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In this study, effects of altitude on free diesel spray morphology, macroscopic spray characteristics and air-fuel mixing process were investigated. The diesel spray visualization experiment using high-speed photography was performed in a constant volume chamber which reproduced the injection diesel-like thermodynamic conditions of a heavy-duty turbocharged diesel engine operating at sea level and 1000 m, 2000 m, 3000 m and 4500 m above sea level. The results showed that the spray morphology became narrower and longer at higher altitude, and small vortex-like structures were observed on the downstream spray periphery. Spray penetration increased and spray angle decreased with increasing altitude. At altitudes of 0 m, 1000 m, 2000 m, 3000 m and 4500 m, the spray penetration at 1.45 ms after start of injection (ASOI) were 79.54 mm, 80.51 mm, 81.49 mm, 83.29 mm and 88.92 mm respectively, and the spray angle were 10.9°, 10.8°, 10.7°, 10.4°and 9.8° respectively.

The thermal and mechanical loads of the engine rise dramatically with the increase in engine power density, which places higher demands on the design of the piston. In this paper, the design development of a steel piston for a marine diesel engine belonging to 190 series heavy-duty diesel engines was studied. The design methods including material selection and structural design were used to finished the preliminary design. In the meanwhile, the design philosophies of the aluminum alloy piston and composite piston for the 190 series diesel engines were used for reference in the design process. The designed steel piston was tested in the engine durability bench test and simulated for reliability. The results showed that the failure of the steel piston occurred at the same position in both the test and the simulation. The cause of cracking in the steel piston was analyzed, and the insufficient strength of the local structure led to high-cycle fatigue failure.