Toward Abatement of Soot Emissions: Tracking Nucleation in Flames

Transcription

1 1 Toward Abatement of Soot Emissions: Tracking Nucleation in Flames Francesco Carbone Department of Mechanical Engineering and Materials Science Yale University, New Haven, CT Acknowledgments: Prof. Alessandro Gomez, Prof. Antonio D Alessio Prof. J. Fernandez de la Mora, Prof. M. Attoui, Prof. M. Long. Dr. L. Figura, K. Gleason, F. Cattaneo, S. Moslih, Mr. N. Bernardo Research supported by: AFOSR (Grant #FA , 0018, Dr. Julian Tishkoff) NSF (Grant #CBET , Dr. Arvind Atreya and Dr. Ruey-Hung Chen) U.S. ARO (Grant #W911NF , Dr. Ralph A. Anthenien)

2 2 Motivation Ingredients leading to soot emissions in real devices: Molecular Growth Chemistry Nucleation and Aerosol Dynamics Diffusion Transport / Fluid Mechanics Specific Fuel Composition High Pressure Local Fuel/Oxidizer Mixing Deeper understanding of soot nucleation may suggest strategies for substantial emissions abatement

3 3 Approach Plate Residence D, time nm in flame 1 Fuel + Oxidizer Ingredients leading to Soot emissions from real devices: Molecular Growth Chemistry Specific Fuel Composition Nucleation and Aerosol Dynamics High Pressure Diffusion Transport / Fluid Mechanics Local Fuel/Oxidizer Mixing Carbone et al., Aerosol Sci. Tech 2016 Carbone et al., Combust. Flame 2017, in press

4 4 Soot Formation Aerosol and Optical Techniques AMU 1E+8 1E+7 1E+6 1E+5 1E+4 1E+3 0 Residence D, time nm in flame 1 Particle Oxidation Physical & Chemical (by C 2 H 2 ) Particle Growth Nucleation (Inception)? HACA Mechanism (Hydrogen abstraction ACetylene Addition) Wang & Frenklach, Combust. Flame 1997 Radical Pathway (Propargyl recombination) Miller & Melius, Combust. Flame 1992 D Anna et al., Combust. Flame 2001 Experimental and Theoretical Gap 1E+2 PAHs 1E+1 Gas Molecules (e.g. C 2 H 2 ) Wang Proc. Combust. Inst E Adapted from Bockhorn, 1994 Fuel Polycyclic Aromatic Hydrocarbons (PAHs) Analytical Chemistry Techniques

5 5 Gas Phase Microsampling PMS TCD Residence D, time nm in flame 1 Carboxen (Ni) Methanizer FID Ethylene/Air - Φ = 2.07 Significant CO and H 2 Molecular Growth Sooting Flame HP-1 GC/MS MS Thermal Conductivity Detector (TCD): H 2, N 2, O 2, CH 4, CO, C 2 H 4 Flame Ionization Detector (FID): CO, CO 2, CH 4, C 2 H 2, C 2 H 4, C 2 H 6 Mass Spectrometer (MS): Hydrocarbons up to 3-rings Equivalence ratio φ = (C/O)/(C/O) stoich

6 6 Molecular Growth Temperature, K D-COMSOL Model A-OPPDIFF 800 ISF data 600 TC results C2H2 5 CH Robust modelling of small hydrocarbons Growth of benzene bottleneck to soot Quantitative experimental database on PAHs Aromatic growth models are not quantitative mole fraction 2E-4 1E-4 0E+0 1E-5 Benzene 0 Naphthalene E-3 Model mole fraction 0E+0 1E-4 mole fraction E C3H435 C4H2 40 mole fraction 5E-6 0E+0 1E-5 0 Acenaphthylene Model mole fraction 0E+0 1E-4 mole fraction 3E-4 2E-4 1E-4 0E HAB, mm Solid Lines 1D Kinetic model without Soot (Blanquart et al. 2009) Dashed Lines 1D Kinetic model with Soot (Saggese et al. 2015) mole fraction 5E-6 0E+0 Model mole fraction 0E HAB, mm

