New Approaches for Exhaust Gas Sensing

Abstract

Steadily increasing emission standards for passenger cars and heavy duty vehicles combined with the need for fuel efficiency lead to novel powertrain concepts, for example to leanly operated gasoline direct injection engines, or to novel exhaust gas aftertreatment concepts such as Lean NO x Traps (LNT), ammonia selective catalytic reduction catalysts for NO x reduction (SCR), or even to a combination of both. Also, diesel particulate filters (DPF) are in series production.To control these novel exhaust gas aftertreatment systems and to monitor onboard the proper operation of these systems (on-board diagnosis, OBD), novel exhaust gas sensors are required or are at least be very helpful. Since the development of exhaust gas sensors has always to be seen in interaction with the corresponding exhaust gas aftertreatment systems, novel types of exhaust gas sensors have gained in importance just recently, when the time was ripe for novel exhaust gas aftertreatment concepts. This article reports on several types of NO x sensors and ammonia sensors.Additionally, a very recent novel concept is presented. Here, the catalyst itself works as a sensing device that gives directly information on its own status. The readout can be wirebound (demonstrated for LNT and SCR) or even be wireless by applying radio frequency techniques. It will be shown that this allows to detect the oxygen loading degree of three-way catalysts very precisely. It can be also applied to determine the ammonia loading of SCR catalysts and the soot loading of DPF.As a conclusion, these novel methods may provide a future alternative for low emission-aiming engine control as well as for OBD of low emission vehicles with novel exhaust gas aftertreatment systems. However, it is clear that all novel sensors or systems do not only have to meet the technical requirements but also have to be very inexpensive, reliable, and cost effective.R. Moos (*)

Optical methods for sensing and imaging oxygen: materials, spectroscopies and applications

“…It offers robust analytical information that is insensitive to photobleaching, migration or varying concentration of fluorophores, and variations in illumination intensity, at least in a first approximation. Sensing of oxygen via anisotropy is based on the fact that polarization depends on the decay time of the OSP 108,109 as can be seen from eqn (9). The decay time of the OSPs is reduced by oxygen so that anisotropy can be related to the concentration (or partial pressure) of oxygen.…”

“…This so-called lambda probe (for a review, see ref. 9) was developed by the Bosch company during the late 1960s and is based on a zirconia ceramic coated on both the exhaust and reference sides with a thin layer of platinum to form a solid-state electrochemical fuel cell, where CO (if present) is oxidized by oxygen to form CO 2 . Both heated (4300 1C) and (less often) nonheated forms are known.…”

Electrochemical deposition of gold on indium zirconate (InZrOx with In/Zr atomic ratio 1.0) for high temperature automobile exhaust gas sensors

“…Among these applications, detection of automobile exhaust gases specifically requires robust solid-state sensing devices that are stable and capable of withstanding harsh conditions such as temperature in the range of 500-600 °C [2][3][4][5]. Metal oxide based chemoresistive devices are particularly attractive for this purpose due to their simple structure, ease of fabrication, excellent miniaturization capability, ruggedness, and low cost [5,6]. To date, a large number of metal oxides have been explored for their sensitivity towards various exhaust gases and they have been reviewed extensively in recent years [6][7][8][9][10][11][12].…”