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The target of substantial CO₂ reductions in the spirit of the Kyoto Protocol as well as higher engine efficiency requirements has increased research efforts into hybridization of passenger cars. In the frame of this hybridization, there is a real need to develop small Internal Combustion Engines (ICE) with high power density. The two-stroke cycle can be a solution to reach these goals, allowing reductions of engine displacement, size and weight while maintaining good NVH, power and consumption levels. Reducing the number of cylinders, could also help reduce engine cost. Taking advantage of a strong interaction between the design office, 0D system simulations and 3D CFD computations, a specific methodology was set up in order to define a first optimized version of a two-stroke uniflow diesel engine. The main geometrical specifications (displacement, architecture) were chosen at the beginning of the study based on a bibliographic pre-study and the power target in terms.

In spite of the increasingly stringent emission standards, the constant growth of road traffic contributes to climate change and induces detrimental effects on the environment. The European REWARD project (REal World Advanced Technologies foR Diesel Engines) aims to develop a new generation of Diesel engines complying with stricter post Euro 6 legislation and with lower CO2 emissions. Among the different technologies developed, a fuel-efficient two-stroke Diesel engine suited for C-segment passenger cars will be designed and experimentally evaluated. One major challenge for two-stroke engines is the achievement of an efficient scavenging. As the emptying of the in-cylinder burnt gases and the filling by fresh gases is performed at the same time, the challenge consists in removing as much burnt gases as possible while avoiding the by-pass of fresh air toward the exhaust line.

A full 3D Large Eddy Simulation (LES) of a four-stroke, four-cylinder engine, performed with the AVBP-LES code, is presented in this paper. The drive for substantial CO₂ reductions in gasoline engines in the light of the global energy crisis and environmental awareness has increased research into gasoline engines and increased fuel efficiencies. Precise prediction of aerodynamics, mixing, combustion and pollutant formation are required so that CFD may actively contribute to the improvement/optimization of combustion chamber, intake/exhaust ducts and manifold shapes and volumes which all contribute to the global performance and efficiency of an engine. One way to improve engine efficiency is to reduce the cycle-to-cycle variability, through an improved understanding of their sources and effects. The conventional RANS approach does not allow addressing non-cyclic phenomena as it aims to compute the average cycle.