Exhaust system with oxidation catalytic converter |
1 | Primary catalytic converter |
2 | Oxidation catalytic converter |
3 | Differential pressure sensor |
4 | Rear muffler |
5 | Soot particulate filter |
6 | Temperature sensor upstream of soot particulate filter |
7 | CAT temperature sensor |
8 | Oxygen sensor upstream of TWC [KAT] |
P49.10-A068-74
Overview
This document contains information on:
General
Function requirements
Function
General
As a vehicle catalytic converter, the oxidation catalytic converter ensures the removal of exhaust gas emissions that arise during fuel combustion. It converts pollutants, i.e. carbon monoxide (CO), hydrocarbons (HC), and nitric oxide (NO), into carbon dioxide (CO2), water (H2O), and nitrogen dioxide (NO2). As an upstream component, the oxidation catalytic converter additionally contributes to the NOx removal process for exhaust gases. For this purpose, it converts nitric oxide (NO) into nitrogen dioxide (NO2).
Function requirements
Engine in operation
Function
The oxidation catalytic converter fulfills a precleaning function within the exhaust system.
As a result of the conversion of hydrocarbons, the particulate mass contained in the exhaust gas is reduced. The soot particles consist partially of hydrocarbons, which are released from the particle nucleus as the temperature increases. The oxidation of these hydrocarbons in the oxidation catalytic converter results in a reduction in the particulate mass by 15 to 30 %.
A high concentration of nitrogen dioxide, which occurs as a result of the oxidation of nitric oxide, is relevant for the downstream components of the exhaust system (e. g. soot particulate filter, SCR catalytic converter).
The oxidation catalytic converter additionally acts as a catalytic burner for raising the exhaust gas temperature. The reaction heat released during oxidation makes it possible to increase the exhaust gas temperature downstream of the oxidation catalytic converter. A catalytic burner is used for regenerating the soot particulate filter, for example. To reach the required regeneration temperature in the exhaust gas, an in-engine post injection additionally introduces carbon monoxide emissions and hydrocarbons.
Because of the high oxygen concentration in the exhaust gas, the mode of operation of the oxidation catalytic converter already starts at an operating temperature of approx. 170 °C. The oxidation catalytic converter reaches its highest conversion rate of approx. 90 % at its optimal operating temperature of approx. 250 to 350 °C . To reach the optimum temperature range quickly, the oxidation catalytic converter is installed near to the engine.