Is H2SO4(aq) + 2KOH(aq) → K2SO4(aq) + 2H2O(l) a combustion

No. This is a double displacement reaction.

This is because the only spectator ion is potassium ion, K+. Sulfuric acid is a strong acid, but only for the first H+ which is produced. The remaining HSO4^- ion is a weak acid, and is only minimally ionized. (*) Potassium hydroxide is a strong base and is completely ionized. As for the products, K2SO4 is completely ionized, but water is not. H+ and OH- combine to make molecular water

H2SO4(aq) + 2KOH(aq) → K2SO4(aq) + 2HOH(l) ….. “molecular” equation
H+ + HSO4^- + 2K+ + 2OH- → 2K+ + SO4^2- + 2HOH(l) …. ionic equation
H+ + HSO4^- + 2OH → SO4^2- + 2HOH(l) ……. net ionic equation

It changes food into energy that the organism can use.