Optical Measurements of Soot Particle Size, Number Density, and Temperature in a Direct Injection Diesel Engine as a Function of Speed and Load

In-cylinder measurements of soot particle size, number density, and temperature have been made using optical measurements in a direct injection diesel engine. The measurements were made at one location approximately 5 mm long and 1.5 mm wide above the bowl near the head. Two optical techniques were used simultaneously involving light scattering, extinction and radiation. An optical probe was designed and mounted in a modified exhaust valve which introduced a beam of light into the cylinder and collected the scattered and radiating light from the soot. The resulting measurements were semi-quantitative, giving an absolute uncertainty on the order of ± 50% which was attributed mainly to the uncertainty of the optical properties of the soot and the heterogeneous nature of the soot cloud. Measurements at three speeds and three overall equivalence ratios were made. For all of the operating conditions the soot in the measurement volume increased in size to a maximum followed by a rapid decrease. The peak soot diameters were in a range of 30 - 50 nm. Peak soot diameter, soot volume fraction, and soot temperature appeared to increase with equivalence ratio at the measurement location. The results also suggested the soot cloud to be very dense with peak soot volume fraction near 4-6 × 10^-6 and thick with a soot cloud thickness approximately 0.4 - 0.6 times the length from the piston to the head.