Operating oxygen sensor

The function of the oxygen sensor and the closed loop fuel metering system is to maintain the air and fuel mixture at the stoichiometric condition as it passes into the engine for combustion ie, there should be no excess air or excess fuel. The main purpose is to permit the TWC catalyst to operate effectively to control HC, CO, and NO emissions. The oxygen sensor is located in the exhaust system ahead of the catalyst so that it is exposed to the exhaust of aU cylinders (see Fig. 4). The sensor analyzes the combustion event after it happens. Therefore, the system is sometimes caUed a closed loop feedback system. There is an inherent time delay in such a system and thus the system is constandy correcting the air/fuel mixture cycles around the stoichiometric control point rather than maintaining a desired air/fuel mixture. 

Voltage Cell Type Oxygen Sensor The operation of the zirconia oxygen sensor utilizes the conduction of oxygen ions by virtue of anion or oxygen ion vacancies in the crystalline lattice. " The anion vacancies are created when the... 

Tends to burn visually cleaner at the exliaust tailpipe, since it operates in a closed-loop electronic mode (oxygen sensors interacting with the powertrain control module) to maintain an ideal air/fucl ratio of 14.7 1. 

At the same time, many practical issued associated with the use of optical oxygen sensors in food packs still remain. These have to be addressed to adapt the existing sensing materials and prototype systems for real-life applications, achieve the required sensor specifications, operational performance and safety. Considerable technological developments and effort in eliminating current problems and bottlenecks are required, to facilitate widespread use of the oxygen sensors by food and packaging industry. 

Figure 9.6. Stability of a lifetime-based fiberoptic oxygen sensor over a period of 100 h of continuous operation. Lifetime techniques are insensitive to the process of photobleaching only in the absence of excited state reactions. Excited state reactions of the sensor-carrier system cause drifts in the observed lifetime with photobleaching. They are avoided by limiting the concentration of the sensor in the carrier. (From Ref. 21 with permission.)...

Several oxygen sensors based on oxygen pumping with stabilised zirconia have been reported (Hetrick, Fate and Vassell, 1981). This type of oxygen sensor is able to measure the oxygen partial pressure in the exhaust gas from the engine in lean burn. The operating principle of the... 

Recent emission control system development in the automotive industry has been directed mainly towards the use of three-way or dual bed catalytic converters, This type of converter system not only oxidizes the hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas but will also reduce the nitrous oxides (NO ). An integral part of this type of system is the exhaust oxygen sensor which is used to provide feedback for closed loop control of the air-fuel ratio. This is necessary since this type of catalytic converter system operates efficiently only when the composition of the exhaust gas is very near the stoichiometric point. 

Steady-State Mass Balance Method In theory, the Ki a in an apparatus that is operating continuously under steady-state conditions could be evaluated from the flow rates and the concentrations of the gas and liquid streams entering and leaving, and the known rate of mass transfer (e.g., the oxygen consumption rate of microbes in the case of a fermentor). However, such a method is not practical, except when the apparatus is fairly large and highly accurate instruments such as flow meters and oxygen sensors (or gas analyzers) are available. 

Special electrochemical sensors that operate on the principle of the voltammetric cell have been developed to measure substrates such as oxygen and glucose. In the Clark oxygen sensor, a 1.5 V potential difference is applied between a silver anode and a platinum cathode which are both in contact with a KCl solution separated from the sample by a membrane permeable to oxygen (Fig. 19.6). 

The principle of their operation is the same, but the method of implementation of the sensor is largely dependent on the conditions of the application. Thus, a zirconia sensor for measurement of 02 in molten steel (1,600°C) has to be designed in such a way that the thermal expansion coefficients of the different layers in this device are matched. On the other hand, a room-temperature potentiometric oxygen sensor can be constructed (Yamazoe et al., 1987) by using another set of materials ... 

High temperature oxygen sensors are finding an increasing use in a variety of applications including monitoring and control of industrial processes(1) and of internal combustion engine operation(2) ... 

In the last 20 years, several different types of oxygen sensors based on 02 pumping have been developed(lO). All these sensors have the common characteristic that their signal output is linearly proportional to the ambient oxygen partial pressure. Their other characteristics, however, such as response time, temperature and absolute pressure dependence, and effect of gas flow depend on the specific design and mode of operation of the sensor. 

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. 

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