燃油
rán yoú · HSK 7
fuel oil
⛽ 燃 = burn + 油 = oil; burnable oil, i.e. fuel oil
燃 (rán, to burn) plus 油 (yóu, oil) compounds into the oil that gets burned for power. 油 carries the water radical 氵, marking it as a liquid.
油 — water radical 氵 + 由 (yóu, phonetic)
油 is a phono-semantic compound. The 氵 radical signals a liquid, while 由 supplies the sound. Originally referring to a river name, it was extended to mean oil or fat — any thick, flowing liquid — which became its dominant modern sense.