Internal Combustion Engines - cefrc.princeton.edu · prior written permission of the owner, Rolf D. Reitz. Internal Combustion Engines . I: Fundamentals and Performance Metrics

1 PCI-2-5, 2018

Copyright ©2018 by Rolf D. Reitz. This material is not to be sold, reproduced or distributed without prior written permission of the owner, Rolf D. Reitz.

Internal Combustion Engines I: Fundamentals and Performance Metrics

Prof. Rolf D. Reitz,

Engine Research Center, University of Wisconsin-Madison

2018 Princeton-Combustion Institute Summer School on Combustion

Course Length: 9 hrs (Mon.- Wed., June 25-27)

Hour 5: Premixed Charge Spark-ignited engines


2 PCI-2-5, 2018

Short course outline:

Internal Combustion (IC) 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, Thermodynamics and 0-D modeling Hour 2: 1-D modeling, Charge Preparation Hour 3: Engine Performance Metrics, 3-D flow modeling

Day 2 (Computer modeling/engine processes)

Hour 4: Engine combustion physics and chemistry Hour 5: Premixed Charge Spark-ignited engines Hour 6: Spray modeling

Day 3 (Engine Applications and Optimization) Hour 7: Heat transfer and Spray Combustion Research Hour 8: Diesel Combustion modeling Hour 9: Optimization and Low Temperature Combustion

Spark Ignition Engine

Turbulent Flame Propagation • G-equation description of combustion • Laminar and turbulent flame speeds • Primary heat release calculation • Flame quench due to mixture stratification Post-flame Chemistry • CO oxidation, H2-O2 reactions • Pollutant formation mechanisms

Knocking Combustion • Auto-ignition mechanisms • Location / intensity

SI engine combustion modeling

Flame propagation Models with Detailed Chemistry

Liang, 2006

3 PCI-2-5, 2018

Spark plug


What is a turbulent flame?

Law, 2014

ST

Ensemble of thin (laminar) flamelets, interacting with the flow turbulence. Due to increased surface area, turbulent flame “brush” propagates at enhanced velocity

LT L

T

AS S

A= ∑

AT

LA∑

4 PCI-2-5, 2018


Laminar flame speed: balance between reaction and diffusion

iT T

dYS = Ddt

5 PCI-2-5, 2018

2

2 /i ii

Y YDt x

∂ ∂ ω ρ∂ ∂

= +

20

,21

/N

f i i pi

T TD h ct x

∂ ∂ ω ρ∂ ∂ =

= − ∆∑

( ) 1/( ) [1/(1 )]mS x St mDU x St e

−− = +

2

2 ( )U UD F Ut x

∂ ∂= +

∂ ∂1( ) (1 )m mF U U Uβ += −

1DS

mβ

=+

Consider the single component system:

unburned

burned unburned

T TUT T

−=

−with and

Admits a traveling wave solution

where

2

( 1)D D mmS m

δβ

+= =and

U

x

S

1.0

0

δ

- Mallard, Le Chatelier ~

Hour 5: Premixed Charge Spark-ignited engines Reitz, 1981

Quenched broken reaction zones

Kl lδ=

K Fl l=

Combustion regime diagram

Flamelets

Turbulent flame structure

1/ 433/ 4ReK Il lν

ε−

= =

( ) 0/ |p T

Fu L

cl

Sλ

ρ=

Kolmogorov/Batchelor length scales:

Laminar flame thickness:

Ghandhi, 2012

~ 20 µm

It is not possible to resolve a turbulent flame on a practical engine simulation grid

Peters, 2000

Liang, 2007

6 PCI-2-5, 2018

Engine flames


GkDGSGvvtG

TTu

vertexf~~~~)(

~0 ∇−∇=∇⋅−+

∂∂

ρρ

Turbulent flame speed correlations

( )1/ 2 1/ 222 2

2 24 3 4 34 3

0 1 1

1 1 exp2 2

m ignT

L F F l F

C t t a b a bS l l u la bS I b l b l S lτ

⋅ − ′ = + − − ⋅ − + + ⋅

Progress Term

1.5

1 1 0.16≥ ⋅ = ⋅k m I mkr C l Cε

ετ k

=

K

u

K

F

L

F

rl

Su

llI

ρρ

⋅−

′

⋅−= 2

151

2/32/1

0

Transition criterion:

Characteristic Timescale:

Stretch factor:

