Advanced fundamental topics Flammability & extinction limits Description of flammability limits Chemical kinetics of limits Mechanisms of limits Buoyancy effects - upward & downward Conduction heat loss to tube walls Radiation heat loss Aerodynamic stretch Chemical fire suppressants Ignition limits Basic mechanisms Theory Lewis number effects Influence of geometry, flow, ignition source AME 514 - Spring 2017 - Lecture 2

Flammability and extinction limits Reference: Ju, Y., Maruta, K., Niioka, T., "Combustion Limits," Applied Mechanics Reviews, Vol. 53, pp. 257-277 (2001) Too lean or too rich mixtures won't burn - flammability limits Even if mixture is flammable, still won't burn in certain environments Small diameter tubes Strong hydrodynamic strain or turbulence High or low gravity High or low pressure Understanding needed for combustion engines & industrial combustion processes (leaner mixtures  lower Tad  lower NOx); fire & explosion hazard management, fire suppression, ... AME 514 - Spring 2017 - Lecture 2

Flammability limits - basic observations Limits occur for mixtures that are thermodynamically flammable - theoretical adiabatic flame temperature (Tad) far above ambient temperature (T∞) Limits usually characterized by finite (not zero) burning velocity at limit Models of limits due to losses - most important prediction: burning velocity at the limit (SL,lim) - better test of limit predictions than composition at limit AME 514 - Spring 2017 - Lecture 2

Premixed-gas flames – flammability limits 2 limit mechanisms, (1) & (2), yield similar fuel % and Tad at limit but very different SL,lim AME 514 - Spring 2017 - Lecture 2

Flammability limits in vertical tubes Most common apparatus - vertical tube (typ. 5 cm in diameter) Ignite mixture at one end of tube, if it propagates to other end, it's "flammable" Limit composition depends on orientation - buoyancy effects Upward propagation Downward propagation AME 514 - Spring 2017 - Lecture 2

Chemical kinetics of limits Lean hydrocarbon-air flames: main branching reaction (promotes combustion) is H + O2  OH + O; d[O2]/dt = -1016.7[H][O2]T-0.8e-16500/RT [ ]: mole/cm3; T: K; R: cal/mole-K; t: sec Depends on P2 since [ ] ~ P, strongly dependent on T Why important? Only energetically viable way to break O=O bond (120 kcal/mole), even though [H] is small Main H consumption reaction H + O2 + M  HO2 + M; {M = any molecule} d[O2]/dt = -1015.2[H][O2][M]T0e+1000/RT for M = N2 (higher rate for CO2 and especially H2O) Depends on P3, nearly independent of T Why important? Inhibits combustion by replacing H with much less active HO2 Branching or inhibition may be faster depending on T and P AME 514 - Spring 2017 - Lecture 2

Chemical kinetics of limits Rates equal ("crossover") when [M] = 101.5T-0.8e-17500/RT Ideal gas law: P = [M]RT thus P = 103.4T0.2e-17500/RT (P in atm)  crossover at 950K for 1 atm, higher T for higher P …but this only indicates that chemical mechanism may change and perhaps overall W drop rapidly below some T Computations show no limits without losses – no purely chemical criterion (Lakshmisha et al., 1990; Giovangigli & Smooke, 1992) - for steady planar adiabatic flames, burning velocity decreases smoothly towards zero as fuel concentration decreases (domain sizes up to 10 m, SL down to 0.02 cm/s) …but as SL decreases, d increases - need larger computational domain or experimental apparatus Also more buoyancy & heat loss effects as SL decreases …. AME 514 - Spring 2017 - Lecture 2

Chemical kinetics of limits Ju, Masuya, Ronney (1998) Ju et al., 1998 AME 514 - Spring 2017 - Lecture 2

Aerodynamic effects on premixed flames Aerodynamic effects occur on a large scale compared to the transport or reaction zones but affect SL and even existence of the flame Why only at large scale? Re on flame scale ≈ SL/ ( = kinematic viscosity) Re = (SL/)() = (1)(1/Pr) ≈ 1 since Pr ≈ 1 for gases Reflame ≈ 1  viscosity suppresses flow disturbances Key parameter: stretch rate () Generally  ~ U/d U = characteristic flow velocity d = characteristic flow length scale AME 514 - Spring 2017 - Lecture 2

