Lambda value

Where R is the gas constant, T is the temperature, and F is the Faraday constant. Caused by the logarithmic correlation between the gas concentration and the voltage signal, the potentiometric measurement is best suited for measurements of small amounts of oxygen. A well-known application of this principle has been realized in the so called lambda-probe for automotive applications where they are used to control the lambda value within a small interval around 1 = 1. The lambda-value is defined by the relation between the existing air/fuel ratio and the theoretical air/fuel ratio for a stoichiometric mixture composition ... 

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... 

It is, however, very common to use the so-called partial lambda which enables evaluation of the process of selection of original variables for calculation of an optimum set of features. This partial lambda is the ratio of two WILKS lambda values, Asetl and Aset 2, where Asetl holds for the smaller set of features and Aset2 is computed after adding a feature to the former set ... 

An interesting part of the technique was the way in which the equal lambdas were obtained. One strain of E. coli had a growth rate that was inhibited by a chemical (Nalidixic acid) while the other strain was essentially immune to the compound (see the third graph in Figure 6.1). By adding the proper amount of the chemical, it was possible to alter the growth rate so as to make the resulting lambda values equal. The chemostat with an inhibitor will be studied in Chapter 4. 

It has been a common practice in the design of emission control technologies to calculate the exhaust gas lambda value from the exhaust gas composition. On the basis of some simplifying assumptions, the following can be derived ... 

Figure 18. Engine out emission of CO, HC and NO.v fuel consumption and power output of a gasoline fueled spark ignition engine as a function of the lambda value.

Figure 20. (a) Basic concepts for the catalytic aftertreatment of the exhaust gas from spark ignition internal combustion engines, (b) Range of the lambda values in which various catalytic after-treatment concepts are operated. 

Figure 49. Evolution of the exhaust gas temperature in front of the catalytic converter, the exhaust gas lambda value and the hydrocarbon concentration in the exhaust gas, for two different engine designs, as a function of the time during the first four minutes of the US-FTP 75 test cycle. Reprinted with permission from ref. [39], 1993 Society of Automotive Engineers, Inc.

Figure 51. Conversion of CO, HC and NO., over a three way catalyst as a function of the exhaust gas lambda value (monolith catalyst with 62cellscm", three-way formulation with Pt 1.42gl , Rh 0.28gl ), fresh engine bench test A/F scan at 623 K exhaust gas temperature space velocity 60000NIC h dynamic conditions frequency 1 Hz amplitude 0.5 A/F).

As of today, three types of lean burn engines are proposed (Fig. 94) [60, 61]. The first type always operates in the lean burn range, with a lambda value between 1.5 and 1.6. The exhaust gas composition will be net oxidizing at all vehicle driving... 

Allison DB, Faith MS, Nathan JS. Risch s lambda values for human obesity. Int. J. Obes. 1996 20 990-999. 

Comment the lambda value measured with the help of lambda probes in cars is nothing but a degree of titration, here the degree of oxidation of the petrol by the oxygen of the air. The burning of petrol can be considered a redox titrationi... 

Due to a lower mechanical strength 8 Due to a reduced lambda value, and if lambda > 30 Due to a greater mechanical strength Hydraulic permeability of water... 

Special attention has been given to new experimental test conditions, such as the 25 weeks at 70 °C ageing test and the acceleration test, which were not used previously. This paper shows what range of declared lambda values are to be expected using this new method. These declared lambda values are then compared to 25-year predictions using the Huntsman Polyurethanes lambda ageing predictive model. 

Fig. 3 Emf of the solid electrolyte cell versus lambda value [3]...

Figure 6.18.1 shows a typical exhaust gas composition of a gasoline powered engine as well as the fuel consumption and engine output as a function of the lambda value X, which is defined as the actual air-to-fuel ratio to the ratio at stoichiometric conditions, that is, if the fuel is combined with all free oxygen to form CO2, H2O, and SO2 without any excess O2 in the flue gas ... 

Figure 6.18.6 shows the influence of the lambda value on the conversion of CO, hydrocarbons (HCs), and NO on a three-way catalyst. The window of optimal operation is narrow and close to A, = 1. Thus, a measurement of the 02-content is needed, and the signal of this so-called lambda sensor is fed back to the fuel injection system, which adjusts the air-to-fuel ratio. 

Figure6.18.6 Influence of lambda value on the conversion of CO, hydrocarbons (HCs), and NO, reached with a typical three-way catalyst.

The oxidation of HCs and CO requires an oxidizing atmosphere and the conversion of NO requires a reducing atmosphere. Thus a compromise has to be found to convert at least a main proportion of all three pollutants. The window of optimal operation is narrow and close to a lambda value of unity. At the end of the 1990s a new generation of automotive exhaust catalysts was developed, the NQr storage catalyst needed for lean burn engines. 

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