Reciprocating Internal Combustion Engines Prof. Rolf D. Reitz, Engine Research Center, University of Wisconsin-Madison 2014 Princeton-CEFRC Summer Program on Combustion Course Length: 15 hrs (Mon.- Fri., June 23-27) Copyright ©2014 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 CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays

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) Part 1: IC Engine Review, 0, 1 and 3-D modeling Part 2: Turbochargers, Engine Performance Metrics Day 2 (Combustion Modeling) Part 3: Chemical Kinetics, HCCI & SI Combustion Part 4: Heat transfer, NOx and Soot Emissions Day 3 (Spray Modeling) Part 5: Atomization, Drop Breakup/Coalescence Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Day 4 (Engine Optimization) Part 7: Diesel combustion and SI knock modeling Part 8: Optimization and Low Temperature Combustion Day 5 (Applications and the Future) Part 9: Fuels, After-treatment and Controls Part 10: Vehicle Applications, Future of IC Engines 2 CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays

R/D L/D Breakup length Blob injection model ERC Spray modeling Discrete drop model KH Model RT Model Kelvin-Helmoltz Rayleigh Taylor Linearized instability analysis KH-RT Spray Models Nozzle flow/cavitation Jet atomization Drop breakup Drop collision/coalescence Drop drag Multi-component fuel evaporation Spray-wall impingement Beale, CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays

Droplet drag modeling Steady-state Stokes viscous drag, added-mass and Basset history integral dv/dt = General form Drop distortion (TAB model) 4 CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Liu, 1993

Turbulence & drop dispersion Monte Carlo method Drop-eddy interaction time Eddy life time Residence time  = l 5 CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Gosman, 1981 Stokes # St=t e /t p

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 = 40 liquid spreads into surface layer At high temperatures film boiling takes place 40  We 40  We   d/2 U We n 2  6 CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Wachters, 1966

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: where 0 < p <1 random number 7 CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Naber, 1988

ERC wall impingement models Rebound or slide based on We Enhanced breakup due to drop destabilization B 1 =  We 3 1  B 40  We 3 1  B 8 CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Senecal, 1997 Lippert, 2000

9 CEFRC3-6, 2014 Wet wall impingement – grid independent model Saffman lift force on splashed drops Splash mass ratio Glauert analytical solution Drop splash criterion Wall Jet Model Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Deng, 2014

10 CEFRC3-6, 2014 RwRw RwRw Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays HwHw RwRw Deng, 2014

11 CEFRC3-6, 2014 HwHw HwHw HwHw HwHw Effect of ambient pressure Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Deng, 2014

Drop Vaporization –well understood for single component, low ambient pressure –D 2 Law Sirignano, 1999 Law, Aggarwal, CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays

KIVA vaporization models Frossling correlation Mass transfer number Sherwood number Fuel mass fraction at drop surface Vapor pressure P v from thermodynamic tables Amsden, 1989 Lefebvre, CEFRC3-6, 2014 Y1*Y1* Y1Y1 r Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays

Drop heat-up modeling Change in drop temperature from energy balance Rate of heat conduction to drop from Ranz-Marshall correlation where 14 CEFRC3-6, 2014 TdTd T∞T∞ r Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Amsden, 1989 Lefebvre, 1989

Ra, 2003 TbTb TsTs TdTd T∞T∞ T r qoqo qiqi TdTd TsTs T amb TbTb TsTs TdTd qoqo qiqi T r TdTd TsTs Normal evaporation heating Normal evaporation cooling Boiling heating T s =T b TdTd T∞T∞ T r qoqo qiqi TdTd TsTs Flash boiling cooling T s =T b TdTd T∞T∞ qoqo qiqi r T TdTd TsTs Vaporization regimes 15 CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays

Normal evaporation energy balance mass balance TdTd TsTs Boiling evaporation (T b from Clausius Clapeyron equation) Superheated droplet correlation (Adachi et al., 1997) Vaporization regimes 16 CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Ra, 2003

Diesel Continuous f p (I) Discrete g p (mw i ) Single comp approx Gasoline 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 Multi-component fuel modeling 17 CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Ra, 2003 Lippert, 1997

