It looks to me as though the mixture does a pretty good job of spreading around, so the concentration of flame around the valve can't be explained by the mixture sticking around the valve. Could it be that liquid fuel adheres to the valve, causing the additional flame around the valve. I'm surprised that the explosion is not more volatile in general.
Is the sequence posted edited at all? The piston doesn't seem to rise to tdc enough to account for 4 cycles. Am I missing something?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13