A laboratory-scale bluff body combustor is mapped for its stability and flame dynamics of non-premixed flames with three fuels, namely, pure H2, H2[sbnd]CH4 mixture, and H2[sbnd]CO mixture, the last one representing syngas. Unsteady pressure measurements and high-speed OH* and CH*/CO2* chemiluminescence imaging are simultaneously performed. The combustor behaviour with syngas is markedly different than the other two in exciting high frequency oscillations, typically at the third harmonic longitudinal acoustic mode of the duct at high air flow Reynolds numbers (Re). In contrast, the H2[sbnd]CH4 excites only the fundamental longitudinal mode, and pure H2 excites up to the first harmonic. The latter two are observed to lock on to the shear layer mode of the bluff body wake, whereas the H2[sbnd]CO case locks on to thrice the Strouhal number associated with the shear layer mode, commensurate with the excitation of the third harmonic natural acoustic mode. Time-averaged OH* and CO2* chemiluminescence images show large-scale structure for the H2[sbnd]CH4 case compared to heat release rate zones aligned with the shear layer in the pure H2 and H2[sbnd]CO cases. Cross-sectionally averaged chemiluminescence profiles exhibit a streamwise stagger in the peaks of OH* and CO2*, suggesting two heat release rate zones, that could excite the acoustic oscillations. The instantaneous profiles indicate a convective delay between the two heat release rate zones that is close to the third harmonic acoustic time scale. The sequential of H2 oxidation to OH followed by CO oxidation by OH to form CO2 are considered to be responsible for the high frequency excitation in the case with the H2[sbnd]CO mixture when compared to the other two cases. © 2019 Hydrogen Energy Publications LLC