In this paper, a four-stroke engine diesel was employed to investigate the effects of different fuel mixture ratios of diesel and ethanol on engine performance and emission characteristics in terms of cylinder temperature, heat release rate, brake power, brake thermal efficiency, brake specific fuel consumption, and cylinder pressure. The corresponding simulation model of diesel engine was developed by AVL-Fire coupled CHEMKIN code, and an improved chemical kinetics mechanism containing 34 reactions and 19 species was employed to simulate the fuel spray process and combustion process. The simulation model was validated by experimental results under 100% and 50% load conditions and used to simulate the combustion process of diesel engine fueled with pure diesel and diesel–ethanol blends with 10%, 20%, and 30% ethanol by volume, respectively. The results showed that the increase of ethanol content in the blended fuel had a certain negative impact on the performance characteristic of diesel engine and significantly improved the emission characteristic of the engine. With the ethanol proportion in the blended fuel increased to 10%, 20%, and 30%, the brake thermal efficiency of the engine increased by 2.24%, 4.33%, and 6.37% respectively. However, the brake-specific fuel consumption increased by 1.56%, 3.49%, and 5.74% and the power decreased by 1.58%, 3.46%, and 5.54% respectively. In addition, with the ethanol proportion in the blended fuel increased to 10%, 20%, and 30%, the carbon monoxide emission decreased by 34.69%, 47.60%, and 56.58%, and the soot emission decreased by 7.83%, 15.24%, and 22.52% respectively. Finally, based on the combining fuzzy and grey correlation theory, nitrogen oxide emission has the highest correlation with engine power and brake-specific fuel consumption. The values reach 0.9103 and 0.8945 respectively. It shows that nitrogen oxide emission and cylinder pressure have a significant relationship on engine power and brake-specific fuel consumption.

In this paper, 8.0 mm thickness 2205 duplex stainless steel (DSS) workpieces were welded with a keyhole tungsten inert gas (K-TIG) welding system under different welding speeds. After welding, the morphologies of the welds under different welding speed conditions were compared and analyzed. The microstructure, two-phase ratio of austenite/ferrite, and grain boundary characteristics of the welded joints were studied, and the microhardness and tensile properties of the welded joints were tested. The results show that the welding speed has a significant effect on the weld morphology, the two-phase ratio, grain boundary misorientation angle (GBMA), and mechanical properties of the welded joint. When the welding speed increased from 280 mm/min to 340 mm/min, the austenite content and the two-phase ratio in the weld metal zone (WMZ) decreased. However, the ferrite content in the WMZ increased. The proportion of the Σ3 coincident site lattice grain boundary (CSLGB) decreased as the welding speed increased, which has no significant effect on the tensile strength of welded joints. The microhardness of the WMZ and the tensile strength of the welded joint gradually increased when the welding speed was 280–340 mm/min. The 2205 DSS K-TIG welded joints have good plasticity.

In this paper, 8 mm thickness 2205 duplex stainless steel (DSS) plates were successfully welded using keyhole tungsten inert gas welding (K-TIG) welding, and numerical simulations were performed applying the finite element method. Three models of combined heat source were adopted to verify accuracy of experiment. The welding process under different welding speeds were simulated, and the temperature field, molten pool shape, and thermal cycle curve were calculated. The welding simulation results show that a combined model consisting of the ellipsoid heat source and the conical heat source is more suitable for K-TIG welding. The results of the microstructure analysis of the welded joint showed that when the welding speed was increased from 280 mm/min to 340 mm/min, the austenite content and the ferrite and austenite grain size decreased. The evolution laws of welded joint morphologies, microstructure and grain sizes under different welding speed conditions were consistent with the analysis results of simulated molten pool morphologies, temperature field distributions and thermal cycle curves. It is proved that this kind of simulation method can effectively simulate the K-TIG welding process and ensure the welding quality, which is a guide for industrial applications.

To improve the combustion and emission characteristics of diesel engines, methanol-diesel fuels with different mixing ratios (DM0, DM10, DM20, DM30, and DM40) were used to investigate the effects of methanol addition on the combustion and emission of a four-stroke diesel engine in terms of cylinder pressure, brake power, brake-specific fuel consumption, and nitrogen oxides, soot, and carbon monoxide emissions. Firstly, an improved entire diesel engine model was developed using AVL-BOOST software and validated by the experimental results. The results showed that the increase of methanol content in the fuel mixture had a negative impact on the performance characteristic of the diesel engine, but significantly improved the emission characteristic of the diesel engine. With the methanol ratio in the mixed fuel increased to 10%, 20%, 30%, and 40%, the cylinder pressure of the engine increased by 0.89%, 1.48%, 2.29%, and 3.17%, respectively. However, the power decreased by 3.76%, 6.74%, 11.35%, and 15.45%, the torque decreased by 3.76%, 6.74%, 11.35%, and 15.45%, respectively, and the brake specific fuel consumption increased by 3.77%, 6.92%, 12.33%, and 17.61%, respectively. In addition, with the methanol ratio in the mixed fuel increased to 10%, 20%, 30%, and 40%, the carbon monoxide emission decreased by 21.32%, 39.04%, 49.81%, and 56.59% and the soot emission decreased by 0.25%, 8.69%, 16.81%, and 25.28%, respectively. Therefore, the addition of methanol to the fuel can improve the combustion and emission characteristics of the engine.

In this paper, metal inert gas (MIG) welding of 6082-T6 aluminum alloy with a thickness of 4 mm was simulated using a double ellipsoidal heat source. Based on the simulation results, the evolution of the microstructure, the strengthening mechanism of mechanical properties, and the corrosion characteristics of the welded joint were studied further. The thermal cycle curve of the welded joint was obtained through numerical simulation. When the heat input was 2.34–2.75 KJ/mm, the temperature of the welded joint reached the melting point of the material. With the increase in welding heat input, the weld metal (WM) organization changed from the dendrite to the cellular crystal transformation and presented a uniform distribution. The precipitation of the strengthened phase was inhibited at 2.75 KJ/mm. When the heat input changed from small to large, the tensile strength and toughness first increased and then weakened. Dimple distribution of tensile fractures was observed with a scanning electron microscope. When the welding heat input was 2.57 KJ/mm, the mechanical properties of the joint were the best. The tensile strength can reach 76.62% of the base material, and the elongation after breaking can reach 59.38% of the base material. However, it was concluded through studying electrochemical corrosion that the corrosion resistance of welded joints under this parameter was the worst. This may be caused by the presence of Cu, Fe, Si, Mg, and other compounds, and was proven to be Mg₂Si through EDS analysis.