Dragonfire Assault( Dragon Magic, p. 17)
You can augment your most powerful melee attacks with draconic power.
Power Attack (PH) , STR 13, CHA 11, dragonblood subtype,
When you use Power Attack to increase the damage dealt from your attack, you can choose for the extra damage to be of the fire type instead of its normal type. Make this choice for each attack after it is resolved but before damage is dealt. This is a supernatural ability.
If you have the Draconic Heritage feat or if you are a half-dragon, the extra damage is of the energy type (acid, cold, electricity, fire, or sonic) that corresponds to your heritage or your draconic parent instead. II your feat or your parent is not associated with one of these energy types, this feat has no effect for you,