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Efficiency of spark ignition (SI) engines is limited towards high loads by the occurrence of knock, which is linked to the octane number of the fuel. Running the engine at its optimal efficiency requires a high octane number at high load whereas a low octane number can be used at low load. Current project aims at developing an “Octane on Demand” (OOD) concept: the fuel octane number is adjusted “on demand” to prevent knock occurrence by adapting the fuel RON injected in the combustion chamber. Thus, the engine cycle efficiency is increased by always keeping combustion phasing at optimum. This is achieved by a dual fuel injection strategy, involving a low-RON base-fuel and a high-RON octane booster. The ratio of fuel quantity on each injector is adapted to fit the RON requirement function of engine operating conditions. This OOD concept requires a good characterization of the octane requirement needed to run the engine at its optimal efficiency over the entire map.

Reduction of CO2 emissions is becoming one of the great challenges for future gasoline engines. The aim of the current research program (OOD: Octane On Demand) is to use the octane number as a tuning parameter to simultaneously make the engine more efficient and reduce CO2 emissions. The idea is to prevent knock occurrence by adapting the fuel RON injected in the combustion chamber. Thus, the engine cycle efficiency is increased by keeping combustion phasing at its optimum. This is achieved by a dual fuel injection strategy, involving a low-RON base fuel (Naphtha or Low RON cost effective fuel) and a high-RON octane booster (ethanol). The ratio of fuel quantity on each injector is adapted at each engine cycle to fit the RON requirement as a function of engine operating conditions. A first part of the project, described in [18], was dedicated to the understanding of mixture preparation resulting from different dual-fuel injection strategies.