set afire vs set on fire

set afire and set on fire both are verbs.

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

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

Other synonyms of set afire include set ablaze, set aflame.

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