Reciprocating Internal Combustion Engines

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Reciprocating Internal Combustion Engines Prof. Rolf D. Reitz, Engine Research Center, University of Wisconsin-Madison 212 Princeton-CEFRC Summer Program on Combustion Course Length: 9 hrs (Wed.

1 Reciprocating Internal Combustion Engines Prof. Rolf D. Reitz, Engine Research Center, University of Wisconsin-Madison 212 Princeton-CEFRC Summer Program on Combustion Course Length: 9 hrs (Wed., Thur., Fri., June 27-29) Hour 5 Copyright 212 by Rolf D. Reitz. This material is not to be sold, reproduced or distributed without prior written permission of the owner, Rolf D. Reitz. 1 CEFRC5 June 28, 212

2 2 CEFRC5 June 28, 212 Short course outine: Engine fundamentals and performance metrics, computer modeling supported by in-depth understanding of fundamental engine processes and detailed experiments in engine design optimization. Day 1 (Engine fundamentals) Hour 1: IC Engine Review,, 1 and 3-D modeling Hour 2: Turbochargers, Engine Performance Metrics Hour 3: Chemical Kinetics, HCCI & SI Combustion Day 2 (Spray combustion modeling) Hour 4: Atomization, Drop Breakup/Coalescence Hour 6: Heat transfer, NOx and Soot Emissions Day 3 (Applications) Hour 7: Diesel combustion and SI knock modeling Hour 8: Optimization and Low Temperature Combustion Hour 9: Automotive applications and the Future

3 CEFRC5 June 28, 212 ERC Spray modeling Blob injection model R/D L/D Breakup length L C a 1 2 r=b / f(t) RT Model Beale &Reitz, 1999 Kelvin-Helmoltz Rayleigh Taylor Linearized instability analysis

3 3 CEFRC5 June 28, 212 ERC Spray modeling Blob injection model R/D L/D Breakup length L C a 1 2 r=b / f(t) RT Model Beale &Reitz, 1999 Kelvin-Helmoltz Rayleigh Taylor Linearized instability analysis KH Model = e t Spray Models Nozzle flow/cavitation Jet atomization Drop breakup KH-RT Drop collision/coalescence Drop drag Multi-component fuel evaporation Spray-wall impingement Discrete drop model

4 4 CEFRC5 June 28, 212 Droplet drag modeling Liu, SAE 9372 Steady-state Stokes viscous drag, added-mass and Basset history integral dv/dt = General form F 6 r g v 1 ( r3 g ) dv dv dt t 6r2 dt ' g dt ' t t ' L V d dv/ dt C D A f g U 2 2 {U / U} C d.424, Red 1 1 2/3 24 Re d (1 Re d / 6), Red 1 Drop distortion (TAB model) y 8y 2 U y 5 2 l rel l rd lrd 3 l rd Cd Cd, sphere ( y)

5 5 CEFRC5 June 28, 212 Turbulence & Drop Dispersion Monte Carlo method u u u G( u ) 4 / 3k 3/2 exp(3 u 2 / 4k) St <<1 Drop-eddy interaction time Eddy life time Residence time Vortex structure St >>1 St ~1 S t = t(u-v)/2r t= 2 L r 2 /9 g t e l / 2k / 3 t p l / u v l =C 3/4 k 3/2 / = l t int min(t e,t p ) Gosman & Iaonnides, 1981

6 6 CEFRC5 June 28, 212 Spray Wall Impingement At low approach velocities (We) drops rebound elastically With hot walls cushion of vapor fuel forms under the drop As approach velocity is increased, normal velocity component decreases and drop may break up Beyond We = 4 liquid spreads into surface layer At high temperatures film boiling takes place Wachters & Westerling, 1966 We 2 L U n d/2 We =.678We exp( -.88 We ) o i i We 4 We 4

7 Dry Wall Impingement Models Stick - drops stick to the wall Reflect - drops rebound Slide/Jet - incident drop leaves tangent to the surface From mass and momentum conservation: y p = - ln{1 - p(1 - exp( - b)} b where < p <1 random number exp( b ) + 1 sin a = ( ) /1 + ( p / b ) exp( b ) Naber & Reitz, SAE CEFRC5 June 28, 212

radial penetration (cm) 8 CEFRC5 June 28, 212 ERC Wall Impingement Model Rebound or slide based on We Enhanced breakup due to drop destabilization B 1 = 1.

