Avl

(1)

AVL-BOOST COMBUSTION MODELS

(2)

 Spatial Discretization

 Single Zone

(Zero-Dimensional)

 Two Zone

(Quasi-Dimensional)

 Ignition Type (Mixture Preparation)

 Spark Ignition

 Compression Ignition

 ROHR Type

 ROHR Input

 ROHR predicted by Combustion Model

 Source

 Standard BOOST

 User Coding

(3)

SPATIAL DISCRETIZATION / SINGLE ZONE

Governing

Equations

 Energy Conservation







d

dm

h

d

dQ

d

dQ

d

dV

p

d

u

m

d

_BB BB w F c c



















c c c

m

R

T

V

p



1 



 Perfect Gas Equation

 Thermodynamic State Vector



















c c c c c

C

T

p

S



 















FV CP FB C c

mf

C



 



















n G c

mf

C

.

1 1



Classic / General Species Transport

 

C

c C/G

(4)

SPATIAL DISCRETIZATION / TWO ZONE /1

 Energy Conservation for burned and unburned Zone



b b b u u u



c

m

R

T

m

R

T

V

p



1 







 Perfect Gas Equation

 Thermodynamic State Vector















burned c

S





d

dm

h

d

dm

h

d

dQ

d

dQ

d

dV

p

d

u

dm

b BB b BB b u Wb F b c b b , ,















_

















d

dm

h

d

dm

h

d

dQ

d

dV

p

d

u

dm

BBu u BB b u Wu u c u u , , b b b b c

u

m

R

T

p

,

u u u u c

u

m

R

T

p

,

u BB u BB b BB b BB

dm

h

dm

h

_, _,



_, _,

dV

p

_c F

dQ

Wb

dQ

Wu

dQ

h

u

dm

b

(5)

Vibe Single Zone

 ROHR Approach

 Parameter Data Source

 Fitting Result of Combustion Analysis Tool (BOOST-Burn)  Experience





 1

1 



  









m y a m c BT B

e

y

m

a

Q

d

dQ



c o

y









... Combustion Progress

 

 





















           0 1

1

m a BT B

Q

e

Q

  



 Released Energy

(6)

ROHR INPUT FOR SPARK IGNITION ENGINES /2

Table Single Zone

 Data Source

Result of Combustion Analysis Tool (BOOST-Burn)

 Adaptation

For physical reasons preprocessing performed to guarantee monotonic increase of Fuel Burned

(7)

ROHR INPUT FOR SPARK IGNITION ENGINES /3

Hires et al

 Required Input

Vibe Combustion Parameters and Ignition Delay for Reference Operating Point

Vibe Two Zone / Table Two Zone

 Same ROHR Approach as for Single Zone

 State Vector of Burned Zone allows to calculate:

 NOx Production (Extended Zeldovich)  CO Production

(Onorati)

 State Vector of Unburned Zone allows to calculate:

 Required Octane Number

a t t T B n MFB S OC UBZ

_dt

e

p

A

ON

1 % 8 5

1

100 _



















 Model Approach for Variation of Ignition Delay and Combustion Duration dependent on Engine Speed 3 / 2 3 / 1 ,



































s

f

n

ref ref ref ref c c



3 / 2 3 / 1































s

f

n

id

ref ref ref ref

s ... laminar flame speed

(8)

PREDICTED ROHR FOR SPARK IGNITION ENGINES /1

FRACTAL COMBUSTION MODEL

Motivation

 All mentioned ROHR Types require input based on experimental data which

show usually a strong dependency on the operating point (speed,

load-signal) of the engine.

 For optimization issues (variable valve timing, engine control strategies, ...) a

predictive combustion model which handles the influence of residual gas

content and charge motion is required.

 This requirement can be fulfilled in a wide operation point range by the new

introduced Fractal Combustion Model

(9)

PREDICTED ROHR FOR SPARK IGNITION ENGINES /2

FRACTAL COMBUSTION MODEL

Characteristics /1

The Fractal Combustion Model is based on a physical model of the flame front

propagation:

 Geometric Combustion Chamber Input Data leads to a Relation between Piston Position, Geometric Free Flame Surface and Burned Zone Volume

 Increase of Burned Zone Volume is a function of Laminar Burning Speed and Geometric Free Flame Surface.

