
COMBUSTION CHAMBERS AND PROCESSES 75
so that better mixing leads to more efficient burning
of lean mixtures and hence contributes to better fuel
economy.
4 The provision of two exhaust valves minimizes the
intensity of hot-spots in the combustion chamber,
thereby avoiding too high combustion temperatures
which can promote the formation of polluting nitro-
gen oxides in the exhaust gases.
5 The four-square arrangement of the valves allows the
spark plug to be centrally positioned in the combus-
tion chamber, so that flame travels can be both
equalized and minimized for good detonation control.
An increase in compression ratio may then be possibl ...