Aerodynamic effects on premixed flames Strong stretch ( ≥ w ~ SL2/ or Karlovitz number Ka  /SL2 ≥ 1) extinguishes flames Moderate stretch strengthens flames for Le < 1 Buckmaster & Mikolaitis, 1982a (Ze = b in my notation), cold reactants against adiabatic products SL/SL(unstrained, adiabatic flame) ln(Ka) AME 514 - Spring 2017 - Lecture 2

Lewis number tutorial Le affects flame temperature in curved (shown below) or stretched flames When Le < 1, additional thermal enthalpy loss in curved/stretched region is less than additional chemical enthalpy gain, thus local flame temperature in curved region is higher, thus reaction rate increases drastically, local burning velocity increases Opposite behavior for oppositely curved flames AME 514 - Spring 2017 - Lecture 2

TIME SCALES - premixed-gas flames See Ronney (1998) Chemical time scale tchem ≈ /SL ≈ (a/SL)/SL ≈ a/SL2 a = thermal diffusivity [typ. 0.2 cm2/s], SL = laminar flame speed [typ. 40 cm/s] Conduction time scale tcond ≈ Tad/(dT/dt) ≈ d2/16a d = tube or burner diameter Radiation time scale trad ≈ Tad/(dT/dt) ≈ Tad/(L/rCp) (L = radiative heat loss per unit volume) Optically thin radiation: L = 4sap(Tad4 – T∞4) ap = Planck mean absorption coefficient [typ. 2 m-1 at 1 atm] L ≈ 106 W/m3 for HC-air combustion products trad ~ P/sap(Tad4 – T∞4) ~ P0, P = pressure Buoyant transport time scale t ~ d/V; V ≈ (gd(Dr/r))1/2 ≈ (gd)1/2 (g = gravity, d = characteristic dimension) Inviscid: tinv ≈ d/(gd)1/2 ≈ (d/g)1/2 (1/tinv ≈ Sinv) Viscous: d ≈ n/V Þ tvis ≈ (n/g2)1/3 (n = viscosity [typ. 0.15 cm2/s]) AME 514 - Spring 2017 - Lecture 2

Time scales (hydrocarbon-air, 1 atm) Conclusions Buoyancy unimportant for near-stoichiometric flames (tinv & tvis >> tchem) Buoyancy strongly influences near-limit flames at 1g (tinv & tvis < tchem) Radiation effects unimportant at 1g (tvis << trad; tinv << trad) Radiation effects dominate flames with low SL (trad ≈ tchem), but only observable at µg Small trad (a few seconds) - drop towers useful Radiation > conduction only for d > 3 cm Re ~ Vd/n ~ (gd3/n2)1/2 Þ turbulent flow at 1g for d > 10 cm AME 514 - Spring 2017 - Lecture 2

Flammability limits due to losses Golden rule: at limit Why 1/b not 1? T can only drop by O(1/b) before extinction - O(1) drop in T means exponentially large drop in reaction rate w, thus exponentially small SL (could also say heat generation occurs only in /b region whereas loss occurs over  region) AME 514 - Spring 2017 - Lecture 2

Flammability limits due to losses Heat loss to walls tchem ~ tcond  SL,lim ≈ (8)1/2a/d at limit or Pelim  SL,limd/a ≈ (8)1/2 ≈ 9 Actually Pelim ≈ 40 (USE Pelim ≈ 40 NOT 9) due to temperature averaging - consistent with experiments (Jarosinsky, 1983) Upward propagation in tube Rise speed at limit ≈ 0.3(gd)1/2 due to buoyancy alone (same as air bubble rising in water-filled tube (Levy, 1965)) Pelim ≈ 0.3 Grd1/2; Grd = Grashof number  gd3/n2 Causes stretch extinction (Buckmaster & Mikolaitis, 1982b): tchem ≈ tinv or 1/tchem ≈ Sinv Note f(Le) < 1 for Le < 1, f(Le) > 1 for Le > 1 - flame can survive at lower SL (weaker mixtures) when Le < 1 AME 514 - Spring 2017 - Lecture 2

Difference between S and SL long flame skirt at high Gr or with small f (low Lewis number, Le) (but note SL not really constant over flame surface!) AME 514 - Spring 2017 - Lecture 2

