Dynamics of soot surface growth and agglomeration by enclosed spray combustion of jet fuel

Abstract

Understanding the dynamics of soot formation and growth during combustion of jet fuel is essential for mitigation of aircraft engine emissions. Here, soot formation during enclosed spray combustion of jet fuel is investigated for its capacity to form soot with comparable characteristics to that from aircraft engines. For this, microscopy, scanning mobility particle, X-ray diffraction & Raman spectroscopy measurements and discrete element modeling (DEM) are employed along the flame centerline at various Effective eQuivalence Ratios (EQR). The DEM-derived mobility and primary particle size distribution dynamics are in excellent agreement with those measured at 5–63 cm height above the burner (HAB) for the measured temperature and soot volume fraction. At low EQR (1.46 and 1.59), soot surface growth stops at residence time, t = 4–7 ms, resulting in median soot primary particle diameters, d¯p, of ∼ 14 nm. At longer t (high HAB), agglomeration takes over increasing the median mobility diameter from 16 to 88 or 145 nm at EQR of 1.46 or 1.59, respectively, without altering d¯p and having the disorder over graphitic Raman band ratio, D/G = 0.9 ± 0.01 and a crystallite length, Lc = 1.24 ± 0.02 nm. In contrast, increasing EQR from 1.59 to 1.88, enhances soot surface growth, increases d¯p up to 23 nm and results in more graphitic soot having D/G = 0.8 ± 0.01 and Lc = 1.47 ± 0.01 nm. Furthermore, the D/G of soot is inversely proportional to its d¯p that is determined largely by surface growth.