B5.1 - Recent Developments in Automotive Exhaust Gas Sensing

SENSOR+TEST Conferences 2009
2009-05-26 - 2009-05-28
Congress Center Nürnberg
Proceedings SENSOR 2009, Volume I
B5 - Gas Sensors
R. Moos - Universität Bayreuth, Bayreuth, Germany
227 - 231


Increasing fuel costs combined with the pressure on the automotive industry to reduce CO2 emissions lead to booming market shares for Diesel passenger cars. They are operated leanly. Therefore, nitrogen oxide (NOx) removal with conventional three way catalysts (TWC) is not possible. At the same time, NOx emission limits have been strongly reduced. Leanly operated gasoline direct injection engines are another way for reducing fuel consumption. Both lean concepts require novel exhaust gas aftertreatment concepts, especially for NOx abatement.

The ammonia SCR process prevails for NOx removal of coal power plant exhausts. This process has been adapted for automotive requirements. For heavy duty vehicles, systems are already in serial application, and recently, they have been serialized for passenger cars as well.

NOx storage catalysts (often denoted as lean NOx traps, LNT) were developed and have been introduced for gasoline direct injection engines. Here, during a lean phase, NOx is adsorbed and stored in the form of nitrates. Nitrate reduction occurs in a short rich phase, just before the NOx storage capacity of the LNT is exhausted and it begins to let pass NOx.

In the meantime, LNTs are also in serial production for the aftertreatment of Diesel engine exhausts, as well as the SCR system is in discussion for gasoline direct engines. Even the combination of both NOx removal technologies, in which ammonia is formed during a short rich phase, is in serial application. For both novel NOx removal technologies, ammonia SCR and LNT, novel exhaust gas sensors that supplement the well-known and mature lambda-probe might be helpful.

Due to the strongly reduced particulate matter limits, Diesel particulate filters have been serialized. Besides a differential pressure sensor to detect the exhaust back pressure and to initiate filter regeneration, a soot sensor might be helpful to detect cracks in or damages of a Diesel particulate filter, which would result in a low backpressure but also in a low particulate reduction efficiency. However, soot sensors are not considered here.