Investigation of compression temperature in highly charged spark-ignition engines

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.