Investigation on Soot Formation of n-Heptane-Oxygen-Argon Mixtures in a High Pressure Shock Tube

Abstract

In this work, soot formation processes during self-ignition of n-heptane-oxygen-argon mixtures have been investigated using an optical measurement technique in a high-pressure shock tube. In order to achieve conditions relevant to Diesel engine combustion, three pressure levels (15 bar, 25 bar and 35 bar) have been chosen. The equivalence ratio was varied between 2.0 and 4.0. The soot formation process can be described by the time dependence of the mean particle diameter, the soot volume fraction and the soot production rate. These parameters are dependent on temperature, pressure and mixture composition. In order to investigate these quantities in situ, the dispersion quotient method was used. The attenuation of two laser beams (488 nm and 633 nm) caused by soot particles was recorded. From these signals the time-resolved mean diameter of the particles was determined applying the Mie-theory of scattering. Particle number density, soot volume fraction and soot production rate were also calculated. Key rds: Soot formation, Soot volume fraction, Dispersion quotient method