Effects of prenol and isoprenol addition on soot and PAH formation in ethylene/methane counterflow diffusion flames

•The effect of prenol/isoprenol addition on soot and PAH formation in diffusion flame is tested.•Soot and PAH formation is enhanced with prenol and isoprenol addition.•Prenol shows stronger effect on promoting soot and PAH formation than isoprenol.•The discrepancies on the effect of PAHs and soot promotion between prenol and isoprenol can be explained by the different decomposition pathways.