Does combustion have a negative entropy or positive entropy?
It really depends, but most likely a positive entropy.
If the number of gas molecules increases during a process, the change in entropy will be positive. In the combustion of propane:
there are 6 molecules of gas on the left, and 7 molecules of gas on the right. The increase in gas molecules increases the disorder, and therefore the change in entropy is positive.
Very clear explanation on this page: http://www.chemistry-reference.com/rxns/