Simulation of Aftertreatment Thermal Management Strategies for Low-Load Operation

The low-NOx regulation for heavy duty trucks proposed by California’s Air Resources Board (CARB) will present a significant challenge to truck, engine and aftertreatment system manufacturers. This regulation will include a new test cycle representative of low-load operation. With low-load cycles, NOx conversion by the SCR (selective catalytic reduction) system is limited primarily by the exhaust temperature; thus, thermal management will dominate development. Simulation can be used to examine different thermal management strategies, and to define high-level requirements for new components. In this study, modeling was used to investigate SCR performance on two different low-load cycles, including the one selected by CARB for the low-NOx regulation. First, the “thermal deficit” of the cycle was quantified using a constant heat input. Next, direct heating of the exhaust with a fuel mini-burner or an electric heater, using realistic controls, was simulated to determine their capability to overcome the thermal deficit. For comparison, the performance of a dual-injection SCR system on these cycles was also modeled.