1.
If something burns up or if fire burns it up , it is completely destroyed by fire or strong heat.
The satellite re-entered the atmosphere and burned up...
Fires have burned up 180,000 acres of timber.
PHRASAL VERB : V P , V P n (not pron) , also V n P
2.
If something burns up fuel or energy, it uses it.
Brisk walking burns up more calories than slow jogging.
PHRASAL VERB : V P n (not pron) , also V n P