Function of Advancer
It Fools the ECU by manipulating the signals to ECU by various sensors. It intercepts the sensor signals & sends corrected/manipulated signals to the ECU so the ECU Advances the ignition timing as per the sensor signal automatically.
Basically it is installed so that ignition timing of the vehicle remains at default settings for PETROL as u drive on PETROL and automatically advances when you convert to CNG, without having to move the DISTRIBUTOR physically. So the vehicle runs perfectly on PETROL as well as on CNG.