Detailed Numerical Simulation of Droplet Combustion

Auto-ignition and combustion of single fuel droplets of methanol, n-heptane and iso-octane are studied. The numerical simulations are based on a detailed vaporization model, a detailed transport model and detailed chemical kinetics. The governing equations of the two phases are solved in a fully coupled way. The influence of different physical parameters like droplet temperature, gas phase temperature, ambient gas pressure and droplet velocity on the ignition process is investigated and the results are compared. It turns out that the ambient gas temperature highly influences the ignition delay time similar to the case of the auto-ignition of a homogeneous gas mixture. The ignition delay time decreases with increasing pressure, which can also be observed in homogeneous gas mixtures. This decrease can be described by a rational law. The influence of the droplet temperature is negligible. In addition the ignition delay time is almost independent of the droplet velocity, provided that the flow is not too strong, so that the flame is ”blown out”.