A Method to Detect the Mixed Petrol Interface by Refractive Index Measurement With a Fiber-Optic SPR Sensor

A method based on fiber-optic surface plasmon resonance (FO-SPR) to detect mixed petrol is proposed to realize real-time, rapid monitoring of the mixed petrol interface in transportation pipelines. When the sensing region of the FO-SPR sensor was immersed in the petrol sample, the mixed petrol could be detected by measuring the refractive index of the petrol, which responds to the resonance wavelength in the SPR curve. Numerical simulation was performed according to the optical fiber theory and the SPR principle to optimize the structural parameters of the sensor. The optimized sensor can reflect small changes of the refractive index for mixed petrol detection. Next, the end-reflection FO-SPR sensor was designed and fabricated. The fiber was rotated in addition to the revolution of the coating disc to realize a uniform coating of the circumferential surface of the fiber core during vacuum coating. A wavelength modulation optical measurement system with the FO-SPR sensor was constructed. Petrol 90#, Petrol 93#, Petrol 97#, and their mixtures were measured. The experimental results indicated that this method could detect different mixing ratios of petrol with good repeatability, which lays the technical foundation for fast and accurate online detection of the mixed petrol interface in transportation pipelines.