Flammability limits due to losses Downward propagation – sinking layer of cooling gases near wall outruns & "suffocates" flame (Jarosinsky et al., 1982) tchem ≈ tvis Þ SL,lim ≈ 1.3(ga)1/3 Pelim ≈ 1.65 Grd1/3 Can also obtain this result by equating SL to sink rate of thermal boundary layer = 0.8(gx)1/2 for x =  Consistent with experiments varying d and a (by varying diluent gas and pressure) (Wang & Ronney, 1993) and g (using centrifuge) (Krivulin et al., 1981) AME 514 - Spring 2017 - Lecture 2

Flammability limits in vertical tubes Upward propagation Downward propagation AME 514 - Spring 2017 - Lecture 2

Flammability limits in tubes Upward propagation - Wang & Ronney, 1993 AME 514 - Spring 2017 - Lecture 2

Flammability limits in tubes Downward propagation - Wang & Ronney, 1993 AME 514 - Spring 2017 - Lecture 2

Flammability limits – losses - continued… Big tube, no gravity – what causes limits? Radiation heat loss (trad ≈ tchem) (Joulin & Clavin, 1976; Buckmaster, 1976) What if not at limit? Heat loss still decreases SL, actually 2 possible speeds for any value of heat loss, but lower one generally unstable AME 514 - Spring 2017 - Lecture 2

Flammability limits – losses - continued… Doesn't radiative loss decrease for weaker mixtures, since temperature is lower? NO! Predicted SL,lim (typically 2 cm/s) consistent with µg experiments (Ronney, 1988; Abbud-Madrid & Ronney, 1990) AME 514 - Spring 2017 - Lecture 2

Reabsorption effects Is radiation always a loss mechanism? Reabsorption may be important when aP-1 < d Small concentration of blackbody particles - decreases SL (more radiative loss) More particles - reabsorption extend limits, increases SL Abbud-Madrid & Ronney (1993) AME 514 - Spring 2017 - Lecture 2

Reabsorption effects on premixed flames Gases – much more complicated because absorption coefficient depends strongly on wavelength and temperature & some radiation always escapes (Ju, Masuya, Ronney 1998) Absorption spectra of products different from reactants Spectra broader at high T than low T Dramatic difference in SL & limits compared to optically thin AME 514 - Spring 2017 - Lecture 2

Stretched flames - spherical Spherical expanding flames, Le < 1: stretch allows flames to exist in mixtures below radiative limit until flame radius rf is too large & curvature benefit too weak (Ronney & Sivashinsky, 1989) Adds stretch term (2S/R) (R = scaled flame radius; R > 0 for Le < 1; R < 0 for Le > 1) and unsteady term (dS/dR) to planar steady equation Dual limit: radiation at large rf, curvature-induced stretch at small rf (ignition limit) AME 514 - Spring 2017 - Lecture 2

Stretched flames - spherical Theory (Ronney & Sivashinsky, 1989) Experiment (Ronney, 1985) AME 514 - Spring 2017 - Lecture 2

Stretched counterflow or stagnation flames Mass + momentum conservation, 2D, const. density () (ux, uy = velocity components in x, y directions) admit an exact, steady (∂/∂t = 0) solution which is the same with or without viscosity (!!!):  = rate of strain (units s-1) Similar result in 2D axisymmetric geometry: Very simple flow characterized by a single parameter , easily implemented experimentally using counter-flowing round jets… AME 514 - Spring 2017 - Lecture 2

Stretched counterflow or stagnation flames S = dux/dx – flame located where ux = SL Increased stretch pushes flame closer to stagnation plane - decreased volume of radiant products Similar Le effects as curved flames Homework problem – determine effect of stretch rate S on SL, and extinction limit in terms of Damköhler number Z/S AME 514 - Spring 2017 - Lecture 2

Premixed-gas flames - stretched flames Stretched flames with radiation (Ju et al., 1999): dual limits, flammability extension even for Le >1, multiple solutions (which ones are stable?) AME 514 - Spring 2017 - Lecture 2

Premixed-gas flames - stretched flames Dual limits & Le effects seen in µg experiments, but evidence for multivalued behavior inconclusive Guo et al. (1997) AME 514 - Spring 2017 - Lecture 2

