The effects of intake air temperature on soot formation and evolution in an optically-accessible D.I. diesel engine.

摘要

New techniques for quantitative planar imaging of soot were developed in a laminar diffusion flame and then applied in an optically-accessible engine to identify the effects of intake air temperature on soot formation. Based on a Rayleigh analysis of simultaneously obtained laser-induced incandescence (LII) and light scattering images, the technique provides a quantitative measure of soot volume fraction, particle diameter and number density of the soot field within the engine. To supplement the information obtained from the quantitative measurements, direct photography and tailpipe soot measurements were also performed.; Multi-plane volume fraction imaging at the baseline condition correlated well with total cylinder sampling work in the literature. The highest soot concentrations were observed at measurement planes that corresponded to the deepest regions of the combustion chamber for a production engine. Examination of the early crank angle volume fractions reveals that the premix-burn portion of the combustion event produces little soot.; The quantitative imaging study of intake air temperature effects indicates that soot production increases with temperature primarily due to shifts in the placement and duration of the premix-burn fraction. Average particle diameter and number densities computed over the active areas of the imaging results indicate that the local particle size and number density of the soot is relatively unaffected by shifts in the intake air temperature.; Histograms of the particle size and number density images indicate several features unique to the soot formation process. Particle diameter histograms exhibit a near log-normal shape. The number density images provide a measure of the number of particles per unit volume and exhibited highly concentrated regions during the initial burning period. Histograms of the number density images were found to have a bimodal type shape at early crank angles. The peak at higher number densities is indicative of regions of active soot formation whereas the lower number density peak represents more diffuse soot regions. At later angles, the bimodal character of the number density histograms decreases.