RESUMO
This study aims to explore the factors that influence the emission characteristics of multiple pollutants from non-road mobile machinery (NRMM) under real-world conditions and to establish a data-driven method for calculating accurate emission factors. This research focused on NRMM excavators meeting the third-stage emission standards and identified the actual work characteristics of 108 excavators in different scenarios based on a self-developed testing system for 368,000 h. Additionally, a portable emission testing system (PEMS) was used to study the instantaneous emission characteristics under different driving styles and modes for 10 EC210 excavators with the largest engineering construction inventory. The results showed that the average time proportions of idling, working, and moving modes for excavators were 21 %, 66 %, and 13 %, respectively. The results also revealed that the instantaneous emission rates of multiple pollutants varied significantly under different driving styles and modes. Driving style affected the hydraulic pump power change rate through hydraulic pilot pressure, and engine load surge caused turbocharger response delay and in-cylinder combustion deterioration, which affected pollutant emissions. Driving mode affected the emission characteristics of idling, high-speed idling, moving, and working modes of excavators through the external characteristics corresponding to the engine speed gear set. The data-driven method for calculating emission factors differed from the traditional method for most indicators to varying degrees. In terms of fuel-based emission factors (EFfs), except for the EFfNOx indicator, which was 7.859 % higher than the traditional method, the other three indicators were significantly lower than the traditional method. In terms of power-based emission factors (EFps), except for EFpPM and EFpPN, the other two indicators were much higher than the traditional method. EFpCO and EFpNOx were 7.93 % and 20.332 % higher than the traditional method, respectively. It is recommended to use the data-driven method based on the actual driving data distribution to provide scientific support for accurately establishing the emission inventory.
RESUMO
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.
RESUMO
Off-road machinery, especially construction equipment, is one of the most important pollutant sources of the deterioration in the air quality of Chinese urban areas owing to its large quantity and to the absence of stringent emission requirements. In this study, we used a portable emission measurement system (PEMS) to measure the exhaust pollutant emission characteristics for 13 pieces of construction machinery including excavators and hydraulic crushers under different working conditions, such as real-world operating condition, free accelerating condition, and overloading condition, innovatively adopting the method of synchronizing video recording and emission measurement to divide the operation process of construction machinery under different working conditions into different action stages. In addition, the relationship between the emission characteristics and the maintenance history of 13 pieces of construction machinery was analyzed. The present study exploits this recent progress to enrich the measurement method of off-road mobile machinery light absorption coefficient (LAC), which does not depend on the measurement environment and the type of equipment. There are three significant findings from the study that can be noted. To begin with, the exhaust LAC in the excavation operation stage was the highest in the real-world operating condition. The main reason for it is that the engine load was suddenly increased during this stage; due to the response lag characteristics of the turbocharger, the intake charge was delayed, so the quality of oil and gas mixture in the cylinder becomes worse, and the concentration of local mixture is higher. Therefore, insufficient combustion of the mixture leads to a large amount of soot formation. Second, when the real-world operation is unavailable, the free accelerating condition was not applicable, but the overflow loading condition is suitable for replacing the real-world operating condition to measure the excavator exhaust LAC. Finally, as for in-use construction machinery, regular maintenance is an effective measure to reduce the engine exhaust LAC. Our findings contribute to improving the efficiency and accuracy of the environmental protection department's evaluation of the exhaust LAC of off-road mobile machinery and promoting the application of different technologies for high-emission off-road mobile machinery to reduce pollutant emissions so that it can continue to be used.