Abstract: H₂/air rotating detonation wave(RDW) was investigated in the plane-radial rotating detonation engine by experiments. The effect of equivalence ratio on the propagation modes of the RDW and detonation-wave parameters was studied. Results show that, when the mass flow rate remains constant, the RDW pressure peak and velocity increase with the equivalence ratio increasing under one propagation mode. The RDW propagates more steadily at higher equivalence ratio. The influence of equivalence ratio on propagation mode varies with mass flow rate. When mass flow rate is less than 100 g/s, the propagation mode of RDW does not change, and the RDW propagates in single-wave mode. When mass flow rate is larger than 150 g/s, with the equivalence ratio increasing, the propagation mode of RDW converts from single-wave mode into dual-wave mode, and then changes into asymmetric dual-wave mode, and finally changes to single-wave mode again. Furthermore, the low frequency oscillation was discovered in the asymmetric dual-wave mode. The oscillation frequency is approximately 300 Hz. As the mass flow rate increases, the triple-wave mode appears in the combustor. Results also show that, with the increase of mass flow rate, the equivalence ratio lower limit of dual-wave mode decreases, and the upper limit of asymmetric dual-wave mode increases. The boundary between dual-wave mode and asymmetric dual-wave mode is weakly dependent on mass flow rate.