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• High-integrated optical circuits are important for the optical interconnect in the future high-capacity optical communications system. • A methodology to realize the fabrication of a hybrid-core planar waveguide by using multi-step photolithography is proposed and demonstrated to increase the integration density. • The demonstrated device provides coupling ratios for the fundamental mode that are higher than 92.0 % and 91.6 % for the TE and TM polarizations over the C + L band. • The proposed methodology can be further developed to realize the fabrication of a two-material system heterogeneous integrated photonic device. We propose a methodology for fabricating a hybrid-core planar waveguide mode multiplexer using multi-step photolithography and demonstrate the manipulation of the fundamental mode without affecting the high-order modes in the experiment. We design and fabricate the proposed mode multiplexer, and our experimental device provides coupling ratios for the fundamental mode that are higher than 92.0 % and 91.6 % for the transverse-electric (TE) and transverse-magnetic (TM) polarizations and the modal crosstalks are lower than −10.6 dB and −10.4 dB for the TE and TM polarizations, respectively, over the C + L band. The device is confirmed to be low sensitivity to the state of polarization. The proposed methodology can be further developed to realize the fabrication of a two-material system heterogeneous integrated photonic device. [ABSTRACT FROM AUTHOR]

• We propose a co-planar optical power splitter based on cascaded hybrid-core vertical directional couplers, which serves to split arbitrary ratio power of arbitrary guide modes. • We fabricate the optical power splitter using micro-fabrication facilities. • Our fabricated chip demonstrates power splitting for the E 11 , E 21 and E 12 modes between two few-mode waveguides. • The experimental device shows that optical power splitting ranges can be larger than 11.0 dB, 12.1 dB and 11.3 dB for the E 11 , E 21 and E 12 modes, respectively, over the C + L band and beyond. • The proposed optical power splitter could be used in the mode division-multiplexing systems where power splitting for arbitrary guide modes in few-mode waveguide is required in the ultra-broadband wavelength range for mode manipulating, such as mode power distribution, mode dependent loss equalization and all-optical MIMO signal processes. We propose a co-planar optical power splitter based on cascaded hybrid-core vertical directional couplers, which serves to split arbitrary ratio power of arbitrary guide modes. We fabricate the optical power splitter using micro-fabrication facilities. Our fabricated chip demonstrates power splitting for the E 11 , E 21 and E 12 modes between two few-mode waveguides. The experimental device shows that optical power splitting ranges can be larger than 11.0 dB, 12.1 dB and 11.3 dB for the E 11 , E 21 and E 12 modes, respectively, over the C + L band and beyond. The proposed optical power splitter could be used in the mode division-multiplexing systems where power splitting for arbitrary guide modes in few-mode waveguide is required in the ultra-broadband wavelength range for mode manipulating, such as mode power distribution, mode dependent loss equalization and all-optical MIMO signal processes. [ABSTRACT FROM AUTHOR]

The optimization of three-way catalyst (TWC) design and layout is important for reducing mobile source emissions and requires numerical modeling. To date, the high computational cost of accurate models has inspired the development of numerous tradeoff approaches; however, none of them is fully satisfactory. To address this gap, we herein theoretically and experimentally explore the key design and layout factors influencing TWC performance under transient driving conditions, starting with the optimization and verification of a simplified reaction mechanism. This mechanism is used to construct a semidecoupled posttreatment GT-Power model featuring boundary conditions derived from experimental and upstream engine modeling results, and experiments on a real engine are carried out to evaluate the model accuracy. The performance of three posttreatment systems is analyzed to identify the key performance-affecting parameters, and the following conclusions are drawn. (1) For a single reactor, cell density is the most important factor influencing pressure loss. (2) The exhaust temperature rapidly decreases in the longitudinal direction of the reactor in the initial start stage, although the reaction rate always decreases in this direction during the whole cycle. (3) One-dimensional plug-flow reactor simulations do not account for inhomogeneity and local turbulence, thus overestimating the performance of large reactors. (4) Under the employed conditions, the exhaust temperature is sufficiently high for pollutant conversion, although the efficiency of this conversion often decreases in the high-speed stage. Moreover, we show that high-speed adaptation can be enhanced by increasing the crosswise size of the reactor and propose a new reactor structure. Compared with our model, this structure is characterized by a lower catalyst loading and NO x conversion efficiency but achieves higher hydrocarbon and CO conversion efficiencies. Thus, our study provides a useful and effective method for evaluating the design/layout of posttreatment devices and facilitates the development of more efficient TWCs, contributing to the establishment of a more ecofriendly society. [Display omitted] • Experimental and semidecoupled numerical method was used to explore TWC influencing factors. • A detailed surface reaction mechanism was simplified, optimized and verified by literature results. • Cell density is the most important factor for pressure loss. • Suitable increase of reactor's crosswise size may enhances high speed adaptation. • A new model with the fewest catalyst was proposed with improvements of HC and CO conversion. [ABSTRACT FROM AUTHOR]

