OPTICAL SOOT PARTICLE-SIZE AND NUMBER DENSITY-MEASUREMENTS IN A DIRECT-INJECTION DIESEL-ENGINE

Optical measurements of soot particle size and number density have bee n made in-situ in a direct injection diesel engine using a light scatt ering and extinction measurement technique. Simultaneously, the radiat ion from the soot particles was measured and used to estimate the thic kness of the soot cloud and temperature of the soot particles. The mea surement was taken at a fixed location near the center of the spray pl ume. Soot particle size was found to increase slightly during the comb ustion event reaching a peak diameter of approximately 40 nm. As the i njection process and combustion ended, the soot particle size dropped rapidly to below 20 nm before the signal became too small to measure. Soot volume fraction reached a maximum near 7 x 10(-5). The soot cloud was not only dense but thick, indicating that the soot was not confin ed to a thin reaction layer but rather filled more than half of the pa th length from the piston to the cylinder head. Rates of soot formatio n and oxidation appeared faster at the higher temperatures and pressur es of the engine in comparison to laboratory diffusion flames.