Experiments and theoretical approaches on the burning behaviors of single n-heptane droplet

Abstract

This study was conducted to improve the theoretical prediction of the burning characteristics of an n-heptane droplet by comparing them with experimental results. To achieve this, numerical approaches were conducted by assuming that the droplet combustion can be described by both quasi-steady behavior for the region between the droplet surface and the flame interface, and transient behavior for the region between the flame interface and ambient surrounding. Comparisons were considered for droplet diameter (dt), flame diameter (df), flame standoff ratio (FSR), and viscous drag induced fluxes which are Stefan flux and thermophoretic flux for various initial droplet diameter (d0) and oxygen (O2) concentration conditions. It was revealed that the flame diameter (df) and flame standoff ratio (FSR) initially increase dramatically and approach quasi-steady behavior within the observation period, and the flame standoff ratio (FSR) increases a little with the initial droplet diameter (d0) both experimentally and theoretically. The value of flame diameter (df) decreases from its maximum value when oxygen (O2) concentration is increased from a value of 18% to 40%. The burning rate (K) constant becomes higher as the oxygen (O2) concentration increases since the increase of oxygen (O2) concentration produces a higher maximum flame temperature (df) which enhances the effective thermo-physical properties of the gas-phase bounded by droplet and flame front.