The amount if time taken for a fuel/air mixture to combust mainly depends on the richness of the fuel mixture. When the engine is under low load with a lean air/fuel mixture the degree of ignition advance will need to be large to allow for the slow combustion of this mixture. Conversely when the engine is under load a richer air/fuel mixture is used to provide more power. This richer mixture has a faster combustion time so the degree of ignition advance needs to be reduced to keep the peak combustion pressure just beyond TDC.
To achieve this variation of ignition advance in modern engines load mapping is used. Information is sent from either a throttle potentiometer or a manifold pressure sensor to indicate how much load the engine is under. Therefore, load mapping varies the amount of ignition advance in relation to engine speed and load.
The picture below is a simulation our Sparkz GUI software. The GS8 package is able to use 5 maps to provide a 3D map of the engines performance. We will assume the load mapping is being carried out by a throttle potentiometer.
Map 1 is used when the engine is under zero load i.e. when then the throttle position is zero. As the throttle is increased to 25% of full throttle, the ignition angle is interpolated between the values of Map 1 and Map 2. This process this continued through the range of throttle positions until the throttle is at 100% and the engine is using Map 5.
The precision that load mapping provides allows the engine to operate at it's most efficient and clean throughout the range of load conditions.
