Combustion and emission characteristics of premixed biogas mixtures: An experimental study

In this study, effects of fuel composition, swirl number and hydrogen addition on combustion and emission characteristics of various biogas mixtures were experimentally investigated. To this end, a laboratory scale combustor and a swirl stabilized premixed burner were designed and manufactured. Later on, this combusting apparatus was equipped with flow, control, safety and measurement tools, hence entire test system was constituted. Combustion and emission characteristics of tested biogas mixtures were determined by measuring temperature and species (CO₂, CO, O₂ and NO) distributions throughout the combustion chamber. Additionally, flame structures of tested biogas mixtures were evaluated by examining flame luminosity, visible flame length and flame thickness from instantaneous flame images. Results of this study showed that both radial and axial temperature distribution variations of tested biogas mixtures differently alter with hydrogen addition based on the gas composition. Although flame temperature increases with swirl number at burner outlet, it presents a non-monotonous dependence on swirl number outside the flame region because of the modified flow characteristics. This is also the case for emissions of CO₂.     

China's regional sustainability and diversified resource allocation: DEA environmental assessment on economic development and air pollution

Environmental protection, including the prevention of air pollution and health hazard materials such as PM2.5 and PM10, is now a very serious policy issue in China after attaining the rapid economic growth and development. The PM stands for “Particular Matter”, indicating the size of both solid particles and liquid droplets found in air. Unfortunately, the economic development has produced a serious healthcare problem in not only China and other surrounding nations. To enhance people's healthcare and appeal a good national image to the world, China is recently looking for the new industrial and environmental policy direction to attain social sustainability in terms of economic development and environmental prevention. To discuss policy implications on the new policy direction, this study utilizes Data Envelopment Analysis (DEA) for assessment on its regional performance by incorporating PM2.5 and PM10 as undesirable outputs, along with two disposability concepts (i.e. natural disposability and managerial disposability). No previous DEA study has incorporated the amount of PM2.5 and PM10 in empirical investigation. Using a simulated data set for the period of 2013–2014, this study measures the efficiency of municipality cities under four different types of regional classifications. The empirical results indicate that the Chinese government should distribute its economic resources to cities, which locate in the northwest region (including Lanzhou, Xining, Yinchuan and Urumqi), and reinforce more strict regulation on energy consumptions for environmental prevention in major cities (e.g. Beijing, Tianjin, Shanghai and Chongqing). The industrial policy change from the economic growth to the environment protection is essential for the future of China, which is currently the second largest economic power in the world. The environmental protection can enhance the China's image of contributing in economics, industry and environmental protection to all other nations. It can be envisioned that the new policy effort reduces the regional imbalance and increases the social sustainability in China. The empirical findings and policy implications discussed in this study are applicable to not only China but also other industrial and developing nations and those are useful in guiding their industrial and environmental policy development.     

FEM modeling of multilayered textile composites based on shell elements

The paper presents a shell element based unit cell approach for numerical homogenization of fiber reinforced textile laminates. The modeling strategy is set up within the framework of the Finite Element Method. Multilayer laminates comprising equal weaves are considered and the constituents, i.e. the tows as well as the unreinforced matrix pockets are discretized by shell elements only which are coupled appropriately. A study on the effective extensional laminate-shell stiffnesses is presented, the results are discussed, and are compared to approaches found in the literature. Additionally, geometrically nonlinear simulations are conducted and the results are compared with experimental tests from literature.     

Numerical analysis and experiment of composite sandwich T-joints subjected to pulling load

This paper presents an investigation into the failure mechanism and alternative design of composite sandwich T-joints subjected to pulling load. Based on a conventional design of sandwich T-joint as the baseline, numerical modeling and analysis using finite element (FE) method was performed to assess the strength against pulling load. The effect of a cutout in the web panel near the joint has been considered. To validate the models, sandwich T-joint samples were manufactured and tested. Detailed FE analysis and inspection of the experimental results indicated that the failure was mainly due to the excessive stress in the adhesive between the cleat flange and the T-joint base panel. The manufacture defects, which reduced the strength of the T-joint test samples had also been investigated. This has been further demonstrated by experimental results of repaired T-joint samples. A very good correlation between the test data and FE results were obtained. An unconventional design of T-joint for simpler manufacture process was proposed. Based on the design, T-joint samples were modeled, manufactured and tested to demonstrate the manufacture process and evaluate the improved strength.     

