Optimization of Phase Shift-Based Capacitive Sensor for Water Content Detection in Biodiesel

Biodiesel has attracted the interest of both researchers and industries as a substitute for fuel oil. However, it still faces issues that need to be resolved, including the quality of biodiesel water content. The presence of water in biodiesel may affect the spray and combustion properties of the engine and can damage the biodiesel diesel mixture. In this paper, we design and construct a non-intrusive phase shift-based capacitive detector to measure the water content of biodiesel. The sensor is designed as semi-cylindrical concave electrodes mounted on the outer wall of a pipe, where signal conditioning circuits and control software are prepared for real-time measurement. A simulation-based transfer function analysis is conducted to investigate the influence of the two input driving compensating signals of capacitance-to-voltage converter on the phase difference. The optimum results are obtained when the value of one signal gain is half that of another gain. The experimental results also confirm such optimum conditions. Measurement of the water content concentration in biodiesel B100 is also performed, which indicates that the capacitive sensor system successfully detects the change in small water concentration in biodiesel.