Turbulence stretch Curvature

Discrete Particle Ignition Kernel (DPIK) model

rk

Fan, 2000

Peters, 2000

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Hour 5: Premixed Charge Spark-ignited engines Liang, 2007

8 PCI-2-5, 2018

Laminar flame speed

0.90

0.85

0.80

0.75

0.70

0.65

0.60

0.55

Peak

Bur

ning

Vel

ocity

(m/s

)

Paraffins Olefins Aromatics

toluene

o,p xylene

Oxygenates

cyclohexane

benzene

anisole

ethanol

MTBEmethylcyclopentane

1,2,4-trimethylbenzene

iso-octene

n-butane propane

ethane

methane

n-pentane

iso-octane

iso-pentane

iso-butane

n-hexane

t-butylbenzene

i-propylbenzene

m-xylene

ethylbenzene

n-propylbenzene

1-butene

2-pentene

1-hexene

2-butene

3-heptene

cyclopentene

2-methyl-2-butene2-methyl-1-butene

propene

1,3,5-trimethylbenzene

1-pentene

cyclopentane

n-heptane

1-heptene

1-octene

neopentane

C-C-C C=C-C C-C-OH methanol

Hour 5: Premixed Charge Spark-ignited engines Farrell, 2005

End Gas Auto-ignition

(detailed kinetics)

G-Equation Flame

propagation Burnt Gas

Discrete particle ignition model

ST from flame speed correlations

GkDGSGvvtG

TTu

vertexf~~~~)(

~0 ∇−∇=∇⋅−+

∂∂

ρρ

Ignition and level set (G-equation) models

Burned gas: G>0 Unburned gas: G<0

Liang, 2007

9 PCI-2-5, 2018


Partially Premixed Flame (DI Engine)

Φ ≈ 1

Φ > 1

Φ < 1

CO2, H2O, CO, NO…

O2, O, NO …

Fuel Droplets

Diffusion

Diffusion

End-gas Flame Post-flame Zone Front Zone

CH4, CO, H, H2 …

10 PCI-2-5, 2018

Validation - PFI gasoline engine

Bore × Stroke 89 mm × 79.5 mm

Compression Ratio 12 : 1

Engine Speed 1500 rev/min

PFI Mode Spark timings (ATDC) -44, -40, -36, -32

MAP (kPa) 65

Based on MIT PRF Mechanism (25 species, 51 reactions)

Model constants: Cm1=2.0, Cm2=1.0 (Fixed in all cases)


Validation - PFI engine operation

Evolution of Temperature

11 PCI-2-5, 2018


Spark Timing = 40 BTDC

Evolution of the G=0 surface

CA = -20 ATDC CA = -5 ATDC

CA = 10 ATDC CA = 20 ATDC

Validation - PFI engine operation

Spark Timing -44, -40, -36, -32 ATDC Engine Speed 1500 rev/min

-100 -50 0 50 1000.0

0.5

1.0

1.5

2.0

2.5

PFI mode-32 OATDC

EXPT SIMU

-100 -50 0 50 1000.0

0.5

1.0

1.5

2.0

2.5

PFI mode-36 OATDC

EXPT SIMU

-100 -50 0 50 1000.0

0.5

1.0

1.5

2.0

2.5

PFI mode-40 OATDC

EXPT SIMU

-100 -50 0 50 1000.0

0.5

1.0

1.5

2.0

2.5

EXPT SIMU

PFI mode-44 OATDC

12 PCI-2-5, 2018


Role of flame propagation

Explore Kinetics-Controlled Formulation for Turbulent Flame Propagation: After ignition kernel stage, each cell is modeled as a WSR, detailed chemistry is applied. “Flame propagation” is controlled by heat conduction and auto-ignition.

-80 -60 -40 -20 0 20 40 60 800.0

0.5

1.0

1.5

2.0

2.5

Transition from kernel to G-eqn-20 ATDC

EXPT G-equation Kinetics only

Spark timing-44 ATDC

PFI mode

-80 -60 -40 -20 0 20 40 60 800.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Transition from kernel to G-eqn at -20 ATDC

DI mode

Spark timing-32 ATDC

EXPT G-equation Kinetics only

Mallard-Le Chatelier propagating wave speed: = iT

dYS Ddt

13 PCI-2-5, 2018


Kinetics Controlled G-equation

Summary: Auto-ignition chemistry alone is NOT sufficient to properly model flame propagation.

