Fundamental analysis of thermal overload in diesel engines: Hypothesis and validation

'Thermal Overload' can be defined as a condition under which design threshold values such as the surface temperature of combustion chamber components is exceeded. In this paper, a low λ value is identified as the most probable cause of voluminous flame production, resulting in high surface temperatures of engine components, i.e., engine thermal overload. Test results indicated that the flame became voluminous when the excess air ratio, λ was low, and the exhaust temperature increased from 775 to 1000 °C with λ changing from 1.12 to 0.71. Temperature indicating paints were applied on two piston crowns to investigate the effect of the voluminous flame on component surface temperature. The piston crown with high rates of hot corrosion was very close to matt glaze (much in excess of the design temperature), which proved that high surface temperature and salt deposition on the crown in the heavily burned away regions could have been caused by flame and fuel impingement, respectively. A numerical calculation was presented to estimate the flame temperature for various air excess ratio, which provides a guidance for the operation conditions of diesel engines to avoid engine thermal fatigue due to thermal overload.