What kind of fuel does the Olympic flame use? Why not go out?

The internal combustion system of the torch is to install a set of equipment inside the torch, so that the torch can keep burning in a certain range of complex environment for a period of time after being ignited, and complete the relay transmission. The first thing to be solved is fuel. Propane was chosen as the torch of Beijing Olympic Games. Propane mainly produces water vapor and carbon dioxide after combustion, which will not pollute the environment. More importantly, propane can adapt to a wide temperature range, and it can still produce a saturated vapor pressure above 1 at MINUS 40 degrees Celsius, which is higher than the external atmospheric pressure and forms combustion; Moreover, the flame produced by propane is bright yellow, and when torchbearers run, the dynamic fluttering flame is more eye-catching in different backgrounds.

An important innovation of the torch internal combustion system of Beijing Olympic Games is to set up a "double flame" scheme. After the gas flows out, part of it enters the main combustion chamber of the burner, forming a relatively full flame outside the torch. The other part enters the precombustion chamber and keeps a relatively small but very stable flame in the torch. If extreme conditions occur, the flame in the main combustion chamber goes out, and the pre-combustion chamber can still keep burning, so as to ensure that the torch will not go out.