Chemical fire suppressants Key to suppression is removal of H atoms H + HBr  H2 + Br H + Br2  HBr + Br Br + Br + M  Br2 + M -------------------------------- H + H  H2 Why Br and not Cl or F? HCl and HF too stable, 1st reaction too slow HBr is a corrosive liquid, not convenient - use CF3Br (Halon 1301) - Br easily removed, remaining CF3 very stable, high CP to soak up heat Problem - CF3Br very powerful ozone depleter - banned! Alternatives not very good; best ozone-friendly chemical alternative is probably CF3CH2CF3 or CF3H Other alternatives (e.g. water mist) also being considered AME 514 - Spring 2017 - Lecture 2

Chemical fire suppressants AME 514 - Spring 2017 - Lecture 2

Flame ignition - basic concepts Experiments (Lewis & von Elbe, 1987) show that a minimum energy (Emin) (not just minimum T or volume) required for ignition Emin lowest near stoichiometric (typically 0.2 mJ) but minimum shifts to richer mixtures for higher HCs (why? Stay tuned…) Prediction of Emin relevant to energy conversion and fire safety Lewis & von Elbe, 1987 Minimum ignition energy (mJ) AME 514 - Spring 2017 - Lecture 2

Flame ignition - basic concepts Emin related to need to create flame kernel with dimension () large enough that chemical reaction (w) can exceed conductive loss rate (/2), thus  > (/w)1/2 ~ /(w)1/2 ~ /SL ~  Emin ~ energy contained in volume of gas with T ≈ Tad and radius ≈  ≈ 4/SL AME 514 - Spring 2017 - Lecture 2

Predictions of simple Emin formula Since  ~ P-1, Emin ~ P-2 if SL is independent of P Emin ≈ 100,000 times larger in a He-diluted than SF6-diluted mixture with same SL, same P (due to  and k [thermal conductivity] differences) Stoichiometric CH4-air @ 1 atm: predicted Emin ≈ 0.010 mJ ≈ 30x times lower than experiment (due to chemical kinetics, heat losses, shock losses …) … but need something more (Lewis number effects): 10% H2-air (SL ≈ 10 cm/sec): predicted Emin ≈ 0.3 mJ = 2.5 times higher than experiments Lean CH4-air (SL ≈ 5 cm/sec): Emin ≈ 5 mJ compared to ≈ 5000mJ for lean C3H8-air with same SL - but prediction is same for both AME 514 - Spring 2017 - Lecture 2

Predictions of simple Emin formula  hard to measure, but quenching distance (q) (min. tube diameter through which flame can propagate) should be ~  since Pelim = SL,lim q/ ~ q/ ≈ 40 ≈ constant, thus should have Emin ~  q3P Correlation so-so AME 514 - Spring 2017 - Lecture 2

More rigorous approach Assumptions: 1D spherical; ideal gases; adiabatic (except for ignition source Q(r,t)); 1 limiting reactant (e.g. very lean or rich); 1-step overall reaction; D, k, CP, etc. constant; low Mach #; no body forces Governing equations for mass, energy & species conservations (y = limiting reactant mass fraction; QR = its heating value) AME 514 - Spring 2017 - Lecture 2

More rigorous approach Non-dimensionalize (note Tad = T∞ + Y∞QR/CP) leads to, for mass, energy and species conservation with boundary conditions (Initial condition: T = T∞, y = y∞, U = 0 everywhere) (At infinite radius, T = T∞, y = y∞, U = 0 for all times) (Symmetry condition at r = 0 for all times) AME 514 - Spring 2017 - Lecture 2

Steady (?!?) solutions If reaction is confined to a thin zone near r = RZ (large ) This is a flame ball solution - note for Le < > 1, T* > < Tad; for Le = 1, T* = Tad and RZ =  Generally unstable R < RZ: shrinks and extinguishes R > RZ: expands and develops into steady flame RZ related to requirement for initiation of steady flame - expect Emin ~ Rz3 … but stable for a few carefully (or accidentally) chosen mixtures AME 514 - Spring 2017 - Lecture 2

Steady (?!?) solutions AME 514 - Spring 2017 - Lecture 2 How can a spherical flame not propagate??? Space experiments show ~ 1 cm diameter flame balls possible Movie: 500 sec elapsed time AME 514 - Spring 2017 - Lecture 2

Computations by Tromans and Furzeland, 1986 Lewis number effects Energy requirement very strongly dependent on Lewis number! 10% increase in Le: 2.5x increase in Emin (PDR); 2.2x (Tromans & Furzeland) Computations by Tromans and Furzeland, 1986 AME 514 - Spring 2017 - Lecture 2

