1. During combustion period, the heat fluxes to the chamber walls can reach as high as 10 mW/m2.
The flux varies substantially with location. The regions of the chamber that are contacted by
rapidly moving high temperature gases generally experience the highest fluxes. In region of
high heat flux, thermal stresses must be kept below levels that would cause fatigue cracking.
So temperatures must be less than about 400°C for cast iron and 300°C for aluminium alloy
for water cooled engines. For air-cooled engines, these values are 270°C and 200°C respectively.
2. The gas side surface temperature of the cylinder wall is limited by the type of lubricating oil
used and this temperature ranges from 160°C to 180°C. Beyond these temperature, the properties
of lubricating oil deteriorates very rapidly and it might even evaporates and burn, damaging
piston and cylinder surfaces. Piston seizure due to overheating resulting from the failure
of lubrication is quite common.