Carbonaceous aerosols from Diesel fuel pyrolysis in shock tube

The pyrolysis of a complex liquid fuel, whose characteristics are listed in Table I, has been investigated in high temperature and pressure conditions (P=9-12 bar, T=170O-2500 K) behind reflected shock waves in argon atmosphere using a conventional diaphragm-type shock tube. The measurement section, placed 50mm from the end plate, has been provided with optical accesses (Fig. 1). Light extinction measurements were performed in the visible (lambda=514.5nm) and in the infrared (lambda=1300nn) using an Ar+ enhanced laser (P=3W) and a diode laser (P=5mW) respectively. Scattering measurements in the visible were also performed. To discriminate the scattered and extincted light against thermal radiation, a high speed turbine chops at about 15kHz the Ar+ laser beam, while the diode laser is internally modulated at 20kHz. The fuel was fed in the shock tube as a finely dispersed aerosol. At this aim, a commercial aerosol system for biomedical applications was used, argon being the carrier gas. Mie theory was applied to determine the droplet size and number concentration of the fuel aerosol before the shock arrival. The scattered light from the particle cloud was simultaneously collected under three fixed angles (theta_i=30°, 60° and 120°) and the size and number concentration of droplets were inferred measuring the scattering cross sections CVV(theta_i) and the dissimetry ratios CVV(theta_i)/CVV(theta_j).