Octane-on-Demand as an Enabler for Lowering the CO_2 Footprint of Mobility: From Engine Tests to Vehicle Demonstration and Life Cycle Analysis

摘要

Although recent technologies like downsizing and boosting have significantly contributed to increasing the efficiency of spark ignition engines, the engine performance still remains limited by knock, which is linked to the fuel resistance property to auto-ignition. However, a high-RON quality fuel is not needed all the time to achieve the maximum efficiency of a spark ignition engine, especially in urban driving conditions. Based on this, having a co-optimized fuel engine technology whereby the fuel anti-knock quality is customized to match the real-time requirements of an otherwise conventional spark-ignition engine, fully makes sense. This is the essence of so-called octane-on-demand. This paper reviews the major achievements of a dual fuel technology co-approach to address the CO_2 challenge from a complete well-to-wheel standpoint, and paves the way for an ultimate and innovative on-board fuel upgrading system. Beyond the characterisation of the octane requirement of an up-to-date 1,6 L GDI engine, extensive experimental tests enabled the design of the most promising fuel couple and engine hardware technology. Of the various fuel combinations tested, RON 71 low octane gasoline as the primary fuel, and ethanol as the octane booster were identified as a relevant fuel couple. Driven by improving the CO_2 emissions while controlling both together, the fuel booster consumption, the knock management in transient, and the direct injector fouling risk, the engine architecture with low-octane gasoline in PFI and ethanol booster in GDI were revealed as perfectly appropriate. OD simulations, representative of a C segment vehicle over the WLTC cycle, showed that the OOD concept delivers 4% of CO_2 benefit (tailpipe emissions) when compared to the original engine version with E5. This figure was confirmed when running a fully drivable light Peugeot 308 vehicle. A complete CO_2 analysis from well-to-wheel identified that the CO_2 intensity of the current OOD concept is around 9% lower than conventional RON 95 E5 fuel. Finally, recent simulations demonstrated that 25% of tank-to-wheel CO_2 emission reduction is achievable when mixing the OOD approach with the up-most technology trends including engine rightsizing, compression ratio increase, EGR and mild-hybridization.