This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 煚 is uncertain. It visually combines 日 (sun) above 巨 and 火 (fire), but the original semantic and phonetic roles of these components are unclear.
With no clear meaning, picture a giant sun (日) over a huge (巨) fire (火) — an overwhelming blaze, but its true sense is unknown.
For ケイ, imagine a mysterious fire that looks like a giant letter K: K -> ケイ, but the kanji's meaning remains hidden.