What is the voltage oxygen sensor in the exhaust gas? A little technical approach to the topic will not hurt anyone. The more that sometimes you will have to face certain deadlines, even when repairing a car. The information contained in the article below will certainly help a little. Without a doubt, it is worth learning a few words about the voltage oxygen sensor. Be aware that it exists at all.
Sensor and equilibrium oxygen in exhaust gases
Oxygen, which is in a mixture of fuel and air, is used in the combustion process. At this time, the nitrogen-oxygen binding process also occurs. These two components of air do not react with each other until the limit of 1800 degrees Celsius is exceeded. In the combustion chamber, due to pressure and temperature higher than 1800 degrees, there is a reaction between nitrogen and oxygen. Which, as a consequence, produces nitrogen oxides. They reduce the amount of oxygen that is important in the combustion process. In addition, the exhaust gases leaving the chamber contain free oxygen, which is the result of:
unused oxygen in the combustion process (a result of the poor composition of the mixture, too short time or inappropriate conditions for such a process),
- unnecessary oxygen in the process of fuel combustion (when lean fuel).
Restoring thermodynamic balance
Determining the exact composition of the mixture burned based on the amount of oxygen in the exhaust gas is possible after examining the amount of equilibrium oxygen. Each oxygen sensor does this by restoring the thermodynamic balance between individual exhaust components. It then comes into contact with the catalytic layer that is part of the sensor measuring element. During such a restoration of thermodynamic balance, the following occurs:
reduction of nitrogen oxides decomposition into the original nitrogen and oxygen version,
restored oxygen from oxides and free oxygen from flue gases oxidize carbon monoxide and unburned hydrocarbons. Then carbon dioxide and water vapour are formed.
Such reactions cause the oxygen sensor to measure the amount of equilibrium oxygen released from the exhaust gas. Do not be surprised. However, it will be different oxygen than that measured in the exhaust gas analysers, which take into account only free oxygen.
What is a voltage oxygen sensor – construction
It must be said that a voltage oxygen sensor is the most commonly used type of sensor that determines the level of oxygen in the exhaust gas. From the outside, the exhaust stream flowing through the exhaust system catches the measuring element. In turn, inside there is a sensor filled with atmospheric air, which is colloquially called reference air. This oxygen content in the air is constant and does not change.
The main and very important part of the voltage oxygen sensor is the so-called special ceramics. It consists of a solid electrolyte made of zirconia, stabilized with yttrium oxide. Both sides, inner and outer, are covered with thin layers of platinum. It has a special porous structure that lets gas through. It should be added here that the inner layer is a positive electrode and the outer layer is a negative electrode. Porous protective ceramics preserve the outer electrode and special ceramics that are exposed to contact with combustion residues.
The operating temperature of a voltage oxygen sensor is usually from 350 degrees Celsius to even 850 degrees Celsius. New oxygen sensors work at lower temperatures, from 220 degrees Celsius to 250 degrees Celsius. The measurement is possible due to the restoration of thermodynamic balance between exhaust gas components, in contact with the negative electrode. As a result, equilibrium oxygen appears from the exhaust gas. The amount of which can be measured by comparison with constant oxygen content in the reference air.
Voltage oxygen sensor signal
The oxygen sensor signal is the voltage between the external and internal electrodes measured with a voltmeter. This value depends on the amount of equilibrium oxygen. The value of the signal voltage depends on the composition of the burned mixture. Occurs when the exhaust gases affect the measuring element, and additionally, they are from the combustion of the stoichiometric mixture.
The average reference voltage is 450mV. The oxygen sensor driver program interprets the reference voltage value. When the signal voltage is greater than the reference value, then there is an interpretation that says that the exhaust gas covering the sensor is the result of burning a rich mixture.
However, when the signal value is lower than the reference voltage value, then the exhaust gases come from lean combustion. The voltage oxygen sensor controller will only receive information if the mixture is rich or lean. He will not receive any other information, even on the composition of the burnt mixture.