8 radial penetration (cm) 8 CEFRC5 June 28, 212 ERC Wall Impingement Model Rebound or slide based on We Enhanced breakup due to drop destabilization B 1 = Senecal, SAE B 1 4 B 1 3 B 1 4 B measured (Naber et al.) predicted (present) measured (Booth) predicted (present) time (ms) We 4 We 4

9 9 CEFRC5 June 28, 212 Drop Vaporization well understood for single component, low pressure D 2 Law Sirignano, 1999; Law ; Aggarwal SAE Liquid-Vapor Interface: Equilibrium or Non-equilibrium YR T Tinf Mass transfer with surroundings: vaporization, condensation, gas solubility Drop R Internal circulation and profiles: temperature, concentration, velocity TR r Y Yinf Heat transfer to drop: convection (conduction), radiation Relative Drop Motion

10 1 CEFRC5 June 28, 212 KIVA Vaporization Models Frossling correlation R dr/ dt DBSh/ (2 1 r) Amsden, 1989 Lefebvre, 1989 Mass transfer number B Sherwood number * ( Y1 Y1 ) /(1 Y Fuel mass fraction at drop surface * 1 Sh (2..6 Re d 1/ 2 Sc 1/ 3 ) Y 1 * W 1 / {W 1 W ( ) p p v (T d ) 1)} Vapor pressure P v from thermodynamic tables ln(1 B) B

11 11 CEFRC5 June 28, 212 Drop Heat-up Modeling Change in drop temperature from energy balance 4 r 3 c T 4 r 2 RL( T ) 4 r 2 Q 3 d l d d d d Amsden, 1989 Lefebvre, 1989 Rate of heat conduction to drop from Ranz-Marshall correlation where Q d (T 2 T 1 )Nu / (2 r) Nu (2..6Re d 1/ 2 Pr 1/ 3 ) ln(1 B) B

12 12 CEFRC5 June 28, 212 Vaporization regimes Ra & Reitz, 23 q o q o q i T d m q i T d m Boiling heating Flash boiling cooling T Ts T amb T Ts q o m q o m T b T s T b T d Tq amb i T d q i T d T d Normal evaporation heating r T s Normal evaporation cooling r T T s =T b Ts T amb T T d Ts T amb T d T s =T b r r

13 13 CEFRC5 June 28, 212 Normal evaporation energy balance CPm m L( Ts ) hi, eff ( Td Ts ) ( T Ts ) 2roC Pm [ CA]( yf yfs ) Sh exp 1 Nu Nu yfs yf m gm ln(1 BM ) gm ln(1 ) g h 1 y m =Sh D/d o,eff mass balance Flash Boiling evaporation (T b from Clausius Clapeyron equation) Fs CPm m L( Tb ) ( hi, eff sh)( Td Tb ) ( T Tb ) 2roC Pm [ CA]( yf 1) Sh exp 1 Nu Nu T Td Tb Vaporization regimes.76t ( T Superheated.26 sh droplet 2.33 correlation.27t (5 T (Adachi et al., ) 13.8T (25 T ) 5) 25). L(T s )m =q i +q o h i, eff, e e eff t Ra & Reitz, 23 e q T d T s m

$distribution or mole fraction [%] distribution or mole fraction [%] Multi-component fuel modeling Diesel Gasoline diesel A Aromatic [%] 34 Sulfur [ppm] 1.5 Parafins [%] 33 Napthenes [%] 33 Olefin [%].$

14 distribution or mole fraction [%] distribution or mole fraction [%] Multi-component fuel modeling Diesel Gasoline diesel A Aromatic [%] 34 Sulfur [ppm] 1.5 Parafins [%] 33 Napthenes [%] 33 Olefin [%].2 Cetane# ~43 C/H ratio 7.14 diesel B ~ Common automotive fuels are multi-component Components: Various molecular weights and chemical structures Three approaches; i) single component approximation ii) continuous multi-component iii) discrete multi-component Discrete g p (mw i ) Lippert & Reitz, 1997, Ra & Reitz 23 I = gasoline composition iso-octane approximation Single comp approx molecular weight Continuous f p (I) 14 CEFRC5 June 28,

