New HCCI/CAI combustion process development : Methodology for determination of relevant fuel parameters

To pass the simultaneous emission requirements for near zero pollutant and for low CO2 , which are the challenges of future powertrains many research studies are currently carried out over the world on new engine combustion processes, such as the Controlled Auto-Ignition (CAITM ) for gasoline engines and the Homogeneous Charge Compression Ignition (HCCI) for diesel engines. These new processes have the potential to reduce, by a factor from 10 to 100, the NOx and articulate emissions (PM) in comparison with a typical gasoline or diesel engine. The main issue in the development of such combustion modes remains the limited range of engine speed and load that enable good engine running, according to required levels for NOx and noise emissions. One of the most promising ways to increase the CAI combustion range lies in the formulation of dedicated fuels, optimised to enhance combustion initiation by modifying and controlling the auto-ignition characteristics and/or the fuel physical and chemical properties. To select the fuels, a new procedure has been set-up that allows a better characterization of the fuel impact on engine running in CAI, for various conditions of speed and load. The use of this methodology for a large set of fuels, formulated according to their auto-ignition characteristics, volatility and chemical composition has underlined the complexity of the action of fuel and has enabled one to point out the most influent fuel characteristics to over as large as possible requirements.