Emissions Evaluation and Modeling of PM Emissions under Real-World Driving of an Ultra-Low NOx Tier 3 Light-Duty Diesel Vehicle 2021-01-0504

Currently, light-duty Diesel engines face great challenges to meet more stringent EPA emissions regulations while achieving above 30 miles/gallon fuel economy and maintaining a relatively low cost for the nitrogen oxides (NOx) and particulate matter (PM) or soot aftertreatment systems. This paper is focused on two aspects of this challenge, which are how NOx and PM emissions in real-world driving are controlled and the impacts of NOx and PM or soot controls have on fuel economy. The vehicle tested was a model year (MY) 2018 class-2 light-duty (LDT2) General Motors Diesel pickup truck. Real-time NOx and engine-out soot emissions, as well as engine control parameters, were measured over standard EPA certification test cycles and extensive urban and highway driving. Our study found that NOx emissions were well controlled during both real-world urban and highway driving and PM emissions were strongly linked to how NOx emissions were controlled, which is either via exhaust gas recirculation (EGR) or selective catalytic reduction (SCR) dominant during different driving conditions and how fast the air flow is controlled. Increased fuel injection mass with EGR dominant NOx control during frequent take-offs from stops and rapid accelerations under typical urban driving are the main reasons of higher soot emissions compared with soot emissions from highway driving. The study demonstrated that the Diesel particulate filter (DPF) regeneration frequency doubles from designed real-world urban driving compared to highway driving, indicating the associated fuel penalty also doubles. A 50-neuron neural network engine-out soot model requiring less than 1 kB random access memory (RAM) was developed and verified with the extensive real-world driving data. The neural network soot model can predict soot emissions very similar to the real time measurements, which is important for DPF soot load estimation, DPF efficiency diagnosis, as well as evaluation of the impacts on fuel economy and emissions under real-world driving conditions.