Turbulence enhancing effect on flame propagation speed in SI engines CANNOT be neglected.

PFI case Spark timing = -44 ATDC

Role of flame propagation

14 PCI-2-5, 2018


Particulate emissions

15 PCI-2-5, 2018

Regulated emissions PM2.5

Greatest health risk - fine particles can lodge deeply into the lungs

New challenge - engines must meet particulate number-based regulations (PN).

Euro 6: PN limit 6.0x1011 particles/km for vehicles produced after 2017. California Air Resources Board (CARB) LEV III: Total PM mass: 3.8 mg/km for 2014 and 1.9mg/km for 2017 PN: 3.8x1012 and 1.9x1012 particle/km.

Kittelson, 1998 Hour 5: Premixed Charge Spark-ignited engines

ECN Spray A soot modeling (More details later – Hour 7)

16 PCI-2-5, 2018

Physical process Expression

Inception:A4soot

C2H2 surface growth

Coagulation

O2 oxidation

OH oxidation

PAH condensation

Transport equations

Wang, 2014

Vishwanathan, 2010


17 PCI-2-5, 2018

Jiao, 2014

70,000 cells at BDC, including the intake and exhaust manifolds and cylinders.

Spark plug: at center of cylinder head. Completely homogeneous fuel/air mixture at IVC Experiment: EPA Tier II EEE certification fuel, 28% aromatics. ERC KIVA code simulations: DPIK ignition model, G-Equation combustion model. Fuel: iso-octane/28% toluene by volume. MultiChem mechanism: ic8h18/nc7h16/c7h8/PAH (79 species & 379 reactions)

Soot mass and particle diameter prediction Premixed charge SI engine particulate modeling


•18

Soot formation prediction

-40 -20 0 20 40 60 800.00

0.01

0.02

0.03

0.78; 0.26 0.98; 0.33 1.2 ; 0.41 1.3 ; 0.44 1.4 ; 0.48 1.5 ; 0.51

Incy

linde

r soo

t (g/

kg-f)

Crank Angle (deg)

Φ; C/O

680 700 720 740 760 780 800 CAD

Soot mass no longer reduces significantly after 80 ATDC Soot produced at 80 ATDC increases with increase φ Soot formation dominates first - then soot oxidation begins to play a key role Peak in-cylinder soot mass increases w/ an increase of φ

18 PCI-2-5, 2018

Jiao, 2014 Hour 5: Premixed Charge Spark-ignited engines

-4 -3 -2 -1 0 1 2 3 4500

100015002000250030003500

Incylinder temperatureG

(-)

Te

mpe

ratu

re (K

)

Radial position (cm)

TDC

-2-101234

G (-)

-4 -3 -2 -1 0 1 2 3 40

5x10-10

1x10-9

2x10-9

2x10-9

C2 H

2 mass fraction (-)

A4 m

ass

fract

ion

(-)


A4 mass fractionTDC

01x10-42x10-43x10-44x10-45x10-46x10-4

C2H2 mass fraction

TDC φ =1.5

C2H2

A4

----------------burnt-----------------

----------------burnt-----------------

19 PCI-2-5, 2018


-4 -3 -2 -1 0 1 2 3 40

1x10-6

2x10-6

3x10-6

4x10-6

Soot mass fraction


TDC

10-610-510-410-310-210-1100101

O2 mass fraction OH mass fraction

O2 , O

H m

ass fraction (-)

Soo

t mas

s fra

ctio

n (-)

-4 -3 -2 -1 0 1 2 3 41x10-21x1001x1021x1041x1061x108

1x10101x1012

TDC Number density

Num

ber d

ensi

ty (#

/cm

3 )

Particle size (nm

)


0

100

200

300

400 Particle size

TDC φ =1.5

nd

dp

O2

OH soot

---------------burnt-------------

---------------burnt-------------

20 PCI-2-5, 2018


-4 -3 -2 -1 0 1 2 3 40

2x10-7

4x10-7

6x10-7

8x10-7

1x10-6

Soot mass fraction


800 aTDC

02x10-5

4x10-5

6x10-5

8x10-5

1x10-4

O2 mass fraction OH mass fraction

O2 , O

H m

ass fraction (-)

Soot

mas

s fra

ctio

n (-)

-4 -3 -2 -1 0 1 2 3 41x10-21x1001x1021x1041x1061x108

800 aTDC Number density

Num

ber d

ensi

ty (#

/cm

3 )

