About Ballooning
Burners
The introduction of the propane-fuelled burner in the late 1950s was an important factor in the development of the sport of modern hot air ballooning. Propane has many advantages as a fuel, which derive mainly from its properties. For example: (i) it can be compressed under moderate pressures (i.e. 7 bar) to form a liquid at room temperature (i.e. 20 deg C); (ii) it is a concentrated form of energy (i.e. 50 MJ/kg); (iii) it is relatively light, even in liquid form (i.e. density 0.5 kg/litre); (iv) it burns efficiently in the presence of air, generating only carbon dioxide and water vapour.
Propane burns most efficiently in vapour form, after being pre-mixed with the correct proportion of air
to ensure optimal combustion. In order to achieve this, propane is withdrawn from the cylinder
in liquid form, and flows through a hose to the burner exit valve. On the way, it passes through a series
of coils, where it is heated by the flame from the burner, vapourising it. The propane vapour is then mixed
with an appropriate quantity of air before exiting through the blast valve (at the base of the set of coils),
where it is ignited. This produces a roaring pale yellow/blue flame, which extends towards the centre of the balloon
envelope, heating the air inside.
Most burner systems also have the option of burning liquid propane directly, bypassing the vapourising coils and air pre-mix system. This produces a broader, darker yellow flame and is much quieter. This burner, which is generally known as the "cow burner", is used when flying over livestock or areas sensitive to noise.
Almost all balloons have more than one burner nowadays, so that a back-up is available, in the (rare) event of a burner problem developing during flight.