Combustion is a chemical reaction caused by heat reacting a fuel and an oxidant, and one property that determines the efficiency of a combustive reaction is the surface area of the reaction.

水は超高熱水蒸気となり、油の燃焼面積を拡大させて完全燃焼を実現します。

So this sentence is saying something like this:

"As the water vapor becomes super heated steam, the combustive surface area of the oil expands, achieving total combustion."

I would say 'water vapor' instead of just 'water' because you already know the water is in gas form.

Hope this helps