Development of Diesel combustion chambers for automotive engines: potential of the 2 valve design

摘要

As customers are becoming more and more exigent for quality and cost effective products, the Diesel engine of the 21st century must provide much more than low fuel consumptions. On that way, the efficient improvements in turbocharging technology and the development of reliable and versatile injection devices have for instance allowed it to become fun to drive with a smooth noise level compatible with the most comfortable limousines. Nevertheless, the confirmation of this success in the forthcoming years highly depends on the capability of the engineers to drastically reduce the natural engine out emissions of pollutant gases and therefore to limit the after treatment overall cost. This challenge clearly is the key point to secure the role of the Diesel power train as the major actor for reducing CO{sub}2 rejections and global warming. If the recent development of the 4 valve technology has allowed to achieve power densities higher than 60 kW/l, it is meaningful to wonder about the future of the 2 valve design whose fabrication cost and compactness for small and medium size vehicles remain first order advantages. Besides a reduced air filling at high engine speed, this design generally leads to non symmetrical combustion chambers and is therefore harder to optimize. Aim of this paper is to show how these difficulties have been solved on middle range engines while respecting Euro IV regulation, and to identify potential solutions for the future.