Flame Chemistry and Diagnostics

Size: px

Start display at page:

Download "Flame Chemistry and Diagnostics"

Martin Watkins
5 years ago
Views:

Flame Chemistry and Diagnostics High-Temperature Oxidation of (1) n-butanol and (2) C 4 - Hydrocarbons in Low-Pressure Premixed Flames Nils Hansen, Michael R. Harper, William H.

1 Flame Chemistry and Diagnostics High-Temperature Oxidation of (1) n-butanol and (2) C 4 - Hydrocarbons in Low-Pressure Premixed Flames Nils Hansen, Michael R. Harper, William H. Green Bin Yang, Hai Wang, Enoch Dames Sandia National Laboratories Massachusetts Institute of Technology Princeton University University of Southern California 2 nd Annual Conference of the CEFRC Aug 17 th -19 th, 2011, Princeton, NJ 1

2 Outline Background and Motivation Experimental Details Photoionization Mass Spectrometry Targeted Flame Conditions n-butanol Flame Chemistry C 4 - Hydrocarbons Flame Chemistry: iso-butene as a test case 2

3 n-butanol Background and Motivation Several studies have been targeted on a fundamental understanding of its combustion chemistry Models are best tested against in-situ species measurements in simple (laminar, premixed) burner-stabilized flames. Detailed species profiles will provide a very strict test of the combustion chemistry models. C 4 - Hydrocarbons C 4 -hydrocarbons combustion data are still of scarcity except for 1,3- butadiene. Combustions of 1-butene (1-C 4 H 8 ), n-butane (C 4 H 10 ), isobutene (ic 4 H 8 ), iso-butane (ic 4 H 10 ) at both fuel-rich and stoichiometry conditions are desired In particular, iso-butene is an important intermediate of the pyrolysis and oxidation of iso-butanol. 3

$synchrotron-generated VUV photons allows identification of species by mass by ionization energy Experimental mole fraction profiles are compared with flame model predictions Reaction path and$

4 Experimental Details ALS-Based Flame-Sampling Molecular-Beam Mass Spectrometry Flames are analyzed with molecular beam time-of-flight mass spectrometry Photoionization with tunable synchrotron-generated VUV photons allows identification of species by mass by ionization energy Experimental mole fraction profiles are compared with flame model predictions Reaction path and sensitivity analysis are performed 4

5 Experimental Details Targeted n-c 4 H 9 OH Flame Conditions Flame 1 Flame 2 Flame 3 Flame Oßwald* n-c 4 H 9 OH mol% H mol% O mol% Ar mol% pressure Torr Equivalence Ratio this study More than 40 isomer-resolved species with ion masses ranging from 2 (H 2 ) to 74 (C 4 H 9 OH) are quantified for each flame. * Data taken from: P. Oßwald, H. Güldenberg, K. Kohse-Höinghaus, B. Yang, T. Yuan, F. Qi Combust. Flame, 2011, 158,

6 Experimental Details Targeted C 4 - Flame Conditions ic 4 H 8 ic 4 H 8 ic 4 H 10 ic 4 H 10 1-C 4 H 8 1-C 4 H 8 C 4 H 10 C 4 H 10 Equivalence Ratio C/O ratio Pressure (Torr) Inlet velocity (cm/s) Fuel (slm) O 2 (slm) Ar (slm) ic 4 H 8 ic 4 H 10 1-C 4 H 8 C 4 H 10 6

7 n-butanol: Combustion Chemistry Modeling Modeling Construction Approach The n-butanol mechanism has been generated with the RMG of the Green group Simulations of the low-pressure flames are sensitive to the i-c 4 H 5 (CH 2 =CH- C=CH 2 CH 2 -CH=C=CH 2 ) thermochemistry, but are not for the shock tube, RCM, and JSR experiments 7

8 n-butanol: Flame Chemistry Insights Assessment of the Model s Predictive Capabilities Mole fraction profiles of the major species are predicted accurately A more powerful test is provided by comparing modeled and experimental profiles of intermediate species

9 n-butanol: Flame Chemistry Insights Conceivable n-butanol Consumption Pathways 9

10 n-butanol: Flame Chemistry Insights Rates of n-butanol Consumption The formation of the CH 3 CH 2 CH 2 CHOH (a-c 4 H 9 O) radical is predicted to be slightly preferred The fission of C-C bonds of n-butanol are only significant at high temperatures of the Oßwald et al. flame 10

11 n-butanol: Flame Chemistry Insights Consumption of the a-c 4 H 9 O Radical CH 3 -CH 2 -CH 2 - CH-OH The a-c 4 H 9 O + O 2 reaction is the main route to n-butanal Oßwald et al. did not seperate butenols from n-butanal 11

12 n-butanol: Flame Chemistry Insights Consumption of the b-c 4 H 9 O Radical CH 3 -CH 2 - CH-CH 2 -OH The decomposition of b-c 4 H 9 O is the main route to 1-butene Formation of a propenol isomer is not significant 12

13 n-butanol: n-butanol Summary and Outlook Summary Three sets of low-pressure n-butnol flames have been measured The model s predictive capabilities for high-temperature oxidation of n-butanol have been improved n-butanol oxidation is inititated by H-abstraction by H, O, and OH formation of a-c 4 H 9 O is preferred C-C bond fissions are only important at high temperatures and the waterelimination reaction is not important under the current conditions Subsequent disproportionation reactions of the C 4 H 9 O radicals and fast b- scissions govern the formation of smaller intermediates A paper describing the model has been submitted to Phys. Chem. Chem. Phys. Outlook Experimental (and modeling) work of flames fueled by iso-butanol are (almost) completed and will be presented next year We initiated work on iso-pentanol 13

