Feasibility Assessment of a Pre-turbo After-Treatment System with a 1D Modeling Approach

A numerical study was carried out to determine the relative impact of diesel engine after-treatment system placement on engine performance. The objective of the study was to investigate the advantages and disadvantages of placing the after-treatment system upstream of the turbocharger as opposed to the more conventional downstream location. The study was conducted under both steady state and transient operating conditions. The after-treatment system involved in this study consisted of a Diesel Oxidation Catalyst (DOC) followed by a Diesel Particulate Filter (DPF) directly downstream of the former. The DOC and DPF models were correlated with experimentally-obtained, individual, pressure drop and warm-up data sets for each device. In an additional step for transient studies, chemical reactions were modeled within the DOC to simulate HC and CO oxidation, and their associated exothermic behavior.

Results indicate that under steady state conditions, a pre-turbo after-treatment system is more desirable than a post-turbo one in terms of fuel economy. This fuel economy advantage however is quite marginal for an after-treatment system with a relatively unloaded DPF. Under transient conditions, results show less impressive response times for a pre-turbo after-treatment system compared to its post-turbo counterpart. Exothermic chemical reactions in the DOC help improve transient behavior in the pre-turbo system, but not significantly enough to overcome the large thermal inertia of the DPF which dominates the problem.