Autoignition Dynamics of N-dodecane Droplets under Normal Gravity

Experimental observations of two-stage autoignition dynamics of fiber-supported normal dodecane droplets in air under normal gravity are presented for a range of pressures and temperatures. High-speed shadowgraph imaging of the autoignition process reveals cool-flame and hot-flame front-formation and propagation dynamics. During two-stage ignition, a cool-flame kernel is first formed below the droplet; it then propagates toward the droplet along the fuel-vapor plume, and subsequently a hot-flame kernel is established behind the cool-flame front which rapidly expands, engulfing the droplet and establishing the classical diffusion flame. Results for the cool-flame and hot-flame kernel locations and their propagation speeds are presented for a range of ambient pressures, varying between normal atmospheric pressure and super-critical pressures and temperatures.