15 15 CEFRC5 June 28, 212 Continuous system of a liquid phase + Semi-continuous mixture system of vapor phase fuel and ambient gas: G p Continuous Multi-Component p F Multi-component model formulation ( I) x f ( I) x ( I p N s1 p s I s ) p=l,v Discrete system of a liquid phase + Discrete mixture system of vapor phase fuel and ambient gas: G p Discrete Multi-Component N F 1 F N s p F ( I) x ( I I ) x ( I F s1 p s I s ) continuous phase discrete phase discrete phase of fuel Vapor phase transport equation, 2 2, discrete phase of air/fuel mixture n n Vapor phase transport equation, p I f p ( I) di ( n, 1, 2, ) [ y n n n [ fv ] [ fv v] I J IdI Sg t i ] [ yiv] ( Diy i ) sg, i t Assumed distribution function : - func 1 ( I ) ( I ) [ yf ] [ yfv] ( DyF ) S f ( I) exp[ ] t ( ) Ra & Reitz, 23, 29 g

16 probabilty density probabilty density DMC Model Test Modeled species contents* species MW Mass fraction Diesel A (US narrow-cut Diesel) c14h c12h c16h c18h Diesel B (Euro Diesel) c14h ic8h c1h c12h c16h c18h Diesel A Diesel B molecular weight [g/mol] Ra & Reitz, molecular weight [g/mol] 16 CEFRC5 June 28, 212

$mass fraction mass fraction 17 CEFRC5 June$ 12 MW=199.61.2.1.15.1.8.6.4.5.2. ic8h18 c1h22 c12h26 c14h3 c16h34 c18h38.

Diesel B MW ini =2 Ra & Reitz, 29 CA=-14 (~

17 mass fraction mass fraction 17 CEFRC5 June 28, 212 Component distributions MW= MW= ic8h18 c1h22 c12h26 c14h3 c16h34 c18h38. ic8h18 c1h22 c12h26 c14h3 c16h34 c18h38 Diesel B MW ini =2 Ra & Reitz, 29 CA=-14 (~ first ignition timing)

18 mole fraction mole fraction 18 CEFRC5 June 28, 212 Multi-component spray vaporization Ra & Reitz, 29 Gasoline Do=3 m Vinj=1 m/s 2. ms after SOI MW= MW= ic5h12 ic6h14 ic7h16 ic8h18 C9H2 C1H22 C12H26 ic5h12 ic6h14 ic7h16 ic8h18 C9H2 C1H22 C12H26 component component

Non-ideal mixing using UNIFAC Method Jiao, SAE 211-1-387 For mixtures composed of polar components, both initial and final boiling points in the

$Vapor pressure of pure comp. i ; Pm x Li, Total mixture pressure Mole fraction of comp. i in liquid phase; x Mole fraction of comp.$

19 Non-ideal mixing using UNIFAC Method Jiao, SAE For mixtures composed of polar components, both initial and final boiling points in the distillation curve are not well predicted assuming Ideal Mixing (Raoult s Law) - misses the azeotrope behavior of the mixture. x P x vap, i i i L, i Pm Differences in size and shapes of the molecules Energy interactions between functional groups [3] H H H - C - C - OH H H Pvap, i Vapor pressure of pure comp. i ; Pm x Li, Total mixture pressure Mole fraction of comp. i in liquid phase; x Mole fraction of comp. i in gas phase Fredenslund, 1975 i 19 CEFRC5 June 28, 212

20 2 CEFRC5 June 28, 212 Ethanol/gasoline surrogate mixture Pfahl,1996, Jiao, 211

21 Droplet radius [cm] Temperature [ C] 21 CEFRC5 June 28, 212 Drop evaporation simulation Jiao, SAE Droplet lifetime Time [s] Adding ethanol decreases vapor pressure - but with non-ideal effects, vapor pressure first increases Adding ethanol broadens boiling temperature range Phase diagram of mixture of ethanol and 9-component gasoline surrogate, P amb =1bar Temp. vs. mole fraction nounifac UNIFAC 15 C x ethanol

22 Temperature [ C] Temperature [ C] Distillation curve Andersen, 21 Experiment Jiao, SAE nounifac E E1 E2 E5 E85 E1 Simulation E2 has the lowest initial boiling temperature UNIFAC E E1 E2 E5 E85 E1 6 Simulation Volume [%] Volume [%] 22 CEFRC5 June 28, 212

23 23 CEFRC5 June 28, 212 Surrogate fuels - 18 component model alkanes aromatics cycloalkanes PAH corrected

Hydrocarbon concentration (% mass) 24 CEFRC5 June 28, 212 Diesel Hydrocarbon Class Distributions and Surrogates 1 Paraffins Alkylbenzenes Polynuclear aromatics Naphthenes Benzene(MAH) Anand, 211 8 6