Abstract In the present study, the possibility and limitation of lean burn in a motorcycle engine were explored, from the aspect of exhaust emissions. The CO and NOx emissions were studied by experimental measurements and combined simulations on a twin-spark motorcycle gasoline engine under wide range of operating conditions. The results illuminated that, the CO emissions drop sharply when air/fuel mixture changed from rich to lean. Particularly, at full load the CO emission decreases by about 4 times when λ changed from 0.85 to 1.1, and it keeps decreasing to only about one-tenth at λ = 1.2. Besides, at λ = 1.1 and full engine load the NO emission is about 2.4 times of that at λ = 0.85. Not so much variation has been observed between λ = 1.1 and λ = 1.2. This indicates enlarging the lean burn range will not further deteriorate NOx emission, but benefit from CO emission by a large margin. It is further found the variation in CO emission amount between λs is not mainly due to which reaction is in favor, but due to the amount of its precursors. Besides, almost all the NO is produced by the thermal-NO mechanism. Highlights • CO and NOx emissions of a twin-spark motorcycle engine were studied over a wide range condition. • CO emissions drop sharply when air/fuel mixture changed from rich to lean operation. • NOx emission is not deteriorated much when used more lean mixture after λ > 1.1. • The CO value between λs is not mainly due to which reaction is in favor, but due to the amount of its precursors. • Almost all the NO is produced by the thermal-NO mechanism. [ABSTRACT FROM AUTHOR]

Considering the noble metals resources used in Three-way catalysts are extremely limited, traditional Three-way catalysts can no longer meet the increasingly stringent emissions control standards economically. For more efficient emissions control, we first time to perform a multi-parameters comparative investigation on catalytic converter design for high performance motorcycles with considerations of converter's structure/size, layout and engine working status under World-wide Motorcycle Test Cycle to explore novel design methods of Three-way catalysts. Based on the several models designed for test, the original transient emissions are measured to explore engine's working performances and factors that impact raw emissions, the integrated effect of converter structure/size and layout on emissions conversion efficiency is also explored. In this study, Model 1 is double catalytic structure while Model 2 and Model 3 are single structure, detailed parameters about these models are expressed as the format "Length, Diameter or long/short axis for ellipse, Cell density" as: Model 1-front: 42 mm, 123 mm, 200 cpsi; Model 1-rear: 123 mm, 95/65 mm, 300 cpsi; Model 2: 85 mm, 100 mm, 400 cpsi; Model 3: 82 mm, 130 mm, 300 cpsi. Catalytic conversion efficiency of CO, THC and NO x are ranked as Model 3: 88.13% > Model 1: 85.95% > Model 2: 84.89%, Model 1: 93.73% > Model 3: 89.76% > Model 2: 85.79% and Model 1: 98.27% > Model 2: 92.58% > Model 3: 87.05%, respectively. Small-size catalytic converters have quicker warm-up and poorer heat preservation capacity, that's why Model 2 has the highest catalytic efficiency for CO in cold stage and the lowest overall, Meanwhile, Model 2 has the best trade-off performance. We hope to provide useful knowledge that guides the converter design/application. • Transient emissions characteristics of a motorcycle under real driving cycle were investigated. • Effects of converter structure/size, layout and working status on conversion efficiency were explored. • Double catalytic structure has the best conversion efficiency, but it also has the highest cost. • Model 2 (85 mm, 100 mm and 400 cpsi) has the best trade-off performance. [ABSTRACT FROM AUTHOR]

