Stanford University Research Program Shock Tube/Laser Absorption - PowerPoint PPT Presentation

Stanford University Research Program Shock Tube/Laser Absorption Studies of Chemical Kinetics Ronald K. Hanson Dept. of Mechanical Engineering, Stanford University Some of the work presented here is • Experimental Methods unpublished. Please check with RKH/DFD • Butanol Kinetics before regarding the data as final or importing it into publications. We would • Methyl Ester Kinetics also value feedback from team members • Future Work regarding our data and how it might be modeled. rkhanson@stanford.edu dfd@stanford.edu CEFRC Second Annual Conference August 17 ‐ 19, 2011 1

Please Note Some of the work presented here is unpublished. Please check with RKH/DFD before regarding the data as final or importing it into publications. We would also value feedback from team members regarding our data and how it might be modeled. rkhanson@stanford.edu dfd@stanford.edu 2

Experiment Types Goal: High ‐ quality databases to validate detailed mechanisms • Ignition delay times provide global targets – Shock tubes provide constant ‐ volume data over wide pressure range • Species time ‐ histories provide strong constraints on mechanisms – Laser absorption can provide species time ‐ histories for: OH, CO, CO 2 , CH 2 O, H 2 O, CH 3 , CH 4 , C 2 H 4 , fuel, … • Direct determination of elementary reaction rate constants – For reactions where estimates/theory are not sufficient 3

Kinetics Shock Tube 1 Kinetics Shock Tube 2 Experimental Approach Aerosol Shock Tube High Pressure Shock Tube 4

Advances in Shock Tube Methodology • Tailored driver gas/new driver geometry provide extended test time for access to low T • Driver inserts provide highly uniform reflected shock conditions approaching constant U/V • Aerosol shock tube provides access to low ‐ vapor ‐ pressure fuels • Gasdynamic modeling of shock tube flows to account for facility effects and energy release 5

Access to Low Temperatures • Longer driver length and tailored gas mixtures can provide longer test times (> 40 ms) 2x Driver Extension • Shock tubes now can overlap with RCMs 7 6

Improvement in Temperature Uniformity Problem: Ignition delay times are • artificially shortened by non ‐ ideal facility effects!! dP/dt ≠ 0 • Solution: Driver Inserts • Results : Near ‐ ideal constant ‐ volume performance!! dP/dt ≈ 0 P 5 V RS T 5 7

Aerosol Shock Tube for Low ‐ Vapor ‐ Pressure Fuels Diagnostics: • Pressure • Droplet scattering • Fuel time history Dump Tank • OH* emission Aerosol Tank Driver Section Driven Section Evaporated Aerosol Ultrasonic Nebulizers • Does not require heated shock tube • Eliminates fuel cracking and partial distillation • Provides access to low ‐ vapor ‐ pressure fuels: large methyl esters, bio ‐ diesel surrogates 8

Current Laser Capabilities for Species Detection for real ‐ time, in situ sensing Visible Infrared Ultraviolet 2.3  m CN 388 nm CO CH 3 216 nm 2.5  m CH 431 nm H 2 O NO 225 nm 2.7  m NCO 440 nm CO 2 O 2 227 nm Fuel 3.4  m NO 2 472 nm HO 2 230 nm 5.2  m NH 2 597 nm NO CH 2 O 305 nm 9.2  m HCO 614 nm MeOH OH 306 nm MF 9.2  m NH 336 nm 10.5  m C 2 H 4 Coherent MIRA Ti ‐ Sapphire Spectra ‐ Physics 380 Ring NovaWave Mid ‐ IR DFG

Kinetics Shock Tube 1 Kinetics Shock Tube 2 Butanol Kinetics 10

Overview of Butanol Studies • Ignition delay times : 1.5 ‐ 45 atm, 800 ‐ 1600 K Butanol isomers, high and low pressure • Species time ‐ histories : N ‐ Butanol pyrolysis: OH, H 2 O, CH 2 O, C 2 H 4 , CH 4 , CO N ‐ Butanol oxidation: OH, H 2 O, C 2 H 4 • Direct determinations of elementary rxn. rate constants : Butanol+OH=products, all isomers Butene+OH= Products, all isomers 11

Survey of Ignition Delay Times: Butanol Isomers at Low Pressure 1333 K 1538 K 1429 K 1250 K Lines - MIT (2011) Variation in ignition delay times 1-butanol 2-butanol - tert-butanol slowest 2-but i-butanol t-but i-but - 1-butanol fastest t-butanol 1000 1-but t ign [us] MIT (2011) mechanism - Fair agreement with 4% O 2 /Argon t- & i-butanol data 1.5 atm,  =1.0 100 - Poorer agreement with 1- & 2-butanol data 0.60 0.65 0.70 0.75 0.80 0.85 Data of sufficient quality to 1000/T 5 [1/K] refine reaction mechanisms What happens at high pressure? 12

Survey of Ignition Delay Times: 2 ‐ Butanol Variation with Pressure 1538 K 1333 K 1177 K 1053 K Lines - MIT (2011) 3 atm 1.5 atm 19atm Very low scatter ( � 5-10 %) consistent 43atm with uncertainty in T 1000 Ignition delay times scale t ign [us] approximately as P -0.7 MIT (2011) model P-dependence 2-Butanol consistent with 2-butanol data 4% O 2 /Argon 100  ~1.0 Data of sufficient quality to refine 0.6 0.7 0.8 0.9 1.0 reaction mechanisms 1000/T 5 [1/K] Next step: need for species time ‐ histories! 13

