The target of substantial CO_2 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, OD 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. Using 3D CFD, the expansion/scavenging/compression phases were computed in order to evaluate the scavenging characteristic and the in-cylinder aerodynamics level which mainly depend on the combustion chamber geometry and on the intake and the exhaust manifolds and strategies. The scavenging characteristic was then used in OD computations in order to evaluate each engine configuration in terms of power and consumption on the entire engine map. Indications were then deduced in order to guide the design office for the engine optimization. One configuration was chosen to be built and tested on the test-bench. In the present paper the specific methodology is described and several indications are given for the preliminary design of such a two-stroke Diesel engine.
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