The Role of Advanced Combustion in Improving Thermal Efficiency

Engine Technologies

Caterpillar Non Confidential

CAT, CATERPILLAR, their respective logos, “Caterpillar Yellow” and the POWER EDGE trade dress, as well as corporate and product identity used herein, are trademarks of Caterpillar and may not be used without permission.

The Role of Advanced Combustion in Improving Thermal Efficiency

Chris Gehrke, Hari

Sivadas, Tim Bazyn

and David Milam –

Caterpillar Inc

2008 DEER ConferenceDearborn, MI

August 4, 2008

DOE Contract DE-FC26-05NT42412

DOE Technology Development Manager: Roland Gravel

NETL Project Manager: Carl Maronde

Caterpillar Confidential: XXXXXEngine Technologies


How much more reciprocator efficiency is needed?

Needs to meet EPA 2010 andnon-road Tier 4 emissions requirements

Current focus of HECC program

2007 baseline

46%Reciprocator

Efficiency Bra

ke T

herm

al E

ffici

ency

Exhaust Waste Heat Recovery

and Air System Efficiency

55% Aggressive heat recoveryand component efficiency assumptions

Not currently practical formobile applications

Goal: minimum 10% improvement in reciprocator efficiency



Objectives

What are the combustion system challenges related to achieving higher brake thermal efficiency?

What are potential technologies to address these challenges?

What are the barriers in making these technologies viable?



Need to Consider Other System Interactions

Need to balance combustion system and heat recovery system requirements

–

Boost requirements–

Equivalence ratioregen_frequency_and_duration_effects

0

0.5

1

1.5

2

2.5

3

3.5

0 2 4 6 8 10

regen_interval (h)

est_

bsfc

_pen

alty

(%)

4_g/L 5.2_g/L inc_freq inc_soot

DPF

Reg

ener

atio

n Fu

el C

onsu

mpt

ion

Pena

lty (%

)

DPF Regeneration Interval (h)

Impact of DPF Regeneration on Fuel Consumption

regen_frequency_and_duration_effects

0

0.5

1

1.5

2

2.5

3

3.5

0 2 4 6 8 10

regen_interval (h)

est_

bsfc

_pen

alty

(%)


DPF

Reg

ener

atio

n Fu

el C

onsu

mpt

ion

Pena

lty (%

)

regen_frequency_and_duration_effects

0

0.5

1

1.5

2

2.5

3

3.5

0 2 4 6 8 10

regen_interval (h)

est_

bsfc

_pen

alty

(%)


DPF

Reg

ener

atio

n Fu

el C

onsu

mpt

ion

Pena

lty (%

)

DPF Regeneration Interval (h)

Impact of DPF Regeneration on Fuel Consumption

Need to minimize fuel consumption from aftertreatment regeneration

–

Minimize soot emissions

Increased boost and less heat recovery



Impact of the Combustion System on Thermal Efficiency

1.

Efficiency of expansion work extraction

2.

Quality of the exhaust energy to heat recovery devices

3.

Fuel consumption from A/T thermal management (ie. DPF regeneration)

4.

Engine parasitic loads–

Cooling fan, fuel system

Maximize geometric expansion ratio, optimal combustion phasing, short combustion duration, minimize in-cylinder heat transfer

Minimize boost requirements vs. optimal equivalence ratio

Minimize soot emissions vs. optimal equivalence ratio

Minimize heat rejection, fuel injection pressure, etc.



Potential Combustion System Technologies

Combustion System Challenges

Short, optimally phased combustionTolerance for higher equivalence ratiosLow soot emissions

High BMEP mixing controlled combustionCompatible with HCCI/PCCI Low soot emissions

Premixed combustion (HCCI/PCCI)

Lifted-flame diffusion combustion



Premixed Combustion (HCCI/PCCI)

AdvantagesShort combustion duration

Premixed low smoke

Low Temp Combustion potential NOx benefit

ChallengesBenefit limited to low loadNeed to transition to conventional diesel combustion at higher loadsCombustion chamber / injector nozzle configuration must be compatible with conventional combustion

30%

35%

40%

45%

50%

450 950 1450 1950

BMEP (kPa)Th

erm

al E

ffici

ency

(%)

Production Engine

Diesel PCCI

4% improvement with PCCI

Goal: 46%

4% fuel consumption improvement



0.00.20.40.60.81.01.2

05101520253035404550Injection Timing (deg BTDC)

AVL

Sm

oke

Technical Challenges with HCCI/PCCI

190 MPa160 MPa130 MPa

0.000.200.400.600.801.001.201.40

0 250 500 750 1000BMEP (kPa)

AVL

Sm

oke

33%34%35%36%37%38%39%40%

Bra

ke T

herm

al E

ffici

ency

Conventional DieselPCCI Combustion

Diesel Boiling Range (T10-T90) Typical C15 at 450 kPa BMEP

300400500600700800900

-180 -150 -120 -90 -60 -30 0

Crank Angle (deg)