Lewis number effects Why does minimum MIE shift to richer mixtures for higher HCs? Leeffective = effective/Deffective Deff = D of stoichiometrically limiting reactant, thus for lean mixtures Deff = Dfuel; rich mixtures Deff = DO2 Lean mixtures - Leeffective = Lefuel Mostly air, so eff ≈ air; also Deff = Dfuel CH4: DCH4 > air since MCH4 < MN2&O2 thus LeCH4 < 1, thus Leeff < 1 Higher HCs: Dfuel < air, thus Leeff > 1 - much higher MIE Rich mixtures - Leeffective = LeO2 CH4: CH4 > air since MCH4 < MN2&O2, so adding excess CH4 INCREASES Leeff Higher HCs: fuel < air since Mfuel > MN2&O2, so adding excess fuel DECREASES Leeff Actually adding excess fuel decreases both  and D, but decreases  more AME 514 - Spring 2017 - Lecture 2

Dynamic analysis RZ is related (but not equal) to an ignition requirement Joulin (1985) analyzed unsteady equations for Le < 1 (,  and q are the dimensionless radius, time and heat input) and found at the optimal ignition duration which has the expected form Emin ~ {energy per unit volume} x {volume of minimal flame kernel} ~ {adCp(Tad - T∞)} x {Rz3} AME 514 - Spring 2017 - Lecture 2

Dynamic analysis Joulin (1985) Radius vs. time Minimum ignition energy vs. ignition duration AME 514 - Spring 2017 - Lecture 2

Effect of spark gap & duration Expect “optimal” ignition duration ~ ignition kernel time scale ~ RZ2/ Duration too long - energy wasted after kernel has formed and propagated away - Emin ~ t1 Duration too short - larger shock losses, larger heat losses to electrodes due to high T kernel Expect “optimal” ignition kernel size ~ kernel length scale ~ RZ Size too large - energy wasted in too large volume - Emin ~ R3 Size too small - larger heat losses to electrodes Sloane & Ronney, 1990 Kono et al., 1976 Detailed chemical model 1-step chemical model AME 514 - Spring 2017 - Lecture 2

Effect of flow environment Mean flow or random flow (i.e. turbulence) (e.g. inside IC engine or gas turbine) increases stretch, thus Emin Ballal and Lefebrve, 1975 AME 514 - Spring 2017 - Lecture 2

Effect of ignition source Laser ignition sources higher than sparks despite lower heat losses, less asymmetrical flame kernel - maybe due to higher shock losses with shorter duration laser source? Lim et al., 1996 AME 514 - Spring 2017 - Lecture 2

References Abbud-Madrid, A., Ronney, P. D., "Effects of Radiative and Diffusive Transport Processes on Premixed Flames Near Flammability Limits," Twenty Third Symposium (International) on Combustion, Combustion Institute, 1990, pp. 423-431. Abbud-Madrid, A., Ronney, P. D., "Premixed Flame Propagation in an Optically-Thick Gas," AIAA Journal, Vol. 31, pp. 2179-2181 (1993). Ballal, D. R., Lefebvre, A. H., “The influence of flow parameters on minimum ignition energy and quenching distance,” 15th Symposium (International) on Combustion, Combustion Institute, 1975, pp. 1473-1481. Buckmaster, J. D. (1976). The quenching of deflagration waves, Combust. Flame 26, 151 -162. Buckmaster, J. D., Mikolaitis, D. (1982a). The premixed flame in a counterflow, Combust. Flame 47, 191-204 . Buckmaster, J. D., Mikolaitis, D. (1982b). A flammability-limit model upward propagation through lean methan-air mixtures in a standard flammability tube. Combust. Flame 45, pp 109-119. De Soete, G. G., 20th Symposium (International) on Combustion, Combustion Institute, 1984, p. 161. Dixon-Lewis, G., Shepard, I. G., 15th Symposium (International) on Combustion, Combustion Institute, 1974, p. 1483. Frendi, A., Sibulkin, M., "Dependence of Minimum Ignition Energy on Ignition Parameters," Combust. Sci. Tech. 73, 395-413, 1990. Joulin, G., Combust. Sci. Tech. 43, 99 (1985). AME 514 - Spring 2017 - Lecture 2