 Continuous system of a liquid phase + Semi-continuous mixture system of vapor phase fuel and ambient gas:  Vapor phase transport equation,  Assumed distribution function : Continuous Multi-Component continuous phasediscrete phase  Discrete system of a liquid phase + Discrete mixture system of vapor phase fuel and ambient gas:  Vapor phase transport equation, discrete phase of fuel discrete phase of air/fuel mixture  - func Discrete Multi-Component Multi-component model formulation Yi, 2001 Ra, 2003, CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays

speciesMWMass fraction Diesel A (US narrow-cut Diesel) c14h c12h c16h c18h Diesel B (Euro Diesel) c14h ic8h c10h c12h c16h c18h Modeled species contents* Diesel A Diesel B DMC model tests 19 CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Ra, 2009

CA=-14 (~ first ignition timing) MW= MW= Fuel component distributions Diesel B MW ini = CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Ra, 2009

Multi-component spray vaporization Gasoline Do=300  m Vinj=100 m/s 2.0 ms after SOI 21 CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Ra, 2009

Non-ideal mixing using UNIFAC method Fredenslund, 1975 Vapor pressure of pure comp. i ; Total mixture pressure Mole fraction of comp. i in liquid phase; Mole fraction of comp. i in gas phase H H H - C - C - OH H H 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. Differences in size and shapes of the molecules Energy interactions between functional groups [3] Jiao, CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays

Ethanol/gasoline surrogate mixture Pfahl,1996 Jiao, CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays

Drop evaporation simulation - Droplet lifetime - Temp. vs. mole fraction 15 0 C Jiao, CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays

25 CEFRC3-6, 2014 Distillation curve Experiment Simulation Andersen, 2010 Simulation E20 has the lowest initial boiling temperature Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Jiao, 2011

Surrogate fuels - 18 component model alkanes aromatics cycloalkanes PAH corrected 26 CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Anand, 2011

Diesel hydrocarbon class distributions and surrogates FUELS for Advanced Combustion Engines (FACE) Measured hydrocarbon class distributions 20 species physical property surrogate database Anand, CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays

Chemical structure and activity coefficients of Face #9 surrogates Departure from Raoult’s law - Non-ideal vaporization influences heavy-end of distillation curve *  * Anand, CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays

Example - face fuel #1 surrogate composition Batch distillation modeled as flash boiling droplet Physical property surrogates Distillation profile Chemical classes PC – normal paraffins IP – iso-paraffins MCP – mono cyclo paraffins DCP – di-cycloparaffins AB – Alkyl benzenes PA – poly aromatics 29 CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Anand, 2011

4 mm 3mm 2 mm 1 mm 0.5 mm 0.25mm Coarse mesh: Drop drag over-predicted Fine mesh: Drop coalescence under- predicted Putting them all together - Grid independent spray models Gas-jet sub-grid momentum exchange near nozzle 30 CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Abani, 2008

6-hole injector; Iso-octane; constant volume chamber, cold ambient; Injection pressure: 120, 200bar; chamber pressure: 12bar; INJ P=120bar Spray model validation (Wang SAE ) Expts: Mitroglou, CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Wang, 2010

Diesel and other fuels; Constant volume chamber; various temperatures; Varying chamber densities: 13.9, 28.6, 58.6kg/m^3. Schlieren imaging Validation – evaporating sprays Naber, 1996 Pickett, Sandia National Laboratory, "Engine Combustion Network", Siebers, CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays

Predicted vapor and liquid penetrations. Experimental data of Naber and Siebers (1996) and Pickett (2007). Diesel fuel injection, nozzle diameter 257 mm, injection pressure 1370bar, gas temperature 1,000K, gas density 58.6 kg/m 3. Evaporating diesel spray – grid size and time step independency Wang, CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays

Evaporating diesel spray - liquid length Comparison of model results with experimental liquid penetration length data Injection Pressure : 135 MPa Fuel : DF2 Orifice Diameter : 246 µm Liquid Penetration Length Juneja, 2004 Siebers, CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays

