Development of Vehicle Exhaust Flow Measurement Calibration Device

Vehicle exhaust flow is difficult to measure accurately and with high precision due to the highly transient nature of the cyclic events which are dependent on engine combustion parameters, varying exhaust gas compositions, pulsation effects, temperature and pressure. Bag mini-diluter (BMD) is becoming one of the few technologies chosen for SULEV and PZEV exhaust emission measurement and certification. A central part of the BMD system is an accurate and reliable exhaust flow measurement which is essential for proportional bag fill. A new device has been developed to accurately and reliably calibrate exhaust flow measurement equipments such as the E-Flow. The calibration device uses two different size laminar flow elements (LFE), a 40 CFM (1.13 m³/min) LFE for low end calibration and a 400 CFM (11.32 m³/min) LFE for higher flows. A blower is used to push flow through a main flow path, which then divides into two flow pathways, one for each of the two LFE's. A diverter valve is used to control the flow to the different flow paths with any excess flow being diverted outside of the cart to waste. A detailed description of the construction of the calibration device and the software is discussed in this paper. Calibration data and a repeatability study are discussed and analyzed.