The sequence is composed of two alternating patterns. 8, 14, 11, 14, 18 (no). Looking at pairs: 8-2=6, 14-6=8, 11-?=2, 14-6=8. Actually, alternating: 8, 14, 11, 14, 18 and 2, 6, ?, 6, 12. The missing number 9 completes a logical step in the second sub-series.