Particle size (nm)


0100200300400500

Particle size

800 ATDC φ =1.5

soot

O2

OH

dp

nd

21 PCI-2-5, 2018


10 1001x102

1x103

1x104

1x105

1x106

1x107

1x108

1x109

1x1010

dN/d

log(

d p) (#

/cm

3 )

dp (nm)

0.8; 0.26 0.98; 0.33 1.2; 0.41 1.3; 0.44 1.4; 0.48 1.5; 0.51

Φ; C/O

referenceexpt

Experiment [1] Simulation

Nearly identical PSDs until about φ =1.3, nd sharply declines with increase of dp. When φ >1.3, nd consistently increases with increasing φ , and decreases gradually with increasing dp.

For φ <1.4, shape of PSDs is very flat and broad, which is different from experiment, but looks like PSDs for A/F of 14.6 for engine loads lower than 4 bar in Ref. [2].

For φ =1.4 and 1.5 , magnitude of nd of small particles are well represented, nd decreases with increasing dp.

[1] Hageman, 2013. [2] Maricq, 1999

10 1001x102

1x103

1x104

1x105

1x106

1x107

1x108

1x109

1x1010

Aver

aged

par

ticle

num

ber d

ensit

y (#

/cm

3 )

dp (nm)

0.78; 0.26 0.98; 0.33 1.2 ; 0.41 1.3 ; 0.44 1.4 ; 0.48 1.5 ; 0.51

Φ; C/O

22 PCI-2-5, 2018

Jiao, 2014

Particulate size distributions


Knocking combustion in SI engines

-20 -10 0 10 20 30 400

2

4

6

8

10

12

14

16

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

Pres

sure

(MPa

)

Crank Angle (oATDC)

Position 1

Band

-pas

s filt

ered

pre

ssur

e (M

Pa)

PPmax

Simulated local pressures are filtered by a Butterworth band-pass filter Pass-band frequencies used: 5~25 kHz

Knock Index: max,1

1 N

nn

KI PPN =

= ∑

Power Index: 2

1

1 V

Vdisp

PI pdVV

= ∫

Numerical Transducers

Resonant frequencies based on classical wave equation (C. Draper 1938) :

Resonant frequency

f10 f20 f01 f30 f40 f11

Analytical value (kHz)

6.7 11.2 14.0 15.4 19.4 19.5

, ,s

m n m ncfB

απ

=

23 PCI-2-5, 2018

Liang, 2007 Hour 5: Premixed Charge Spark-ignited engines

Factors affecting knock intensity: End-gas auto-ignition tendency; Piston movement.

Spark timing=-10 ATDC Light knock

Spark timing=-25 ATDC Severe knock

Knocking combustion in SI engines

24 PCI-2-5, 2018

Liang, 2007 Hour 5: Premixed Charge Spark-ignited engines

Pressure oscillations during knock

25 PCI-2-5, 2018

Wang, 2013 Hour 5: Premixed Charge Spark-ignited engines

Heat transfer during knock

Compared to non-knocking case, engine knock significantly enhances wall heat transfer.

Energy loss via heat transfer during combustion period is nearly 40% of total fuel energy under heavy knocking conditions, and is nearly 4 times heat transfer of non-knocking condition.

Oscillating flow during knocking at 10.0 CA and 10.2 CA

**

1ln( / ) (2.1 33.4) ( )1

2.1ln( ) 2.5

p w c

w

dpc u T T T y Qu dtq

y

νργ

+

+

+ + − +−=

+ -10 0 10 20 30 400

200

400

600

800

1000

wall h

eat t

rans

fer /

JEner

gy (J

)

Crank Angle (deg)

non-knocking

0

200

400

600

800

1000

new WHT model orig. WHT model

26 PCI-2-5, 2018

Wang, 2013


27 PCI-2-5, 2018

“Superknock - stochastic pre-ignition” Super-knock is severe engine knock triggered by pre-ignition randomly, sometimes after many thousands of engine cycles

Wang, 2014 Kalghatgi, 2018


Predicted pressure oscillations during knock

0 5 10 15 202

4

6

8

Pres

s (M

Pa)

Crank (Deg)

1e-7 1e-6 1e-5

pressures at wall

5000 10000 15000 20000 25000 300000.00

0.05

0.10

0.15

0.20

FrequencyAm

plitu

de

-100000-80000-60000

5000 10000 15000 20000 25000 30000Frequency

Phas

e

Power spectrum shows high energy in 3rd circumferential mode

Wang, 2013

28 PCI-2-5, 2018


29 PCI-2-5, 2018


Summary: Auto-ignition chemistry alone is NOT sufficient to properly model flame propagation.

