At what temperature should I simmer bolognese to avoid burning? Bolognese requires a long period of low heat cooking or simmering, according to some recipes several hours.

At what temperature should I simmer, in order to avoid burning / overcooking, while still achieving caramelization, reduction and breaking down of the vegetables?

I am talking about the temperature of the sauce, while it simmers.
Depending on what other tasks you have for the day, consider sliding the sauce (and your Dutch Oven) into your oven for 6 hours or so. 


  Slow Cooker Setting = Oven Temp Low = 185-200F High =
  280-300F


I cook my Brunswick Stew this way at 250F (covered 3 hours, uncovered 3 hours). The last 3 hours allows the sauce/broth to thicken through evaporation. The temp allows the stew to "simmer" without repeatedly stirring, worrying over it, and zero scorching! Plus, I'm free to tend to other things. 

Related:
Technique: Slow Cooking with a Slow Cooker
Slow Cooker vs Dutch Oven: A Conversion Guide