A detailed numerical investigation on evaporation and combustion of isolated n-heptane and n-dodecane droplet in argon-oxygen atmosphere

This paper presents a comprehensive numerical framework for simulating the evaporation and combustion of isolated fuel droplets using the Lagrangian–Eulerian method in a three-dimensional computational domain. The study has been carried out in two phases, evaporation and combustion. For evaporation, the effect of temperature, pressure, gravity and inert gas as ambient gas is numerically investigated. The numerical results of the squared normalized droplet diameter ${(d/d_0)}^2$ with respect to time ($t/d_0^2$) were compared with the experimental data of other researchers and showed good agreement. The numerical simulation was performed for the combustion of isolated n-heptane and n-dodecane with the initial droplet diameter of $0.05\text{mm}$ and the ambient temperature ($T_a$) in the range of $750K-1000K$ and ambient pressure ($P_a$) of $2MPa-3MPa$. This study investigated the two-stage ignition process and the effect of argon-oxygen mixture as ambient gas on the auto-ignition delay time for n-heptane and n-dodecane fuel droplet. A detailed kinetic mechanism (DKM) and the perfectly stirred reactor (PSR) model were utilized to analyze the effect of ambient gases of air (AG-1) and argon-oxygen mixture (AG-2). The results showed that cases using AG-2 as the ambient gas exhibited a stronger cool flame and an increased auto-ignition delay time at moderate ambient temperatures ($T_a=800-850K$) compared to AG-1. Conversely, the auto-ignition delay time was decreased at elevated ambient temperatures $(T_a>=900K)$.