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The interaction of turbulent premixed methane combustion with the surrounding flow field can be studied using optically accessible test rigs such as a rapid compression expansion machine (RCEM). The high flexibility offered by such a test rig allows its operation at various thermochemical conditions at ignition. However, limitations inherent to such test rigs due to the absence of an intake stroke do not allow turbulence production as found in IC-engines. Hence, means to introduce turbulence need to be implemented and the relevant turbulence quantities have to be identified in order to enable comparability with engine relevant conditions. A dedicated high-pressure direct injection of air at the beginning of the compression phase is considered as a measure to generate adjustable turbulence intensities at spark timing and during the early flame propagation.

This paper compares the fuel consumption of a lightweight passenger car for three different SI engine concepts, all with rated power of about 40 kW: a classical SI engine with moderate maximum speed, a low-displacement but high-speed engine that exploits the maximum allowed mean-piston speed and a low-displacement but highly supercharged engine with moderate maximum speed. All engines are simulated with a thermodynamic process simulator, the results of the supercharged version are validated with experiments. For each engine, a CVT and an automated gearbox is considered. Fuel consumption is estimated with a quasi-static driving cycle simulator which is based on engine fuel consumption maps and physical models of the vehicle with all its relevant subsystems. The simulations are performed for constant vehicle speed as well as for US and European driving cycles.