Characteristics of White and Black Smoke Emission from Diesel Engine

Emission characteristics of white smoke or soluble organic fraction (SOF) and black smoke or dry soot from diesel engine were studied by means of mini-dilution tunnel method and Soxhlet extraction method. Further, the contribution of lubricating oil and that of presoot ascribed to condensed hydrocarbon droplet to SOF emission were discussed. The influences of intake air temperature and humidity on SOF and dry soot emission were also studied. It is shown that the characteristics of SOF and dry soot emission are well clarified against the CO2 concentration considered to relate with the combustion temperature and O2 concentration. The SOF emission per unit fuel consumed (SOF emission ratio) is high in the case of low CO2 concentration region or light load because of the high presoot emission ratio in this region. The ratio of presoot to SOF is about 70% when the engine is in idling. On the other hand, lubricating oil emission ratio is almost constant over a wide range of load. So, in the case of heavy load; low presoot emission region; the ratio of lubricating oil to SOF becomes high. The higher the intake air temperature, the lower is the SOF emission at the light load due to the decrease in presoot emission, while the dry soot emission is not varied. To raise the intake air humidity decreases not only the SOF emission, but also the dry soot emission, since the OH radical increases in the combustion process.