PN Emissions from Heavy-Duty Diesel Engine with Periodic Regenerating DPF

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Abstract
Periodic increases of PN, PM, and regulated gases associated with DPF regeneration from a heavy-duty truck equipped with a diesel particulate filter (DPF; non-SCR truck) and from a heavy-duty diesel engine equipped with a DPF and a urea-SCR (SCR engine) were investigated. Both met Japanese 2009 regulations. From both exhausts, PN emissions two orders of magnitude higher than the European legislation limit were observed in the regeneration cycle, and these emissions gradually decreased in subsequent cycles. This can be explained by the relation between the filtering efficiency and the amount of loaded soot in the DPF. No emissions particular to regeneration, such as soot fragments, were observed. In some cases, higher PN emissions were observed from the SCR engine. This may be because of the difference in DPF performance, but there is a possibility that some particles were produced in the urea-SCR system. NOX emissions from the SCR engine increased during regeneration because of the increase in engine-out NOX emissions in order to lower the regeneration temperature and the drop in NOX removal efficiency of the SCR system due to the high exhaust gas temperature. Certification values of PM and PN were calculated as the weighted averages of periodic changes. The contributions of the first three cycles, starting from regeneration, to PN were 99% for the non-SCR truck and 88% for the SCR engine. These suggest that PN emissions in normal conditions have almost no effect on the certification values. In the PM measurement, the effect of tunnel blank was high.

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