How does Sanji produce fire in Water? As you know, Sanji has a move called Diable Jamble, where he somehow manages to generate fire on his leg by rotating with great speed.

We have seen this move first when he was fighting CP9.

According to science, fire can be generated by friction, but it should be spontaneous. This explains as to how he was able to generate while he was fighting CP9 at Enies Lobby.

But after the timeskip, when the Straw Hat Pirates were on their way to Fishman Island, they encountered a Kraken. How did Sanji generate fire in water?

In water, there is no rough material via which, fire can be generated.

And even if it is somehow achieved, how can the fire not get extinguished by the water!?
As usual, Oda Eiichiro has a "creative" explanation for that too! Oda blatantly disobeys the Laws of our world in One Piece.

In SBS Volume 44, when asked how Sanji could beat Jabra by heating his leg, without burning it, Oda's response was:


  Sanji's leg is not hot!! His heart was burning so much hotter!!


If asked your question, he would probably say something like:


  Learning Haki, spending 2 years chased by Okamas, and being separated from ladies, especially Nami-san and Robin-chan, has made his heart burn much hotter!!! Even water cannot extinguish his burning heart!!!


I know, it doesn't feel satisfying, but this is how Oda-sensei's "explanations" usually are!