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In the field of low-frequency noise control, the acoustic metamaterials have received extensive attention from researchers. However, the existing work mainly focuses on small structures with fixed boundaries, which is quite different from engineering applications. Based on the membrane-type acoustic metamaterials, this paper uses a rigid thin plate to replace the tensioned membrane, design and manufacture of two new types of local resonance structure and studies their sound insulation properties. First, the metamaterial samples with a small size of 100mm in diameter and a large-size square with a side length of 506mm were produced, and the sound TL of the two was tested through the impedance tube and the reverberation chamber-anechoic chamber, respectively. The results show that the new structure can form an obvious sound insulation frequency band at low frequencies. Based on the finite element method, a metamaterial acoustic transmission loss calculation model is established.

The spark ignition engine particulate number (PN) emissions have been correlated to a particulate matter index (PMI) in the literature. The PMI value addresses the fuel effect on PN emission through the individual fuel species reactivity and vapor pressure. The latter quantity is used to account for the propensity of the non-volatile fuel components to survive to the later part of the combustion event as wall liquid films, which serve as sources for particulate emission. The PMI, however, does not encompass the suppression of vaporization by the evaporative cooling of fuel components, such as ethanol, that have high latent heat of vaporization. This paper assesses this evaporative cooling effect on PN emissions by measurements in a GDI engine operating with a base gasoline which does not contain oxygenate, with a blend of the gasoline and ethanol, and with a blend of the gasoline, ethanol, and a hydrocarbon additive so that the blend has the same PMI as the original gasoline.

We studied the influence of extreme pressure (EP) antiwear additive on the emission and distribution of particulate matters (PMs), since EP antiwear additive is necessary to improve the property of lubricating oil with the downsizing development of engines. We used a four-cylinder, turbocharged, and inter-cooled system with SAE15W-40 lubricant diesel engine. Pure diesel and fuel blends with varying weight percentages (0.5%, 1.0%, and 1.5%) of EP antiwear additive were used. Engine speed increased by increments of 400 from 1,200 rpm to 2,800 rpm under medium load and full load. The DMS500 was used to acquire particle data, and the Wave Book was employed to record oil and cylinder pressure. Conclusions drawn from the experiments suggest that EP antiwear additive has significant effects on PM emissions and distributions. Increments and decrements were observed on the number of accumulation mode particles and nucleation mode particles with BDAW-0.5.