This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
炴 combines 火 (fire) with 央, which likely contributes the sound. The exact historical development is uncertain.
With fire 火 beside 央, picture a bright flame at the center of a dark room, but its exact meaning remains unclear.
For ヨウ, imagine a yo-yo catching fire: yo -> ヨウ, and the flame dances at the center of the string.