SOOT FORMATION IN A SHOCK-TUBE UNDER ELEVATED PRESSURE CONDITIONS

High pressure soot formation from methane, ethylene, acetylene, propan e and n-heptane was studied at rich burning conditions applying the sh ock tube technique. Pressure behind reflected shock was varied between 15 and 100 bar. Time resolved measurements of soot particle diameter and number density were carried out using an extinction-scattering tec hnique at 488 nm. It could be shown that soot formation at high pressu res is characterized by particle diameters below 30 nm that decrease w ith pressure. The corresponding high particle number densities in the range of N approximate to 10(12) - 10(13) 1/cm(3) turned out to be con siderably higher than at atmospheric conditions. This behavior has to be attributed to reduced coagulation coefficients in the transition re gime between free molecular and continuum flow. It was found that an i ncrease in carbon concentration has a strong promoting influence on so ot volume fraction. Total pressure, however, does significantly enhanc e soot yield at pressures up to 30 bar and loses its dominance at high er pressures.