Simplified Cost-effective Aftertreatment System for Electrified Diesel Applications 2020-37-0023
The Diesel powertrain remains an important CO2 reduction technology in specific market segments due to its inherent thermodynamic combustion efficiency advantages. Diesel powertrain hybridization can bring further potential for CO2 emissions reduction. However, the associated reduction in the exhaust gas temperature may negatively impact the performance of the exhaust aftertreatment (EAT) system and challenge the abatement of other emissions, especially NOx. Considering that active urea-SCR systems may be required to ensure compliance with the legislative limits, the total cost of the hybrid Diesel powertrain is expected to increase even more, therefore making it less commercially attractive.
We present a model-based analysis of a 48V Diesel mild hybrid electric vehicle (MHEV) which is combined with an exhaust aftertreatment (EAT) system using Lean-NOx trap (LNT) technology. The overall de-NOx performance is further enhanced with the addition of passive SCR catalysts to benefit from the on-board ammonia formation during rich combustion events. Since the modeling framework is fully physico-chemically informed, it allows the investigation of various topologies, catalyst geometrical and chemical properties. Moreover, the model includes a simplified virtual engine model and a virtual ECU to allow closed loop simulation of the engine + control + aftertreatment for various LNT/SCR control strategies.
Four different powertrain topologies of the MHEV system are considered to identify the optimal balance between the fuel consumption improvement and the negative impact on the EAT system. For the latter, four different multi-brick EAT layouts are simulated, with different combinations of LNT, DPF and passive SCR/SCRoF components. Simulation results reveal that appropriate selection of the powertrain and EAT configuration, together with proper sizing of the components, can result in a cost-effective EAT system able to meet lower than Tier 3 BIN125 emission limits
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