A time-resolved measurement technique for particulate number density in diesel exhaust using a fast-response flame ionization detector

Abstract

The fast-response flame ionization detector (FRFID) has been used widely to measure, in real time, the concentration of unburnt hydrocarbons in internal combustion engines. In this study, a FRFID is modified to measure, simultaneously, the concentration of the gaseous hydrocarbons and the number density of soot particulates present in the exhaust of a turbocharged Dl diesel engine. The system is also capable of differentiating the hydrocarbon fraction of the particulates from that of gaseous hydrocarbons, hence providing information for deducing the amount of gaseous hydrocarbon that is adsorbed by or condensed onto the surface of the particulates. Another unmodified FRFID, with a particulate collector placed immediately upstream of it, is used to determine the total particulate matter in terms of mass concentration. Experimental results show that the particulate number density measured by the modified FRFID is correlated well with the mass concentration determined by the filtration method under various engine operating conditions. The hydrocarbon fraction of the particulates shows a similar trend to the gaseous hydrocarbon present in the raw exhaust gas stream under various steady-speed engine test runs. A transient engine load acceptance test concludes the usability of this modified FRFID to measure, on a time-resolved basis, the particulate number densities with trends similar to those of generally known smoke opacities.