Preferential vaporization effects on the ignition of multi-component droplets

Preferential vaporization can affect the combustion characteristics of both liquid and solid phases. In the present study, the focus was on ignition using the paradigm of propane/n-heptane bi-component droplets. Numerical simulations were carried out at a pressure of 20 atm, an ambient air temperature of 1400 K, various droplet radii (200/100/50 mu m), and various liquid phase propane mole fractions (0.05/0.10/0.20/0.30/0.40) to investigate the effect of the light, i.e., more volatile component, on ignition. A modified version of an existing Lagrangian transient one-dimensional reacting flow code was used in spherical coordinates to capture the controlling mechanisms of ignition. The results showed that the ignition delay time decreases as the light component (propane) concentration increases. Additionally, the ignition delay time was found to increase with the droplet radius, due to the lower diffusion fluxes. Reaction pathway analysis provided insight into the interplay of the kinetics of the two components and their effect on the ignition. It was determined that the concentration of propane (the lighter and more volatile component) is dominant in the gas phase at the early stages of evaporation, and, as a result, it drives the droplet ignition process.