Development of the Combustion System for General Motors' High-Efficiency Range Extender Ecotec Small Gas Engine

General Motors has developed an all-new Ecotec 1.5 L range extender engine for use in the 2016 next generation Voltec propulsion system. This engine is part of a new Ecotec family of small displacement gasoline engines introduced in the 2015 model year. Major enhancements over the range extender engine in the current generation Voltec propulsion system include the adoption of direct injection (DI), cooled external exhaust gas recirculation (EGR), and a high 12.5: 1 geometric compression ratio (CR). Additional enhancements include the adoption of high-authority phasers on both the intake and exhaust camshafts, and an integrated exhaust manifold (IEM). The combination of DI with cooled EGR has enabled significant thermal efficiency gains over the 1.4 L range extender engine in the current generation Voltec propulsion system at high engine loads. The addition of a high geometric CR and high- authority camshaft phasers for extended late intake valve closing (LIVC) operation has enabled improved low- and mid-load engine efficiency. The combination of DI and high-authority camshaft phasers has minimized the full-load engine torque loss inherent with traditional high CR and LIVC implementations. The combustion system was developed with extensive use of computational fluid dynamics (CFD) simulation for optimization of in-cylinder mixing and combustion. These tools aided in the sorting and selection of the combustion chamber, ports, piston, and fuel injector. Extensive single- and multi-cylinder engine testing and development was also employed to refine and optimize the engine combustion system.