In-c

ylin

der G

as T

emp

(K)

T10T90

Diesel PCCI operating range limited by–

Smoke emissions –

Non-optimal phasing (degrades BSFC)

Technical Challenges–

EGR/IVA insufficient to control diesel combustion phasing without sacrificing equivalence ratio

–

Low volatility of diesel fuel (liquid fuel impingement)



Need an alternative method of combustion phasing control to maintain the following …

–

optimal combustion phasing–

sufficient compression ratio –

acceptable equivalence ratio–

sufficient pre-mixing

Some NOx A/T potentially requiredto extend load range

Cylinder pressure and rise rate constraints will limit load range and efficiency benefit

–

Conventional diesel combustion needed to reach full load (2100 kPa

BMEP)

Thermal Efficiency Potential of HCCI/PCCI Combustion

30%

35%

40%

45%

50%

450 650 850 1050 1250 1450 1650 1850 2050BMEP (kPa)

Bra

ke T

herm

al E

ffici

ency

(%)

Production EngineDiesel PCCIAdvanced PCCI PotentialRise Rate Limit

3 - 7% improvement with Advanced PCCI



Technologies to Increase HCCI/PCCI Load Range

Variable Compression Ratio Effective means of extending load range at the expense of compression ratioOptimal phasing does not outweigh expansion ratio loss to reach full loadMay be adequate if using HCCI/PCCI only for NOx emissions control Does not address diesel liquid fuel impingement

US Patent 7,370,613



Technologies to Increase HCCI/PCCI Load Range

Engine Operating Range vs

Derived Cetane NumberCR 12 &14

0

200

400

600

800

1000

1200

1400

1600

1800

20 25 30 35 40 45 50

IQT Derived Cetane Number

Min

and

Max

Mul

ti B

MEP

/ kP

a

Diesel

Maximum Achievable Load

Minimum Achievable Load

1200 rpm

FuelsLoad range is affected by cetane numberHigh volatility fuel increases the injection window (mixing)No commercially available fuel meets all requirementsInvestigating diesel / gasoline fuel blends

Boiling Range (T10-T90) vs Crank Angle Typical C15 at 450 kPa BMEP

300

400

500

600

700

800

900

-180 -150 -120 -90 -60 -30 0

Crank Angle (deg)

In-c

ylin

der G

as T

emp

(K)

Gasoline Boiling Range

DieselBoilingRangeT10

T10T90

T90



“Lifted Flame”

Combustion

Low soot combustion technology–

Entrain enough air prior to liftoff length (equivalence ratio <2) such that soot is not formed in combustion region (SAE 2001-01-0539)

Requires small injector orifices –

Increased compatibility with PCCI/HCCI Order of magnitude smoke reduction



Challenges with Lifted Flame Combustion

Technology does not easily scale up with engine size–

Potentially compatible with mid-range and smaller sized engines with current injection pressure capability and hole sizes.

–

Need more holes or higher injection pressure for heavy-duty application–

for 15L, ~500 MPa

injection pressure w/ 6 holesor 12 holes at 300 MPa

Effect of Increasing Number of Plumes on Emissions Performance

Smoke emissions become problematic with increased number of holes

Are spray plume interactions to blame?

300 MPa



Challenges with Lifted Flame Combustion

6 hole 10 hole 14 hole

No significant differences in non-evaporating spray characteristics

Next Step: Investigate evaporating and combusting sprays



Summary

To achieve 55% brake thermal efficiency, the efficiency of the combustion system / reciprocator must be increased.

HCCI/PCCI (low temperature combustion) potentially offers increased thermal efficiency with reduced requirements for DPF regeneration. Demonstrated 4% BSFC improvement below 750 kPa BMEP.

Inability to adequately control combustion phasing and liquid fuel impingement limits the load range and thermal efficiency benefit of diesel HCCI/PCCI

Lifted flame combustion is a potential low-soot diffusion combustion technology that offers increased compatibility with HCCI/PCCI. Demonstrated order of magnitude soot reduction.

Many challenges must be solved to achieve a production viable, high thermal efficiency combustion system



•In-cylinder heat transfer

•Exhaust Availability

•Leverage advanced materials CRADA

Collaborations

University of Wisconsin

Engine Research Center

Lund University

AEC MOU

•Program coordination

•Test/Analysis

•Truck/Machine system integration and packaging

•Combustion

•Optical diagnostics

•Fuel spray and

combustion

•Fuels effects

•Fuels effects

•Combustion Chemistry/modeling

•Closed loop control

•Transient controls

•Vehicle calibration

•Sensors

Engine Technologies


CAT, CATERPILLAR, their respective logos, “Caterpillar Yellow” and the POWER EDGE trade dress, as well as corporate and product identity used herein, are trademarks of Caterpillar and may not be used without permission.

Documents

The Role of Advanced Combustion in Improving Thermal Efficiency