Functioning Of The Timing Light; Advance - TechoTest 138-E Manual Del Usuario

__________________________________________________________________________ TIMING LIGHT
1.0 -

FUNCTIONING OF THE TIMING LIGHT

1.1 -

Advance

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°.
OPERATING INSTRUCTIONS
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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