Audi A3

since 1997 of release

Repair and car operation

Audi A3
+ Maintenance instruction
+ Current leaving and service
+ Engine
+ Systems of cooling, heating
- Power supply system and production of the fulfilled gases
   + Power supply system
   + System of injection of fuel
   + System of injection of the diesel engine
   - System of production of the fulfilled gases
      Operation of the catalytic converter
      Security measures for an exception of damages of the catalytic converter
      Removal and installation of system of release
      Checking of system of release
      Replacement of the central/additional exhaust silencer
      Check of system of release on tightness
      Replacement of the sensor of oxygen
+ engine Electric equipment
+ Manual box of gear shifting
+ Automatic transmission and models with a full drive
+ Coupling and power shafts
+ Brake system
+ Suspension bracket and steering
+ Body
+ Onboard electric equipment
+ Elektroskhema


Operation of the catalytic converter


All engines are equipped by one or several catalytic converters for purification of exhaust gases.
The catalytic converter has the central ceramic part of a cellular design–3–covered with a layer of the carrier. On a layer of the carrier there are the salts of precious metals operating as converters. The catalytic converter is fixed in the case-1-by means of the insulating basic layer–2–compensating at the same time thermal expansions of the catalytic converter.

Catalytic converter

1 case
2 consolidation
3 honeycombs of catalytic converter

Petrol engines

To reduce by means of the catalytic converter harmful emissions, systems of injection should dose out precisely amount of the injected fuel necessary for combustion. The sensor of oxygen is in a reception pipe in front of the catalytic converter and is washed by a stream of the fulfilled gases. The sensor of oxygen represents the electronic sensor measuring the content of oxygen in final gases and representing its type of fluctuations of tension. Information from the sensor of oxygen is transferred to the control unit of system of injection. The received value allows to regulate structure of an air-petrol mix. On the one hand it is necessary, as service conditions (the idling, full gas), on the other hand, constantly change as optimum reburning of fuel in the catalyst occurs only in this case if final gases contain fuel enough.

That in the catalyst there was a fuel reburning, it is necessary to have temperature 300 – 800°С. For this purpose the bigger content of fuel in a mix, than for pure burning is necessary.

Applied catalytic converters of petrol engines represent so-called three-functional devices. In adjustable process of transformation oxidation of an oxide of carbon (WITH) and hydrocarbon (NANOSECOND), and also reduction of concentration of oxides of nitrogen (NOx) is carried out.

Gases on an entrance of the catalytic converter and products on its exit

The catalytic converter and system of a retsirkulyatsiya of the fulfilled gases of the diesel engine

The fulfilled gases of the diesel engine also are cleared in the catalytic converter. Thus it is a question of the noncontrollable oxidizing catalytic converter. Such catalytic converter turns oxides of carbon containing in fulfilled gases and hydrocarbonic connections into CO2 and H2O.

Decrease in concentration in the fulfilled gases of the diesel engine of oxides of nitrogen (NOx) is reached thanks to existence of additional system of regeneration of the fulfilled gases (EGR system).

On a final collector of the engine the valve of system of the retsirkulyatsiya, operated by vacuum is located. Its task is the direction of a part of the fulfilled gases in chambers of combustion of the engine that promotes decrease in temperature of the fulfilled gases and by that to decrease in concentration of harmful substances.