In order to improve the accuracy of numerical simulation, a new heat transfer model is developed by using a modular approach in the Anstalt für Verbrennungskraftmaschinen (AVL)-Boost software. The improved heat transfer model mainly considers the effects of the swirl and boiling heat transfer inside the engine. In addition, a chemical kinetics mechanism including 475 reactions and 134 species is employed to predict the combustion of diesel engines fueled with biodiesel. The result shows that the boiling heat transfer will occur, especially in the high-temperature area. Analysis shows that the improved model is reliable and its precision is increased. Finally, the perturbation method is employed to investigate the relatively important inputs as the complex nonlinear function with a lot of output data and input data produced by the improved model. The relative effects of different parameters such as EGR, injection mass, injection timing, compression ratio, inlet air pressure, fuel injection pressure, exhaust pressure and inlet air temperature on performance and emission characteristics are compared. The eight parameters are investigated on four outputs of brake power, Brake Specific Fuel Consumption (BSFC), NOx and HC. The injected fuel mass plays an important role in emissions and performance. The EGR, compression ratio and inlet air pressure have a great effect on the HC and NOx emission.

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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, the microstructure and impact toughness of a S32101 duplex stainless steel underwater local-dry keyhole tungsten inert gas welded joint were studied. The impact toughness value of the underwater weld metal reached 78% of the onshore weld metal, which is in accordance with the underwater welding standards. The proportion of austenite in the underwater weld metal was 0.9% lower than that of the onshore weld metal. The proportion of the Σ3 coincidence site lattice boundaries and random phase boundaries in the underwater weld metal, which significantly influence the impact toughness of the weld metal, were smaller than that of the onshore weld metal.

Q690E high strength low alloy (HSLA) steel plays an important role in offshore structures. In addition, underwater local cavity welding (ULCW) technique was widely used to repair important offshore constructions. However, the high cooling rate of ULCW joints results in bad welding quality compared with underwater dry welding (UDW) joints. Q690E high strength low alloy steels were welded by multi-pass UDW and ULCW techniques, to study the microstructural evolution and mechanical properties of underwater welded joints. The microstructure and fracture morphology of welded joints were observed by scanning electron microscope and optical microscope. The elemental distribution in the microstructure was determined with an Electron Probe Microanalyzer. The results indicated that the microstructure of both two welded joints was similar. However, martensite and martensite-austenite components were significantly different with different underwater welding methods such that the micro-hardness of the HAZ and FZ in the ULCW specimen was higher than that of the corresponding regions in UDW joint. The yield strength and ultimate tensile strength of the ULCW specimen are 109 MPa lower and 77 MPa lower, respectively, than those of the UDW joint. The impact toughness of the UDW joint was superior to those of the ULCW joint.

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