HCCI and Stratified-Charge CI Engine Combustion …...HCCI and Stratified-Charge CI Engine Combustion Research John E. Dec Yi Yang and Nicolas Dronniou Sandia National Laboratories

HCCI and Stratified-Charge CI Engine Combustion Research

John E. Dec Yi Yang and Nicolas Dronniou

Sandia National Laboratories

May 15, 2012 – 9:30 a.m.

U.S. DOE, Office of Vehicle Technologies Annual Merit Review and Peer Evaluation

Program Manager: Gurpreet Singh Project ID: ACE004

This presentation does not contain any proprietary, confidential, or otherwise restricted information.

Timeline ● Project provides fundamental

research to support DOE/Industry advanced engine projects.

● Project directions and continuation are evaluated annually.

Budget ● Project funded by DOE/VT:

FY11 – $750k FY12 – $760k

Barriers ● Increase the efficiency of HCCI

(LTC). ● Extend HCCI (LTC) operating

range to higher loads. ● Improve the understanding of

in-cylinder processes.

Partners / Collaborators ● Project Lead: Sandia ⇒ John E. Dec ● Part of Advanced Engine Combustion

working group – 15 industrial partners ● General Motors – specific collaboration ● LLNL – support kinetic modeling ● Univ. of Michigan – thermal strat. ● Univ. of New South Wales, Australia ● Chevron – advanced fuels for HCCI ● LDRD – advanced biofuels project

(internal Sandia funding)

Overview

Objectives - Relevance

FY12 Objectives ⇒ Increased Efficiency, High Loads, Improved Understanding

● Improve the Efficiency of Boosted HCCI/SCCI: Systematically investigate the effects of key engine operating parameters to determine: – Their effects on thermal efficiency. – The highest efficiency attainable with current engine configuration.

● Effects of Gasoline Ethanol Content: Determine the effects of expected variations in ethanol content of pump gasoline on HCCI/SCCI efficiency and high-load capability.

● Investigate the changes in thermal stratification (TS) with operating conditions ⇒ Speed, intake temperature (Tin), wall temperature and swirl.

● Support modeling of chemical-kinetics at LLNL and TS at the Univ. of Michigan and General Motors ⇒ provide data and analysis.

Project objective: to provide the fundamental understanding (science-base) required to overcome the technical barriers to the development of practical HCCI or SCCI engines by industry.

Approach

● Metal engine ⇒ conduct well-characterized experiments to isolate specific aspects of HCCI/SCCI combust. Determine cause-and-effect relationships. – Improved efficiency: Systematically vary operating parameters while holding

other key parameters constant ⇒ Tin, fueling rate, speed, fueling strategy, Pin. – Ethanol content of gasoline: E0, E10, and E20 effects on performance.

● Optical engine ⇒ detailed investigations of in-cylinder processes. – Thermal stratification: Apply PLIF-based thermal-imaging using a vertical laser

sheet to simultaneously image both the boundary layer (BL) and bulk gas.

● Computational Modeling: – Support LLNL improvement of kinetic mechanisms ⇒ gasoline surrogate – Univ. of Michigan & GM ⇒ Modeling/analysis of thermal stratification (TS).

● Combination of techniques provides a more complete understanding.

● Transfer results to industry: 1) physical understanding, 2) improved models, 3) data to GM to support analysis of TS and R&D of boosted HCCI engines.

● Use a combination of metal- and optical-engine experiments and modeling to build a comprehensive understanding of HCCI/SCCI processes.

Sandia HCCI / SCCI Engine Laboratory

All-Metal Engine

Optical Engine

Optics Table

Dynamometer

Intake Plenum

Exhaust Plenum

Water & Oil Pumps & Heaters

Flame Arrestor

● Matching all-metal & optical HCCI research engines. – Single-cylinder conversion from Cummins B-series diesel.

Optical Engine

All-Metal Engine

● Bore x Stroke = 102 x 120 mm ● 0.98 liters, CR=14

Metal-engine ⇒ Fuel is gasoline (AKI = 87), E10, E20

NOx and soot emissions > 10x below US-2010

Accomplishments ● Determined effects of all main operating parameters on thermal efficiency.

