Application of Dynamic Skip Fire for NO _x and CO2 Emissions Reduction of Diesel Powertrains

Dynamic Skip Fire (DSF®) has been shown to significantly reduce CO2 on gasoline engines and has been in mass production since 2018. Diesel Dynamic Skip Fire (dDSF™) builds upon the technology and extends it to diesel engine applications. dDSF is an advanced cylinder deactivation technology that allows the deactivation of any number of cylinders dynamically to deliver the requested torque while maintaining acceptable noise, vibration, and harshness (NVH) performance. NO_x regulations are becoming progressively more stringent on light, medium and heavy-duty (HD) diesel engines. Meeting low NO_x standards is becoming increasingly challenging, especially in lightly loaded operating conditions where maintaining ideal aftertreatment system efficiency is difficult. Most existing techniques to increase aftertreatment temperatures at low loads incur a fuel consumption penalty, which increases greenhouse gas emissions. In this study, dDSF is shown to combine benefits by reducing both NO_x and CO₂ simultaneously. Detailed studies were conducted on a Cummins X15 HD diesel engine. Engine testing and vehicle level simulation studies were followed by transient testing conducted on an engine dynamometer as well as on-road vehicle tests. NVH testing and evaluation was performed at the vehicle level to characterize vehicle response and ensure acceptability. dDSF calibrations were optimized to provide best thermal benefits at low loads. System level considerations such as coordination of air handling and fueling during transitions between firing densities, detection of valve actuation errors and mitigation of oil consumption concerns were studied. Results from system simulations using engine test data show 74% reduction of NO_x and 5.0% reduction in CO2 on the Low Load Cycle (LLC) compared to the baseline engine with conventional thermal management. This simultaneous reduction helps compliance of NO_x regulations while also reducing overall greenhouse gas emissions.