References Giovangigli, V. and Smooke, M. (1992). Application of Continuation Methods to Plane Premixed Laminar Flames, Combust. Sci. Tech. 87, 241-256. Guo, H., Ju, Y., Maruta, K., Niioka, T., Liu, F., Combust. Flame 109:639-646 (1997). Jarosinsky, J. (1983). Flame quenching by a cold wall, Combust. Flame 50, 167. Jarosinsky, J., Strehlow, R. A., Azarbarzin, A. (1982). The mechanisms of lean limit extinguishment of an upward and downward propagating flame in a standard flammability tube, Proc. Combust. Inst. 19, 1549-1557. Joulin, G., Clavin, P. (1976). Analyse asymptotique des conditions d'extinction des flammes laminaries, Acta Astronautica 3, 223. Ju, Y., Masuya, G. and Ronney, P. D., "Effects of Radiative Emission and Absorption on the Propagation and Extinction of Premixed Gas Flames" Twenty-Seventh International Symposium on Combustion, Combustion Institute, 1998, pp. 2619-2626. Ju, Y., Guo, H., Liu, F., Maruta, K. (1999). Effects of the Lewis number and radiative heat loss on the bifurcation of extinction of CH4-O2-N2-He flames, J. Fluid Mech. 379, 165-190. Krivulin, V. N., Kudryavtsev, E. A., Baratov, A. N., Badalyan, A. M., Babkin, V. S. (1981). Effect of acceleration on the limits of propagation of homogeneous gas mixtures, Combust. Expl. Shock Waves (Engl. Transl.) 17, 37-41. Lakshmisha, K. N., Paul, P. J., Mukunda, H. S. (1990). On the flammability limit and heat loss in flames with detailed chemistry, Proc. Combust. Inst. 23, 433-440. Levy, A. (1965). An optical study of flammability limits, Proc. Roy. Soc. (London) A283, 134. AME 514 - Spring 2017 - Lecture 2

References Kingdon, R. G., Weinberg, F. J., 16th Symposium (International) on Combustion, Combustion Institute, 1976, p. 747-756. Kono, M., Kumagai, S., Sakai, T., 16th Symposium (International) on Combustion, Combustion Institute, 1976, p. 757. Kono, M., Hatori, K., Iinuma, K., 20th Symposium (International) on Combustion, Combustion Institute, 1984, p. 133. Lewis, B., von Elbe, G., Combustion, Flames, and Explosions of Gases, 3rd ed., Academic Press, 1987. Lim, E. H., McIlroy, A., Ronney, P. D., Syage, J. A., in: Transport Phenomena in Combustion (S. H. Chan, Ed.), Taylor and Francis, 1996, pp. 176-184. Ronney, P.D., "Effect of Gravity on Laminar Premixed Gas Combustion II: Ignition and Extinction Phenomena," Combustion and Flame, Vol. 62, pp. 120-132 (1985). Ronney, P.D., "On the Mechanisms of Flame Propagation Limits and Extinction Processes at Microgravity," Twenty Second Symposium (International) on Combustion, Combustion Institute, 1988, pp. 1615-1623. Ronney, P. D., "Understanding Combustion Processes Through Microgravity Research," Twenty-Seventh International Symposium on Combustion, Combustion Institute, Pittsburgh, 1998, pp. 2485-2506 Ronney, P.D., Sivashinsky, G.I., "A Theoretical Study of Propagation and Extinction of Nonsteady Spherical Flame Fronts," SIAM Journal on Applied Mathematics, Vol. 49, pp. 1029-1046 (1989). Sloane, T. M., Ronney, P. D., "A Comparison of Ignition Phenomena Modeled with Detailed and Simplified Kinetics," Combustion Science and Technology, Vol. 88, pp. 1-13 (1993). AME 514 - Spring 2017 - Lecture 2

References Tromans, P. S., Furzeland, R. M., 21st Symposium (International) on Combustion, Combustion Institute, 1986, p. 1891. Wang, Q., Ronney, P. D. (1993). Mechanisms of flame propagation limits in vertical tubes, Paper no. 45, Spring Technical Meeting, Combustion Institute, Eastern/Central States Section, March 15-17, 1993, New Orleans, LA. AME 514 - Spring 2017 - Lecture 2