The mitigation of mode-switching challenges of spark-assisted compression ignition engines through powertrain electrification

Abstract

Spark-assisted compression ignition (SACI) is a novel combustion strategy that combines the fuel efficiency benefits of high EGR dilution, high compression ratio, and lean operation. Though the efficiency benefit is significant, SACI has several control and calibration challenges. To resolve this limitation, switching combustion modes between SACI and SI-only combustion is implemented. This work demonstrates the synergistic benefit of mild hybridisation on improving torque tracking compared to a non-hybrid SACI vehicle. A tip-in performed on a one-dimensional engine model shows a significantly reduced mode-switching challenge as the electric machine can adapt torque during mode changes, offsetting transport delays and actuator constraints. Furthermore, a vehicle model demonstrates that an electric machine can reduce the number of required mode transitions over four drive cycles from 15-40%. In addition to control benefits, the SACI powertrain also demonstrated 4-5% higher fuel economy compared to an SI-only powertrain in each vehicle configuration.