Audi 80/Avant (B4)
since 1991-1995 release
Repair and operation of the car
+ Technical specification
+ System of production of the fulfilled gases
+ Cooling system
+ Fuel tank and fuel pump
+ Air filter and airintaking channels
+ System of injection
+ Transmission and transmission
+ Suspension bracket and steering
+ Brake system
+ Anti-blocking system of brakes
+ Wheels and tires
+ Body electrical system
- System of ignition
Various systems of ignition
Principle of work of ignition
Impulses for the control unit
Regulation on a detonation
Security measures during the work with system of ignition
Repair of system of ignition
Diagnostics of system of ignition
Sensor of detonation combustion
Elements of high voltage
Replacement of spark plugs
Check of the moment of ignition
+ Signaling devices
+ Devices and auxiliary devices
+ Heating and ventilation
+ Body elements
+ Search of malfunctions
System of ignition
The system of ignition provides the correct passing of process of combustion in the engine thanks to purposefully "shot" igniting sparks. And everything occurs precisely because at average 3000 rpm of the engine each cylinder needs 25 sparks a second. So the 4-cylinder engine will need 100 sparks a second, 6000 in a minute, 360 000 in an hour and so on.
That ignition can
In order that in a spark plug in the combustion chamber in general the spark could slip, between electrodes of a spark plug there has to be tension of at least 30 000 Century. The rechargeable battery gives, however, only 12 V of tension. Thus, tension of the accumulator needs to be increased repeatedly. Flash duration not the tenth, and not 100-th, but thousand fractions of a second. Once it works a little sooner or later, and efficiency of ignition, and thereby and engine capacity will be lowered.
When there is an ignition?
The spark has to slip precisely at the right time. However to establish when there is this most necessary moment, not so simply.
VMT and advancing of ignition
With increase of turns of the engine the igniting spark has to jump earlier and earlier as – we already mentioned it in the last section – mix of fuel and air needs constantly same time to ignite. Only thus combustion happens at the right time namely when the piston only begins the movement down.
Combustion of mix of fuel and air depends, however, and on its structure. If the pedal of an accelerator is squeezed out very little ("partial loading"), ability of mix in combustion chambers to ignition decreases: therefore it burns down more slowly and for this reason has to ignite earlier.
In other situations it is necessary that the moment of ignition moved towards late ignition. Ignition in that case happens only when the piston passed VMT for a long time. Thus, ignition occurs practically in a release step that improves composition of exhaust gases, but worsens engine capacity. According to the aforesaid, late ignition is only correct, for example, during the operation of the engine in the mode of compulsory idling (for example, at the movement under a hill with the released accelerator pedal).