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A novel arrangement of four fibres was used to probe the fuel concentration at 4 different positions along the longitudinal axis of a transparent engine cylinder at 5 different times during the induction and compression strokes. By using a reference calibration experiment we derived variations in the air/fuel ratio at times in the engine cycle when the inlet and exhaust valves are closed. We used this technique to examine the effects of inlet-port swirl and injection timing for a number of fuels including 2 refinery streams. We also traced the different spatial distributions of spectrally resolved aromatic and paraffinic components from the same fuel during engine operation.

Various fluorescence tracers were assessed for their applicability for simultaneously measuring fuel distributions of different volatility classes. Tracers were chosen to show significantly different boiling behaviour representing three volatility classes of non-fluorescing multi-component fuels. Fluorescence properties of the markers were investigated using a heated static high-pressure cell with respect to emission behaviour, temperature and pressure dependence and quenching influences. A combination of ketonic and aromatic tracers appeared to be ideal for simultaneous imaging purposes since fluorescence is emitted in separate spectral regions with little overlap. Simultaneous measurements of the fuel distribution of two volatility classes were performed in a port fuel injected engine showing significant differences in the fuel distributions of low and mid boiling fractions in early stages of compression.