Modern fuel injection systems for gasoline direct-injection (GDI) engines operate with high injection pressures that provide good atomisation but also result in increased spray momentum with fuel droplets travelling across the combustion chamber and potentially impinging onto piston and liner surfaces, especially before the engine becomes fully warm. One of the adverse consequences of the injectors becoming fouled with deposits is a change in the spray pattern and increased spray liner interaction, the impact of which is discussed from both the perspective of the lubrication and the combustion.

In the second part of the talk an in-situ Raman spectroscopy method is described whereby a single-cylinder GDI engine is specially modified to measure fuel concentration within the lubricant film on the cylinder liner in real time. Using a calibration curve based on known GTL8 oil and iso-octane mixtures, the Raman intensity ratio allowed estimation of fuel dilution during and after injection under motoring conditions. Although oil fluorescence sometimes interfered with the signal, the study showed that this approach is a feasible way to monitor fuel–lubricant mixing directly inside an operating engine.