Sensors combustion

Such a situation may arise, for example, in the combustion sensor in which the species of interest is methane and the other combustibles are different higher molecular weight hydrocarbons. The catalyst, in this case, can be Pt and the preferentially catalyzed reaction is as follows. 

Also for CO sensing, the present sensors are available only for the field of security not for environmental use because of the insufficient sensitivity and selectivity to monitor CO in the atmosphere. Examples of CO sensor which have been improved their sensitivity and selectivity are, for example, SnO semiconductor sensors operated under periodic temperature cycle[85-87], a electrochemical sensor using nafion membrane[88], a catalytic combustion sensor composed of catalysts and hydrophobic pol uner[89], a SnOj diode sensor doped with Pd[90] and an optical fiber catalytic sensor with Au/CogO as combustion catalyst[91]. 

Fig. 2 Basic principles of solid electrolyte cells Left oxygen sensor (Nemst sensor), Right combustible sensor (mixed potential sensor) [2]...

The sensor with the most important limitations is the traditional catalytic or pellistor type percent Lower Explosive Limit (LEL) combustible gas sensor. In spite of the millions of combustible sensor-equipped atmospheric monitors in service around the world, there is still a lot of misinformation and misunderstanding when it comes to the performance characteristics and limitations of this very important type of sensor. Understanding how combustible sensors detect gas is critical to correctly interpreting readings and avoiding misuse of instruments that include this type of sensor. 

Pellistor type combustible sensors and photoionization detectors represent complementary, rather than competing, detection techniques. Pellistor sensors are excellent for the measurement of methane, propane and other common combustible gases that are not detectable by means of a PID. On the other hand, PIDs can detect large VOC and hydrocarbon molecules that are effectively undetectable by pellistor sensors, even when the catalytic sensor is operable in ppm measurement ranges. The best approach for VOC measurement in many cases is to use a multi-sensor instrument equipped with both a pellistor LEL sensor and a PID sensor. 

A. Splinter, J. Stiirman, O. B artels, W. Benecke, Micro membrane reactor a flow a through-membrane for gas pre-combustion. Sensor Actual B-Chem., 2002,83, 169-174... 

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. 

J. W. Butier and co-workers, FastKesponse Zirconia Sensor-Fased Instrument for Measurement of the Air (Fuel Katio of Combustion Exhaust, SAE 840061, Society of Automotive Engineers, Warrendale, Pa., 1984. 

Minimization of pollutants from the combustion chamber. This approach consists of designing the engine with improved fuel-air distribution systems, ignition timing, fuel-air ratios, coolant and mixture temperatures, and engine speeds for minimum emissions. The majority of automobiles sold in the United States now use an electronic sensor/control system to adjust these variables for maximum engine performance with minimum pollutant emissions. 

Implementation of advanced performance degradation models, necessitate the inclusion of advanced instrumentation and sensors such as pyrometers for monitoring hot section components, dynamic pressure transducers for detection of surge and other flow instabilities such as combustion especially in the new dry low NO combustors. To fully round out a condition monitoring system the use of expert systems in determining fault and life cycle of various components is a necessity. 

Application The zirconia oxygen sensor is widely used for combustion control processes and for air/fuel ratio regulation in internal combustion engines. The closed-end portion of the electrode tube is inserted into the exhaust gas stream. In the control of industrial combustion processes, no out stack sampling system is required. 

In combustion processes tests, it has been noticed that Pd-catalyzed SnO, sensors follow the variations in the concentration of CO in the combustion gases, even in the case of solid fuels. 

Torvela. H., A. Harkoma-Mattila, and S. Leppavuori. Characterization of a Combustion Process Using Catalysed Tin 0,xide Gas Sensors to Detect CO from F.niission Gases. Sensors Actu ators B1 (1990), pp. 83-86. 

Required locations of gas detectors (sensors) are often specified by the authority having jurisdiction. For example, API RP 14C recommends certain locations for combustible detectors. These recommendations have been legislated into requirements in U.S. Federal waters by the Minerals Management Service. RP 14C should be referred to for specific details, but, basically, combustible gas detectors are required offshore in all inadequately ventilated, classified, enclosed areas. The installation of sensors in nonenclosed areas is seldom either required or necessary. Ignitible or high toxic levels of gas seldom accumulate and remain for significant periods of time in such locations. 

Most combustible gas detector sensors are installed in the upper portions of buildings for the detection of natural gas. However, in many cases the vapor which flashes off oil in storage tanks can be heavier than air. Below grade areas should be considered for sensor installations where heavier-than-air vapors might collect. 

Oxygen sensors for air/fuel control in combustion engines (niobium oxide, Nb205, is also used for this application). 

The fuel cell and automotive markets seem to be a large market for low-cost (< 100/ sensor) hydrogen sensors. Low power sensors are in high demand for multiple-point operations in fuel cells and internal combustion engines. 

Carbon Monoxide Evolution. Determination of the carbon monoxide evolved during combustion of polymer samples in NBS Chamber experiments was carried out using a Telegan CO Sensor (Type 3F). Quoted values are the numerical averages of three independant determinations. 

Combustion control for domestic hot water production is another important area where modern sensor technology comes in. New developments are discussed in Chapter 3.2. 

Security and safety Intruder alarm Security systems Fire detection systems, with sensors for - temperature - toxic gases like CO, C02, exhaust gases, smoke, etc. - combustible gases like CH4, C2H6 flame detection, fire detectors, caravans with gas detectors, etc. 

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