A photometric-turbidimetric fusion sensor for measuring the water content in diesel with sensitivity increase by the extended infrared path capillary

Petroleum-based diesel is the main energy supply for heavy-duty vehicles and industrial equipment. Excessive water in the diesel would affect engine performance directly and even lead to serious accidents. In this paper, a new on-board compact sensor for detecting water content in diesel is proposed, which is composed of LED, photodetector, special metal waveguide capillary and ultrasonic cavity. Especially, the metal waveguide capillary with extended optical path can significantly improves the measurement accuracy meanwhile decrease the size. The small ultrasonic oscillation cavity is connected with the metal waveguide capillary to ensure the saturated water droplets to be evenly mixed with petroleum-based diesel before being detected. Then, the photometric - turbidimetric fusion method is proposed to measure the total water contents in different states (i.e., dissolved water, emulsified water and free water) in the diesel. The designed metal waveguide capillary with extended optical path improves sensor accuracy by the way of multiple reflections of light. In addition, the sensor is installed in the line between the fuel tank and the engine, then, the actual water pumped into the engine can be accurately measured. The experimental results show that the root mean square of the prediction error (RMSEP) is only 7.34 ppm, which is much lower than the optical sensor based on non-dispersive infrared spectroscopy of 18.6 ppm. The sensor fabricated in this paper finds application in detecting water content in diesel, which has the advantages of high sensitivity, small volume, and are suitable for on-board detection.