Audi A4

since 1994 release

Manual of the car

Audi A4
+ Running gear
+ Regular servicing
+ Engines
+ Turbo-supercharging
+ System of an exhaust
+ Cooling system
+ Fuel tank and fuel pump
+ Air filter and channels of absorption
+ System of injection
+ Coupling
+ Transmission and main transfer
+ Suspension bracket of wheels and steering
+ Brakes
+ Wheels and tires
+ Electrotechnical equipment
- System of ignition
   What provides ignition
   When there is an ignition of fuel-air mix?
   Different systems of ignition
   So there is an ignition spark
   Executive body
   System brain
   The signals coming to the control unit
   Adjustment of a detonation
   Be careful in the address with ignition
   Works on system of ignition
   Search of malfunctions in ignition
   Ignition distributor
   Knot of high voltage
   Replacement of spark plugs
   Right choice of spark plugs
   Check of the moment of ignition
+ Lighting
+ Alarm equipment
+ Tools and devices
+ Heating and ventilation
+ Body details
+ Salon
Search of malfunctions
Technical characteristics

When there is an ignition of fuel-air mix?

The drawing illustrates the concept "Top Dead Point" and "Lower Dead Point". The space between them is the working volume of the cylinder. On the contrary, between the highest position of the piston (2) and bottom edge of a head of the block of cylinders (1) the combustion chamber is shown.

Basic element of system of ignition of the four-cylinder engine with a working volume of 1,6 l is the separate coil of ignition (1) and the terminal cascade (3) with the socket (2). Distribution of tension of ignition on cylinders carries out the ignition distributor here.

Package of coils of ignition of the six-cylinder engine with uncovered the engine (static distribution of ignition). Figures on sockets of high voltage are explained to what cylinder there is a wire.

In the 92 kW engine of 1,8 l the ignition coil on the cylinder 3 serves also the cylinder 1, and the ignition coil on the cylinder 4 – also the cylinder 2. Above on coils of ignition the terminal cascade is installed.

Ignition of the 110 kW turbo engine of 1,8 l: each cylinder has an own coil of ignition (1–4).

The spark has to slip in the combustion chamber at the right time. Combustion of fuel-air mix happens most effectively while it is compressed up to the most minimum volume. This maximum compression is reached during that moment when the piston at end of the course of compression wants to pass from progress to the return movement of a working step. Before the piston passes to the movement in the opposite direction, a share of a moment it is in the highest point of a trajectory of the movement. This point is called "top dead point" (TDP).

So, the ideal moment of ignition is that moment when the piston only begins the return movement. The compression is maximum, and the piston can be wrung out with a force to the engine block.

Despite it, would be wrong to determine the ignition moment precisely in the top dead point. As fuel-air mix needs certain time (about 1/3000 c) before its ignition and development of total pressure of combustion. Therefore the moment of ignition is determined for earlier term. We speak about "an ignition advancing". Therefore the starting shot for a spark sounds even during the movement of the piston up, and pressure of combustion develops right after VMT.

Top dead point and advancing of ignition

With increase in speed of the engine the spark of ignition has to slip earlier and earlier since – as it was already told – fuel-air mix always needs the same time for ignition. Combustion process precisely in due time is only this way carried out namely when the piston only starts over again moving back. Combustion of fuel-air mix depends also on its structure. At slightly wrung out accelerator pedal (at "partial loading") mix in combustion chambers has the lowered ability to ignition therefore it burns down more slowly and for this reason ignition has to work with a big advancing too.

Installation of ignition with delay

In other situations it is necessary to shift the ignition moment in the direction of "delay". Ignition occurs when the piston passed the top dead point for a long time. I.e. ignition is carried out almost on an exhaust step that improves composition of exhaust gases, but worsens engine capacity. Therefore, late ignition can be correct when the engine works without loading in the mode of swing of the car (for example, downhill without gas).