Lithium-ion power batteries are used in groups of series-parallel configurations. There are Ohmic resistance discrepancies, capacity disparities, and polarization differences between individual cells during discharge, preventing a single cell from reaching the lower limit of the terminal voltage simultaneously, resulting in low capacity and energy utilization. The effect of the parameter difference (difference in parameters) of individual cells on the performance of the series-parallel battery pack is simulated and analyzed by grouping cells with different parameters. The findings reveal that when cells are connected in series, the capacity difference is a significant factor impacting the battery pack's energy index, and the capacity difference and Ohmic resistance difference are significant variables affecting the battery pack's power index. When cells are connected in parallel, the difference in Ohmic internal resistance between them causes branch current imbalance, low energy utilization in some individual cells, and a sharp expansion of unbalanced current at the end of discharge, which is prone to overdischarge and shortens battery life. Interestingly, we found that when there is an aging cell in a series-parallel battery pack, the terminal voltage of the single battery module containing the aging single cell will decrease sharply at the end of discharge. Evaluating the change rate of battery module terminal voltage at the end of discharge can be used as a method to evaluate the aging degree of the battery module. The research results provide a reference for connecting batteries to battery packs, particularly the screening of retired power battery packs and the way to reconnect into battery packs.

The pre-chamber ignition system scavenged with natural gas can effectively improve the in-cylinder combustion process and extend the lean-burn limit of natural gas engines. The scavenging process affects the flow field and fuel-air mixture concentration distribution in the pre-chamber and affects the combustion process in the pre-chamber as well as the ignition process in the main chamber. This has a significant influence on the performance of natural gas engines. It is supposed that the ratio of natural gas remaining in the mixture inside the pre-chamber at the ignition timing affects the combustion process in the pre-chamber. To verify this suppose, an independent injection system for injecting natural gas into the pre-chamber is designed and experiments are carried out on a single-cylinder natural gas engine. The ratio of natural gas remaining in the mixture inside the pre-chamber at the ignition timing is adjusted by changing the injection start angle of the scavenging process. The combustion process in the pre-chamber and the main chamber are analyzed using the in-cylinder pressures. The results indicate that, with the delay of the injection start angle, the ratio of natural gas remaining in the mixture inside the pre-chamber at the ignition timing increases, the combustion process in the pre-chamber is enhanced, the maximum pressure difference between two chambers increases and appears earlier. The energy of the hot jets and the penetration of the jets increase, which enhances the combustion process in the main chamber.

Prechamber jet ignition is a promising technology that enables stable ignition and fast combustion by combining thermal effects, chemical kinetics, and turbulent disturbance. The development and application of the prechamber ignition require a comprehensive and in-depth understanding of the operating characteristics of the prechamber ignition in the real engine working cycle. Therefore, numerical simulations are conducted to explore the operating performance of the prechamber ignition applied to a large-bore natural gas engine in this study. The differences between the passive prechamber (PPRE) and active prechamber (APRE) near the lean burn limit are compared. The results show that the jet ignition performance of the PPRE is hampered by the high residual gas coefficient and lean mixture in the prechamber under lean burn conditions. The ignition mode of the PPRE is similar to torch ignition, and the combustion process in the main chamber is mainly turbulent flame propagation. The ignition mechanism of the APRE is flame jet ignition. The main chamber combustion process presents a two-stage heat release characteristic, which can be subdivided into three phases: the initial flame development phase, the rapid combustion phase, and the late combustion phase. The heat release rate during the initial flame development phase depends on the physical and chemical properties of the prechamber jet and the mixture conditions in the main chamber. During the rapid combustion phase, the flame propagation along the radial direction of the jet largely depends on the time scale of the chemical reaction. The heat release rate depends on the coverage area of the jet, the jet residual momentum, and the turbulent flame speed. During the late combustion phase, the flame propagation is mainly affected by the turbulent flame speed. These results provide theoretical guidance for the subsequent application of prechamber ignition systems in various powertrains.