Emission control

In order to keep up with the increasingly strict emissions regulations, exhaust gas recirculation systems are required.

Cooled exhaust gas reduces the peak combustion temperature. This significantly reduces the amount of nitrogen oxides. Additionally, cooled gases are denser than warmer ones. This means that at the same boost pressure, a larger volume of gas fits into one cylinder filling. This produces a “leaner” combustion which also improves fuel consumption and particulate emissions.

Nowadays all modern diesel engines must be fitted with EGR systems in order to comply with exhaust gas regulations.

Exhaust gas is removed immediately after the cylinder and mixed with the intake air. This means that less oxygen reaches the cylinder, which results in a lower combustion temperature. As a result, the amount of nitrogen oxides in the exhaust gas can be reduced by up to 50 %. In petrol engines, this can also reduce carbon dioxide emissions and fuel consumption.

Exhaust gas flaps are an important element in modern engines for emission control and increased comfort. They direct the exhaust gas into different exhaust tracts depending on the operating state.

Fields of application for areas close to the engine:

• DeNOx catalytic converters
• Low-pressure exhaust gas recirculation
• HC absorbers

Motorservice’s product range encompasses pneumatic and electrical exhaust gas flaps as well as exhaust gas flaps for motorcycles. All flaps are designed for extreme gas temperatures from –40°C to +950°C and a durability of over 1,000,000 switching cycles.

Lambda sensors measure the residual oxygen in the exhaust gas. This produces a lambda value, which the engine management system uses to regulate the mixture composition for the most optimal combustion possible.

Lambda sensors are the most important element in engine management systems in terms of ensuring perfect engine running with low emissions.

High operating temperatures and aggressive exhaust gas place high demands on lambda sensors. You should therefore choose specialist products for emission control.

Exhaust gas temperature sensors monitor the hot exhaust gas flow and protect components from overheating. Typical applications include protecting components which are sensitive to temperatures, such as turbochargers and all forms of catalytic converters, monitoring the free-burning process of the diesel particulate filter, controlling the optimal temperature range for catalytic converters and measuring the EGR exhaust gas temperature as part of on-board diagnostics (OBD). In the event of critical overheating, the control unit responds with suitable measures to reduce the temperature, e.g. through reduced performance (limp home function).

Motorservice covers around 1,400 vehicle types with 30 exhaust gas temperature sensors.

Secondary air pumps are high-speed one or two-stage blowers. These draw in ambient air and inject them into the exhaust manifold downstream of the exhaust valves. In petrol engines this ensures a noticeable reduction of a large amount of carbon monoxide and unburnt hydrocarbons during the cold start phase – when the catalytic converter has not yet reached working temperature.

The secondary air valves are located between the secondary air pump and the exhaust manifold. The secondary air valve performs multiple tasks:

• The non-return function stops exhaust gas, condensate or pressure peaks in the exhaust tract from causing damage to the secondary air pump.
• The shut-off function ensures that secondary air is only routed to the exhaust manifold in the cold start phase.

Electrical secondary air valves have shorter opening and closing times and are more resistant against sticking due to soot or dirt.

Pneumatic secondary air valves have proven their worth over decades. They need to be actuated by a switchover valve.

This type of secondary air valve opens due to pressure from the secondary air pump.