24 Hydrocarbon concentration (% mass) 24 CEFRC5 June 28, 212 Diesel Hydrocarbon Class Distributions and Surrogates 1 Paraffins Alkylbenzenes Polynuclear aromatics Naphthenes Benzene(MAH) Anand, species physical property surrogate database 2 FACE#1 FACE#2 FACE#3 FACE#4 FACE#5 FACE#6 FACE#7 FACE#8 FACE#9 FUELS for Advanced Combustion Engines (FACE) Measured hydrocarbon class distributions

Chemical Structure and Activity Coefficients of Face #9 Surrogates component chemical structure

88 Decalin (C 1 H 18 ) 1.3 n-decane (C 1 H 22 ) 1.6 n-hexadecane (C 16 H 34 ).95 n-eicosane (C 2 H 42 ).

7 Pentylbenzene (C 11 H 16 ) 1.8 Tetralin (C 1 H 12 ) 1.17 Heptylbenzene (C 13 H 2 ) 1.

25 Chemical Structure and Activity Coefficients of Face #9 Surrogates component chemical structure activity coefficient at 373 K n-tetradecane (C 14 H 3 ) 1.1 Cyclohexane (C 6 H 12 ).88 Decalin (C 1 H 18 ) 1.3 n-decane (C 1 H 22 ) 1.6 n-hexadecane (C 16 H 34 ).95 n-eicosane (C 2 H 42 ).81 Phenanthrene (C 14 H 1 ) 2.22 m-xylene (C 8 H 1 ) 1.6 m-cymene (C 1 H 14 ) 1.7 Pentylbenzene (C 11 H 16 ) 1.8 Tetralin (C 1 H 12 ) 1.17 Heptylbenzene (C 13 H 2 ) 1.1 Departure from Raoult s law - Non-ideal vaporization influences heavy-end of distillation curve * p i, v x x i, v i, l P P i sat, i * Anand, CEFRC5 June 28, 212

26 Surrogate mass fraction Distillation temperature (K) Example - Face Fuel #1 Surrogate Composition Distillation profile Measured Model Evaporated fraction Chemical classes PC normal paraffins IP iso-paraffins MCP mono cyclo paraffins DCP di-cycloparaffins AB Alkyl benzenes PA poly aromatics.1.5 n-dodecane(pc) n-octadecane(pc) Batch distillation modeled as flash boiling droplet tmh(ip) hmn(ip) cyclohexane(mcp) decalin(dcp) m-cymene(ab) q o qi T s =T b Physical property surrogates n-heptylbenzene(ab) n-pentylbenzene(ab) T T d T d m Ts tetralin(ab) T amb r naphthalene(pa) 26 CEFRC5 June 28, 212

27 CEFRC5 June 28, 212 Putting them all together - Grid

25mm Gas-jet sub-grid momentum exchange near nozzle Abani SAE

coalescence underpredicted Nozzle Hole = + Liquid Spray

27 27 CEFRC5 June 28, 212 Putting them all together - Grid independent spray model 4 mm 3mm 2 mm 1 mm.5 mm.25mm Gas-jet sub-grid momentum exchange near nozzle Abani SAE Coarse mesh: Drop drag over-predicted Fine mesh: Drop coalescence underpredicted Nozzle Hole = + Liquid Spray Droplets (Solved) Entrained Air (Modeled Better axial relative velocity for droplets Z

Local SMD (um) Droplet Axial Velocity (m/s) Spray Tip Penetration (mm) Spray model validation (Wang SAE 21-1-626) Wang, INJ SAE P=12bar 21-1-626 6-hole injector; Iso-octane; constant volume 9

28 Local SMD (um) Droplet Axial Velocity (m/s) Spray Tip Penetration (mm) Spray model validation (Wang SAE ) Wang, INJ SAE P=12bar hole injector; Iso-octane; constant volume 9 chamber, cold ambient; Injection pressure: 8 12, 2bar; chamber pressure: 12bar; Expts: Mitroglou, 26 mesh=3mm, dtmax=1e-6s mesh=2mm, dtmax=1e-6s mesh=1mm, dtmax=1e-6s experiment mesh=3mm, dtmax=1e-6s mesh=2mm, dtmax=1e-6s 1 mesh=1mm, dtmax=1e-6s experiment Time (ms) time (ms) mesh=3mm, dtmax=1e-6s mesh=2mm, dtmax=1e-6s 1 mesh=1mm, dtmax=1e-6s experiment..5 time (ms) CEFRC5 June 28, 212

