Optimizing hybrids FOR COST AND EFFICIENCY Figure 5: Modular engine friction-reduction measures. Cam Carrier Valve Train Module Variabilities - DVVT / VVL Cylinder Head Module Miller and Performance Variants Atkinson NA Variant VCS System Compression ratio spread up to 6 units / up to 6500 rpm. * Fastest and reproducible switching behavior * No additional energy demand for VCS control in fuel economy position (high CR). Figure 6: Components of AVL's variable-compression system. particle filter to control particulates in all operating conditions. Robust compliance with real driving emissions limits demands 3-way catalytic conversion and therefore stoichiometric combustion in the whole engine map. Figure 4 illustrates the limitations of different measures to support this, in terms of fuel consumption and achievable power ratings. Measures start with active exhaust gas cooling in the form of an integrated exhaust manifold, already implemented on many turbocharged gasoline engines. Water injection can extend the stoichiometric operation up to high power from 120 kW/L to above 170 kW/L and will be the choice for concepts prioritizing power and emissions over fuel consumption. 22 April 2021 Figure 7: Modular cylinder head and valve train assembly. On the other hand, Miller-cycle valve timing with high geometric compression ratio and extended expansion offers a route to improve brake thermal efficiency while limiting the achievable power density. Power density can be maintained by increasing boost pressure to compensate for the short valve-opening duration. Variable compression ratio (VCR) is an enabler to maximize the potential of Millerization for higher- performance variants. The implementation as a 2-step system using a switchable connecting rod design with hydraulic actuation has been described in detail: https://www.sae. org/publications/technical-papers/content/2017-01-0634/. As shown, the 2-step VCR with a compression ratio range of 10 at part load to 15 at full load gives most of the benefit expected from a continuously variable system. In combination with variable intake valve lift, VCS proves to be very effective both in view of stochiometric range and minimum fuel consumption. The efficiency targets for next-generation combustion engines will AUTOMOTIVE ENGINEERING ALL IMAGES: AVL *https://www.sae.org/publications/technical-papers/content/2017-01-0634/