Comparison Among DMS 500, EEPS SMPS, MSS, EC/OC, CPMA, Using Laboratory Soot Particles

Transcription

1 Comparison Among DMS 500, EEPS SMPS, MSS, EC/OC, CPMA, Using Laboratory Soot Particles Imad Khalek & Vinay Premnath Engine, Emissions & Vehicle Research Division Cambridge Particle Meeting, July 3, 2015 Southwest Research Institute San Antonio, Texas

2 Background All metrics such as number, surface area, and mass are still needed to assess the impact of vehicle particle emissions on human health: The PM2.5 mass is used and continue to be used because there isn t sufficient ambient data for other metrics, compared to PM2.5 Moving forward, particle size distribution instruments such as EEPS, DMS-500, SMPS, and perhaps other instruments can fill that gap by providing information on: Number, surface area and mass in the sub-500 nm size range where nearly all the number and mass emitted from engines are accounted for In order to accomplish such objectives: Understanding the relationships among instruments relative to a trusted reference is important Establishing a consistent operation and data reporting protocol for such instruments are also important Establishing a database for various metrical relationships for different combustion sources is also critical 2

3 Focus The focus of this talk is to discuss some preliminary data on comparing various instruments that include: OC/EC, MSS, EEPS, DMS-500, SMPS, and CPMA 3 of 43

4 Test Matrix MiniCAST soot generator was used to generate soot particles with targeted size distributions Experiment Set 1: Comparison of Mass based instruments 3 MSSs vs Reference Semi-Continuous OCEC (#1) Semi-continuous OCEC (#2) vs Reference OCEC (#1) Experiment Set 2: Comparison of Number based instruments DMS 500 vs EEPS (#3) EEPS (#1) vs EEPS (#3) DMS 500 vs EEPS vs SMPS Analysis of Number Based and Mass Based Moments Experiment Set 3: Tandem DMA-CPMA Measurements Size-wise estimation of Density of Soot Particles generated using MiniCAST Mass Based Moments from Experiment Set 2 using Estimated Density 4

5 Experimental Setup Engine Exhaust Particle Sizer Microsoot Sensor Scanning Mobility Particle Sizer DMS 500 Semi-continuous OCEC 5

6 Soot Concentration vs Elemental Carbon Good Correlation was observed between EC using two separate instruments with one designated as reference Different MSS instruments gave different slopes with EC under the same operating condition: The slopes ranged from 0.97 for MSS 4 to 0.8 for MSS 1 to 0.78 for MSS 2 The instruments had no errors 6

7 DMS & EEPS Number Basis DMS 500 vs EEPS #3 Geometric Mean of particle Size distribution ~ 55 nm EEPS #1 vs EEPS #3 Good correlation was observed between DMS-500 (diesel inversion) and EEPS (Soot Inversion) Good correlation was observed between two EEPS using soot inversion model 7

8 EEPS Inversion Model-Number GNMD EEPS ~ 59 nm TSI Engine Exhaust Particle Sizer (EEPS #3) Inversion Models Soot (Empirical) Compact (Empirical) Default (Theoretical + Empirical) Relationship among inversion models is not consistent for different mean size distributions GNMD EEPS ~ 39 nm GNMD EEPS ~ 59 nm GNMD EEPS ~ 39 nm ~21% difference ~25% ~26% 8

9 DMS 500 Inversion Model-Number GNMD DMS500 ~ 67 nm DMS 500 Inversion Models Mono-modal Compact Mono-modal Aggregate Diesel Aggregate Mono-modal Aggregate Model Reported Lower Concentration GNMD DMS 500 ~ 43 nm GNMD DMS ~ 43 nm ~14% difference GNMD DMS ~ 67 nm ~16% 9

10 EEPS, DMS 500, SMPS Number Peak ~ 60 nm Peak ~ 39 nm SMPS Multiple charge correction Diffusion Correction Engine Exhaust Particle Sizer (EEPS #3) Inversion Models Soot (Empirical) Compact (Empirical) Default (Theoretical + Empirical) DMS 500 Inversion Models Monomodal Compact Monomodal Aggregate Diesel Aggregate Differences with the SMPS were observed for both mean sizes 10

11 EEPS, DMS 500, SMPS Number Summary EEPS EEPS DMS DMS 39 nm EEPS & DMS numbers were higher (20 to 30%) than SMPS Geometric mean was close to that of SMPS, except for the aggregate and diesel model with the DMS 59 nm EEPS & DMS numbers were close to that of SMPS Geometric mean was higher with DMS 11

12 EEPS, DMS 500, SMPS Mass Basis Number Peak ~ 60 nm Mass Peak ~ 100 nm One area of obvious inconsistency is for particles > 200 nm with the DMS These modes may need to be excluded from the mass weighting, or treated differently by the software Number Peak ~ 39 nm Mass Peak ~ 75 nm 12

13 Soot Density Estimation via Tandem DMA-CPMA measurements CPMA Experimental Setup Mini CAST (propane based burner) was used to generate soot particles DMA was used to classify 50 nm, 75 nm, 100 nm, 125 nm, 175 nm & 200 nm soot particles SMPS CPC Work is in progress to verify the density prediction using PSL particles Apparent density is lower than predicted for diesel particles. For example, diesel particles have higher apparent density at 50 nm 13

14 EEPS, DMS 500, SMPS Mass Summary EEPS DMS DMS mass was 20% to 40% higher than SMPS EEPS mass was 20% higher, except for the compact condition Assuming ρ = 1 g/cc 14

15 EEPS, Micro-soot Sensor Mass Basis EEPS vs MSS Data gathered for GDI vehicles Instruments involved TSI Engine Exhaust Particle Sizer o Inversion Model: Default AVL Micro-soot Sensor Density assumed to convert from number to mass moment was 1 g/cc Good correlation was observed with MSS, but the slope was less than 1. Using different inversion and a density distribution may change the relationship. The net outcome is not known until it is done. 15

16 Summary The main point of this presentation is to begin the discussion on the ability of number-based size distribution instruments to predict different moments of the size distribution The different inversion techniques introduced recently with EEPS and available in DMS need to investigated further for different moments besides number 16

17 Questions Southwest Research Institute 17