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The latest US emission regulations require dramatic reductions in Nitrogen Oxide (NOx) emissions from vehicular diesel engines. Selective Catalytic Reduction (SCR) is the current technology that achieves NOx reductions of up to 90%. It is typically mounted downstream of the existing after-treatment system, i.e., after the Diesel Oxidation Catalyst (DOC) and Diesel Particulate Filter (DPF). Accurate prediction of input NO₂:NO ratio is useful for control of SCR urea injection to reduce NOx output and NH₃ slippage downstream of the SCR catalyst. Most oxidation of NO to NO₂ occurs in the DOC since its main function is to oxidize emission constituents. The DOC thus determines the NO₂:NO ratio as feedgas to the SCR catalyst. The prediction of NO₂:NO ratio varies as the catalyst in the DOC ages or deteriorates due to poisoning. Thus, the DOC prediction model has to take into account the correlation of DOC conversion effectiveness and the aging of the catalyst.

Upcoming California on-board diagnostics (OBD) regulations require lighting the malfunction indicator lamp (MIL) when a catalyzed diesel particulate filter (CDPF) is inert with respect to nonmethane hydrocarbon (NMHC). Light-off temperature shift detection uses a correlation between CDPF age and the gradual increase in catalyst light-off temperature to determine the age of a CDPF. The proposed OBD strategy necessitates slipping HC past the upstream diesel oxidation catalyst (DOC) to ignite on the CDPF. The best-case OBD solution space requires engine net power levels less than 43 hp on a Cummins ISB. Radial temperature measurements downstream of the DOC revealed regional DOC light-off which would not be able to be detected by a single temperature sensor. CDPF light-off independent of DOC light-off was never observed under any testing, eliminating the possibility of using light-off temperature shift as a detection strategy.

A fast time-scale 1-D dynamic diesel particulate filter model capable of resolving the pressure pulsations due to individual cylinder firing events is presented. The purpose of this model is to investigate changes in the firing frequency component of the pulsating exhaust flow at different particulate loadings. Experimental validation data and simulation results clearly show that the magnitude and phase of the firing frequency components are directly correlated to the mass of particulate stored in a diesel particulate filter. This dynamic pressure signal information may prove particularly useful for monitoring particulate load during vehicle operation.

A gravimetric particulate measurement system, which extracts samples isokinetically from raw exhaust, is presented to quantify the particulate mass stored in diesel particulate filters. The purpose of this measurement system is to facilitate the study of wall-flow filter behavior at different particulate load levels. Within this paper, the design considerations for the particulate measurement system are detailed and its operation is described. The accuracy of the measurement is examined through a theoretical error analysis and direct experimental comparison to the differential weight of a diesel particulate filter. Experimental results are also presented to validate the ability of the system to maintain the isokinetic sampling condition.