Development of metrological standards for traceable particle number measurements of automotive exhaust emissions

Transcription

1 Development of metrological standards for traceable particle number measurements of automotive exhaust emissions WG 3.23: Aerosol and Particle Diagnostics Andreas Nowak, Arne Kuntze, Johannes Rosahl, Margit Hildebrandt, Volker Ebert, Egbert Buhr th PMP meeting, Brussels

2 Overview About PTB: Role of legal metrology Primary PN standard: Needs and procedures PN Results: Inter comparison and PTB setup Conclusion and outlook

3 PTB: To measure is to know About PTB: Federal Ministry of Economics and Technology (BMWi) 170 Mio. budget, plus third party funding Approx permanent staff and 550 non-permanent staff including 110 PhD students Role of PTB in legal metrology: Provides traceability to national standards by calibrating reference standards of verification authorities and notified bodies Type approval and certification according to 23 German laws and regulations (e. g. verification act, law on civilian firearms) Guidance of federal ministries, the verification authorities and notified bodies Guidance of manufacturers in understanding the verification act and the MID Collaboration in respective to international organisations OIML, WELMEC th PMP meeting, Brussels

4 Need for PN-primary standard European and national Legislation UN-ECE R49 und R83 EC No. 692 (2008) EC No. 715 (2007) COM (2005) StVZO ( 47) + MessEG (2015) legal NMIs PTB, METAS, NPL, MIKES, DFM EMRP-Cooperation Part Emission ( ) regulations Development Definition of SI-unit Primary standard for soot-pn committee work Continuous process International standards ISO (2015) PN ISO (2009) Dp Knowledge transfer International key comparison (EURAMET)

5 Procedure of PN inter comparison Establishing NMI capabilities and measurement uncertainties NMI set up facilities and develops their uncertainties Validation via (blind) regional or global inter comparisons Positive results? Calibration and Measurement Capabilities (CMCs) are agreed by international peer-review and included on the Key Comparison Database at

6 PN-comparison: Results of primary method First comparison of its kind for Faraday Cup Aerosol Electrometer (FCAE) in EURAMET 1244 (Mar. 2014): Different types of aerosols: soot; DOS; NaCl DOS-particle with sizes from 20 to 200 nm and conc. at cm - ³ more information see: NPL Report AS 85 R. Högström et al Metrologia 51 (2014) For all participants: Uncertainty of ± 2% for DOS particle regime PTB: Full uncertainty budget of ± 7 % for soot particle size 15 to 150 nm, conc. at 650 to cm - ³ th PMP meeting, Brussels

7 PN-comparison: Results of secondary method Also first comparison of its kind for condensation particle counter (CPC) in EURAMET 1282 (Nov. 2014): Different types of aerosols: soot; silver sintered (more spherical) and unsintered Soot particle size range 23 to 100 nm, conc. 100 to cm³ more information see: NPL Report AS 94 For all participants: Uncertainty budget of ± 7 % for soot regime PTB: Full uncertainty budget of ± 10 % (soot, silver) at this time th PMP meeting, Brussels

8 Nucleation furnace (silver) nm PTB-primary standard for PN condensation particle counter (reference 2) Condensation particle counter condensation particle counter Conditioning unit (p, T, V) UDMPS Distribution unit (PNC: cm -3 ) < Soot generator (Mini-CAST) nm Generators for calibration condensation particle counter selection and monitoring Goal: Suitable calibration aerosols for PMP conform EECPC Faraday Cup Electrometer (reference 1) primary and secondary ref. condensation particle counter condensation particle counter Devices under Test High purity substance for calibration (propane and silver) High monodispersity (Minimization of multiple charges) Sufficient particle number concentration (PNC) Tunable particle diameter between 10 to 100 nm (Dp) Validate morphological properties High thermal stability, up to 350 C

9 normalized concentration raw concentration (cm -3 ) Results of soot generator: operation points Full range of soot generator PMP range for calibration of EECPC 1,0 0,8 0,6 0, ,2x10 5 1,0x10 5 8,0x10 4 6,0x10 4 4,0x10 4 Without secondary dilution 15 nm [1.36] 23 nm [1.36] 41 nm [1.35] 55 nm [1.41] 75 nm [1.50] 0,2 2,0x10 4 0, mobility diameter (nm) 0, mobility size (nm) only PN spectra below 75 nm relevant for calibration narrow PNSD could be observed

