Light-off Investigation of Oxymethylene Ether (OME) Considering the Presence of the Exhaust Components Heptane, Carbon, and Nitrogen Monoxide

Synthetic fuels and fuel blends like OMEs can contribute to tank-to-wheel CO2 emission savings. At the same time, it is known that these fuels have a lower exhaust temperature compared to conventional diesel. This effect has major impact on the exhaust after-treatment system, particularly in cold start conditions. This paper investigates the light-off behavior of exhaust gases containing OMEs by temperature-programmed oxidation experiments using a state-of-the-art oxidation catalyst. The main side product of catalytic oxidation of OMEs between 100 °C and the oxidation temperature T50, which was around 160 °C, was shown to be formaldehyde. While alkane oxidation, in this case heptane, was little influenced by OME oxidation, the oxidation temperature T50 of CO increases by more than 10 °C by OME addition. Nitrogen monoxide impeded the oxidation of OME in a similar way to the other components investigated. Due to the amount of FA produced and its toxicity, it could be concluded that it is necessary to heat up exhaust after-treatment systems of OME diesel engines even faster than conventional diesel exhaust after-treatment systems. The relatively high reactivity of OME on oxidation catalyst can be used by active thermal management approaches.

Combustion Behavior and Kinetics Analysis of Isothermal Oxidized Oils from Fengcheng Extra-Heavy Oil

The low-temperature oxidation (LTO) of heavy oil is of great significance for the combustion front stability, which directly influences the efficiency and safety of in-situ combustion (ISC). To provide feasible heating by artificial ignition before the implementation of ISC in the Xinjiang Fengcheng (FC) oilfields, this paper investigates the oxidation behavior of FC extra-heavy oil and its isothermal oxidized oils. Firstly, FC extra-heavy oil was subjected to isothermal oxidation experiments conducted utilizing an oxidation reactor, and the physical properties of the gaseous products and oxidized oils were analyzed. The combustion behavior of the FC extra-heavy oil and oxidized oils was then studied by non-isothermal thermogravimetry and differential scanning calorimetry. Subsequently, the Friedman and Ozawa–Flynn–Wall methods were adopted to perform kinetic analysis. Oxygen consumption was always greater than the production of CO and CO2, so oxygen addition reactions were the main pathway in heavy oil LTO. H/C decreased to 8.31% from 20.94% when the oxidation temperature rose from 50 °C to 150 °C, which deepened the oxidation degree. The density and viscosity of 200 °C to 350 °C oxidized oils increased at a slower rate, which may be related to the LTO heat effect. The change law of temperature interval, peak temperature, and mass loss of the oxidized oils had a good correlation with the static oxidation temperature. Compared with other oxidized oils, the peak heat flow and enthalpy of 350 °C oxidized oil increased significantly with high-temperature combustion, and were 42.4 mW/mg and 17.77 kJ/mol, respectively. The activation energy of 350 °C oxidized oil began to decrease obviously around a conversion rate of 0.4, which indicates that it was beneficial to coke deposition with stronger activity. Finally, we came up with LTO reaction mechanisms and put forward a reasonable preheating temperature for the application of ISC in FC oilfields.

Influence of Oxidation Temperature on Structure and Mechanical Properties of Titanium

Surface oxidation of pure titanium was performed in the atmosphere to increase the mechanical properties. The effect of oxidation temperature (650-900°C) for 2 h on the microstructure, composition, and mechanical properties of the treated samples was investigated using X-ray diffraction, hardness tester and indentation modulus tester, respectively. The diffusion rate of oxygen in grade-2 pure Ti with different processing temperatures discussed in present research. Based on a result of the examination, the surface hardness was increased first and then decreased as the processing temperature increased. And when the processing temperature at 850°C, the surface hardness reached the maximum value. In addition, the Young's modulus of the treated samples also showed a maximum value of 198.9 GPa for a processing temperature of 850°C. An oxidation condition of 850°C is considered optimal as it provides sufficiently high hardness during practical use.

Oxidation Mechanism of Al-Sn Bearing Alloys

Oxidation of Al-Sn bearing alloy occurs during production, processing and use, which reduces both alloy performance and performance of coatings applied to the alloy surface. Therefore, the oxidation mechanism of Al-Sn bearing alloy is studied at 25, 180, 300, and 500 °C. The oxidation morphologies of the alloy were observed by scanning electron microscopy (SEM), and the oxidation products were determined by X-ray diffraction (XRD). The oxidation weight gain curves were obtained by thermogravimetric analysis. The experimental results show that: Al-Sn bearing alloy is oxidized quickly to form Al2O3. As the oxidation temperature increases, Sn phase start to precipitate along the grain boundary and form networked spheroids of Sn on the alloy surface. The amount of precipitation increases with further increase of the oxidation temperature. Cracks and holes are left in the alloy. The oxide layer is mainly composed of Sn, SnO2, and Al2O3. At 25 °C, oxidation rate of Al-Sn alloy approach zero. At 180, 300, and 500 °C, the oxidation rate increases quickly conforming to a power function, and eventually remains stable at about 3 × 10−6 mg·mm−2·s−1.

Elemental Carbon and Its Fractions during Evolved Gas Analysis with Respect to Pyrolytic Carbon and Split Time

We demonstrated the relationships between elemental carbon (EC) and EC fractions during evolved gas analysis (EGA) for PM2.5 sampled at KOREATECH from 29 March 2018 to 12 May 2018. The EC concentrations were compared to the concentrations of equivalent black carbon to confirm that the level of EC concentrations analyzed in this study was valid. Among various EC fractions and their combination, EC1+EC3 fractions were best correlated with the EC concentrations. Especially, dominant EC fraction was related with the dependence of carbon oxidation quantity on the oxidation temperature. We also examined the relationships between pyrolytic carbon (PyC) and EC concentration with respect to the split time. PyC was correlated with the split time in the phase of oxygen-helium mixture. PyC was close to zero for the split time in the helium phase. It is novel, as far as the authors know, that the correlation between PyC and the split time under NIOSH 5040 protocol was reported with regard to EGA. We believe that our study helps to identify what causes uncertainty in the quantification of PyC.

Friction and Wear of Oxide Scale Obtained on Pure Titanium after High-Temperature Oxidation

High-temperature oxidation was performed at temperatures from 600 to 750 °C over a period of 24 h and 72 h. It was shown in the study that the oxide scale became more homogeneous and covered the entire surface as the oxidation temperature increased. After oxidation over a period of 24 h, the hardness of the produced layers increased as the oxidation temperature increased (from 892.4 to 1146.6 kgf/mm2). During oxidation in a longer time variant (72 h), layers with a higher hardness were obtained (1260 kgf/mm2). Studies on friction and wear characteristics of titanium were conducted using couples with ceramic balls (Al2O3, ZrO2) and with high-carbon steel (100Cr6) balls. The oxide films produced at a temperature range of 600–750 °C led to a reduction of the wear ratio value, with the lowest one obtained in tests with the 100Cr6 steel balls. Frictional contact of Al2O3 balls with an oxidized titanium disc resulted in a reduction of the wear ratio, but only for the oxide scales produced at 600 °C (24 h, 72 h) and 650 °C (24 h). For the ZrO2 balls, an increase in the wear ratio was observed, especially when interacting with the oxide films obtained after high-temperature oxidation at 650 °C or higher temperatures. The increase in wear intensity after titanium oxidation was also observed for the 100Cr6 steel balls.

High-Temperature Oxidation Behavior of Fe–10Cr Steel under Different Atmospheres

Using a thermogravimetric analyzer (TGA), Fe–10Cr steel was oxidized in dry air and in a mixed atmosphere of air and water vapor at a relative humidity of 50% and a temperature of 800–1200 °C for 1 h. The oxidation weight gain curves under the two atmospheres were drawn, the oxidation activation energy was calculated, and the phase and cross-sectional morphology of the iron oxide scales were analyzed and observed by X-ray diffractometry (XRD) and optical microscopy (OM). The results showed that when the oxidation temperature was 800 °C, the spheroidization of Fe–10Cr steel occurred, and the oxidation kinetics conformed to the linear law. At 900–1200 °C, the oxidation kinetics followed a linear law in the preliminary stage and a parabolic law in the middle and late stages. In an air atmosphere, when the oxidation temperature reached 1200 °C, Cr2O3 in the inner oxide layer was partially ruptured. In an atmosphere with a water vapor content of 50%, Cr2O3 at the interface reacted with H2O to generate volatile CrO2(OH)2, resulting in a large consumption of Cr at the interface. At the same time, a large number of voids and microcracks appeared in the iron oxide layer, which accelerated the entry of water molecules into the substrate, as well as the oxidation of Fe–10Cr steel, and caused the iron oxide scales to fall off. Due to the volatilization of Cr2O3 and the conversion from internal oxidation to external oxidation, the internal oxidation zone (IOZ) of Fe–10Cr steel under water vapor atmosphere decreased or even disappeared.