Exhaust flow meters (EFM) measure the amount of exhaust gas during type approval tests of diesel and petrol fuelled vehicles. They are embedded in portable emissions measurement systems (PEMS), together with analysers which measure pollutants in the exhaust gas. The European Union adopted Real Driving Emissions legislation in 2016 - 2018 in which real-driving emission tests using PEMS are a requirement for type approvalof vehicles. SI-traceable calibration of the exhaust flow meter and analysers in PEMS for real driving conditions is a challenging task. Currently a conformity factor is employed to acknowledge the fact that the calibration of PEMS components in accurately controlled laboratory conditions does not consider all factors contributing to overall PEMS uncertainty in a real-driving type approval test. The EFM uncertainty is a dominant uncertainty component in PEMS measurements. A need exists for traceable quantitative uncertainty characterization not limited to transients in the exhaust flow, flow pulsations, gas composition, temperature, and drift of the flow meter. As part of the European Metrology Programme for Innovation and Research (EMPIR) research project 19ENV09 “MetroPEMS”, this paper (I) presents a generic uncertainty analysis of the EFM using state-of-the-art knowledge, and (II) presents first measurement results of quantitative and (partly) traceable assessment of factors contributing to the overall uncertainty of the EFM. While some experimental results show that the EFM matches legislative accuracy requirements, other experiments indicate that this is not generically proven for all possible on-road conditions in which the PEMS are used.

With the atmospheric air as the working fluid, the premature unchoking phenomena were investigated with 18 sets of critical flow Venturi nozzles under 8 types of upstream flow conditions. Unlike the available research, there were no clear relationship between the upstream flow condition and the flow rate fluctuation and flow rate recovery for the premature unchoking phenomena. However, the diverse and unsteady characteristics of the premature unchoking phenomena were shown. With the comparison of upstream flow conditions, the new disturbance might be resulted from the “improper” upstream flow condition, which might influence the intensity and the position of the shock in the diffuser section of CFVN, and finally resulted in the diverse and unsteady characteristics of premature unchoking phenomena.

This numerical study investigates the flow through a cylindrically shaped critical flow Venturi nozzle regarding the transitional behavior of the boundary layer inside the nozzle throat region. For the flow simulations, two different turbulence modeling approaches were used, and the simulation results were validated by comparison with experimental data. Characteristic quantities for describing the boundary layer development, namely the displacement and momentum thickness, were analyzed within the cylindrical part of the nozzle and compared with theoretical predictions based on integral methods for solving the boundary layer equations. Typical laminar and turbulent boundary layer flows could be classified depending on the Reynolds number, where the boundary layer curves show a self-similarity when multiplied by Re1/2 and Re0.139, respectively. The shape factor, defined as the ratio of displacement to momentum thickness, was identified to indicate the transitional region of the nozzle flow. Thus, this parameter can help improving transitional turbulence models based on experimental data.

The boundary layer transition of sonic nozzle is affected by many factors, including Reynolds number, macro structure (throat diameter), meso-micro surface structure (wall roughness, waviness), turbulence intensity, wall heat transfer and so on. Therefore, in order to analyse the influences of macrostructure, meso-micro surface structure and turbulence intensity on boundary layer transition, the Cd and geometric dimension (throat diameter, d, average roughness, Ra, maximum roughness, Rz, and waviness, wa) of sonic nozzles with throat diameter of 1.919 mm, 3.808 mm, and 7.453 mm were experimental investigated and measured. Furthermore, a series of CFD simulations through the transition SST model for axisymmetric nozzles were established to research the variation law of boundary layer transition and Cd of the sonic nozzle when Reynolds numbers ranges from 4.6 × 10^4 to 4.7 × 10^7 and different turbulence intensity (Tu) and meso-micro surface structure (Ra, Rz and wa). The validity of the simulation model was confirmed by the experimental data of National Institute of Metrology of China (NIM). Finally, the relationships between the boundary layer transition and Tu, Ra, Rz and wa were obtained.

The problem of water resources in Central Asia and, especially, in the Republic of Uzbekistan, requests to keep a high-quality and accurate accounting of water and/or liquid consumption using water flow meters of various types, classes and modifications. In turn, there is a need (in the Republic of Uzbekistan - once every two years) to verify and calibrate liquid flow meters, using a specific verification facility. Following the Resolutions of the President of the Republic of Uzbekistan No. PP-2935 dated April 28, 2017, and No. PP-4059 dated December 12, 2018, on December 2018 № PP-4059 for the development of the national standard base of the Republic of Uzbekistan State Institution "Uzbek National Institute of Metrology" (SI "UzNIM") in cooperation with the Agency on Technical Regulation the specifications have been developed for the delivery of Automated verification rig for flow meters, liquid meters (hereinafter referred to as - the rig) for the needs of the SI "UzNIM", approved on January 29, 2019.