Emission characteristics of particulate matter emitted by typical off-road construction machinery

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.