Circuit/System Description
For an overview of the component/system, refer to: Exhaust Aftertreatment System Description
| Component | Description |
|---|---|
| B195 Nitrogen Oxides Sensor | NOx sensors work similar to wide-band O2 sensors. The sensors consist of two measuring cells. In the first cell, an electric pump current is used to separate out the oxygen in the exhaust. The NOx remains and is conveyed into the second chamber. Here a second pump current decomposes the NOx into nitrogen and oxygen. The oxygen concentration is measured and from there the NOx concentration can be calculated.The sensor delivers signals for wide-band lambda, digital lambda and NOx concentration. The sensor is attached to a control module that is calibrated to this particular sensor. The module communicates with the engine control module via serial data. |
| K20 Engine Control Module | The control module controls a series of actuators to ensure optimal engine performance. The control module does this by reading values from a variety of sensors, interprets the data and adjusts the engine actuators accordingly. |
Lean-burn engines operate with excess oxygen. This produces harmful nitrogen oxides (NOx) which are stored in the adsorber catalyst. The nitric oxide (NO) is first oxidized to nitrogen dioxide (NO2). To regenerate the catalyst when the storage capacity is reached, the engine control module cyclically uses a rich, reducing mixture so that the NO2 is converted to nitrogen (N2), water (H2O) and carbon dioxide (CO2).
Two NOx sensors are mounted upstream and downstream of the selective catalytic reduction catalyst. The upstream sensor is used to determine how much reductant should be injected. The downstream sensor is used for adaptation and diagnostic of the system.