A Major Origin of Cyclic Energy Conversion Variations in SI Engines: Cycle-by-Cycle Variations of the Equivalence Ratio and Residual Gas of the Initial Charge

It is demonstrated that the cycle-by-cycle variations in the IMEP of a realistic automobile engine with port fuel injection are dominated by the cyclic fluctuations of the equivalence ratio and residual gas content of the initial charge at least for certain operating conditions. A new spontaneous Raman scattering technique yields simultaneously the densities of fuel, O₂, N₂, and H₂O prior to ignition. In-cylinder equivalence ratio and residual gas content are determined quantitatively with high precision by ratios of densities. Prior-cycle effects are observed and explained by the properties of the initial charge. The results show that cyclic variability can be explained and may he consequently reduced by the help of the new measurement system.