Big Pistons Forever, detonation would undoubtedly be ruinous to the engine, but I have a strong doubt the mixture in question would detonate. Unfortunately, I have no direct experience with that, so can only provide an educated guess that
- low compression (on a diesel scale)
- rich mixture (when flying a circuit)
- the diesel part in the mixture remaining mostly in liquid phase, as opposed to quickly evaporating avgas
would mostly suppress detonation. Whoever has seen this situation in practice, please correct me if I'm wrong!