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There are several drawbacks for lithium-ion batteries at low temperatures, including weak electrolyte conductivity, low chemical reaction rate and greatly increased impedance. Thus, it is inefficient to charge lithium-ion batteries at low temperatures. This work proposes an AC incentive fast charging strategy at low-temperatures for lithium-ion batteries based on the analysis and comparison of the existing charging and heating methods. The charging speed, temperature variation, the capacity loss of the constant current constant voltage (CCCV) charging strategy and the proposed method with different current and frequency conditions are compared and analyzed. The results show that it takes about 1400 s for the proposed method to fully charge a lithium-ion battery in the case of 2.2 A current beginning at 25% state of charge (SOC). In addition, the temperature rises about 8 °C. In contrast, the charging time of the CCCV method is 400 s slower than the proposed method and the temperature of the CCCV method increases only about 2 °C. In the case of 1.5 A current beginning at 0% SOC, the charging time of the proposed method is 500 s faster than the CCCV method. The results indicate that the proposed charging method can significantly improve the charging efficiency of lithium-ion batteries at low temperatures. [ABSTRACT FROM AUTHOR]

Natural gas (NG) direct injection (DI) technology benefits the engine with high efficiency and clean emissions, and the high-pressure gas fuel injection process causes crucial effects on the combustion. This study presents an optical experimental investigation on the high-pressure methane single-hole direct injection and premixed ignition combustion based on a visualization cuboid constant volume bomb (CVB) test rig. The experimental results show that the methane jet process is divided into two stages. The methane gas jet travels at a faster speed during the unstable stage I than that during the stable stage II. The injection pressure causes more influence on both the jet penetration distance and the jet cone area during stage II. The methane jet premixed flame is a stable flame with a nearly spherical shape, and its equivalent radius linearly increases. The methane jet premixed flame area also increases while the flame stretch rate declines. The methane jet premixed flame velocity rises as both the standing time and equivalent ratio increase. The methane jet premixed flame is a partial premixed flame, and the peak of the methane jet premixed flame occurs at greater equivalence ratio ϕ, i.e., ϕ > 2. As the injection pressure rises, the jet premixed flame equivalent radius increases, and the flame velocity linearly increases. The higher the methane injection pressure, the faster the jet premixed flame velocity. [ABSTRACT FROM AUTHOR]