<p>Numerical simulations are performed to investigate the propagation characteristics of ethylene/air rotating detonation waves in a two-dimensional computational domain, by solving the Navier–Stokes equations with an in-house code. Five injection area ratios (100%, 80%, 60%, 50%, and 40%) are adopted to analyze the differences in the structures of the flow field between full-area and discrete injection, as well as the effects of injection area ratios on the stability of rotating detonation waves and the parameters of detonation waves. The results show that under a full-area injection condition, the reverse waves cause the injection blockage and fuel leakage may occur when the height of the accumulated reactants increases rapidly. Under a discrete injection condition, the nonuniformity distribution of the reactants ahead of the wave affects the stability of detonation waves. The detonative front is distorted and wrinkled, accompanied by local extinction and re-ignition, when the injection area ratio is relatively small. As the injection area ratio reduces, the quantity of reactants consumed by deflagrative combustion increases and the pressurization capacity becomes weaker. The inlet mass flow rate decreases, whereas the inlet blocking ratio stays almost constant. In addition, the wave velocity is influenced by the propagation features of the detonation waves.</p>