The analysis and investigation on the microelectrode fabrication by electrochemical machining

Electrochemical machining (ECM), also called the electrolysis machining, has become more and more important in micro-machining in recent years. In this paper, a 510 μm tungsten rod was used as the anode, and nickel plates were used as the cathode to fabricate the micro-pin used in scanning tunneling microscope (STM) by electrochemical polishing. Different from the needle shape in STM, a cylindrical shape of microelectrode is desired for the application in electrochemical drilling. The influence of working parameters on the electrode shape is investigated.Experimental results show that low applied voltage, high concentration electrolyte and an appropriate rotation of electrode are preferred to fabricate microelectrodes with diameter less than 100 μm. A higher rotational speed may result in an electrode of conical shape.     

Experimental study on the compression properties and failure mechanism of 3D integrated woven spacer composites

The compressive experiments on the 3D integrated woven spacer composites with different core heights are performed in the flat and warp direction. Macro-fracture morphology and SEM micrographs have been examined to understand the deformation and failure mechanism. The results show that the core height is an important parameter to influence the compressive properties and failure mechanism. For flat compression, the compressive properties decrease with the core height and load–displacement curves exhibit elastic, plasticity plateau and densification stages. For high core height, yet more than one peak load appears. For warp compression, the compressive properties increase greatly with the core height and the curves only have obvious elastic stage. Meanwhile, the failure mechanism is significantly different under the flat and warp compression. For flat compression, core fiber bundles dominate the failure and three typical failure mechanisms have been obtained for different core heights. For warp compression, it is the face sheet rupture and dislocation between the top and bottom face sheets that dominate the failure of the composites.     

Microstructure and tensile behavior of (BN/SiC)n coated SiC fibers and SiC/SiC minicomposites

Interphase plays an important role in the mechanical behavior of SiC/SiC ceramic-matrix composites (CMCs). In this paper, the microstructure and tensile behavior of multilayered (BN/SiC)_n coated SiC fiber and SiC/SiC minicomposites were investigated. The surface roughness of the original SiC fiber and SiC fiber deposited with multilayered (BN/SiC), (BN/SiC)₂, and (BN/SiC)₄ (BN/SiC)₈ interphase was analyzed through the scanning electronic microscope (SEM) and atomic force microscope (AFM) and X-ray diffraction (XRD) analysis. Monotonic tensile experiments were conducted for original SiC fiber, SiC fiber with different multilayered (BN/SiC)_n interfaces, and SiC/SiC minicomposites. Considering multiple damage mechanisms, e.g., matrix cracking, interface debonding, and fibers failure, a damage-based micromechanical constitutive model was developed to predict the tensile stress-strain response curves. Multiple damage parameters (e.g., matrix cracking stress, saturation matrix crack stress, tensile strength and failure strain, and composite’s tangent modulus) were used to characterize the tensile damage behavior in SiC/SiC minicomposites. Effects of multilayered interphase on the interface shear stress, fiber characteristic strength, tensile damage and fracture behavior, and strength distribution in SiC/SiC minicomposites were analyzed. The deposited multilayered (BN/SiC)_n interphase protected the SiC fiber and increased the interface shear stress, fiber characteristic strength, leading to the higher matrix cracking stress, saturation matrix cracking stress, tensile strength and fracture strain.     

More experience might not bring more safety: Negative moderating effect of pilots’ flight experience on their safety performance

ObjectiveThis study aimed to improve our understanding of the relationship between pilots' total flight hours (TFH), levels of hazardous attitude (HA), and flight safety performance.BackgroundThe negative effect of airline pilots' flight experience on safety performance has received attention but has not been extensively investigated.MethodUsing a sample of 45 Chinese commercial airline pilots, we not only tested the mediation model in which the relationship between TFH and exceedance rate was mediated by HA, but also tested the moderation model in which the relationship between HA and exceedance rate was moderated by TFH.ResultsTFH positively predict flight exceedance rates; more importantly, it moderated the effect of HA on flight exceedance rates. Specifically, TFH exacerbated the negative effect of HA on flight exceedance rates. Meanwhile, the mediating effect of HA was not significant.ConclusionResults implies the nonlinear relationship between TFH, HA, and flight safety performance. The moderation model indicates that the experience-related risks may appear before 5000 h for an individual commercial airline pilot.ApplicationResearchers, safety managers, and policymakers in the aviation industry that conduct pilots' psychological competency research in the Professionalism Lifecycle Management (PLM) system should be aware of the potentially interactive effects of hazardous attitude and experience on commercial airline pilots’ flight safety performance.