The need for significant reduction of fuel consumption and CO 2 emissions has become the major driver for development of new vehicle powertrains today. For the medium term, the majority of new vehicles will retain an internal combustion engine (ICE) in some form. The ICE may be the sole prime mover, part of a hybrid powertrain or even a range extender; in every case potential still exists for improvement in mechanical efficiency of the engine itself, through reduction of friction and of parasitic losses for auxiliary components.A comprehensive approach to mechanical efficiency starts with an analysis of the main contributions to engine friction, based on a measurement database of a wide range of production engines. Thus the areas with the highest potential for improvement are identified.For each area, different measures for friction reduction may be applicable with differing benefits. The proposed measures may be cost intensive, such as the addition of low friction coatings, or variable-capacity pumps, whereas others such as the optimization of cylinder bore distortion or coolant pressure drop by design measures have zero add-on cost. Some are concept level decisions only applicable to a new engine design; others can be implemented without significant investment even for an existing engine design.In this paper the major potential improvements to mechanical efficiency of the internal combustion engine are identified for each engine system. The improvements are ranked in terms of friction benefit and impact on product cost.

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