There is growing interest in application of SCR on DPF (SDPF) for light and heavy duty applications, particularly to provide improvements in cold start emissions, as well as improvements in system cost and packaging [1, 2, 3]. The first of systems containing SDPF are just coming to market, with additional introductions expected, particularly for light duty and non-road applications [4].
To provide real world testing for a new SDPF product design prior to availability of OEM SDPF applications, an SDPF and one SCR catalyst were substituted in place of the original two SCR catalysts and a catalyzed diesel particulate filter (CDPF) on a Ford F250 HD pickup. To ensure that the on-road emissions would be comparable to the production system replaced, and to make sure that the control system would be able to operate without detecting some difference in behavior and seeing this as a fault, initial chassis dynamometer work was done before putting the vehicle on the road.
Two complete systems were prepared, with fresh and reference hydrothermally aged diesel oxidation catalyst (DOC), SCR, and SDPF components. First, the hydrothermally aged reference system components were run on the FTP-75 and other cycles on the application, in the configuration DOC + SDPF + SCR and DOC + SCR + SDPF, as well as DOC + SDPF. The DOC + SCR + SDPF configuration provided more similar emissions and DPF pressure profile to the original system, so this was chosen for the road aging. A similar set of emissions tests were run on the fresh parts, then the system was put on the road with a variety of drivers and operating conditions for 50,000 miles over a period of 17 months. At the end of the aging, the road aged parts and the original hydrothermally aged parts were subjected to a similar combination of tests. This provided both a measure of how the system had aged, and how well the road aged system compared to the initial hydrothermal reference aging that was chosen.