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This paper presents a performance prediction method for piezoelectric injection systems, based on finite element simulations. Two indexes representing the system performance are proposed: jetting velocity and droplet diameter. By combining Taguchi’s orthogonal array method and finite element simulation (FES), a finite element model of the droplet injection process, with different parameter combinations, was established. The two performance indexes, jetting velocity and droplet diameter, were accurately predicted, and their variation with time were investigated. Finally, the accuracy of the predicted results of the FES model was verified by experiments. The errors of the predicted jetting velocity and droplet diameter were 3.02% and 2.20%, respectively. It is verified that the proposed method has better reliability and robustness than the traditional method.

Droplet jetting velocity is one of the most important factors affecting the quality of piezoelectric ejection printing. Due to the nonlinear relationship between the two, predicting the droplet jetting velocity by conventional methods is very time-consuming and impractical. We propose a genetic algorithm (GA) combined with a back propagation neural network (BPNN) to predict the droplet jetting velocity. The network topology and the values of each parameter of the model are designed and validated to elucidate the relationship between the input parameters of the piezoelectric ejection system and the studied droplet ejection velocity. The GA-BP model was trained, tested, and tuned using a database consisting of data generated from finite element calculations, and the results showed an error of 3.34% between the predicted and finite element simulated droplet ejection velocities, which demonstrates the reliability and robustness of the method.

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Five simulating columns were used to investigate the effect of the grain-size distribution and water content of rock on the migration and natural attenuation of diesel fuel in the vadose layer. Natural attenuation of fuel was observed for 90 days. It was shown that as the grain size of the rock increases, the water content that cannot be replaced by diesel fuel in the rock decreases. An increase of the water content has a positive effect on the natural attenuation of diesel fuel.The transport, refining, and use of petroleum products often are accompanied by hydrocarbon leaks or accidental spills [1,2]. The contamination of groundwater by petroleum products has become a serious environmental problem [3][4][5]. A number of methods exist for soil remediation and purifying groundwater of petroleum products: pump-and-treat, air sparging, vapor extraction of hydrocarbons, and in situ biological remediation [6][7][8]. However, these methods are extremely energy intensive or can damage the soil structure [3,[9][10][11][12]. In recent years there has been great interest in the natural attenuation of hydrocarbons.In [13,14] it is shown that under favorable geochemical conditions natural attenuation is a cost-effective alternative method of cleaning soil and groundwater of contaminants. In addition, this method does not destroy the soil structure [13,14].Natural attenuation of contaminants in soil and groundwater occurs as a result of natural processes, which decrease the content or toxicity of the contaminants. These processes include biodegradation, dispersal, dilution, adsorption, volatilization, chemical or biological stabilization or decomposition of contaminants [15][16][17][18]. 231According to [3] natural attenuation of volatile aromatic hydrocarbons in the surface layer of soil is due to their volatilization and dispersal. In addition, hydrocarbon biodegradation, which is determined by the properties of the soil and the local population of soil microorganisms, can occur in soil [19,20]. Since the microorganisms characteristic of a given soil can process a host of hydrocarbons [21], even the soil in Sub-Antarctica contains populations of microorganisms which are capable of biodegrading hydrocarbons [22]. Natural attenuation of contaminants has been widely studied. It has been shown, for example, that reducing conditions of the medium are conducive for attenuation of chlorinated solvents [23]. Field studies have shown that 1,2-dichloroethane undergoes biodegradation into vinyl chloride and ethylene in a natural oxygen-free reducing medium [14]. Natural attenuation can also be used for remediating soil contaminated with methyl-tert-butyl ether (MTBE) [16]. Thus, natural attenuation plays an important role in restoring the physical, chemical, and biological properties of contaminated soils [24,25].There are relatively few articles concerning the effect of the grain-size distribution and water content on the natural attenuation of diesel fuel in the vadose zone. Our objective in the present work is to make a quantitativ...