"Some flames, such as the flame of a burning candle, are hot enough to have ionized gaseous components and can be considered plasma. This subject is, however, hotly debated."
Plasma used by starships in this game has been said to be at millions of degrees Kelvin, so you shouldn't be using flames for comparison as it is only partially in the state of plasma.
As for the OP - it would make more sense to force ejected warp plasma undergo fusion, but a simple explosion nearby wouldn't be enough, so just forget it.
"holy debated" oh... That has to be a wicked pun.
Anyway, Fire or Flame is a very weak form of Plasma but the fact still remains. Plasma is a state of matter and in that highly energized state the matter cannot really "combust" or "explode" because it is already in a plasmodic state.
In other words... You cannot make fire burn because it is already the product of rapid oxidation. If you add more energy to a plasma it may become a hotter form of plasma but unless you manage to convert it all to energy you are not going to make it anything other than plasma. Detonating an explosion in a field of plasma would just make it move away from the explosion rapidly. Putting some form of ignition into plasma would just make the ignition source ignite but it would have very little effect on the plasma other than possibly increasing the amount of energy it had.
Forcing Nuclear Fusion on the Plasma would be incredibly difficult but I suppose it could be done. However, if that was the goal then why not leave behind a couple of mines? They are supposed to have antimatter reactions that make Nuclear detonations look weak.