Turbulence enhancing effect on flame propagation speed in SI engines CANNOT be neglected. Gasoline engine particulate emissions originate in the flame brush and soot particle sizes can be predicted reasonably well. Knocking combustion CFD simulations require refined numerical time steps to resolve detonation wave propagation physics

30 PCI-2-5, 2018


References 2-5:3 Liang, L.; Reitz, R.D., "Spark Ignition Engine Combustion Modeling Using a Level Set Method with Detailed Chemistry," SAE Paper 2006-01-0243, 2006

2-5:4 C.K. Law, Private communication, University of Wisconsin-Madison, 2014

2-5:5 Reitz, R.D., "A Study of Numerical Methods for Reaction-Diffusion Equations," SIAM Journal on Scientific and Statistical Computing, Vol. 2, p. 95, 1981.

2-5:6,7,9-14,23,24 Liang, L., Reitz, R.D., Iyer, C.O. and Yi, J., "Modeling Knock in Spark-Ignition Engines Using a G-equation Combustion Model Incorporating Detailed Chemical Kinetics," SAE paper 2007-01-0165, 2007.

2-5:6 J. Ghandhi, private communication, University of Wisconsin-Madison, 2012.

2-5:6,7 Peters, N. Turbulent Combustion, Cambridge University Press, 2000

2-5:7 Fan, Li, and Reitz, R.D., “Development of an Ignition and Combustion Model for Spark-Ignition Engines,” SAE Paper 2000-01-2809, SAE Transactions, Journal of Engines, Vol. 109, Section 3, pp. 1977-1989, 2000.

2-5:8 Farrell, J., Private communication, University of Wisconsin-Madison, 2005.

2-5:15 Kittelson, D.B., "Engines and Nanoparticles: A Review," Journal of Aerosol Science, 29(5–6): 575-588, (1998).

2-5:16 Vishwanathan, G., and Reitz, R.D.,”Development of a Practical Soot Modeling Approach and its Application to Low Temperature Diesel Combustion,” Combustion Science and Technology, Vol. 182, Issue 8, pp.1050-1082, 2010.

2-5:16 Wang, H., Ra, Y., Jia, M., and Reitz, R.D., “Development of a reduced n-dodecane-PAH mechanism and its Application for n-dodecane Soot Predictions,” Submitted, FUEL, 2014

2-5:17-22 Jiao, Q., and Reitz, R.D., "Modeling of Equivalence Ratio Effects on Particulate Formation in a Spark-Ignition Engine under Premixed Conditions," SAE Technical Paper 2014-01-1607, 2014

2-5:22 Hageman, M., Rothamer, D., Sensitivity Analysis of Particle Formation in a Spark-Ignition Engine during Premixed Operation, in 8th U.S. National Combustion Meeting, 2013.

31 PCI-2-5, 2018


References

2-5:22 Maricq, M.M., Podsiadlik, D. H., Brehob, D. D., Haghgooie, M., Particulate Emissions from a Direct-Injection Spark-Ignition (DISI) Engine, 1999, SAE1999-01-1530.

2-5:25,26 Wang, Z., Wang, Y., and Reitz, R.D., "Pressure Oscillation and Chemical Kinetics Coupling during Knock Processes in Gasoline Engine Combustion" Energy & Fuels, Vol. 26 (12), pp. 7107–7119, 2012, DOI: 10.1021/ef301472g. – see also Vol. 27 (1), pp. 599-599, 2013.

2-5:27 Zhi Wang, Hui Liu, Tao Song, Yunliang Qi, Xin He, Shijin Shuai and Jian Xin Wang, “Relationship between super-knock and pre-ignition,” International Journal of Engine Research, 2014. DOI: 10.1177/1468087414530388.

2-5:27 Kalghatgi, G., “Knock onset, knock intensity, superknock and preignition in spark ignition engines,” International Journal of Engine Research, Vol. 19, pp. 7-20, 2018.

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Internal Combustion Engines - cefrc.princeton.edu · prior written permission of the owner, Rolf D. Reitz. Internal Combustion Engines . I: Fundamentals and Performance Metrics