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.