Since the quality of each component gas tested must ultimately correspond to the operating conditions of the vehicle, the actual test system will cause changes in measured data relative to operating conditions due to factors such as pipe length and system response time. There is a time lag, and the gas measurement principle of each component is different, and the time lag of each component gas is not the same. Therefore, the system eliminates these effects when processing data, so that the results of the final measurement correspond to changing conditions.
The time delay of the five-gas analyzer is an important factor that affects the measurement accuracy of the entire system. If the system cannot properly correct the time difference of each component gas measurement, it cannot accurately reproduce the situation where the concentration changes with the engine operating conditions, making the entire test. Lost the purpose. Therefore, when using a five-gas analyzer to measure emissions from gasoline engine transient conditions, the necessary phase (time delay) corrections must be made to the measurement signal. Due to the influence of pipeline flow resistance and sensor response time, there is always a certain time lag between the measured signal and the evolution of exhaust gas, and the concentration of various pollutants in the discharge is not in one-to-one correspondence with the operating point at that moment. It's lagging behind for a while.
The measurement method is to align the dilution hose with the exhaust pipe of the car and leave some space for the fan to draw ambient air to ensure that the diluted flow rate reaches the specified value. The extracted ambient air and the exhaust gas from the vehicle are mixed in the dilution duct. The flow of the mixed gas is measured in real time by the vortex flowmeter, and the pressure and temperature measured by the pressure and temperature sensor are converted into the standard flow. The oxygen sensor measures the mixed gas. The O2 concentration compares the oxygen content of the diluted gas with the oxygen content of the original exhaust gas. Equation (2) can be used to calculate the proportion of the mass dilution, and the vehicle is calculated from the dilution ratio and the flow rate of the diluent gas per second. The original exhaust gas volume, then the mass of contaminants emitted per second by the motor vehicle based on the discharge volume and the concentration of each component gas measured by the NHA-503 analyzer.
During the calibration process, the frequency converter was used to change the motor speed to change the flow of the fan. Six data points were selected, and each group collected five sets of data and averaged. By comparison, the flow loss before and after the installation of the vortex flowmeter is 014m3/min. This is due to the fact that the diluted air duct after the installation has a certain resistance to the gas, and the pipeline arrangement also has a certain influence on the gas flow. A linear linear regression was performed on the data recorded by the two types of flowmeters to obtain a straight line fitting equation, and the vortex flowmeter was corrected by the equation to improve the accuracy of the measurement. The selection of the fan takes into account that excessive flow rate will affect the measurement of the oxygen sensor, and the fan exhaust flow is set at 6m3/min.
The design of the exhaust pipe sampling port requires a good sampling port to collect the gas that needs to be collected. The tapered inlet can collect air and exhaust gas when the vehicle is inspected. The material of the tapered part is to be able to withstand the exhaust gas discharged from the exhaust pipe and directly contact with the hot exhaust pipe. The tapered inlet of silicon material can withstand the high surface temperature of 316e and is very flexible. The development of the system control software developed by Vmas mainly comes from the NAMA-503 analyzer, vortex flowmeter and oxygen sensor. Therefore, the main control microcomputer must be able to communicate with these three kinds of instruments to realize functions such as instrument control, data acquisition, and calculation. Because the communication methods adopted by the instruments are different, different communication terminals are used to program the system control software. The basic requirements of the system control software are as follows: (1) The NMA-503 analyzer can be calibrated and controlled, and the test data can be tested in real time. Display and record test data; (2) The system can correct the calibration oxygen sensor, display the measured value in real time, and record the test data; (3) The system can display real-time flow and low flow false alarm under the transient standard state of the collected flowmeter; (4) Data access and real-time correction of test data and good human-computer interaction interface are facilitated.
Conclusions (1) According to the requirements of the standard for simple condition test equipment, a simple transient condition emission test system was developed. The experimental results show that the simple transient condition emission test system can meet the test requirements. (2) The developed system control and data acquisition software can realize the control of various functions of the system equipment (calibration, zero adjustment, leakage check, gas over-determination, data storage, etc.), and have a good human-computer interaction interface. (3) A comparative test of multiple vehicle prototypes on the same chassis dynamometer as the CVS test system shows that the developed Vmas test results have a good correlation with the CVS test results and can reflect the transient state of automotive emissions. Case.
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