14 C 4 - Flames: Major Species in iso-butene Flame USC Mech II and imposed, experimental temperature Discrepancies very near the burner: Uncertainties in local temperature and sampling-cone effect 14

15 Mole Fraction (*10-4 ) C 4 - Flames: Minor Species for Fuel-rich iso-butene Flame CH3 CH C2H2 C2H4 C2H Allene C3H3 C3H4 C3H C4H2 C4H4 C4H6 1.0 C6H6 C7H8 30 CH2O Distance from Burner (mm) Well predicted profiles for most flame intermediates C 4 H 4 and C 4 H 6 are underpredicted The USC model requires further improvement for low-pressure isobutene flames 15

16 ic 4 H 8 ROP GasRxn_Total (mole/cm 3 -sec) ic 4 H 7 ROP GasRxn_Total (mole/cm 3 -sec) C 4 - Flames: Rates of Production and Consumption iso-butene ic 4 H 7 tc4h9(+m)=ic4h8+h(+m) ic4h7+h(+m)=ic4h8(+m) 0.0 ic4h8+o=ch3+ch3+ch2co 4.0x10-5 ic4h8+h=ic4h7+h2-2.0x10-5 ic4h8+oh=ic4h7+h2o ic4h8+h=c3h6+ch3 2.0x10-5 ic4h8+oh=ic4h7+h2o CH3CCH2+CH3=iC4H x10-5 ic4h8+h=ic4h7+h2-2.0x10-5 Total ic4h7+h=ch3cch2+ch3-6.0x10-5 Total -4.0x10-5 ic4h7+h(+m)=ic4h8(+m) ac3h4+ch3=ic4h Distance from Burner (mm) Distance from Burner (mm) ic 4 H 8 ic 4 H 7 ac 3 H 4 CH 3 CCH 2 16

17 CH 3 CCH 2 ROP GasRxn_Total (mole/cm 3 -sec) C 6 H 6 ROP GasRxn_Total (mole/cm 3 -sec) C 4 - Flames: Rates of Production and Consumption CH 3 CCH 2 Radical Benzene 4.0x10-7 C3H3+C3H3=>C6H6 2.0x CH3CCH2+CH3=iC4H8 ic4h7+h=ch3cch2+ch3 2.0x C6H5+H(+M)=C6H6(+M) Total C6H5CH3+H=C6H6+CH3-2.0x10-5 ac3h4+h=ch3cch2 pc3h4+h=ch3cch2-2.0x10-7 C4H5-2+C2H2=C6H6+H C6H6+OH=C6H5+H2O C6H5+H2=C6H6+H Distance from Burner (mm) Distance from Burner (mm) ic 4 H 8 ic 4 H 7 ac 3 H 4 C 3 H 3 C 6 H 6 CH 3 CCH pc 2 3 H 4 More benzene formation than the normal alkene ic 4 H 7 C 4 species? 17

18 C 4 - Flames: Missing Reactions for C 4 - Species CH 2 CH CH 3 CH 2 H + H 2 C C CH 2 H 3 C C CH 2 + H 2 C CH 2 H 3 C CH 2 + M H + H CH 2 C C CH 2 H 3 C C CH 2 + M C CH CH 2 CH CH CH 2 H 2 CH CH 2 2 CH 3 CH 2 CH 2 H + H 2 C C CH 2 C CH 2 H + H CH 2 C C CH 2 H 3 C C CH 2 1,3-C 4 H 6 2 CH + M 2 CH 2 CH 2 + H (-H) 18

19 C 4 - Flames: Laminar Flame Speed Predicts reasonably well the shape and magnitude of the newer flame speed curve S. G. Davis, C. K. Law, Proc. Combust. Sci. Tech., 140 (1998) C.K. Law, et.al., Personal communication,

20 C 4 - Flames: Ignition Delay Time The predicted ignition delay times are higher than the experimental data at lower temperatures ( K) Missing C 4 - reactions and uncertainty for reaction rate constants of fuel decomposition H. J. Curran, M. P. Dunphy, J. M. Simmie, C. K. Westbrook, W. J. Pitz, 24 th Symp. (International) on Comb., (1992)

21 C 4 - Flames: Complementary Laser-Based Set-up Laser-induced fluorescence (LIF) Resonantly enhanced multi-photon ionization (REMPI) mass selected detection of PAHs large dynamic range PAH concentrations vary (~1000 ppm 100 ppb) Ions Neutrals 21

22 C 4 - Flames: C 4 - Flames REMPI Phi=1.6 flames 263 nm; 225mj; 4000 shots Iso-isomers have larger soot-tendency 22

23 C 4 - Flames: C 4 - Flames Summary and Outlook Flame species profiles have been measured by MBMS Missing pathways: ic 4 H 7 to 1,3-butadiene Revisions and updates are required for the reaction chemistry of isobutene pyrolysis and oxidation to improve the model s predictive capabilities Quantitative mole fraction profiles for REMPI-MBMS measurements Updated C 4 - hydrocarbons kinetics model 23

Detailed chemistry models for butanols based on ab initio rate coefficients, and comparisons with experimental data

Detailed chemistry models for butanols based on ab initio rate coefficients, and comparisons with experimental data William H. Green, Michael Harper, Mary Schnoor, & Shamel Merchant CEFRC Annual Meeting