Functioning Principle Of The Timing Light; Advance In Gasoline Engines - tecnotest 232-E Mode D'emploi

__________________________________________________________________________ TIMING LIGHT
1.0 -

FUNCTIONING PRINCIPLE OF THE TIMING LIGHT

1.1 -

Advance in gasoline engines

In the controlled ignition engines, the spark firing inside the combustion chamber starts
the combustion.
At the firing two types of mixture form inside the combustion chamber:
the air/fuel mixture to be burnt and the air/fuel mixture already burnt, they
are separated by the combustion flame or flame front.
Between the air/fuel mixture primer (spark firing) and its complete combustion usually
2 milliseconds pass.
The spark has to fire with an ignition advance allowing to have the maximum
combustion pressure
Top Dead Center (TDC).
If the spark fires too early the piston stroke is stopped, while if it fires too late the
maximum compression ratio cannot be exploited (see picture a).
The ignition advance is determined by two variables:
REVOLUTION NUMBER
:
ENGINE CHARGE
NOTA BENE:
Each engine has to have a minimum advance (regardless of the conditions of the
engine to be tested) usually ranging from 5° to 15°.
SERVICE MANUAL
some seconds
: The higher is the revolution number the higher has to be
the ignition advance since the cam shaft revolves more
quickly thus reaching earlier the TDC.
Consequently, the combustion has to be started earlier.
The lower is the engine charge, the higher is the firing
value of the air/fuel mixture hence the combustion is
slower. An advance increase is thus necessary.
after the piston has crossed the
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