(Tin, fueling rate, engine speed, fuel-type, fueling strategy, and Pin) – Found optimal values within constraints (i.e. acceptable ringing, emissions, etc.) – Combined optimal values to obtain highest eff. for current engine config. & fuels.

● Demonstrated indicated thermal efficiencies of 47 – 48% for loads from 8 to 16 bar IMEPg ⇒ for current CR = 14:1 configuration.

● Evaluated performance affects of increasing ethanol content of gasoline, from E0 E10 E20. (E10 complete, E20 initial results ⇒ on track for FY) – Showed max. load increase from 16.3 18.1 20.0 bar IMEPg, respectively.

● Significantly improved temperature-map imaging ⇒ 1) resolution, 2) SNR (signal/noise), & 3) post-processing to remove laser-sheet schlieren effects.

● Quantified variations in TS over range of conditions ⇒ speed, Tin, Twall, swirl – Conducted a PDF analysis of the TS at various conditions. – Initiated analysis of cold-pocket size.

● Supported chemical-kinetic model development at LLNL, and TS modeling at U. Michigan & General Motors ⇒ provided data and analysis.

43.544.044.545.045.546.046.547.047.548.0

20 30 40 50 60 70 80 90 100Intake Temperature [°C]

Gro

ss In

dica

ted

Ther

mal

Eff.

[%]

DI, Ringing = 5DI, CA50 = 376.7PM, Ringing = 5PM, CA50 = 376.7

Early DI vs. PreMixedFueling = 55 mg/inj

Pin = 2 bar, Gasoline

Improving Thermal Efficiency ● Advanced engines using HCCI or partially stratified variations termed

“SCCI” provide high efficiencies (~30% improvement over SI). – Use light-end distillates efficiently, and no aftertreatment for NOX and PM.

● Although thermal efficiencies of HCCI/SCCI are already very good, further increases are desirable.

● Conduct a systematic study of factors affecting thermal efficiency (T-E) and seek the highest efficiency for our current engine configuration.

● Initial work presented last year showed T-E increased with reduced Tin. 1. Const. CA50 ⇒ Moderate increase in T-E

> Higher γ (↓EGR & ↓T) & less heat loss.

2. Const. ringing = 5 MW/m2 (const. PRR) ⇒ Premixed: T-E similar to const. CA50 ⇒ Early-DI: large increase in T-E. > Fuel not completely mixed ⇒ partial fuel

stratification (PFS) effect reduces HRR to allow CA50 advance (discussed later).

● Conclusion: Use the lowest Tin possible.

● Early-DI ⇒ use Tin = 30°

C. Premixed ⇒ Tin = 60°

C, no fuel condensation.

Fueling-Rate Effects ● Increase fueling from lowest φm for

stable combustion with EGR = 0%. – T-E increases with improved C-E. – Ringing increases due to higher φm

and more advanced CA50. – R > 5 or 6 ⇒ knock & incr. heat loss.

● Trade-off between improved C-E and heat loss ⇒ T-E drops for φm > 0.32. – T-E peaks at 47.6%, IMEPg ~9.5 bar

● Hold Ringing = 5 using EGR to retard CA50 ⇒ much higher loads.

● Initial CA50 retard hardly affects T-E, but reduction in T-E increases for CA50 > ~370°

CA. EGR also up.

44.5

45.0

45.5

46.0

46.5

47.0

47.5

48.0

0.3 0.32 0.34 0.36 0.38 0.4Charge-mass Equiv. Ratio [φm]

Indi

cate

d Th

erm

al E

ff. [%

]

93

94

95

96

97

98

99

100

Com

bust

ion

Eff.

[%]

T-E, EGR = 0

C-E, EGR = 044.5

45.0

45.5

46.0

46.5

47.0

47.5

48.0

0.3 0.32 0.34 0.36 0.38 0.4Charge-mass Equiv. Ratio [φm]

Indi

cate

d Th

erm

al E

ff. [%

]

93

94

95

96

97

98

99

100

Com

bust

ion

Eff.