10 Range of Dp mean Range of width Results of soot generator: long term stability Point of interest 23 nm (counting efficiency of 50%) about 1 year of operation Stability of PNSD fit parameter for Dp mean and width of PNSD 8x10 4 6x10 4 Median Minimum Maximum Max Max % x10 4 2x Min 50% 25% Min 75% % 25% Dp mean, nm Sigma Increased stability by thermoconditioning of soot particles, but still not suitable for high thermal stability NMIs decided to use Ag nanoparticles as suitable candidate for these criteria: Advantage: Full calibration of entire PMP-system (VPR, DF and CPC)

11 Ag-Nucleation furnace: PTB Optimization water cooling flange larger furnace with 3 heating zones larger particles increase of residence time optimization flow scheme and T gradient implementation of heating shields: inlet shield with nozzle (different sizes) outlet shield with hoper minimization of Ag-agglomerates water cooling flange at end of tube shock cooling Goal to fulfill PMP size range from 23 to 55 nm

12 max. peak height of PNSD [cm-3] Sigma of PNSD Results for new nucleation furnace For different nozzle sizes at one flow ratio (1:1) from 960 C up to 1300 C 1,E+06 1,E+05 Fit parameter of PNSD 3 2,5 1,E mm nozzle 1:1 1,E mm nozzle 1:1 2 mm nozzle 1:1 1 mm nozzle 1:1 1,E mean mobility diameter [nm] High PNC (> 10 5 cm -3 ) above 15 nm 1,5 1 2 mm nozzle: mean mobility diameter up to 65 nm, relatively broad size distribution 2 mm nozzle well suited for calibration setup

13 Results of nucleation furnace: Particle Shape STEM pictures for different types of tube furnaces Old furnace construction comparable to Scheibel and Porstendörfer New tube furnace at PTB nm nm Without sintering mostly spherical particles

14 PNC of DUT-CPC / PNC of reference CPC PNC DUT-CPC [1/cm³] First calibration: Linearity test of EECPC For PTB-EECPC against Ref. FCAE and Ref. CPC 105% Residual plot Linear regression plot 104% 103% 102% 101% y = 0,9441x + 32,621 R² = 0, % 99% 98% 97% mean + 0, % 95% mean = 96,39% % 93% 92% 91% mean - 0, % PNC of FCAE [1/cm³] PNC FCAE [1/cm³] analysis fulfills ISO (Mar. 2015) based on thermoconditioned soot particles

15 counting efficiency [ 100 %] counting efficiency First calibration: Counting efficiency of EECPC PTB results compared to EURAMET workshop in Leipzig 1,2 1,0 0,8 0,6 0,4 0,2 For soot and silver particles PMP recommendations Dp50 region (±12 %) Plateau region (±10 %) EURAMET workshop 1282 with Ag unsintered 1 st EECPC calibration at PTB with Ag sintered 1 st EECPC calibration at PTB with soot 0, mobility diameter [nm] 1,0 0,8 0,6 0,4 0,2 0,0 Only soot particles (thermoconditioning) DUT EECPC vs. CPC Ref mobility diameter [nm] fit Modell CountingEfficiency (User) Gleichung y = b*(1 - exp((a1-x)/(a2-a1)*ln(2))) Chi-Quadr 2,59099E-4 Reduziert Kor. 0,99828 R-Quadrat Wert Standard fehler efficiency (DUT vs. RefCPC) b 1, ,01533 a1 17, ,20012 a2 26, ,42868 Analysis for fit function based on formula given by ISO (Mar. 2015) Slight underestimation of Dp50 efficiency for all calibration aerosols

16 Conclusion Primary and secondary PN reference method validated via international inter comparison workshops PMP-EECPC calibration setup was build for soot as well as for Ag particles in size range from 15 to 75 nm with suitable PNC up to cm -3 Evaluation of PTB calibration procedures is comparable to ISO

17 Outlook Further optimization of Ag size range to smaller sizes below 10 nm via secondary nucleation furnace Minimization of charge correction factors above 60 nm 2 nd UDMPS with unipolar charging Increasing of PNC for monodisperse fraction Internal Audit is needed to provide external calibration certificates for EECPC end user Establish PTB-EECPC calibration service in middle

18 Metric of WG 3.23 k [m -1 ] Type approval of opacimeter Test reports for opacimeter soot particles Ag particles N [cm -3 ] calibration certificate for EECPC in 2016 Thank you very much for your attention! m[µg/m 3 ] Questions? Test reports for light scattering devices D p [nm] Comparison to TSEM and AFM automotive emission Physikalisch-Technische Bundesanstalt Braunschweig and Berlin Bundesallee Braunschweig Dr. Andreas Nowak andreas.nowak@ptb.de