set on fire vs set ablaze

set on fire and set ablaze both are verbs.

Word	Noun	Adjective	Verb	Adverb
set on fire	No	No	Yes	No
set ablaze	No	No	Yes	No

As verbs, set on fire and set ablaze are synonyms defined as:

Other synonyms of set on fire include set afire, set aflame.

set on fire (verb)	set ablaze (verb)
set fire to; cause to start burning	set fire to; cause to start burning