Temperature compensation of fluorescence intensity-based fiber-optic oxygen sensors using modified Stern–Volmer model

In practical sensing applications, temperature effects are of particular concern, and hence it is necessary to develop the means to correct the fluorescence intensity measurement in accordance with the working temperature. Accordingly, this study develops a modified Stern–Volmer model to compensate for the temperature drift of oxygen concentration measurements obtained using fiber-optic sensors. The oxygen sensors considered in this study are based on teraethylorthosilane (TEOS)/n-octyltriethoxysilane (Octyl-triEOS) or n-propyltrimethoxysilane (n-propyl-TriMOS)/3,3,3-trifluoropropyltrimethoxysilane (TFP-TriMOS) composite xerogels doped with platinum meso-tetrakis(pentafluorophenyl)porphine (PtTFPP).

The experimental results are fitted to the modified Stern–Volmer model in order to compute suitable values for a temperature compensation coefficient at different working temperatures. It is found that the proposed temperature compensation method reduces the difference in the oxygen concentration measurement for working temperatures in the range of 25–70 °C as compared to data without compensation. The linearity and sensitivity of PtTFPP-doped n-propyl-TriMOS/TFP-TriMOS sensor are better than PtTFPP-doped TEOS/Octyl-triEOS sensor for working temperatures in the range of 25–70 °C.

The proposed approach could provide a straightforward and effective means of improving the accuracy of fiber-optic oxygen sensors if a variable attenuator is designed according to the temperature compensation coefficient. Thus, the fiber-optic oxygen sensor with a variable attenuator could work in a broad temperature range without using a temperature sensor.     

Tribo-electrification mechanisms for self-mated carbon steels in dry severe wear process

The tribo-electrification mechanisms and wear behavior are investigated for self-mated metal pairs of iron and carbon steels (0.2% C, 0.45% C, 0.7% C) under the dry severe wear condition in the reciprocating friction tester. Results show that with increasing the carbon percentage of the steels, the formation mechanism of the wear particle varies from the macro-asperity removal of the slip-tongue to the micro-asperity removal of the wedge. Meanwhile, the variation of tribo-electrification with the sliding time appears to be more serious. The polarity of tribo-electrification is significantly influenced by the difference between the wear losses of the plate and pin specimens. This means the tribo-electrification is mainly caused by the effect of the material transfer for self-mated carbon steels. Under the higher surface hardness, the mean amplitude of the friction coefficient is decreased and the mean amplitude of tribo-electrification is increased. Results also show that the mean amplitude of tribo-electrification for self-mated carbon steels is linearly proportional to the electric resistivity and the relative wear rate, but inversely to the dynamic real contact area.     

Plasma-assisted catalytic reforming of propane and an assessment of its applicability on vehicles

A plasma-catalyst hybrid converter operating under atmospheric pressure was developed and a series of experiments were carried out to investigate its hydrogen-rich gas production performance. The hydrocarbon fuel used was propane. In the converter, electrons were energized by an electric field to ionize the propane and air mixture. In addition, a catalyst was installed at the downstream of the reformer to enhance the production of hydrogen-rich gas. Firstly, a parametric study of the operating parameters was carried out to assess the reforming performance of the plasma-catalyst hybrid converter on producing hydrogen-rich gas. This was followed by a feasibility assessment with an engine supplemented by the hydrogen-rich gas produced by the hybrid converter. The ratio of combustion assisting and combustion impeding (A/I) composition was analyzed. It is anticipated that the results would serve as a good guideline for setting-up parameters when reforming hydrocarbon fuels onboard vehicles.     

Application of Fabry-Pérot and fiber Bragg grating pressure sensors to simultaneous measurement of liquid level and specific gravity

An approach is proposed for obtaining simultaneous measurements of the level and specific gravity of a liquid using a dual-pressure-sensor system comprising a fiber Bragg grating (FBG) pressure sensor and a Fabry-Pérot (FP) pressure sensor. In the FBG sensor, the pressure is derived from the FBG wavelength shift induced when the sensor is immersed in the liquid. Meanwhile, in the FP sensor, the pressure is calculated from the change in cavity length which takes place when the sensor is immersed. The advantageous concept of the dual-pressure-sensor system is atmospheric pressure compensation. The experimental results show that the FBG and FP pressure sensors have sensitivities of 0.1495 nm/kPa and 0.1569 μm/kPa, respectively. Analytical formulae are derived for the level and specific gravity of the liquid in terms of the FBG wavelength shift, the change in cavity length, and the vertical separation distance between the two sensors.