29 CEFRC5 June 28, 212 Validation Evaporating sprays Naber & Siebers, SAE 9634 Siebers, SAE 9889, Diesel and other fuels; Constant volume chamber; various temperatures;

29 29 CEFRC5 June 28, 212 Validation Evaporating sprays Naber & Siebers, SAE 9634 Siebers, SAE 9889, Diesel and other fuels; Constant volume chamber; various temperatures; Varying chamber densities: 13.9, 28.6, 58.6kg/m^3. Schlieren imaging Pickett, Sandia National Laboratory, "Engine Combustion Network", 27

Liquid Penetration Length (mm) Evaporating Diesel Spray - Liquid length 1 9 8 Experiment Computation Experiment Computation Experiment Computation 7 6 5 4 3 2 1 7.3 kg/m 3 14.8 kg/m 3 59.

30 Liquid Penetration Length (mm) Evaporating Diesel Spray - Liquid length Experiment Computation Experiment Computation Experiment Computation kg/m kg/m kg/m Temperature (K) Liquid Penetration Length Siebers, SAE 9889, Injection Pressure : 135 MPa Fuel : DF2 Orifice Diameter : 246 µm Comparison of model results with experimental liquid penetration length data Juneja, SAE CEFRC5 June 28, 212

31 Spray Tip Penetration (mm) Spray Tip Penetration (mm) 31 CEFRC5 June 28, mesh=3mm, dtmax=1e-6s mesh=2mm, dtmax=1e-6s 9 mesh=1mm, dtmax=1e-6s Exp.-Liquid Penetration 8 Exp.-Vapor Penetration Evaporating Diesel Spray grid size and time step independency Time (ms) Wang, SAE mesh=2mm, dtmax=1e-6s mesh=2mm, dtmax=5e-6s mesh=2mm, dtmax=5e-7s mesh=2mm, dtmax=2e-7s Exp.-Liquid Penetration Exp.-Vapor Penetration Time (ms) Predicted vapor and liquid penetrations. Experimental data of Naber and Siebers (1996) and Pickett (27). Diesel fuel injection, nozzle diameter 257 mm, injection pressure 137bar, gas temperature 1,K, gas density 58.6 kg/m 3.

32 CEFRC5 June 28, 212 Validation Cummins-Sandia Optical Engine Wang, SAE 21-1-626 Case A (Early Injection, Low Temperature) Case B (Late Injection, Low Temperature) Case C (Long Ignition Delay, High

32 32 CEFRC5 June 28, 212 Validation Cummins-Sandia Optical Engine Wang, SAE Case A (Early Injection, Low Temperature) Case B (Late Injection, Low Temperature) Case C (Long Ignition Delay, High Temperature) IMEP [bar] Injection Pressure [bar] SOI [deg ATDC] Injection Quantity [mg] DOI [deg] Peak Temperature 22 K 22 K 27 K O2 Concentration [Vol %] 12.7 (with EGR) 12.7 (with EGR) 21 (without EGR)

1mm5e-7 2mm2e-6 3mm2e-6 Wang, SAE 21-1-626 (B) Low Temperature, Late Injection 2

33 Liquid Penetration [mm] 33 CEFRC5 June 28, 212 Liquid (A) Low and Temperature, Vapor Fuel Early Penetration Injection Exp Exp Ave 1mm5e-6 1mm2e-6 1mm1e-6 1mm5e-7 2mm2e-6 3mm2e-6 Wang, SAE (B) Low Temperature, Late Injection CAD ATDC (C) High Temperature, Long Injection delay Singh, 27

34 CEFRC5 June 28, 212 Summary Extensively validated spray models accurately capture the physics of vaporizing sprays under engine conditions Realistic fuels with non-ideal vaporization effects can

34 34 CEFRC5 June 28, 212 Summary Extensively validated spray models accurately capture the physics of vaporizing sprays under engine conditions Realistic fuels with non-ideal vaporization effects can be represented Improved spray models provide consistent fuel distribution predictions, which is a prerequisite for combustion modeling and engine optimization. Spray predictions can be independent of mesh size and time step; Recent experimental and modeling work can be accessed through the Sandia Engine Combustion Network (ECN) Singh, 27 Blue: Liquid Scatter Green: UV Fluorescence

5. SPRAY/WALL IMPINGEMENT

5. SPRAY/WALL IMPINGEMENT 5.1 Wall Interaction Regimes Wachters and Westerling (1966), Akao et al. (1980), Senda et al. (1994) and Nagaoka et al. (1994) describe in detail the phenomena observed when drops