Micro-forming is one of the major micro-manufacturing methods with promising application potentials, in which the damage response and fracture behavior need to be insightfully addressed. Among all the damage criteria to predict fracture, GTN model is a widely-used one and able to predict void-dominated fracture in micro-scale deformation. However, it is not very applicable under low stress triaxiality and shear-dominated condition. An in-depth understanding of shear damage and its potential size effect are crucial to explore the micro-scaled damage and fracture mechanisms. This research characterizes the size effect on flow stress via employing a combined constitutive model, and an approach for applying a phenomenological shear damage evolution law to the GTN-Thomason model via considering the size effect is developed. The prediction of micro-scaled fracture in a wide stress triaxiality range is thus enabled. Through simulation and experiment, the proposed model is validated and verified. In addition, stress state parameters including stress triaxiality, Lode parameter, and weight function, are also discussed, and the two damage parameters are analyzed quantificationally to reveal different fracture mechanisms occurring in different stress states and grain sizes. The research thus facilitates the physical insight and in-depth understanding of the size effect on damage evolution and fracture formation in micro-scaled plastic deformation of materials. Unlabelled Image • A new micro-scaled model is proposed for fracture under low stress triaxiality. • Shear damage and its size effect is considered in a phenomenological way. • Void and shear damage can be quantified by two independent parameters. • With the increase of grain size, fracture becomes more shear-dominated. [ABSTRACT FROM AUTHOR]

In the present study, the flow structure and pollutants dispersions were investigated by experiment and simulation on a typical passenger vehicle under simulated traffic light driving pattern. Some important findings were achieved: 1) gaseous pollutants diffuse drastically during first 0.3–0.6 m distance depending on wind velocity, at 1.25 m/s wind speed which is the similar level of exhaust gas, the pollutant concentration rises suddenly at ~0.6 m because exhaust plume is twisted by bottom gas flow, and a low velocity zone is produced; 2) as wind speed increases, the vehicle-induced turbulence is more and more important on pollutant dispersion pattern than exhaust plume dynamics. For instance, at 1.25 m/s and 4.17 m/s wind speeds, pollutants decrease to zero at ~1.6 m behind tail pipe, but at 0 m/s condition, pollutant relative fraction is still at ~0.12 level even at very long distance; 3) solid particle has larger attenuation rate than gaseous pollutants, only after ~0.6 m the particle number (PN) and diameter are very close to background values. Solid particle can diffuse to farther distance in vehicle transverse direction, when a car passes through the pedestrians with a 3 m distance, pedestrians expose to 2.6–3 times higher PN relative to atmosphere with diameters of 28–33 nm, this is very hazardous for human health; 4) exhaust pollutants disperse difficultly when followed by a car with a commonly waiting distance. At free dispersion scenario only behind ~0.6 m, PN decreases to 5800 #/cm3 (background value), but in-cabin PN of the following car (behind 0.8 m) rises to 3.5 × 104 #/cm3 (even after 2–3 times decay through ventilation system). This study provides implications for future studies on transport planning. Unlabelled Image • Gaseous pollutants diffuse drastically during first 0.3–0.6 m distance depending on wind velocity. • With wind speed increasing, pollutant dispersion is more and more determined by vehicle-induced turbulence. • Particles degrade into background at ~0.6 m while gaseous pollutants at least keep at 0.12 fraction till far. • When a vehicle passes with 3 m, pedestrians expose to 2.6–3 times higher PN than atmosphere value with diameters of 28–33 nm. • Exhaust pollutants disperse difficultly when followed by a car with a commonly waiting distance (0.8 m). [ABSTRACT FROM AUTHOR]