[%]

T-E, EGR = 0T-E, Ringing = 5C-E, EGR = 0C-E, Ringing = 5

Gasoline, Pin = 2 bar, Tin = 30°

C, DI-60°

CA

0.0

2.0

4.0

6.0

8.0

10.0

0.3 0.32 0.34 0.36 0.38 0.4Charge-mass Equiv. Ratio [φm]

Rin

ging

Inte

nsity

[MW

/m2 ]

364

366

368

370

372

374

CA

50 [°

CA

]

Ringing, EGR = 0

CA50, EGR = 0

0.0

2.0

4.0

6.0

8.0

10.0

0.3 0.32 0.34 0.36 0.38 0.4Charge-mass Equiv. Ratio [φm]

Rin

ging

Inte

nsity

[MW

/m2 ]

364

366

368

370

372

374

CA

50 [°

CA

]

Ringing, EGR = 0Ringing, Ringing = 5CA50, EGR = 0CA50, Ringing = 5

~75% of max. load

● Best T-E ⇒ Adv. CA50 up to R ≈ 5 for each load (φm). ⇒ Lower loads give higher T-E as long as C-E ≥ ~96.5%.

● At each speed, find highest efficiency point, using procedure on previous slide. – Use Early-DI fueling with Tin = 30°

C.

– Increase fueling (φm) to improve C-E and advance CA50 up to Ringing ≈ 5. > Reached C-E ~96.5%, w/o EGR.

● T-E peaks between 1200 & 1300 rpm.

● Higher fueling required at higher speeds. – With higher fueling, CA50 must be more

retarded to keep Ringing ≤ 5.

● T-E similarly high for 1200 or 1300 rpm.

● Use 1200 rpm to be consistent with previous data.

Engine Speed Gasoline, Pin = 2 bar, Tin = 30°C, Early-DI

45.5

46.0

46.5

47.0

47.5

48.0

48.5

1000 1100 1200 1300 1400 1500 1600Engine Speed [rpm]

Indi

cate

d Th

erm

al E

ff. [%

] DI @ 40°CADI @ 80°CA

0.28

0.30

0.32

0.34

0.36

0.38

1000 1100 1200 1300 1400 1500 1600Engine Speed [rpm]

Mas

s-ba

sed

Equi

v. R

atio

[ φm

]

366

368

370

372

374

376

CA

50 [°

CA

]

DI = 40 CAD, Phi-mDI = 80 CAD, Phi-mDI = 40 CAD, CA50DI = 80 CAD, CA50

● Trade-off between reduced heat losses & more CA50 retard as speed increases.

Fuel Type: E10 vs. Gasoline

● A large fraction of the gasoline sold in the US contains up to 10% ethanol.

● Our E10 is blended from our ON = 87 gasoline + neat ethanol. – Assuming a ON of 99.5 for ethanol,

our E10 has an AKI = 88.1 – Between regular & mid-grade pump

gasoline.

● For Pin = 2 bar, E10 is less reactive. – Significantly less EGR required to

keep Ringing ≤ 5 (CA50s similar). – Higher γ increases efficiency.

● T-E is ~0.4 T-E-percentage units higher with E10 (an increase of 0.9%)

● E10 offers a modest T-E advantage for boosted operation.

363738394041424344454647

0.32 0.34 0.36 0.38 0.4 0.42 0.44 0.46 0.48Charge-mass Equivalence Ratio [φm]

Indi

cate

d Th

erm

al E

ff. [%

]

10

12

14

16

18

20

22

Inta

ke O

2 [%

]

T-E, E10T-E, Gasoline, 2011Intake O2, E10Intake O2, Gasoline, 2011

Pin = 2 bar, Tin = 60°

C, Premixed

Ringing = 5

43

44

45

46

47

48

49

900 1000 1100 1200 1300 1400 1500 1600IMEPg [kPa]

Indi

cate

d Th

erm

al E

ff. [%

]Pin = 2.4 bar, PM

43

44

45

46

47

48

49

900 1000 1100 1200 1300 1400 1500 1600IMEPg [kPa]

Indi

cate

d Th

erm

al E

ff. [%

]Pin = 2.4 bar, PFS

Pin = 2.4 bar, PM

43

44

45

46

47

48

49

900 1000 1100 1200 1300 1400 1500 1600IMEPg [kPa]

Indi

cate

d Th

erm

al E

ff. [%

]Pin = 2.4 bar, DI-60

Pin = 2.4 bar, PFS

Pin = 2.4 bar, PM

Fueling Strategy: PM, PFS, Early-DI Previous work, SAE 2011-01-0897 ● Gasoline autoignition becomes

sensitive to local φ with intake boost. ● Allows use of partial fuel stratification

(PFS) to significantly reduce PRRmax. – Premix ≥ 80% of fuel, late-DI for rest. – Higher loads for same CA50. – Advance CA50 for higher efficiency.

