Lambda-sensor

Fig. 12. Schematic of lambda sensor (a) in exhaust pipe and (b) internal components.

Doped zirconium dioxide is the solid electrolyte in lambda sensors (oxygen sensors used in the field of environmental protection). 

FIS Metal Oxide Lambda Sensor LS-01 for COMBUSTION CONTROLS. Technical In-... 

Lambda-cyhalothrin, in microcapsule formulations, 7 564t Lambda-derived cloning vectors, 12 504-506 Lambda sensor, 10 56 Lambent, commercial defoamer, 3 24 It Lambert-Beer-Bouguer law, 23 126. See also Beer s Law... 

The cost of the exhaust system is lowered by omitting the catalytic converter and the lambda sensor. The transmission is considerably simpler than the multigear... 

Chemometric evaluation methods can be applied to the signal from a single sensor by feeding the whole data set into an evaluation program [133,135]. Both principle component analysis (PCA) and partial least square (PLS) models were used to evaluate the data. These are chemometric methods that may be used for extracting information from a multivariate data set (e.g., from sensor arrays) [135]. The PCA analysis shows that the MISiC-FET sensor differentiates very well between different lambda values in both lean gas mixtures (excess air) and rich gas mixtures (excess fuel). The MISiC-FET sensor is seen to behave as a linear lambda sensor [133]. It... 

The lambda sensor, which is found in cars with catalytic converters, is an example of an oxygen probe based on the principle of selective electrodes. This sensor, which looks like a spark plug, has a zirconium sleeve (Zr02) that behaves as a solid electrolyte. The external wall is in contact with emitted gas while the internal wall (the reference) is in contact with air. Two electrodes measure the potential difference between the two walls, which is indicative of the difference in concentration of oxygen. 

Fig. 11. The A/F ratio ad the lambda sensor s voltage signal. Courtesy of Robert Bosch.

One of the most widely used chemical plants is certainly the exhaust pipe section of an automobile. The exhaust pipe system of automobiles shows all features of a chemical plant, as it consists of a catalytic reactor, supply pipes for the gases, heaters and control equipment such as the lambda sensor. The catalyst carriers of an exhaust pipe are not called micro structured reactors but, considering their micro dimensions, they actually belong to this group of reactors. 

The general form of a lambda sensor is illustrated in Fig. 4.37. The closed end projects into the hot exhaust gas stream heating the sensor to a temperature at which it is sufficiently conductive for the e.m.f. to be measured by a high impedance meter. The input impedance of the meter must be 100 times that of the cell for 1% precision. Corrections for changes in cell temperature (Eq. (4.38)) can be made by monitoring the cell resistance. 

Another important application is in the refining of steels when the oxygen content must be controlled at the parts per million level and monitored continuously on line and many oxygen sensors are currently used in the steel industry for this purpose. The principle of operation is as described for the lambda sensor and one form is shown schematically in Fig. 4.39. In this case the reference activity is established by a chromium metal/chromium oxide mix rather than being defined by air. 

Amperometric mode An advantage of the lambda sensor as described above is its sensitivity close to the 2=1 point where the oxygen activity in the exhaust changes rapidly with burn conditions and consequently so too does the cell e.m.f. The disadvantage is that under lean-bum (oxygen-rich) conditions the log dependence on oxygen activity renders the cell insufficiently sensitive to provide effective control. This shortcoming has led to the introduction of sensors used in the amperometric mode discussed below and illustrated schematically in Fig. 4.40. 

Semiconducting lambda-sensors based on titania have been developed and used for car engine management. However for a variety of reasons, one being sensitivity to surface contamination, the electrolytic sensor dominates. 

Lambda probe — The so-called lambda probe (lambda sensor) is a potentiometric oxygen - gas sensor that is used to monitor the partial pressure of oxygen po2 (oxygen concentration), e.g., in the exhaust gas of cars in order to control the air/fuel ratio that is going to the internal combustion engine. The term lambda originates from the stoichiometry number A which describes the composition of the air/fuel mixture, as follows ... 

Continuous measurement of OSC of the catalyst inserted in the converter is one of the simplest tool to monitor catalyst efficiency. This is known as the On-board diagnostic" (OBD). Sideris has recently reviewed the OBD technologies on the basis of the corresponding patent literature [103]. Even though other techniques are available (temperature sensors, specific sensors for CO, HC and NOx), OBD determined by means of O2 sensors remains the technique the most widely employed in car industry. This technique is based on the generation of periodic rich/lean perturbations monitored by two lambda sensors, one located upstream and the second downstream the converter. Catalysts that have good OSC considerably attenuate the upstream perturbation (with a significant time lag) while virtually dead... 

T24.1 One of the most popular lambda sensors contains zirconia (ZrO ) as a solid electrolyte. This material has a high conductivity for 0 ions at elevated temperatures. The cell responds to the changes in O2 partial pressure in exhaust gas. The reduction potential for 02(g) + 4e" — 20 (s) is proportional to p(02, reference)/p(02, exhaust gas), with partial pressure of O2 in the air as the reference. (See Section 24.49(b) Solid anionic electrolytes and refer to Fig. 24.9). 

The first concept is the closed-loop-controlled three-way catalyst. In this, one type of catalyst, which is placed in the exhaust gas stream, is able to promote all the main reactions that lead to the simultaneous removal of carbon monoxide, hydrocarbons and nitrogen oxides. To balance the extent of the oxidation and the reduction reactions, the composition of the engine-out exhaust gas is maintained at or around stoichiometry. This is achieved by a closed-loop engine operation control, in which the oxygen content of the engine-out exhaust gas is measured up-stream of the catalyst with an electrochemical oxygen sensor, also called lambda sensor. 

The operation of the engine outside of the stoichiometric point affects the amount of CO, HC, NO c and O2 emitted simultaneously, as well as the composition of the hydrocarbon fraction. The oxygen content of the exhaust gas is of particular interest as this is measured by the lambda sensor and is used to control the engine. Figure 52 shows as an example the influence of the exhaust gas oxygen content on the conversion of CO, HC and NO.v, at fixed CO, HC and NO.v content. This experiment was performed in a model gas reactor in which a stoichiometric composition is reached at about 1.0vol%02. With an oxygen content above the stoichiometric... 

Drivetrain - pressure sensor - pedal angle - lambda sensor... 

Pollution legislation continues driving further reductions in engine emissions. The dominant exhaust-gas sensors today and in the near future are oxygen partial pressure sensors - also called lambda sensors. Due to the high temperature of exhaust gas, these sensors are made by ceramics technology in combination with thick-film processing. 

---