A Simple multiplication => to small values because

 The flame front is a very thin and highly wrinkled surface (wrinkled-flamelet

(10)

PREDICTED ROHR FOR SPARK IGNITION ENGINES /3

FRACTAL COMBUSTION MODEL

Characteristics /2

 This wrinkling effect is driven by the in-cylinder turbulent flow and chiefly

responsible for the increased burning rate.  The relation between geometric free and

effective (highly wrinkled) flame area can be described by a fractal structure.

 Fractal is a mathematical method

describing irregular geometry with self similarity (length of British coast?). Mandelbrot Set

Burned Gas

Unburned Gas

S

_L

S

_L

S

_L

u’

L

(11)

PREDICTED ROHR FOR SPARK IGNITION ENGINES /9

FRACTAL COMBUSTION MODEL

Extension to stratified charge

• Input possibility for 1D distribution of

fuel vapor and combustion product

concentration (stratified charge) in

the direction of flame propagation

• 1D distribution can be imported from

AVL FIRE in-cylinder simulation

(standard output )

(12)

PREDICTED ROHR FOR SPARK IGNITION ENGINES /10

FRACTAL COMBUSTION MODEL

Project Experience

• The fractal combustion model has the

potential to predict the influence of the

valve timing variation on the rate of heat

release.

• Out of 7 parameters for the combustion

model only the

2 turbulence parameters

are function of engine speed and valve

timing.

• The tuning of the turbulence parameter is

based on 3D CFD results.

BSFC [g/kWh]

(13)

PREDICTED ROHR FOR SPARK IGNITION ENGINES /11

OPEN CHAMBER GAS ENGINE COMBUSTION MODEL

 Main features:

 2 Zone (unburned/burned) flame propagation model

 Arrhenius / Magnussen approach

combination for ignition delay simulation

 In-cylinder turbulence level (used for the relation between laminar and turbulent flame speed) is sourced by swirl and squish flow

 Combined with BOOST Classic Gas Properties Preparation Tool which allows to generate properties for arbitrary fuel blends (e.g. lean gas as mixture of CH4, CO2, …), as alternative to general

(14)

ROHR INPUT FOR COMPRESSION IGNTION ENGINES /1

Vibe Single Zone

 ROHR Approach

 Fitting Result of Combustion Analysis Tool (BOOST-Burn)  Experience





 1

1 



  









m y a m c BT B

e

y

m

a

Q

d

dQ



c o

y









... Combustion Progress  Evaporation Assumption

 ROE (Rate of Evaporation) is direct linked to ROHR



d

dQ

H

d

dm

_FV

_

1

_B

(15)

ROHR INPUT FOR COMPRESSION IGNTION ENGINES /2

Double Vibe (Single Zone)

 ROHR Approach

Superposition of 2 Vibe

Functions to meet Premixed Combustion Peak and/or more Complex Injection Strategies

 Fitting Result of Combustion Analysis Tool (BOOST-Burn)  Experience 2 1 Vibe B Vibe B B

d

dQ

d

dQ

d

dQ































(16)

ROHR INPUT FOR COMPRESSION IGNTION ENGINES /3

Woschni/Anisits

Vibe Two Zone / Table Two

Zone

 Same ROHR Approach as for Single Zone

 State Vector of Burned Zone allows to calculate:  NOx Production (Extended Zeldovich)  CO Production (Onorati)  Soot Production (Bolochous)

Table Single Zone

 Identical to spark ignition engines +

Evaporation Assumption

 Required Input

Vibe Combustion Parameters and Ignition Delay for Reference Operating Point

 Model Approach for Variation of Combustion Duration and Vibe Parameter m dependent on Engine Speed and Ignition Delay

5 . 0 6 . 0 ,



































ref ref ref c c

n

AF



3 . 0 , , 6 . 0



























































ref IVC ref IVC ref IVC IVC ref ref

n

T

p

id

m

 Ignition delay according to relations found by Andree and Pachernegg (exceeding

(17)

PREDICTED ROHR FOR COMPRESSION IGNTION ENGINES /1

AVLMCC COMBUSTION MODEL

AVLMCC Combustion Model

 Model Approach

Mixture controlled combustion (MCC) part of heat release is controlled by fuel

quantity available and the spray induced turbulent kinetic energy density.

