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Abstract:In order to study the characteristics of diesel spray impinging in small-size internal combustion (IC) engine, the laboratorial platform of spray impingement is used to visualize the droplet impact phenomenon. A high-speed camera is used to record the whole process of the spray. An experimental research is accomplished under the impingement phenomenon of diesel spray on the wall with a fixed injection volume of 25 mg, injection pressure of 40 MPa, wall-injector distance of 40mm and orifice diameter of 0.26 mm. The computational fluid dynamics (CFD) simulation is carried out and the turbulence kinetic energy (TKE) distribution diagram is obtained. The results show that the maximum spray radius is 29.3 mm and maximum spray height is 10.2 mm at 2.8 ms. The spray impingement phenomenon presents the "blanket" shape. The simulation results are similar to the experimental results with the average error of the spray height within 3%.

A two-step double-side friction stir welding (DS-FSW) technique was proposed to join 20 mm thick Mg-Y-Nd magnesium alloy plates. FSW was first carried out on one side of the butt joint, and then the plates were left-right reversed for the other side welding. The DS-FSW joint was free of defects and the weld nugget zone (NZ) showed fine equiaxial grains. An overlap zone with ultrafine grain ( ∼ 2.19 µm) and dispersive particles existed between the two welding tracks, beneficial to the integrity of the joint. The ultimate tensile strength (σ UTS ), yield strength (σ 0.2 ), and elongation rate (δ) of the joint were 277. 6, 204.1 MPa, and 7.27%. A high joint efficiency (σ UTS ratio between the joint and parent material) was achieved at ∼ 82.6%.