This paper points out some issues of the current analytical methods for PM(Particulate Matter) composition emitted from diesel engines equipped with CR-DPF(Continuously Regenerated - Diesel Particulate Filter) and discusses the causes and mechanisms.
Under the test conditions with CR-DPF, PM composition, not including soot (i.e., SOF(soluble organic fraction), sulfate, bound water), often exceeds the actual PM mass when the bound water is calculated by the equation of 1.3 times of sulfate and eventually the soot in the PM leads to a minus value. In this study, the coefficient (1.3) for the bound water calculation has been examined and a lower coefficient value is proposed for the expected reasons, such as the effects of the filter materials (hydrophobic glass fiber filter) on the PM collection. Sulfate is thought to be trapped inside the filter due to less carbon existing in the exhaust gases and the bound water is decreased due to the hydrophobicity of the filter.
Also SOF increasing phenomenon was observed when 500ppm sulfur diesel fuel was used for a diesel engine with CR-DPF compared to an engine without CR-DPF. The experimental data with GC-AED analysis, a SOF recovery test and an adsorption test of exhaust emissions using a glass fiber filter paper doped with sulfuric acid, indicated that light exhaust gases were adsorbed on the produced sulfate which consisted mainly of sulfuric acid. It is concluded that the current test method using a filter paper for PM composition analysis leads to this SOF increasing phenomenon.