What will be the future combustion and fuel-related technology challenges?

Engine and fuels for transport are facing a double challenge: ○ bring local pollution to the levels requested by W.H.O. city air quality standard, ○ reduce CO 2 emission in order to minimize global warming risk. These goals stimulate the development of both conventional and alternative engines and fuel technologies. New combustion processes known as Controlled Auto-Ignition (CAI ) for gasoline engines and Homogeneous Charge Compression Ignition (HCCI) for diesel engines are the subjects of intensive research world-wide and particularly at IFP. Because of the thermo-chemical conditions of the charge, the thermal NOx formation is, in principle, much lower than with the typical flames of conventional engines. Indeed, these new combustion processes bring down NOx to very low level without post-treatment, while maintaining a very high thermodynamic efficiency of the combustion. The control of such combustion is complex due to the number of technological and fuels parameters to take into account. Considering fuels, it appears that their formulation could have an important impact on the optimal operating ranges of both CAI or HCCI. Then, tailored fuel formulation, based on a close selection of qualities of combustion initiation, vapor formation, blend preparation, interaction with residual gas and flame diffusion, will strongly contribute to the success of these new combustion processes. The targets of these new combustion modes induce to consider new key parameters for fuels. For example, fuel parameters, such as the octane of the gasoline or the cetane of the diesel fuel, which have key values for conventional combustion might not have similar value for CAI and HCCI combustion. One further view could even raise the question of one unique fuel for a unique combustion process.