Recent Results with E10 (C-E ≥ 96%) ● PFS is also effective with E10 (~9%DI).

– Higher T-E and higher load.

● Early-DI fueling, further increases T-E. – Mixture similar to PFS, and Tin reduced

to 30°

C, less heat loss & higher γ. ● Example at Pin = 2.8 bar, const. fueling

shows increased T-E with increasing PFS and early-DI with Tin = 30°

C .

50

60

70

80

90

100

110

340 350 360 370 380 390Crank Angle [°CA]

Pres

sure

[bar

]

3% DI @ 300°CA6% DI @ 300°CA9% DI @ 300°CA13% DI @ 300°CA17% DI @ 300°CA20% DI @ 300°CA

Gasoline, φm = 0.44, Tin = 60°

C, CA50 = 374°

CA

43

44

45

46

47

48

49

900 1000 1100 1200 1300 1400 1500 1600IMEPg [kPa]

Indi

cate

d Th

erm

al E

ff. [%

]Pin = 2.4 bar, DI-60Pin = 2.4 bar, PFSPin = 2.4 bar, PMPin = 2.8 bar, DI-60Pin = 2.8 bar, PFSPin = 2.8 bar, PM

Early DI Tin=30°

C

PFS PreMixed

Increase Fueling

● PFS and Early-DI fueling increase T-E significantly for the same load.

E10, Tin = 60°

C

Pin = 2 bar

42

43

44

45

46

47

48

49

800 1000 1200 1400 1600 1800IMEPg [kPa]

Indi

cate

d Th

erm

al E

ff. [%

]

Pin = 2.4 bar, PM

Pin = 2.4 bar, PFS

Pin = 2.4 bar, DI-60

42

43

44

45

46

47

48

49

800 1000 1200 1400 1600 1800IMEPg [kPa]

Indi

cate

d Th

erm

al E

ff. [%

]

Pin = 2.0 bar, PMPin = 2.0 bar, PFSPin = 2.4 bar, PMPin = 2.4 bar, PFSPin = 2.4 bar, DI-60Pin = 2.8 bar, PMPin = 2.8 bar, PFSPin = 2.8 bar, DI-60Pin = 3.0 bar, PMPin = 3.0 bar, PFSPin = 3.2 bar, PMPin = 3.3 bar, PMPin = 3.4 bar, PM

Intake Pressure and Fueling Strategy ● Data acquired for wide range of intake pressures (Pin = 2.0 to 3.4 bar),

and three fueling strategies (PM, PFS, and Early-DI) show similar trends. – Load increases with boost, but curve shape is similar.

E10, Ringing = 5 MW/m2, C-E ≥ 96%

● For each Pin, T-E decreases with increased load mainly due to requirement to retard CA50 to prevent excessive ringing. EGR also increases with load.

● Replot T-E data against CA50.

42

43

44

45

46

47

48

49

364 366 368 370 372 374 376 378 380CA50 [°CA]

Indi

cate

d Th

erm

al E

ff. [%

]

Pin = 2.0 bar, PMPin = 2.0 bar, PFSPin = 2.4 bar, PMPin = 2.4 bar, PFSPin = 2.8 bar, PMPin = 2.8 bar, PFSPin = 3.0 bar, PMPin = 3.0 bar, PFSPin = 3.2 bar, PMPin = 3.3 bar, PMPin = 3.4 bar, PM

42

43

44

45

46

47

48

49

364 366 368 370 372 374 376 378 380CA50 [°CA]

Indi

cate

d Th

erm

al E

ff. [%

]

47

48

49

50

51

52

53

54

Sim

ulat

ed T

herm

al E

ff. [%

]

Pin = 2.0 bar, PMPin = 2.0 bar, PFSPin = 2.4 bar, PMPin = 2.4 bar, PFSPin = 2.8 bar, PMPin = 2.8 bar, PFSPin = 3.0 bar, PMPin = 3.0 bar, PFSPin = 3.2 bar, PMPin = 3.3 bar, PMPin = 3.4 bar, PMSimulation

