In the competition for the powertrain of the future the internal combustion engine faces tough challenges. Reduced environmental impact, higher mileage, lower cost and new technologies are required in order to maintain its global position both in public and private mobility.
For a long time, researchers have been investigating the so called Homogeneous Charge Compression Ignition (HCCI) that promises a higher efficiency due to a rapid combustion - i.e. closer to the ideal thermodynamic Otto cycle - and therefore more work and lower exhaust gas temperatures. Consequently, a rich mixture to cool down the turbocharger under high load may no longer be needed. As the combustion does not have a distinguished flame front it is able to burn very lean mixtures, with the potential of reducing HC and CO emissions. However, until recently, HCCI was considered to be reasonably applicable only at part load operating conditions.
The 3D-CFD engine development tool QuickSim, which has been developed at the FKFS in cooperation with the IVK/University of Stuttgart, is able to simulate the entire flow path of the engine, including both flame propagation and HCCI combustion. In a recent project with the German Aerospace Center (DLR) it was possible to calibrate the parameters of the auto-ignition HCCI model using a highly variable free piston linear generator.
This paper addresses the potential of virtual engine development in the creation of a new combustion process for series engines. The described process is called Spark-Assisted Compression Ignition (SACI). It utilizes a pre-chamber spark plug to initialize and control the following auto-ignition. This prevents accidental combustion and also ensures an auto-ignition that is less dependent on the environment and transient conditions, while maintaining the efficiency and emission advantages of a conventional HCCI combustion (auto-ignition of the air-fuel mixture merely regulated by local thermodynamic variables in the combustion chamber).
