Spatially Resolved Air-Fuel Ratio and Residual Gas Measurements by Spontaneous Raman Scattering in a Firing Direct Injection Gasoline Engine

Single-cycle air-fuel ratio (AFR) and residual gas content of the fresh charge have been measured in a firing spark ignition engine with direct fuel injection. Various engine parameter sets concerning mixture formation have been compared. The measurement setup is sensitive enough to resolve cyclic deviations of spatial air-fuel ratio gradients. This has been achieved by Linear Raman Scattering (LRS), that is performed along a line (1D LRS) in the combustion chamber of the IC engine using a spatially resolving optical multichannel analyzer as the detector. The present work aims to investigate the feasibility and accuracy of such measurements under approximately realistic conditions. The combustion chamber of the engine has been slightly modified for optical access, so that its shape is still very similar to realistic engines. The engine has been operated at homogeneous load conditions with a multi-component model fuel. Potential sources of inaccuracy of the single-cycle LRS measurements, such as photon statistical noise and LIF interferences from PAHs (polyaromatic hydrocarbons), are discussed and quantified in detail. Further information on the achieved spatial resolution is also given.