Evaluation of 48V Technologies to Meet Future CO2 and Low NO _x Emission Regulations for Medium Heavy-Duty Diesel Engines 2022-01-0555

The Environmental Protection Agency (EPA) and California Air Resources Board (CARB) have recently announced rulemakings focused on tighter emission limits for oxides of nitrogen (NO_x) from heavy-duty trucks. As part of the new rulemaking CARB has proposed a Low Load Cycle (LLC) to specifically evaluate NO_x emission performance over real-world urban and vocational operation typically characterized by low engine loads, thereby demanding the implementation of continuous active thermal management of the engine and aftertreatment system. This significant drop in NO_x levels along with continued reduction in the Green House Gas (GHG) limits poses a more significant challenge for the engine developer as the conventional emission reduction approaches for one species will likely result in an undesirable increase in the other species. One pathway to simultaneously reduce NO_x and CO₂ emissions and achieve these future emission regulations is through the application of 48V electrification for engine and aftertreatment system. Compared to the high voltage systems, 48V electrification offers a relatively lower cost solution to meet future regulations. In addition, the 48V system requires lower integration efforts, reduces safety concerns and offers a lower weight solution which are all key drivers for the heavy-duty market.

In the current study, a cost-effective 48V technology package for the next generation of high efficiency diesel engines is evaluated. The baseline engine model was calibrated against test data from a 2017 6-cylinder 7.7L Phase I GHG complaint diesel engine with a 228kW power rating. The baseline engine was further integrated with an advanced 48V technology package for fuel consumption reduction and aftertreatment thermal management. The selected engine technology package includes electrification of the air handling system using 48V E-Turbo and 48V EGR pump, friction reduction with downspeeding and cylinder deactivation for thermal management. In addition, a physics-based model for the baseline aftertreatment system meeting the 2010 NO_x emissions regulations was developed and calibrated against experimental data. The aftertreatment model was then used to define an advanced aftertreatment system that included application of a novel aftertreatment warm-up concept that applies a 48V electrically heated catalyst in combination with a fuel doser and a low temperature SCR catalyst to reduce cold start emissions. Finally, the advanced engine and aftertreatment system were coupled for complete system simulations. The results show that by applying the proposed 48V technology package, the 0.02 g/bhp-hr low NO_x emission levels can be achieved while simultaneously meeting the 2027 Phase 2 GHG emission standards.