The pressure-temperature explosion limits of homogeneous mixtures of hydrogen and air are characterized by a Z-shaped response dominated by nonlinear chain branching and terminating reactions. Such a nonlinear response is expected to be further modified in the presence of convective-diffusive transport for initially nonpremixed systems subjected to aerodynamic straining. Our recent experimental, computational, and analytical studies on nonpremixed counterflowing hydrogen versus heated air have shown that while ignition can be indeed delayed by aerodynamic straining due to the reduced residence time, the response is however extremely insensitive for the second limit because of the associated fast chain branching reactions. It is further found that ignition at this limit is dominated by radical proliferation instead of thermal feedback. Expanding on this concept, we shall then present results on ignition in oscillatory, turbulent, and supersonic flows, on the phenomenon of two-staged ignition, and on the use of hydrogen as an ignition agent. Skeletal reaction mechanisms have also been identified to facilitate computational simulation