Automotive Engineering > Exhaust train

A central theme in the operation of combustion engines is the cleaning of the exhaust gases and their conversion into substances that are not hazardous to the environment. For this purpose, catalytic converters and diesel particulate filters are used in the exhaust gas systems of the engines to enable compliance with prescribed exhaust gas limits.

The central functional element of a catalytic converter for motorized vehicles is, according to the state of the art, usually a honeycomb body made of cordierite, which is coated with porous Al2O3, other oxides and a catalytically active metal of the platinum group or an alloy of the same. For optimum combustion at around 500 °C to CO2, H2O and N2, the operation of a three-way catalytic converter requires control of the fuel/air ratio with the help of a l sensor, the central functional element of which is a solid electrolyte made of doped ZrO2 ceramic, today usually of the type Y-TZP.

This technology is not sufficient in the operation of diesel engines as, on account of the excess O2 in their exhaust gases, the NOx is not reduced to N2. With further technical measures, however, a substantial reduction in the NOx is achieved.

The exhaust gas of diesel engines also contains particles of soot that are collected by honeycomb ceramics and burnt off at regular intervals. For this application, ceramic honeycombs made of SiC are interesting as this type of material brings the following properties:

  • High mechanical resilience
  • High stiffness
  • High wear resistance
  • High thermal stability
  • High thermal shock resistance
  • Long-term durability in operating conditions
  • Electrically conductive

The recirculation of the exhaust gases into the exhaust gas flow leads to a substantial decrease in the temperature of the exhaust gas and consequently to a much reduced content of NOx in the exhaust gas down to its complete elimination. An important functional element of such a valve is the valve body in direct contact with the exhaust gas as this is exposed to both high thermal stress and potential abrasive and corrosive attack by constituents of the exhaust gas. For this application, the use of, for example, non-oxide ceramics is expedient as reliably operating valve components with long-term durability.

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Products for the application
Exhaust train

Diesel particulate filters, catalytic converters

      Honeycombs

exhaust gas control valves

      Bearing bushes

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