Why is the torch fuel of Sydney Olympic Games 65% butane 3 and 5% propane, while the "Xiangyun" torch only uses propane?

Propane and butane are environmentally friendly gases, and the combustion products are carbon dioxide and water! The reason why the torch of Sydney Olympic Games uses two fuels is that it is transmitted underwater. Fuel is the key to the torch burning underwater. Scientists have tried various fuels and conducted various experiments. (The effect was not particularly good at first, and they even planned to cancel the underwater transmission. Finally, they found a fuel composed of butane and propane in a certain proportion. This fuel can not only be burned underwater, but also will not pollute the water body.

So the underwater relay appeared for the first time in the history of the Sydney Olympic torch relay. That is, a section of the torch relay route is carried out under the sea. The Olympic torch relay not only successfully solved the problem of underwater torch relay, but also broke the iron law of incompatibility between fire and water. The torch relay of the Beijing Olympic Games is carried out on land, so there is no need to use a mixed fuel of two gases, just propane.