Deflagration-to-detonation transition (DDT) of methane-acetylene-air and propane-acetylene-air mixtures was experimentally studied to extend availability of pulse detonation engines using liquid fuels. The detonation tube has a total length of 7194 mm and an inner diameter of 50 mm. Volumetric percentage of acetylene in the mixed fuels ranged from 0 % to 100 % under the condition that total equivalence ratio was kept constant of 1.0. The experimental results show that increase in volumetric percentage of acetylene causes faster flame acceleration and earlier detonation transition. DDT was observed for the methane-based mixtures containing acetylene of more than 50 % in fuel and for the propane-based mixtures with acetylene of more than 20 %. Cell size of methane-acetylene-air mixtures and propane-acetylene-air mixtures increased with decrease in volumetric percentage of acetylene in the mixed fuel. Cell size of methane-acetylene-air mixtures was found to be proportional to the calculated reaction induction length in the case that volumetric percentage of acetylene was more than 60 %, whereas the ratio of the calculated reaction induction length to the cell size was dependent on volumetric percentage of acetylene for propane-acetylene-air mixtures.