Overlap period is the period in crank angle degrees during which both inlet and exhaust valves are open to assist in clearing the products of combustion from the cylinder. Is it affected by ambient conditions?
The overlap angle is negligibly affected by atmospheric conditions.
It depends mainly on the performance required by the engine. Higher clearance is typical of the race engines running at maximum speed. Lower clearance is used by standard engines, in order to minimize fuel loss to the exhaust and fule consumption. There is no definite value.
The overlap angle is influenced by several factors, e.g. the engine speed, the combustion chamber geometry, the number and arrangement of valves, the aspiration system (if the engine has a turbo or compressor charger). In addition, the performance targets and the emission targets play an important role. Small capacity engines with higher rpm may have values between 10 and 20 degrees, some racing engines up to 30 degrees. Supercharged engines normally have lower values. Which type of engine do you focus?
Of course the overlap period is intended for clearing the cylinder from the products of combustion of the previous cycle. But in gasoline engines this is associated with loss of fuel as part of the charge is used in the clearing process. So what is the optimum period for accomplishing the process without losing too much fuel into the exhaust.
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