N ‐ Butanol Pyrolysis • First shock tube/laser absorption speciation study of n ‐ butanol pyrolysis • OH (306 nm) • H 2 O (2.5 microns) • CH 2 O (305 nm) • CO (4.6 nm) • C 2 H 4 (10.5 microns) n ‐ Butanol • CH 4 (3.4 microns) 14

N ‐ Butanol Pyrolysis: Species Time ‐ Histories OH and H 2 O OH & H 2 O time ‐ histories reveal large variation in model performance • • Clear opportunity for model refinement 15

N ‐ Butanol Pyrolysis: Species Time ‐ Histories CH 2 O and CO Formaldehyde and CO uniformly underpredicted! • • Measured OH+H 2 O+CH 2 O+CO account for >90% of O ‐ atoms! • Remaining O ‐ atoms likely in CH 3 CHO, CH 2 CO,… 16

N ‐ Butanol Pyrolysis: Species Time ‐ Histories C 2 H 4 and CH 4 • All models underpredict C 2 H 4 ; better agreement for CH 4 • Measured C 2 H 4 +CH 4 +CO+CH 2 O account for >70% of C ‐ atoms! • Remaining C ‐ atoms likely in C 3 H 6 , C 2 H 6 , C 2 H 2 ,… 17

OH+Butanol → Products First ‐ order removal of OH measured using laser absorption in 30 ppm TBHP/200ppm butanol/argon mixtures 1111 K 1000 K 909 K 3E13 • Strong dependence on Rate Constant [cc/mole/s] isomer 1E13 1-but iso-but 2-but • MIT (2011) Model: Trends not consistent with data 1E12 tert-but • Sarathy (2011) Model: Sarathy (2011) Consistent with data 1E11 0.8 0.9 1.0 1.1 1.2 1000/T [1/K] • Overall rate dependent on product channel chemistry 18

Kinetics Shock Tube 2 Methyl Ester Kinetics Aerosol Shock Tube 19

Overview of Methyl Ester Studies • Ignition delay times : Aerosol Shock Tube Studies Methyl Decanoate Methyl Oleate • Species time ‐ histories during pyrolysis : Methyl Formate: CO, OH, C 2 H 4 , CH 2 O, CH 3 , CH 4 , Me ‐ OH, MF Methyl Acetate/Propanoate: CO, CH 3 , C 2 H 4 Methyl Butanoate: CO, CO 2 , C 2 H 4 , OH • Reflected shock conditions : 1.5 ‐ 6 atm, 1000 ‐ 1400 K 20

Methyl Decanoate Ignition Delay Times: Aerosol Shock Tube Studies Westbrook model: • 3500 species E A = 29.2 • 17000 reactions kcal/mol Westbrook model E A = 42.5 correctly predicts kcal/mol ignition delay times, activation energies, and [O 2 ] dependence Can we apply AST method to larger esters? 21

Methyl Oleate Ignition Delay Times: Aerosol Shock Tube Studies • Data reveal weak dependence on equivalence ratio • Westbrook model: ‐ underestimates ignition delay times by about 50% ‐ captures reveal weak dependence on equivalence ratio Next step: Need for species time ‐ histories! 22

Methyl Formate Pyrolysis: Time ‐ Histories and Rate Data • Species time ‐ histories: CO, OH, C 2 H 4 , CH 2 O, CH 3 , CH 4 , MeOH, MF • Rate constant determination for all three major decomposition channels (Princeton/NUI 2010) using CO (4.6  m) 1: MF → CO+MeOH using MeOH (9.23  m) using CH 4 (3.4  m) 2: MF → CH 4 +CO 2 using CO 2 (2.7  m) 3: MF → 2CH2O using CH 2 O (306 nm) 23

Methyl Formate Decomposition: CH 3 OH+CO channel MF → CH 3 OH+CO CO Time ‐ Histories 1429 1333 1250 1176 1667K 1538 0.20 11 10 Measurement P = 1.48-1.72 atm Dryer et al. 2010 1607K 10 10 0.15 0.1% MF/Ar CO Mole Fraction [%] 1.5 atm -1 ] 1488K 9 10 -1 s 0.10 -3 mol 1376K 8 10 k 1 [cm 0.05 Current study 1285K Best fit 7 10 Dryer et al. 2010 (1.6 atm) Curran et al. 2008 (1.6 atm) 1202K 0.00 6 10 0 200 400 600 800 0.60 0.65 0.70 0.75 0.80 0.85 Time [  s] 1000/T [K] Direct measurement of Excellent agreement at CH 3 OH+CO channel with Dooley et al. (2010) possible with CO laser particularly at lower T 24

Methyl Formate Decomposition: CH 4 +CO 2 channel MF → CH 4 +CO 2 CH 4 Time ‐ Histories 1667 K 1562 1470 1389 1316 1250 Current study 0.4 9 P = 1.36-1.54 atm 10 Dryer et al. 2010 CH4 Mole Fraction [%] Updated k 1 0.3 3% MF/Ar 1408K -1 ] 1.5 atm 8 10 -1 s 3 mol 0.2 k 2 [cm 7 10 1289K 0.1 Current study Best fit Dryer et al. 2010 (1.45 atm) 6 0.0 10 0.0 0.5 1.0 1.5 2.0 2.5 0.60 0.64 0.68 0.72 0.76 0.80 Time [ms] 1000/T [K] Direct measurement of CH 4 +CO 2 channel possible Excellent agreement at with CH 4 or CO 2 laser with Dooley et al. (2010) 25