UV laser-diode fluorescence fibre-sensor for commercial gasolines

In this paper, we report on a fibre-optic probe, coupled to a 404 nm laser-diode, as a fluorescence sensor for monitoring of commercial gasolines. The principle of operation of the sensor is based on quantifying the intensity of the Stokes-shifted fluorescence from some of the heavier polycyclic aromatic hydrocarbons C_xH_y, (x,y) ≥ (14,10), present in gasolines as minor constituents. The relative sensitivity of such a fibre-optics fluorescence probe, as a function of its geometry, is calculated and its performance is investigated for gasolines in the liquid and gaseous phases. The spatial and temporal resolutions achievable by the sensor are discussed as a function of design parameters. Principal component analysis has been applied on a dataset of 36 measured spectra of liquid commercial gasolines and the scores plot of the first two components has allowed the sensor to distinguish between different forecourt suppliers, as well as fuel varieties (unleaded, low-sulphur, etc.). The detection of vapour concentrations of retail gasoline fuel is demonstrated in the range of 0.4% to 120% of combustion stoichiometry at 10 bar and 180°C.