42

43

44

45

46

47

48

49

364 366 368 370 372 374 376 378 380CA50 [°CA]

Indi

cate

d Th

erm

al E

ff. [%

]

Pin = 2.0 bar, PMPin = 2.0 bar, PFSPin = 2.4 bar, PMPin = 2.4 bar, PFSPin = 2.4 bar, DI-60Pin = 2.8 bar, PMPin = 2.8 bar, PFSPin = 2.8 bar, DI-60Pin = 3.0 bar, PMPin = 3.0 bar, PFSPin = 3.2 bar, PMPin = 3.3 bar, PMPin = 3.4 bar, PM

Combustion Phasing (CA50) ● All Premixed and PFS data for Tin = 60°

C collapse into a single band when plotted against CA50. – Appears to be reaching a max. at ~365°

CA ⇒ reasonable with Heat-Transfer.

● Compare with idealized curve ⇒ agrees well. EGR effect in real data.

● With Early-DI fueling & Tin = 30

C, T-E increases additional 0.5 - 1 TE-units.

E10, Ringing = 5 MW/m2, C-E ≥ 96%

Simulation – Constant fueling – Constant EGR – Woschni H-T for max. T-E @ 365°

CA

● Max. T-E for this engine config. 48.3% with Pin = 2.8 bar (Pback = 2.82 bar).

● Little advantage to advancing CA50 beyond ~368 – 370°

CA.

~75% of max. load

4142434445464748495051

4 6 8 10 12 14 16 18IMEPg [bar]

Indi

cate

d Th

erm

al E

ffici

ency

[%]

E0, Pin = 1.0 bar, Tin = 142°C E0, Pin = 1.3 bar, Tin = 121°CE0, Pin = 1.6 bar, Tin = 92°C E0, Pin = 2.0 bar, Tin = 30, 45 & 60°CE0, Pin = 2.4 bar, Tin = 30, 40 & 50°C E0, Pin = 2.8 bar, Tin = 50°C, PME10, Pin = 2.0 bar, Tin = 60°C E10, Pin = 2.4 bar, Tin = 60°CE10, Pin = 2.8 bar, Tin = 60°C E10, Pin = 3.0 bar, Tin = 60°CE10, Pin = 3.3 bar, Tin = 60°C E10, Pin = 2.4 bar, Tin = 30°CE10, Pin = 2.8 bar, Tin = 30°C Max. Load E10, Pin = 3.4 bar, Tin=60°CMax. Load, Gas., SAE 2010-01-1086

Summary of Efficiency Improvements ● T-E increased well above the values for the high-load limit from initial

boost study in SAE 2010-01-1086.

● Gasoline ⇒ reached T-Es of 47 - 47.8% from 8 to 13.5 bar IMEPg.

● E10 ⇒ reached T-Es of 47 – 48.3% from 9.5 to 16 bar IMEPg – Achieve 16 bar IMEPg, 47% T-E with Pin = 2.8 bar, vs. 3.25 bar for gasoline.

High-Efficiency Points, Ringing ≤ 5

● Gasoline reactivity increases with boost ⇒ use EGR to control CA50. – Blending with ethanol significantly

reduces EGR requirement with boost. – More air in charge ⇒ higher fueling.

● E0: O2 limited for Pin ≥ 2.6 bar ⇒ Load limit = 16.3 bar IMEPg.

● E10: ⇒ O2 limited for Pin ≥ 2.8 bar ⇒ Load limit = 18.1 bar IMEPg.

● E20: ⇒ O2 limited for Pin ≥ 3.6 bar ⇒ Load limit = 20.0 bar IMEPg.

● Ringing ≤ 5, ultra-low NOX & soot.

● T-E ⇒ Higher for E10 & E20 at Pin= 2 & 2.4 bar, less EGR. ⇒ Lower at Pin >2.8 bar, more CA50 retard w/ increased load.

● PFS can increase load up to ~15%, for Pin ≥ ~2 bar, if O2 is sufficient.

