Comparative Measurement of Nano-Particulates in Diesel Engine Exhaust Gas by Laser-Induced Incandescence (LII) and Scanning Mobility Particle Sizer (SMPS)

Particulate Matter (PM) from diesel engines is thought to be seriously hazardous for human health. Generally, it is said that the hazard depends on the total number and surface area of particles rather than total mass of PM. In the conventional gravimetric method, only the total mass of PM is measured. Therefore, it is very important to measure not only the mass of PM but also size and number density of particulates. Laser-Induced Incandescence (LII) is a useful diagnostic for transient measurement of soot particulate volume fraction and primary particle size. On the other hand, Scanning Mobility Particle Sizer (SMPS) is also used to measure the size distribution of soot aggregate particulates at a steady state condition. However, the measurement processes and the phenomena used to acquire the information on soot particulate are quite different between the LII and SMPS methods. Therefore, it is necessary to understand the detailed characteristics of both LII and SMPS. In the present study, the size distributions of PM from DI diesel engine are measured by both LII and SMPS simultaneously. In addition, PM mass emission is measured gravimetrically through a dilution tunnel and is separated into SOF and ISOF. The effects of EGR rate and engine load on the results of these particulate measurements are investigated. The different trends in the characteristics of PM emission are shown in each measurement methods for PM. The difference of detailed characteristics between LII and SMPS are illustrated by comparing the measurement results for the particulates. Finally, the problems associated with the measurements using each method are considered and some recommendations have been given for accurate measurement of nanoparticles.