7 7 Novel Diagnostics for Particle Nuclei: HR-DMA and API-TOF Residence D, time nm in flame 1 HEPA Q sh Q DMA Ground Blower Q sh Q TOF dd N dd l n( D) DDDDDD = 2 I FC D ee Q DMA Q sh Q DMA Bertram et al., Atm. Aerosol Meas PP FFFF V DMA To FC Differential Mobility Analyzer (DMA) filters charged molecular clusters/particles based on their sizes (electrical mobility) Measures the number concentration size distribution with High-Resolution (above 20) Time Of Flight (TOF) Mass Spectrometer sorts charged molecular clusters under vacuum based on their mass/charge ratio Measures precisely the mass distribution Atmospheric Pressure Interface (API) necessary to bring the sample to vacuum R FC V FC

8 8 HR-DMA and API-TOF Sampling Challenges Residence D, time nm in flame 1 HEPA Q sh Q DMA Ground Q sh Blower Q TOF V DMA To FC R FC V FC Purposely charge species/particles required to perform measurements Minimize sample transit time to measuring device that may introduce artifacts (e.g., particle coagulation, wall loss, etc.) Quantify flame perturbation (intrusiveness, local cooling/quenching) which may affect chemistry and spatial resolution Need ancillary modeling to account for it

9 9 High Dilution Sampling and Charging; Probe Modelling Ion Seeding Charging Nitrogen Kr 85 DMA VBP ~600 Pa Manometer Burner Excess flow to Vacuum Pump Minimized and quantified the sampling artifacts Pinhole Diamete r Dilution Ratio DR Outflow, P=1atm Nitrogen Stagnation Plate Wall Outflow, P=1atm Nitrogen Outflow, P=1atm- P Temperature, K mm D, Unperturbed 1-D, Streamtube Residence Time, ms Flame products

10 Soot Nuclei Size Distribution Functions 1E mm HR-DMA, Positive 7.5mm HR-DMA, Negative 1E+12.0mm HR-DMA, Positive.0mm HR-DMA, Negative.0mm literature DMA, Positive.0mm literature DMA, Negative dn/dln(d), cm-3 1E+11 1E+ dn/dln(d), cm-3 1E+11 1E+ 1E+9 1E+9 1E Diameter, nm 1E+8 Maricq, Combust. Flame Diameter, nm Soot nuclei form early in the flame, are smaller than 3 nm and cannot be detected with traditional diagnostics The number concentrations inferred by measurements in positive polarity are significantly larger than that in negative polarity ( cm -3 ) The SDFs of nascent soot appear to be monomodal with sub-3nm sizes for HAB up to mm when coagulation in the probe is minimized

11 Soot Nuclei Mass Spectra Chemical versus Physical Growth ion/s/n 11 HAB=5.0mm 1E-1 API-TOF Mass Spectrometry revealed the chemical complexity of soot nuclei 1E-2 1E-3 1E ion/s/n 1E HAB=7.5mm Work-in progress project 1E-2 1E-3 1E-4 ion/s/n 1E HAB=.0mm Periodicities can be recognized in the Mass Spectra 1E-2 D 1.6nm 1E-3 1E D 1.0nm mass/charge In collaboration with Aerodyne Research, ongoing

12 12 Optical Measurements: Soot Global Properties SS FF ii SS FF jj Residence D, time nm in flame 1 Color Ratio Pyrometry ηη ii λλ εε λλ λλ 5 exp = ηη jj λλ εε λλ λλ 5 exp HAB, mm hcc λλkk BB TT 1 dddd 1 hcc λλkk BB TT 1 dddd εε λλ = 1 exp KK eeeeee LL KK eeeeee LL λλ αα Kuhn et al., Proc. Comb. Inst Millikan. J. Opt. Soc. Am Soot volume fraction plateauing (similar to PAHs) Soot undergoes carbonization (ages) in the flame Cooling of flame products (close to plate) causes the sudden nucleation of young soot Ion induced nucleation of hydrocarbons αα soot volume fraction, fv Dispersion exponent, α Temperature, K 1E-6 1E-7 1E-8 1E LE results Pyrometry Model Model B LE-ISF HAB, mm Pyrometry, variable α Model B ISF data HAB, mm

13 13 Conclusion Provided quantitative experimental database on PAHs Measured soot nuclei in the gas-to-particle size range Nuclei are smaller than 3nm and persist throughout the flame Highlighted possible pitfalls in literature data and sampling artifacts Cooling of the flame products causes the sudden nucleation of semi-volatile material mediated by flame ions

14 14 Thank you