It is known that heat transfer effects internal combustion
engine performance, efficiency, and emissions.
As far as performance is concerned, cooling for the
cylinder head, cylinder, and piston is desired because
of problems such as thermal stresses in regions of high
heat flux, deterioration of the lubricating oil film, and
knock and preignition in spark ignition engines. On
the other hand, an increase of heat transfer to the
combustion chamber walls will lower the gas temperature
and pressure within the cylinder, and this
reduces the work per cycle transferred to the piston.
Heat transfer from the working gas to the cooling
system of a conventional diesel engine accounts for
up to 30% of the fuel energy. About 50% of this
energy is lost through the piston and 30% through
the head [I]. Thus efficiency is affected by the magnitude
of engine heat transfer. Changes in gas temperature
due to the heat transfer also impact pollutant
emission formation processes. Generally, a higher
temperature in the cylinder during combustion can
cause an increment in NO, emissions, but a lower
temperature may promote the formation of particulates,
or soot. Therefore, in the sense of emission
control. more attention should be paid to engine heat
transfer.