Dynamic Skip Fire Applied to a Diesel Engine for Improved Fuel Consumption and Emissions

Dynamic skip fire (DSF) is an advanced cylinder deactivation technology where the decision to fire or skip a singular cylinder of a multi-cylinder engine is made immediately prior to each firing opportunity. A DSF-equipped engine features the ability to selectively deactivate cylinders on a cylinder event-by-event basis in order to match the requested torque demand at optimum fuel efficiency while maintaining acceptable noise, vibration and harshness (NVH). Dynamic Skip Fire (DSF) has already shown significant fuel economy improvements for throttled spark-ignition engines. This paper explores the potential benefits of DSF technology in improving fuel economy while maintaining ultra-low tailpipe emissions for light-duty (LD) Diesel powertrains. An analytical model was created using the FEV Complete Powertrain Simulation Platform to conduct a dedicated simulation study of DSF benefits over the Worldwide Harmonized Light Vehicle Test Procedure (WLTP) and a representative Real Driving Emissions (RDE) cycle. The study was conducted on two characteristic vehicle platforms; a mid-size sport utility vehicle (SUV) and a compact, C-segment passenger car. The two Diesel-powered vehicles considered in this analysis each employ a state-of-the-art 2.0-liter, 4-cylinder Diesel engine equipped with high- and low-pressure exhaust gas recirculation (EGR) and a variable geometry turbocharger (VGT). The analysis results obtained so far demonstrate that DSF technology, when applied to a light-duty diesel engine with optimized transmission shift scheduling, can achieve up to 5% fuel economy benefit, while realizing tailpipe nitrogen oxides (NOx) emissions reduction up to 40%. The improved fuel economy is a result of combination of factors, including pumping loss reduction, combustion system efficiency improvement and deceleration cylinder cut-off utilization. The reduction of tailpipe NOx is achieved mainly by improved conversion efficiency in the NOx aftertreatment system due to increased exhaust temperatures with DSF technology.