[Richard L]

Have been quite busy lately, read this a few times but didn't respond.

Interesting topic.

I think this is probable especially the mixture is close to stoichometric. This will happen during the closing of throttle period where the ideal afr can be reached.

For any expolsion to take place, you need some kind of ignition to bring forth and above the flash point. This can be one of the following:

1. Valve over-lapping period, more likely with NA engine with bolt-on turbo or SC.
2. Brurn-rate is slowed down with incorrect afr. This applies to too rich of too lean.
3. Some check-valve based wmi system can continue to spray during pressure down period, more so if long delivery line is used (trunk mount).
4. Residual methanol in the pleumn can cause pre-ignition, before exhaust gas is fully expelled during thr intake stroke.

I cannot think all the above for the time being. if anyone can chime in and suggest more conditions where this can happen.