Auto-ignition of single n-heptane droplets in low-temperature and high-pressure air using Lagrangian–Eulerian approach

Abstract

The objective of this research is to investigate the evaporating, mixing, and auto-ignition processes of isolated fuel droplets using Lagrangian–Eulerian numerical approach. By using Peng–Robinson equation for the phase-equilibrium, the gas solubility at the droplet surface is considered at high-pressure ambient gases. Using perfectly stirred reactor combustion model and a low-temperature detailed mechanism for the n-heptane, the auto-ignition of the premixed fuel vapor–air mixture is verified at a constant pressure. Then, the auto-ignition of a fuel droplet with 60 µm diameter is studied at various low air temperatures. The analysis indicated that the results are strongly mesh dependent in this approach. Therefore, in order to predict the correct values of auto-ignition delay time and maximum gas temperature, the computational mesh size should be chosen in a specific range of cell sizes. Also, the auto-ignition of different size fuel droplets is studied at the air initial temperature of 800 K. It was observed that for accurate results, the computational mesh size should be chosen around seven to eight times the diameter of initial fuel droplets.