flame, blazing, brilliant
燄 centers on intense, visible fire: a flame that blazes brightly and brilliantly.
燄 combines 炎 (flame) with 臽, which likely contributes the sound. The character is built around the idea of fire and blazing.
The right side 炎 already means flame, and the left side 臽 looks like a pit or trap. Picture a pit filled with blazing fire: 燄 is a brilliant flame.
For エン, imagine a brilliant flame at the end of a long tunnel: end -> エン, and the fire blazes at the end.