<div class="section abstract"><div class="htmlview paragraph">The further increase in the efficiency of heavy-duty engines is essential in order to reduce CO<sub>2</sub> emissions in the transport sector. This is also valid for the future use of alternative fuels, which can be CO<sub>2</sub>-neutral, but can cause higher total costs of ownership due to higher prices and limited availability. In addition to thermodynamic optimization, the reduction of mechanical losses is of great importance. In particular, there is a high potential in the piston bore interface, since continuously increasing cylinder pressures have a strong influence on the frictional and lateral piston forces. To meet these future challenges of increasing heavy-duty engine efficiency, AVL has developed a floating liner engine for heavy-duty applications based on its tried and tested passenger car floating liner concept. This article describes the concept of the friction single-cylinder engine developed to measure both the frictional forces and the lateral forces that occur between the piston assembly and cylinder liner during fired engine operation. Four force sensors convert the floating movement of the liner group into the corresponding frictional force. Due to the crank angle based measurement, a very detailed analysis of measures to increase mechanical efficiency of the piston bore interface is possible. In addition, the frictional power can be derived and used to evaluate the CO<sub>2</sub> potential of the technologies investigated. The design of the single-cylinder engine has a high degree of flexibility to enable quick component changes and the use of different cranktrains. In a first study, a variation in the crankshaft offset and the potential of this measure to increase engine efficiency are investigated. The results show a clear influence of the cranktrain geometry on the lateral piston force and also on the frictional force during the upstrokes and downstrokes. This measurement campaign confirms the possibilities of the system to contribute to the development of future highly efficient heavy-duty engines.</div></div>
