Ke Yang’s research while affiliated with Xi’an International Studies University and other places

Battery thermal management (BTM) is crucial for the lifespan and safety of batteries. Refrigerant cooling is a novel cooling technique that is being used gradually. As the core fluid of refrigerant cooling, refrigerants need to possess excellent properties while meeting environmental requirements. This paper elucidates the current state of refrigerants (single refrigerants and mixed refrigerants), synchronously summarizing them from the perspectives of refrigerant properties and refrigerant cooling (immersion and cold plate indirect). It outlines the advantages and disadvantages of single and mixed refrigerants as well as the research and development in the vehicle thermal management system (TMS). The choice of refrigerant directly affects cooling performance, and research on vehicle air conditioning (AC) systems can indirectly guide the BTM. R1234yf and R152a can directly replace R134a, while although R744 has a strong heating capacity, it cannot directly replace R134a. Specific mixed refrigerants reduce the global warming potential (GWP) and flammability issues, thereby improving system efficiency. Additionally, immersion cooling controls the temperature through container pressure. Coordinated control strategies are crucial for indirect cold plate cooling, offering broad prospects for optimizing the cold plate design and intelligent control. The selection of refrigerant and the optimal design of the cooling method greatly improve the thermal performance of the battery. This may promote the good development of BTM.

R134a, commonly used in air conditioning (AC) for electric vehicles, may be gradually limited because its global warming potential (GWP) is 1430. This study combined the advantages of R1234yf and R152a. PR state equation and vdW mixing rule are used to construct the mixing model. The performance of R1234yf/R152a at different mass ratios was analyzed, a new mixture R1234yf/R152a (mass ratio 60.5/39.5) was selected. The cycling performance of mixture and R134a under three different evaporation temperatures was further studied. The results show that R1234yf/R152a belongs to a near-azeotropic mixture. In cycling performance, the R1234yf/R152a per-unit refrigerating capacity (RC) of refrigerant mass is about 12.45 % higher than that of R134a, the per-unit RC of swept volume is about 5.21 % lower than that of R134a. In this case, the GWP is 56.93, and the cost is moderate. The safety grade is A2L, which can replace R134a without changing the original system.

Refrigerant indirect contact phase-change cooling system flows refrigerant into a cold plate and utilizes the phase-change to exchange heat with the battery. However, R134a, commonly used, is being gradually restricted due to its environmental impact. A new kind of near azeotrope mixed refrigerant R1234yf/R152a (mass ratio 60.5:39.5) is proposed under environmental protection and safety. Based on the fluid-structure interaction model, the evaluation of different indirect contact phase-change cooling systems for battery thermal management (BTM) using R1234yf/R152a is investigated. After obtaining battery (150 Ah, 3.2 V LiFePO4) parameters, heat generation power, and main test conditions through experiments, the thermal properties are numerically studied by computational fluid dynamics (CFD). At 1 C discharge rate, the temperature gradient (TG) of single battery and the maximum temperature difference (TD) among batteries are analyzed for two cases: The maximum TD among batteries of Case_b is 6.5°C lower than that of Case_a. In addition, the effect of the mixed refrigerant and traditional liquid cooling on the battery temperature is studied at different evaporation temperatures (ETs) (20°C, 25°C) and different mass flow rates (MFRs) (0.02, 0.10, and 0.18 kg/s). The results show that both the increase of inlet MFR and the reduction of inlet ET may significantly improve the battery module cooling rate. Compared with 0.02 kg/s, as the MFR increases, the temperature drop slopes to 9.56 and 11.2 at 20°C. The battery module temperature uniformity is improved with the increase of ET. Overall, the mixed refrigerant has advantages in temperature uniformity and consistency. The new mixed refrigerant plays a positive role in controlling battery temperature.

In order to further understand the high-temperature reaction process and pyrolysis mechanism of hydrocarbon fuels, the high-temperature pyrolysis behavior of n-tetracosane (C24H50) was investigated in this paper via the reaction force field (ReaxFF) method-based molecular dynamics approach. There are two main types of initial reaction channels for n-heptane pyrolysis, C-C and C-H bond fission. At low temperatures, there is little difference in the percentage of the two reaction channels. With the temperature increase, C-C bond fission dominates, and a small amount of n-tetracosane is decomposed by reaction with intermediates. It is found that H radicals and CH3 radicals are widely present throughout the pyrolysis process, but the amount is little at the end of the pyrolysis. In addition, the distribution of the main products H2, CH4, and C2H4, and related reactions are investigated. The pyrolysis mechanism was constructed based on the generation of major products. The activation energy of C24H50 pyrolysis is 277.19 kJ/mol, obtained by kinetic analysis in the temperature range of 2400-3600 K.

Coal-to-liquid (CTL) base oil, synthesized by Fischer–Tropsch process, has a good prospect for synthetic high-grade lube oil. However, the oxidation induction period of CTL base oil is short, and the oxidation stability is slightly worse. Oxidation stability determines whether the lubricating oil deteriorates during use, which directly affects the service life and high temperature performance of lubricating oil. In this study, the influence of antioxidant additives on the thermal oxidative degradation of CTL base oil was examined. The addition of diphenylamine (L57) and 2,6-di-tert-butyl-4-methylphenol (T501) can inhibit the formation of carbonyl group (C=O), and the oxidation stability of CTL base oil is significantly improved. The results of thermodynamic analysis show that L57 can obviously improve the thermal decomposition performance of CTL base oil. The molecular structure plays an important role in the activation energy for the oil samples. CTL base oil model was established by the experiment result of 13C NMR. Molecular dynamics simulation studies show that the effect of antioxidant can be quantified and compared by the diffusion of antioxidants in CTL base oil. The smaller the diffusion coefficient of the antioxidant in CTL base oil is, the smaller the free volume of O2 in CTL base oil and antioxidation system is, and the better the antioxidation performance is. This study hopes to provide some guidance for the application of CTL base oil in high-grade lube oil market.

The combustion and emission characteristics of n-butanol/coal-derived naphtha blends in homogeneous charge compression ignition (HCCI) combustion mode were experimentally researched on a retrofitted diesel engine. The effects of intake temperature (Tin) and excess-air coefficient (λ) were mainly analyzed. The results show that the peak in-cylinder pressure (Pmax) and peak heat release rate (HRRmax) of all tested fuels show an overall increasing trend as Tin rises. The combustion gets faster and more stable, carbon monoxide (CO) and hydrocarbon (HC) emissions decrease, and the indicated thermal efficiency (ITE) first increases and then decreases. When Tin remains constant, the Pmax and HRRmax decrease and the combustion phase delays as the n-butanol volume fraction increases; CO and HC emissions gradually increase, except for that of lower Tin, which shows a trend of first reduction and then increase. ITE gradually decreases in general, but when Tin is higher than 100°C, coal-derived naphtha containing 24% of n-butanol in volume (B24N76) exhibits the highest ITE. In addition, for all tested fuels, both Pmax and HRRmax decrease as λ increases and the combustion gets slower and less stable; CO and HC emissions deteriorate, and ITE gradually decreases. It is worth noting that B24N76 shows the best combustion stability for all λs and exhibits the lowest CO and HC emissions when λ are 3.0 and 3.5.