This equipment not only analyzes whether vehicle emissions meet relevant national standards, but also analyzes engine malfunctions and serves as an important tool for testing various vehicle performance characteristics. Below, the ICbuy.com editor will discuss the role of gas flow sensors in vehicle exhaust emission detection.
To meet emission standards, a common method is to place a filter in the vehicle's exhaust system to capture tiny particles in the exhaust gas. A drawback of this method is that the exhaust passage gradually becomes clogged as the captured particles accumulate. To remove these accumulated particles, additional fuel is injected into the exhaust gas at a certain point in the passage or directly into the exhaust to increase its temperature. When a catalyst is present in the filter, the high temperature of the exhaust gas is sufficient to burn and vaporize the accumulated particles. This cleaning process is called "regeneration." A problem arises: too frequent regeneration increases fuel consumption; too long intervals reduce engine performance. Therefore, choosing an appropriate timing for regeneration is crucial.
The differential pressure sensor sends a pressure difference signal to the ECU, which uses this pressure difference to determine the degree of particle accumulation in the filter and decides the timing of "regeneration" and the amount of additional fuel injected. Simultaneously, the ECU can also regulate the exhaust gas temperature by controlling the EGR valve. Additionally, the differential pressure sensor can also be used to measure gas flow rate, liquid level, etc.
The method for measuring gas flow rate involves calculating the static pressure of the flow tube by measuring the pressure difference between the pressure in the flow tube and atmospheric pressure. The square root of the static pressure is proportional to the flow rate, thus yielding the flow rate. The SST AFE-01 gas flow sensor from the UK, offered by ICbuy.com, consists of four platinum thin-film resistors, featuring low impedance and a small heating area. Two high-impedance resistors are located on either side of the heater to detect flow velocity and direction, while another resistor detects the gas temperature. The two resistors closest to the heating element are connected in a bridge circuit, generating an output signal for detecting flow velocity and direction.
In the absence of flow, both resistors reach the same heating state. When flow is present, one resistor's temperature drops significantly compared to the other; which resistor's temperature decreases depends on the flow direction, and the temperature difference can be measured, determined by both flow velocity and direction. The flow sensor has a very short heating and response time due to its small thermal mass. This method can detect very minute changes in flow velocity. For higher flow velocities, the temperature sensor can be connected to a constant-temperature anemometer.
