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A variable compression ratio (VCR) technology, that has a new piston-crankshaft mechanism with multi links, has been patented and developed by Nissan for some years (This technology has been detailed in previous SAE paper 2003-01-0921 and 2005-01-1134). This paper will present the use of this VCR technology for Diesel engine. The objective set with the use of VCR for Diesel engine is mainly to reduce as much as possible engine out emission to prepare for long-term, more strict emission standards. Results presented will include the description of the 2l Diesel VCR engine and its VCR mechanism adapted to Diesel constraints. Combustion tests have been performed with the use of HCCI (Homogeneous Charge Compression Ignition) combustion. This technology is still in a research phase in Renault: the adaptation of VCR technology to a Diesel engine consists in the modification of several parts with the addition of lower links, control links and control shaft.

Thanks to a high specific torque, associated to a low fuel consumption, the market share of the Diesel engine has not stopped increasing during the last decade. Nevertheless, due to the strong emissions regulations to come, the challenge of the Diesel will be to save its advantage in CO2 and to drastically reduce NOx and particulate emissions, whilst offering the save driving pleasure. Hence new concepts of combustion are in development in order to keep NOx emissions as low as possible at an acceptable cost. The homogeneous combustion, by generating a lower pollutant level directly in the combustion chamber, seems to be a very promising way in this direction. Especially, the NADI™ concept, developed by IFP has already shown a high potential in NOx and particulate simultaneous reduction, but up to now its relative low specific power at full load compared to the next generation of conventional Diesel engines could be a major drawback for a global application.