ECN Spray A modeling 35 CEFRC3-6, 2014 Temp [K] O 2 [vol%]1513/15/17/21 Density [kg/m 3 ] /15.2/ 22.8/ /15.2/ 22.8/ /15.2/ 22.8/ /15.2/ 22.8/ /15.2/ 22.8/30.4 P inj [MPa]15050/100/150 Computational grid Related sub-models Lift-off length Onset of the averaged OH concentration Ignition delay Maxmium dT/dt Maxmium dOH/dt PhenomenonModel Spray breakupKH-RT instability EvaporationDiscrete multicomponent (DMC) TurbulenceGeneralized RNG k−ε model CombustionSpeedChem Droplet collisionROI model Near nozzle flowGas-jet model Soot formationMulti-step phenomenological Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Wang, 2014

ECN Spray A modeling 36 CEFRC3-6, 2014 Non-reacting mixing process Ambient conditions O20.0 N CO H2O Pressure60.45 bar Temperature900 K Density22.8 kg/m 3 Injector specifications TypeCommon-rail NozzleSingle-hole, 0.89 Nozzle diameter0.084 mm (0.090mm) Injection pressure150 MPa Injection duration6.0 ms Injection fuel mass13.77 mg Liquid and vapor penetrations 1 1. Engine Combustion Network, Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Wang, 2014

ECN Spray A modeling 37 CEFRC3-6, 2014 Physical processExpression Inception:A 4  soot C 2 H 2 surface growth Coagulation O 2 oxidation OH oxidation PAH condensation Transport equations Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Wang, 2014 Vishwanathan, 2010

Reaction mechanism -formulation 38 CEFRC3-6, 2014 n-C 12 H 26 -PAH mechanism 104 species and 444 reactions Reduced n-dodecane mechanism 80 species and 299 reactions Reduced PAH mechanism 42 species and 228 reactions 1 PAH mechanism  A1 formation C 3 H 3 +C 3 H 3 =C 6 H 6 C 3 H 3 +C 3 H 3 =C 6 H 5 +H C 4 H 5 +C 2 H 2 =C 6 H 6 +H C 4 H 3 +C 2 H 2 =C 6 H 5  Larger PAH formation 1. HACA sequence 2. Small radical and molecule 3. Addition reactions between aromatic radicals and molecules n-C12 reaction pathway PAH mechanism validation Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Wang, 2013

Reaction mechanism -validation 39 CEFRC3-6, 2014 Ignition delay 1 Shock Tube 2 JSR 3 1. Narayanaswamy, Mzé-Ahmed, Malewicki, 2013 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Wang, 2013

ECN Spray A modeling 40 CEFRC3-6, 2014 Non-reacting mixing process - Fuel mixture fraction 1. Engine Combustion Network, Predicted mixture fraction distributions agree reasonable well with experimental data in both radial and axial directions by calibrating the spray model constants Axial Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Wang, 2014

Reacting conditions - Soot formation vs. Ambient temperature 41 CEFRC3-6, K 900K 1000K 1100K 1200K Soot ppm Soot ppm Skeen, 2013 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Wang, 2014

ECN Spray A modeling 42 CEFRC3-6, 2014 Soot ppm Soot ppm A4A4 A4A4 D soot Peak 16 nm  The soot formation regions agree with the high A 4 concentration regions;  Predicted soot particle size is in the reasonable range compared to experimental data; Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Wang, 2014

Reacting conditions - Soot formation Overview 43 CEFRC3-6, 2014 Total soot Lift-off length Lift-off Soot Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Wang, 2014

Reacting conditions - Soot formation & model sensitivity 44 CEFRC3-6, 2014 C 2 H 2 surface growth Soot particle coagulation baseline  C 2 H 2 assisted surface growth process is the most important process that affects the soot emission, followed by OH oxidation process;  The surface growth process and the coagulation process affect the soot particle size; Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Wang, 2014

Validation – Cummins-Sandia optical engine 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]56 61 DOI [deg]7710 Peak Temperature2200 K 2700 K O2 Concentration [Vol %] 12.7 (with EGR) 12.7 (with EGR) 21 (without EGR) Wang, CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays

46 CEFRC3-6, 2014 (C) High Temperature, Long Injection delay (A) Low Temperature, Early Injection(B) Low Temperature, Late Injection Liquid and vapor fuel penetration Singh, 2007 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Wang, 2010

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) Blue: Liquid Scatter Green: UV Fluorescence Singh, CEFRC3-6, 2014 Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays