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In this study, layered double hydroxide (LDH) and molybdenum disulfide (MoS2) were used as additives to prepare lubricants. The morphology and particle distribution of the LDH and MoS2 were characterized using a scanning electron microscope and a laser particle size analyzer, respectively. Thermogravimetric analysis was used to compare the performance of the lubricants at high temperature. The extreme pressure and wear resistance performance of the lubricants were tested using a four-ball machine and a fretting-wear machine. Then, the lubricants were applied in a bolt fastener. The loosening torque and surface wear condition at high temperature were compared. By adding LDH and MoS2 to the lubricants, the extreme pressure and wear resistance performance and anti-seize performance at high temperature were improved significantly. The LDH showed better anti-seize performance than the MoS2 because of its strong and stable structure at high temperature. The MoS2 showed better anti-wear performance under a high load because of its soft layered structure. The MoS2 with a larger particle size showed better extreme pressure performance under a high load. The LDH and MoS2 played a synergistic effect under the conditions of high temperature and high load. [ABSTRACT FROM AUTHOR]

The detailed kinetic mechanisms for the reactions of hydrogen cyanide (HCN) and hydrogen isocyanide (HNC) with the methyl radical (CH3) are discussed. These are important reactions in combustion and Titan's atmosphere chemistry and were investigated at the CCSD(T)/cc-pVQZ//M06-2X/6-311++G(2df,2p) level of theory. The multiwell and multichannel potential energy surface (PES) was constructed. The rate constants were determined by using variational transition state theory (VTST) and Master Equation/Rice–Ramsperger–Kassell–Marcus (ME/RRKM) method over a temperature range of 300–2000 K and a pressure range of 1–10 000 torr. Corrections of the Eckart tunneling effect were included and the calculated results were in good agreement with the literature. A clear dependence of the reaction mechanism on temperature and pressure was revealed via detailed kinetic and species analysis. For the HCN reaction, the channel of C-addition forms an intermediate that is dominant at low temperatures and high pressures, leading to the total rate constant exhibiting a pressure dependence, but this dependence disappears at high temperatures. The H-abstraction channel is more competitive with increasing temperatures, but it is still not dominant. For the HNC reaction, the C-addition channel is dominant, and CH3CN and H constitute almost all the products. The proposed temperature and pressure-dependent rate constants can be used in the combustion and atmospheric model development for related systems. [ABSTRACT FROM AUTHOR]

In order to research the high-concentration CO2 effects on ignition delay time (IDT) of diesel surrogate fuel (70% n-heptane/30% toluene), a carbon dioxide effect (CDE) model is established, which considers fuel and ambient gas concentration, density, and temperature influence on autoignition under CO2/O2 atmosphere. Firstly, a chemical model of n-heptane/toluene is established, and the coupling, reduction, and simulation processes are carried out in chemical kinetic software with the IDT as the target parameter. Secondly, a constant volume combustion chamber (CVCC) visualization platform is built by incorporating a high-speed camera system and different working conditions are set in the CO2 volume fraction range (40%-70%) at 3.0 MPa and 850 K for an autoignition experiment. Thirdly, experiment and simulation results are discussed in air, 60% CO2/40% O2, 50% CO2/50% O2, and 40% CO2/60% O2 atmospheres, including the IDT, CO2 effects, temperature sensitivity, and OH radical rate of production (ROP). The results show that the CDE model well predicts the 70% n-heptane/30% toluene IDT under the CO2/O2 atmosphere and the average error in 60% CO2/40% O2 atmosphere is 5.29%. Besides, when the CO2 volume fraction increases from 40% to 60%, the CO2 thermal effect plays a leading role in the IDT prolongation and the OH radical ROP peak of R4 (O+H2O⟶2OH) decreases by 180%. [ABSTRACT FROM AUTHOR]