High-Load Limit: Gasoline E10 E20

2468

10121416182022

0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0Intake Pressure [bar]

Max

imum

IMEP

g [b

ar]

Gasoline, PM

Gasoline, PM, no EGR

2468

10121416182022

0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0Intake Pressure [bar]

Max

imum

IMEP

g [b

ar]

E10, PM

Gasoline, PM

Gasoline, PM, no EGR

2468

10121416182022

0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0Intake Pressure [bar]

Max

imum

IMEP

g [b

ar]

E20, PM

E10, PMGasoline, PM

Gasoline, PM, no EGR

2468

10121416182022

0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0Intake Pressure [bar]

Max

imum

IMEP

g [b

ar]

E20, PME10, PMGasoline, PMGasoline, PM, no EGRGasoline, PFSE10, PFS

R ≤ 5 MW/m2, Pmax < 150 bar

● High-loads limited by Pmax < 150 bar.

32

34

36

38

40

42

44

46

48

0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4Intake Pressure [bar]

Indi

cate

d Th

erm

al E

ff. [%

]

02468101214161820

Exha

ust O

2 [%

]

PM, Gas., SAE 2010-01-1086

32

34

36

38

40

42

44

46

48

0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4Intake Pressure [bar]

Indi

cate

d Th

erm

al E

ff. [%

]

02468101214161820

Exha

ust O

2 [%

]

PM, Gas., SAE 2010-01-1086

PM, E10

32

34

36

38

40

42

44

46

48

0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4Intake Pressure [bar]

Indi

cate

d Th

erm

al E

ff. [%

]

02468101214161820

Exha

ust O

2 [%

]

PM, Gas., SAE 2010-01-1086

PM, E10

PM, E20

32

34

36

38

40

42

44

46

48

0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4Intake Pressure [bar]

Indi

cate

d Th

erm

al E

ff. [%

]

02468101214161820

Exha

ust O

2 [%

]

PM, Gas., SAE 2010-01-1086PM, E10PM, E20PFS, Gas., SAE 2011-01-0897PFS, E10, SAE 2011-01-0897

Intake valve recess Firedeck Injector blank recess

Quartz window Aluminum

New shot-to-shot beam steering correction.

ΔT (K)

before

after

Improved Thermal-Stratification Imaging ● Temperature-maps (T-maps) derived

from PLIF images with toluene tracer.

● Switch to non-intensified, back-illum. CCD camera, mounted closer. ⇒ Greatly improves resolution & S/N.

● Allows accurate image analysis.

● Improved image correction techniques remove stripes with less effect on T. ⇒ Accurate Std-Dev of T-maps.

● TS results mainly from cold structures.

Field of view

CCD vs ICCD doubles resolution and reduces shot noise at TDC by 2.4x

Side-view imaging shows bulk-gas & wall regions

● Quantify TS as the Std-Dev of T’-maps ⇒ avg. Std-Dev of 100 cycles.

● TS increases through compression stroke.

● More TS at lower speeds.

● In agreement, image analysis shows greater probability of cold structures at lower speeds.

Effect of Engine Speed on TS

Probability of Cold Structures

Prob. (%)

320 °CA

600 rpm 1500 rpm

360 °CA

0

5

10

15

20

25

300 310 320 330 340 350 360 370 380Crank Angle [°CA]

Std-

Dev

T' [

K]

600 rpm900 rpm1200 rpm1500 rpm

Speed Effects on TS

● Competing effects of: 1. More time for heat transfer @ lower speeds 2. Higher gas velocities @ higher speeds.

● Increased time appears to dominate over the potential for higher turbulence with increased gas velocities.

● TS increases with decreased speed.

Effects of Tin and Tcoolant on TS

● TS increases with increasing Tin ⇒ also with decreased Tcoolant

● Expected that increased ∆T = Tbulk-gas – Twall would increase TS.

● However, TS converges for CA ≥ 340°

– Mainly because TS curves for the higher

Tin (and greater ∆T) begin to flatten.

● Possibly due to over mixing reducing the TS. ⇒ Effect should be larger for larger ∆T.

● PDFs of temperature distribution also indicate that over mixing could be occurring. – Negative skewness indicates that the PDF

width is increased by mixing in cold gases. – Less skewness for CA > 330°

suggests mixing

out bulk-gas faster than bringing in new cold gas.

