 15 kg / sq cm ( about 220 psi ) which is about 15 times that of normal atmospheric pressure . The contents are primarily butane and propane and at that pressure and ambient temperatures it exists mostly as liquid with an approximate density of half of water .
The gas , when opened into the burner from the household cylinder ’ s regulator , has a density , about twice that of air . LPG is one of the widely used fuels with its chemical energy obtained by combustion with atmospheric oxygen . Without oxygen , the LPG is only just yet another gas . When the regulator of the LPG gas is opened and the knob on the gas stove switched on , the high pressure in the cylinder lets the fuel ‘ leak ’ into the burner before it is lighted ( lit ). Thus , the gas outflows pushing the atmospheric air aside and there is hardly any scope for the atmospheric air to enter into the gas cylinder through the gas pipe .
Further , when the gas has been lit at the burner , the hot combustion product gases ( mostly carbon dioxide and water vapour ) render the vicinity of the flame to very low density letting the tongues of fire and flame to spread upward and away only from the burner . In the absence of any possibility of entry of atmospheric oxygen inward into the cylinder , there is no way the flame of the
SCIENCE FACTS
WINSPIRE : Empowering youth | December , 2016
11
Why is the gas flame limited to the burner of the gas stove and what is the reason for the flame not reaching inside the gas cylinder ?
burner reaches inside the gas cylinder . It is very interesting to note that the atmospheric air , in fact , mixes with the LPG gas at a vent , midway enroute by venture effect , much before the fuel reaches the running burner of the household stoves . From that vent , even , the air does not go backward , sneaking , into the cylinder because the lower density above the flame pulls the air along with the fuel towards the burner only .
In fact , it is largely this ' sucked ' air that has been already mixed with the fuel at the vent that is used during combustion at the burner . In the rare event of blocking of the holes of the burner during combustion , the flame would , worse , surge backward to the vent only because there is air and in case there were no vents , the flame would simply extinguish rather than going into the cylinder because there is neither oxygen nor enough temperature in the cylinder .