Research on the influence mechanism of wall-attached fuel film combustion on the Piston's thermal load and fatigue damage

For engines in high-altitude low-temperature environments, in-cylinder liquid fuel spray inevitably impinges on combustion chamber walls, forming wall-attached fuel film and inducing combustion, which directly affects piston thermal load and fatigue life. Based on transient heat flux data from wall-attached fuel film combustion and Sehitoglu theory, this study analyzes the evolution of piston temperature field, thermal load, and low-cycle thermal fatigue life at 0-8000 m altitudes. Results show that elevated altitude increases liquid-phase fuel spray penetration length (LPL), promoting more wall-attached fuel film and pool fire. Consequently, the temperature of piston throat rises from 212.7 (0 m) to 438.3 °C (8000 m) under idle operation, and piston crown maximum temperature difference surges from 28.2 to 143.5 °C, forming an extreme top temperature gradient. This modifies piston thermal load distribution: piston throat thermal stress under idle operation exceeds rated operation making idle operation critical for thermal fatigue. Additionally, outward expansion of the combustion region and constrained thermal expansion by the cooler ring groove raise the crown edge's tensile stress amplitude from 11.7 to 48.5 MPa. Notably, minimum fatigue life shifts from the throat to the crown edge: at 0 m, the throat (4420 cycles) has shorter life than the edge (36452 cycles); at 8000 m, the throat reaches 171 cycles (high biaxial compressive stress, Poisson effect-reduced strain), while the edge (1.49 × the throat's equivalent strain under uniaxial tensile stress) plummets to 137 cycles, becoming the new fatigue-sensitive region.