Optimization of the combustion system and control strategy for the new hybrid-dedicated 2.5 L TGDI engine

Abstract

Hybrid Electric Vehicles(HEVs) are recognized as a promising mid-term solution for reducing greenhouse gas emissions and accelerating vehicle electrification. This research presents the development of a new hybrid-dedicated 2.5 L turbocharged engine equipped with gasoline direct injection, aiming to achieve high efficiency and dynamic performance for midsize SUV application. To enhance thermal efficiency, the combustion system was optimized by tuning intake cam closing timing and geometric compression ratio, effectively realizing the Atkinson cycle with a high expansion ratio and reduced effective compression ratio. Under low-speed and high-load engine conditions, a multiple injection strategy, including late injection during compression stroke, and a diluted combustion using low-pressure exhaust gas recirculation(LP-EGR), were applied to suppress knocking and improve combustion phasing. The engine test showed a 5% reduction in fuel consumption across high-frequency HEV operating points, while maintaining sufficient power and torque output. Additional improvements in piston geometry and injection strategy contributed to faster catalyst heating and lower engine-out raw emissions. The proposed hybrid system, featuring two motors and a hybrid dedicated engine, demonstrated superior system response through new control strategies. This development provides a viable powertrain solution for future hybrids, combing performance, efficiency, and environmental benefits.