Overview
This document contains information on:
General
Function requirements
Function
General
Exhaust gas cleaning fulfills a central task of the exhaust gas aftertreatment. Exhaust gas cleaning ensures the targeted reduction of exhaust gas emissions.
Function requirements
Engine management ON (circuit 87M)
Engine in operation
Catalytic converters at operating temperature (approx. 300 °C)
Stoichiometric fuel/air ratio in the exhaust gas
Coolant temperature and exhaust gas temperature reached for gasoline particulate filter regeneration phase
Function
The following exhaust gases that are hazardous to health and the environment are generated during fuel combustion, for example:
Nitrogen oxides (NOx)
Hydrocarbon (HC)
Carbon monoxide (CO)
Catalytic converters are used for exhaust gas cleaning. The requirement for efficient exhaust gas cleaning is a defined mixture formation, which ensures a stoichiometric fuel/air ratio in the exhaust gas for cleaning. The optimum effect of the catalytic converter is ensured in this area.
A mixing ratio of 14.7 kg of air to 1 kg of fuel is necessary in order to achieve theoretically complete combustion. The ratio of air to fuel is a "stoichiometric ratio" (lambda λ). If the air volume delivered corresponds to the theoretical air requirement, this results in the value λ = 1.
In diesel engines in particular, but also in spark-ignition engines, there are also exhaust gas emissions in the form of soot particles. A gasoline particulate filter is used for cleaning here.
The following catalytic converters and gasoline particulate filters are used for exhaust gas cleaning:
Diesel engine | Spark-ignition engine |
Oxidation catalytic converter: Vehicle catalytic converter for converting the pollutants of carbon monoxide and hydrocarbons, which are generated during fuel combustion, into carbon dioxide (CO2) and water (H2O). As it is an upstream component, it also contributes to removing NOx from the exhaust gases. To do so, it converts nitric oxide (NO) to nitrogen dioxide (NO2). | Three-way catalytic converter: Vehicle catalytic converter with lambda control for exhaust gas aftertreatment in vehicles with a spark-ignition engine. Carbon monoxide, nitrogen oxide and unburned hydrocarbons are converted into carbon dioxide (CO2), nitrogen (N2) and water (H2O). |
SCR catalytic converter: Vehicle catalytic converter for reducing nitrogen oxide emissions using ammonia (NH3). Ammonia is generated with the aid of a reduction agent. The nitrogen oxide in the exhaust gas reacts with ammonia and oxygen to form molecular nitrogen (N2) and water vapor. | Gasoline particulate filter: Filter unit that filters and stores soot particles that are generated during the combustion process. It also ensures soot particle oxidization during gasoline particulate filter regeneration. |
Gasoline particulate filter: Filter unit that filters and stores soot particles that are generated during the combustion process. It also ensures soot particle combustion during the regeneration of the gasoline particulate filter. |
Depending on the fuel type, injection procedure, combustion temperature and pressure, different concentrations of nitrogen oxide are generated in the exhaust gas during the combustion of the fuel/air mixture. Different types or combinations of catalytic converters are used in order to ensure compliance with the emissions limit value required by law.
Function schematics | |||
Function schematic for exhaust gas cleaning | Engine 608 in model 118, 177, 247Engine 654 in model 118, 167, 177, 247Engine 656 in model 167, 223 | ||
Engine 279 in model 223 | |||
Engine 176 in model 167, 223 | |||
Engine 139 in model 118, 177 | |||
Engine 256 in model 223 | |||
Additional basic functions | |||
Catalytic process, basic function | Engine all (CAR) | ||
Control units | |||
Soot particulate sensor control unit, basic function | Engine 608 in model 118, 177, 247 | ||
Components | |||
Soot particulate filter, basic function | Engine 608 in model 118, 177, 247 |