It might be more related to the boiling points, Kerosene/paraffin being around 180C where as biodiesel is around 360C (both are subjet to variations in content and purity, and target market as well as Kerosene/paraffin having slightly different meanings in different locations).
That certainly seems a possible explanation. However, I would have thought that if it's lit, it's lit, and that flame front is therefore hot enough to ignite more local fuel.
Hence I was musing that if the flame extinguishes after a few minutes then it's running out of fuel, suggesting that the fuel is not climbing the wick sufficiently fast to maintain the flame.
However, if that was indeed the case, I would have expected mixing the bio with something lighter would fix the problem, but it didn't, so, well, I guess I'm wrong.
Suffice it to say, it'd be nice to diagnose this, as I'd quite like a bio greenhouse heater...
I tried mixing various combinations of biodiesel and isopropyl alcohol/methanol up to a mix of 4:1 biodiesel to alcohols, and still problems with yellow flames, ash and the wick burning down. This was in an aladdin 14 type paraffin heater.
You might be able to burn a mix of kerosene and biodiesel if there is not much biodiesel, but that rather defeats the point!
I did build a mini heater that had just a steel bowl with a tall thin chimney and that worked a treat, lit with a rag as a wick then the heat was kept in the chamber and the surface of the biodiesel itself burned.
