Vehicles oxygen sensors

The oxygen sensor closed loop system automatically compensates for changes in fuel content or air density. For instance, the stoichiometric air/fuel mixture is maintained even when the vehicle climbs from sea level to high altitudes where the air density is lower. 

Engines are also designed to use either gasoline or methanol and any mixture thereof (132—136). Such a system utilizes the same fuel storage system, and is called a flexible fueled vehicle (EEV). The closed loop oxygen sensor and TWC catalyst system is perfect for the flexible fueled vehicle. Optimal emissions control requires a fuel sensor to detect the ratio of each fuel being metered at any time and to correct total fuel flow. 

Such tight mixture control is beyond the capability of the traditional carburetor. Consequently, after sorting through a number of alternatives, industry has settled on closed-loop-controlled port-fuel injection. Typically, an electronically controlled fuel injector is mounted in the intake port to each cylinder. A sensor in the air intake system tells an onboard computer what the airdow rate is, and the computer tells the fuel injectors how much fuel to inject for a stoichiometric ratio. An oxygen sensor checks the oxygen content in the exliaust stream and tells the computer to make a correction if the air/fuel ratio has drifted outside the desired range. This closed-loop control avoids unnecessary use ot an inefficient rich mixture during vehicle cruise. 

As mentioned earlier, the oxidation of carbon monoxide and hydrocarbons should be achieved simultaneously with the reduction of nitrogen oxides. However, the first reaction needs oxygen in excess, whereas the second one needs a mixture (fuel-oxygen) rich in fuel. The solution was found with the development of an oxygen sensor placed at exhaust emissions, which would set the air-to-fuel ratio at the desired value in real time. So, the combination of electronics and catalysis and the progress in these fields led to better control of the exhaust emissions from automotive vehicles. 

J. W. Koupal, M. A. Sabourin, and W. V. Qemmens, Detection of Catalyst Failure On-Vehicle Using the Dual Oxygen Sensor Method, SAE 91061, Society of Automotive Engineers, Warrendale, Pa., 1991. 

Sensors based on platinum are used in temperature measurement because of the substantial change of electrical resistivity with temperature. CO detectors are common safety features in homes and industrial buildings. Oxygen sensors, known as Lambda or Exhaust Gas Oxygen (EGO) sensors, use platinum and are a central component of the engine control system in a catalyst-equipped vehicle. 

The best known ceramic is Ti02 which is used in oxygen sensors of this conductor type for various vehicle applications [8], The operating principle is based on changes in the bulk conductivity due to the concentration of oxygen vacancies, indicated by the formulation Ti02 x. 

The current US emission limits for light duty vehicles are achieved for gasoline fueled cars by engines equipped with a controlled threeway catalyst system including an oxygen sensor and fuel injection. For the older engine types dual bed reduction/oxidation catalyst systems are often applied (Ref. 3). 

In order to provide the proper stoichiometrically balanced exhaust gas composition required for use of the three-way catalyst, an air/fuel ratio control system had to be developed for the vehicle. Closed-loop electronic air-fuel ratio control required the installation of an exhaust oxygen sensor and an on-board microprocessor to provide the necessary control capability. 

In parallel with the development of the membrane reformer system, a new concept membrane module, which has a palladium alloy membrane coated on the porous support tube with catalytic activity has been developed (Nishii, 2009). This membrane module is expected to provide a more compact reactor because the reactor does not require a separate catalyst. It is also expected that this module can be manufactured at low cost by applying the industrially-established mass production process used to make oxygen sensors for combustion control in vehicles with internal combustion engines. 

Wire insulated with FIFE is used for connections to oxygen sensors mounted in vehicle exhaust manifolds. In this hot environment, FIFE provides reliable dielectric protection for wiring that is vital to control of exhaust emissions. ETFE is used to insulate wiring for other high-temperature locations near engines, and wiring exposed to hot hydraulic fluid within automatic transmissions. 

Figure 6.14. Fluorescence sensor deployment platforms. (A) CTD Rosette vertical profiler. Water was pumped in series through a fluorometer and other environmental sensors, where instruments were mounted at the bottom of the Rosette and CDOM fluorometer. (Courtesy of R. Conmy.) (B) Towed vehicle with various optical and chemical sensors. (Courtesy of R.F. Chen.) (C) Minishuttle tow-yo vehicle deployed with chlorophyll and NOM fluorometers, dissolved oxygen sensor, and CTD. (Courtesy of R.F. Chen.) (D, E) Buoys, moorings, and gliders are also platforms for optical and environmental sensors. (Courtesy of Cefas.) (See Plate 10.)...

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