One of the critical parameters for the occurrence of spark-knock and pre-ignition of highly charged spark-ignition (SI) engines is the compression temperature. The investigation of the compression temperature and a better understanding of the combustion behaviour inside the combustion chamber are of great importance for avoiding these phenomena and also for further downsizing of engines. Pure rotational coherent anti-Stokes Raman spectroscopy (RCARS) is an innovative tool providing information on the compression temperature by using only two small line-of-sight optical accesses on the cylinder wall. In this work, RCARS measurements were performed in motored and fired operation, and the results obtained from RCARS spectra have been used in combination with isentropic calculations to improve the accuracy of the compression temperature determination. Studies on the compression temperature by the variation of the intake temperature, the engine load, and the fuel were conducted and the influence of evaporation enthalpy on the compression temperature is discussed.

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This work summarizes the numerical analysis of the effect of early fuel injection on the charge motion in a direct injection spark ignition engine concerning cyclic fluctuations of the flow field. The combination of the scale-resolving turbulence model “Scale Adaptive Simulation” and post-processing routines for vortex trajectory visualization allows for a detailed insight into the temporal resolved and cycle-dependent behavior of the charge motion. In the first part, a simplified engine set-up is presented and used as a validation case to ensure correct behavior of the turbulence model and post-processing routines. In the second part, the computational fluid dynamics model of the real engine is introduced. The application of the proposed vortex tracking algorithm is shown, and a short discussion about the transient behavior of the charge motion in this engine set-up is given. The third part describes the analysis of the influence of the fuel injection on the charge motion at different engine speeds from 1000 to 3000 r/min and variations of the intake pressure from 1 to 2 bar. Finally, the impact on different flow field properties at possible ignition timings is discussed. Changes in mean flow field quantities as well as in aerodynamic fluctuations are found as a consequence of fuel injection.

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