Exhaust emission features of variable compression ratio (VCR) diesel engine

One of the important design parameters for internal combustion engines is the geometric compression ratio epsilon. It is defined by the ratio of the maximum volume of the combustion chamber Vmax at the bottom dead centre (BDC) piston position and a minimum volume of the combustion chamber Vmin at the top dead centre (TDC) piston position. Conventional engines have this parameter set unchangeable, what is not the solution ensuring optimal benefits coming from the heat release in the combustion process, especially under altering conditions of load and speed in which they perform powering the road vehicles. It is reflected mainly in exhaust emission problem. Despite a considerable progress, further improving the ecological and energetic performances of the piston engines faces severe system limits, elimination of which requires major changes in engine design, including conversion the fixed compression ratio into the flexible one. For such innovative engine designs with so-called variable compression ratio VCR feature the geometric compression ratio parameter is as the one of the operation regulators. Due to the new development prospect the paper scope is an analysis and showing some results for the impact of compression ratio on the emissions of selected exhaust harmful components for a direct injection diesel engine. The schematics and prototype solutions for VCR technology are briefly presented too.