Premixed combustion

is modeled by a vibe function which parameters are determined from the ROI (Rate of Injection) considering Ignition delay.

Combustion process stages  Injection

 Turbulence  Evaporation  Ignition Delay  Combustion

(18)

PREDICTED ROHR FOR COMPRESSION IGNTION ENGINES /4

AVL MCC COMBUSTION MODEL

PL1 SB1 SB2 MP1 MP2 MP3 MP4 MP5 MP6 MP7 MP8 MP9 MP10 MP11 MP12 MP13 MP14 MP15 MP16 MP17 _MP18 MP19 MP20 CO1 TC1 J1 J2 J3 J4 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 CO2 CAT1 22 R1 CO3 23 24 25 J5 26 27 J6 J7 28 R2 29 30 C1 C2 C3 C4 C5 C6 MP21 MP22 MP23 MP24 R3 31 CL1 32 MP25 R4 33 p_11, T_11 p_21, T_21 p_2_1, T_2_1 p_IM , T_IM p_41, T_41, NOx_S1, ... Intake Throttle EGR Valve p_EGR, T_EGR T_EGRHEO p_31_1, T_31_1 p_31_2, T_31_2 TAZ6 TAZ2 _TAZ3 Wastegate Air Cleaner Charge Air Cooler Exhaust Gas Treatment Devices Intake M anifold R O H R [ J /d e g ] 20 40 60 80 100 120 140 160 180 200 Basis1_Ah_0038.50%.1800 Basis1_Ah_0038_MCC.50%.1800

1-zonig Analyse der 1-zonigen Sim. 1-zonig Analyse der 2-zonigen Sim.

Engine Speed rpm 1800.0 Compression Ratio - 18.500 Energy Balance - 1.0149 Burn_bst_MCC_Ah38_B50.cly BMEP [bar] 8.8542 BMEP [bar] 9.0688 MFB10 [deg] 7.4354 MFB10 [deg] 6.7318 MFB50 [deg] 16.648 MFB50 [deg] 16.089 MFB90 [deg] 31.985 MFB90 [deg] 27.916

Calibration

Parameters

 C_mod combustion constant  C_diss dissipations constant  C_turb turbulent constant

 C_NO NOx formation constant  C_ign ignition delay constant

Project Experience

 Parameters are engine specific but

for than valid for a wide range

(19)

PREDICTED ROHR FOR COMPRESSION IGNTION ENGINES /5

HCCI COMBUSTION MODEL

 Single Zone HCCI

 Simulation based on General

Species Transport

 CHEMKIN compatible

 no CHEMKIN needed

 arbitrary no. of species (CO,

CO2, H2, O, H, ...)

 arbitrary no. of chemical

reactions (two sets for unburned

and burned Zone Chemistry)

C7H16 + O2 = C7H15-1 + HO2 2.500E+13 0.0 48810.0 C7H16 + O2 = C7H15-2 + HO2 2.800E+14 0.0 47180.0 C7H16 + H = C7H15-1 + H2 5.600E+07 2.0 7667.0 C7H16 + H = C7H15-2 + H2 4.380E+07 2.0 4750.0 C7H16 + OH = C7H15-1 + H2O 8.600E+09 1.10 1815.0



_





nSpcGas i i i F

d

dw

u

d

dQ

1







(20)

PREDICTED ROHR FOR COMPRESSION IGNTION ENGINES /6

HCCI COMBUSTION MODEL

 6 Zone HCCI Combustion

 6 zones

 General species transport

 Non uniform species distribution in

zones

 2 Heat Transfer

 Zone to zone (engery potential

driven)

 Boundary zone to wall

 Isooctane mechanism (~291 species

875 reactions in CHEMKIN Format)

(21)

BOOST CLASSIC / GENERAL SPECIES TRANSPORT

Utilites

Calculated

ROHR

Pre-defined

ROHR

Classic

General

Vibe (1zone, 2zone, Hires,...)



Table (1zone, 2zone)



Diesel: MCC



Gasoline: Fractal



HCCI

-



User Coded Combustion Models 



Set Conditions at SHP



 General Species Transport • Flexibility

• CHEMKIN Chemistry can be used comfortably in BOOST (HCCI) • Coupling of Combustion-, Emission- and Aftertreatment models