● TS increases with increased Tin & lower Tcoolant, but gain appears less than expected by TDC.

Temp. PDFs

Skewness of PDFs

Tin Effects on TS

Collaborations ● Project is conducted in close cooperation with U.S. Industry through the

Advanced Engine Combustion (AEC) / HCCI Working Group, under a memorandum of understanding (MOU). – Ten OEMs, Five energy companies, Four national labs, & Several universities.

● LLNL: Support development of chemical-kinetic mechanism for gasoline surrogate mixture, Pitz et al.

● General Motors: Frequent internet meetings ⇒ in-depth discussions. – Provide data to support GM efforts on boosted HCCI & in modeling TS (with UM).

● U. of Michigan: Collaborate on modeling and analysis of TS and boundary-layer development ⇒ provide data and in-depth discussions (with GM).

● U. of New South Wales: Support modeling of ethanol-fueled HCCI.

● Chevron: Funds-In project on advanced petroleum-based fuels for HCCI.

● SNL-LDRD: Funds-In project on biofuels produced by fungi ⇒ collab. with researchers in basic chemistry (C. Taatjes et al.) & Biofuels (M. Hadi et al.).

Future Work Increased Efficiency and Performance of Boosted HCCI ● Explore increasing the thermal efficiency of boosted HCCI by raising the

compression ratio (or expansion-ratio only using a Miller-cycle cam).

● Determine the performance potential of various realistic fuels: – Complete investigation of effects of ethanol content of gasoline (E0 E20). – Expand study to include premium gasoline ⇒ potential compared to E10 or E20.

● Work w/ Cummins to modify cyl. head for spark plug for studies of SA-HCCI. Thermal Stratification ● Expand current studies to: 1) further investigate whether over-mixing limits

TS at some conditions, 2) include variation of piston-top T, & 3) flow effects. – Potential collaboration with J. Oefelein et al. for LES modeling of TS.

● Investigate the potential of obtaining Boundary-Layer Profiles at the piston-top surface from T-map images ⇒ simultaneous Twall & heat-flux data.

Support of HCCI Modeling ● Continue collab. with GM & U. of Mich. on modeling TS and boosted HCCI. ● Continue to collaborate with LLNL on improving chemical-kinetic

mechanisms of single components and gasoline-surrogate mixture.

Summary ● Results presented have significantly improved fundamental understanding

of HCCI / SCCI with respect to the barriers of: 1) increased efficiency, 2) increased load, and 3) improved understanding of in-cylinder processes.

● Examined all key operating parameters affecting thermal efficiency (T-E) of boosted HCCI / SCCI engines ⇒ determined tradeoffs and limits. – Achieved highest gross-ind. T-E for current engine config. and fuel-set of 48.3%. – Demonstrated T-Es of 47-48% from 8 – 16 bar IMEPg using E0 & E10 gasolines.

● Showed that Partial Fuel Stratification significantly improves T-E across the fuel-load range for various Pin ⇒ and it increased high-load limit for given Pin.

● Early-DI fueling gives a PFS-like mixture with similar benefits, and it allows a lower Tin = 30°

C without fuel condensation for a further increase in T-E.

● For boosted HCCI/SCCI, E10 gives higher T-E and higher loads than E0.

● Extended the high-load limit by increasing ethanol content E0 E10 E20. ⇒ Achieved high-loads of 18.1 & 20.0 bar IMEPg for E10 & E20, respect’ly.

● Showed TS increases with engine speed, Tin, lower Tcoolant, and swirl. – Discovered that over mixing may be reducing the TS during late compression for

higher Tin and lower Tcoolant conditions.

Technical Backup Slides

Definitions of T-maps T-map

Average thermal stratification T-map (T=T+T’)

Total thermal stratification

RMS of the 100 T-maps.

Shows the location of the cycle-to-cycle temperature variations.

Average of the 100 T-maps.

Shows only the consistent TS patterns.

Includes both the consistent boundary layers at the walls and the fluctuating TS in the bulk gas.

Driven by in-cylinder turbulence.

Most important for controlling PRR by sequential auto-ignition in HCCI engines.

T’-map Fluctuating thermal stratification

TRMS Cycle-to-cycle variation σ (K)

ΔT (K)