When considered along with Phase 2 Greenhouse Gas (GHG) requirements, the proposed Air Resource Board (ARB) nitrogen oxide (NOx) emission limit of 0.02 g/bhp-hr will be very challenging to achieve as the trade-off between fuel consumption and NOx emissions is not favorable. To meet any future ultra-low NOx emission regulation, the NOx conversion efficiency during the cold start of the emission test cycles needs to be improved. In such a scenario, apart from changes in aftertreatment layout and formulation, additional heating measures will be required.
In this article, a physics-based model for an advanced aftertreatment system comprising of a diesel oxidation catalyst (DOC), an SCR-catalyzed diesel particulate filter (SDPF), a stand-alone selective catalytic reduction (SCR), and an ammonia slip catalyst (ASC) was calibrated against experimental data. The calibrated model was then used to evaluate various advanced aftertreatment system configurations that included the application of an electrically heated catalyst, mini-burner, fuel dosing, passive NOx adsorber (PNA), and ammonia injection. The advanced aftertreatment system capable of meeting the 0.02 g/bhp-hr NOx emission limit with minimum fuel consumption penalty was then coupled to two different advanced engine models. Each of these engine models met the 2027 Phase 2 GHG emission standards but used a different combination of technologies, including downsizing, downspeeding, variable compression ratio (VCR), cylinder deactivation, and turbocompounding. The combined engine and aftertreatment system models were then evaluated on both cold and hot start Heavy-Duty Federal Test Procedure (HD-FTP) test cycles. The results show that with appropriate selection of engine and aftertreatment technology packages, the 2027 Phase 2 GHG emission standards and the proposed 2024 ultra-low NOx emission standards can be achieved simultaneously.
