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Piston slap force is one of the main sources of mechanical engine noise. To obtain a more accurate determination of the piston slap force and minimize piston slap noise, a new simulation model that considers dynamic clearance of the piston skirt and liner has been established in this study. The skirt-liner dynamic clearance is caused mainly by the elastic deformation and thermal deformation of the piston. Comparing three different models, it was found that the impact of dynamic clearance on the piston slap force is reflected mainly in the medium-high frequency, which is the sensitive frequency of the slap noise. Therefore, it is necessary to consider dynamic clearance in the simulation model. In addition, the mechanisms behind the dynamic clearance effect on fluid lubrication, piston dynamics, and piston slap noise were observed. In particular, three typical structural parameters in piston dynamics (the piston pin offset, piston-liner clearance, and piston skirt profile) were studied. The analyses provide guidance for the design of low-noise engines.

Rapid prototyping is an advanced technology, from which the prototypes are built quickly with photopolymers or other materials. The RP manufacture system uses lasers or ultraviolet light to expose surface of liquid resin and builds a three-dimensional part according CAD model in a layer-by-layer way. In spite of the great potentiality, some structural weakness that affect the forming precision of the parts, such as lower strength, larger shrinkage and distortion, have hindered the wide industrial application. Therefore, this study focuses on some technology parameters of the prototypes, such as data process and layer thickness. The paper summaries the influence of data process on forming precision for rapid prototyping. Finally, the significant performance of rapid prototyping for modern industry is discussed. The investigation is beneficial for choosing an optimal parameter in industry.

Perovskite solar cells (PSCs) have attracted unprecedented attention due to their rapidly rising photoelectric conversion efficiency (PCE). In order to further improve the PCE of PSCs, new possible optimization path needs to be found. Here, quasi-heteroface PSCs (QHF-PSCs) is designed by a double-layer perovskite film. Such brand new PSCs have good carrier separation capabilities, effectively suppress the nonradiative recombination of the PSCs, and thus greatly improve the open-circuit voltage and PCE. The root cause of the performance improvement is the benefit from the additional built-in electric field, which is confirmed by measuring the external quantum efficiency under applied electric field and Kelvin probe force microscope. Meanwhile, an intermediate band gap perovskite layer can be obtained simply by combining a wide band gap perovskite layer with a narrow band gap perovskite layer. Tunability of the band gap is obtained by varying the film thicknesses of the narrow and wide band gap layers. This phenomenon is quite different from traditional inorganic solar cells, whose band gap is determined only by the narrowest band gap layer. It is believed that these QHF-PSCs will be an effective strategy to further enhance PCE in PSCs and provide basis to further understand and develop the perovskite materials platform.