CRC Study on Octane Number and Engine Efficiency – Literature Review

February 25, 2014Baltimore, MD

Prepared by K.G. Duleep, H-D SystemsPrepared by K.G. Duleep, H D SystemsDelivered by James Simnick, Co-Chair CRC Performance

Committee

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Outline• Basis for the study• Study objectives• Study methodology by H-D SystemsStudy methodology by H D Systems• Selected Results

Fi di f t ll i t d i• Findings for naturally aspirated engines• Findings for turbocharged/boosted

engines • Data gaps and R&D recommendationsg p

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Basis for the CRC Studyy

• CRC Performance Committee has an Octane GroupO t ’ f i SI C b ti• Octane group’s focus is on SI Combustion

• Combustion R&D, especially SI octane, now has much greater interest than 5+ years agogreater interest than 5 years ago

• Octane Group wanted to know what is current published technology & data gaps?

• Prepared a RFP and solicited bidders, Phases1 - 5• Contracted to H-D Systems, Dr. K.G. Duleep

St d il bl i b it P bli ti• Study available via www.crcao.org website, Publications of “Performance Committee”

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Study Objectivesy j

• Define relationship between octane and engine ffi iefficiency

• Start with comprehensive literature search for technical papers

• Phase 1 : gathered 250 papers based on title and abstract, distill to 45 relevant papers.

• 10 papers directly examined the relationship between efficiency and octane number.

• Then interviews with OEM’s

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Analysis issuesy

• No simple relationship linking compression ratio (CR) and engine efficiencye g e e c e cy

• Engine octane requirement is also affected by:• engine design • operating conditions• operating conditions• engine calibration (AF ratio and spark timing)• fuel composition.In turbocharged/boosted engines:• In turbocharged/boosted engines:• octane may benefit torque and power more than engine thermal

efficiencyVehicle efficiency improvements introduce other• Vehicle efficiency improvements introduce other “complicating” parameters • E.g. downsize the engine!

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Analysis Findingsy g

• Literature review suggested engine OR differed by:– Fuel management (Injection system PFI or DI), and

– Air management (aspirated or turbocharged/boosted).

• For knock resistance key are:• For knock resistance, key are:– Fuel Research Octane Number (RON),

– Sensitivity (ROM – MON)

– Latent heat of evaporation (LHE)

• OEM’s recommended:– Focus on the engine studies,

– Too many uncontrolled parameters in vehicle studies.

N fid ti l d t d i th l i– No confidential data was used in the analysis.

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Study methodologyy gy

• H-D Systems utilized a 2 stage modelFi t li k CR t i th l ffi i• First, link CR to engine thermal efficiency,

• Second, link CR and other variables to fuel octane, sensitivity and LHE.

• Focus on WOT/low RPM (<2000) conditions at =1 for highest engine OR condition.

• The division by engine type/fuel properties/ operating• The division by engine type/fuel properties/ operating conditions resulted in very few data points at the detail level; hence, no statistical analysis is possible.

• Next slides show (some) selected results…

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Indicated Efficiency vs. CR at 1500 RPM

40.00%

41.00%

38.00%

39.00%

ienc

y

37.00%

38.00%

Indi

cate

d Ef

fic

86mm bore

35.00%

36.00% 68.25 mm bore

34.00%7 8 9 10 11 12 13 14 15 16 17

Compression Ratio

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EFFECT OF CR ON TORQUE

115

120

110

115

AT

KLS

A

105

ALI

ZED

TO

RQ

UE

DI 114RON

PFI 114RON

95

100

NO

RM

A

DI 90RON

PFI 90RON

9010 11 12 13 14 15 16

COMPRESSION RATIOCOMPRESSION RATIO

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OCTANE NUMBER vs. KLSA

105

110

100

ER

OI

RON

95

OC

TAN

E N

UM

B

MON

Linear (OI)

Linear (RON)

85

90

80-4 -2 0 2 4 6 8 10 12

KLSA at 1200 RPM, DEGREES

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NIMEP vs. Spark Timing

1

0.9

d N

IMEP

Nor

mal

ized

0.8

0.70 5 10 15 20 25 30

Spark Retard from MBT, deg

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TORQUE vs. RPM WITH DIFFERENT FUELTURBOCHARGED PFI ENGINE CR = 9.5

300

325

250

275

m

92.5 RON

94 6 RON

225

250

TOR

QU

E N

-m 94.6 RON

98.3 RON

106.5 RON

175

200

150

175

0 1000 2000 3000 4000 5000 6000RPMRPM

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SEPARATION OF CHARGE COOLING AND OCTANE EFFECTS ON KNOCK LIMIT

40

45

30

35

Ch

20

25

NET

IMEP

, BA

R

E0

E50, UFI

E50, D!

Charge Cooling

E50,PFI

E50,DI

10

15 Octane Improvement

0

5

0 5 10 15 20 25 30 35CRANK ANGLE AT 50% MASS BURN, ATDC

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Findings for Naturally Aspirated Enginesg y p g

• Benefits from increased octane apparent • 4 to 5 octane increase allows• 4 to 5 octane increase allows

• a one point increase in CR, • or a spark advance increment of 5 to 8 degrees.

• The benefits from increased CR or spark advance are• The benefits from increased CR or spark advance are non-linear and depend on the (CR) starting point.

• The benefits are:• Lowest for small bore engines relative to medium or large bore • For a medium bore engine at 10 CR, a 4 to 5 octane point can

allow a 2% improvement in thermal efficiency. Vehicle efficiency improvement can be larger since engine• Vehicle efficiency improvement can be larger since engine output increases with increased CR.

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Findings for Turbocharged/Boosted Enginesg g g

Turbocharged engines have: Multiple limitations on boost and efficiency Multiple limitations on boost and efficiency So octane number response is dependent upon the operating

condition. At mid range RPM : At mid-range RPM,:

Octane increase can improve torque and efficiency (approx. 1%).

3 5 octane can increase IMEP by 2 bar 3 – 5 octane can increase IMEP by 2 bar Ethanol blending can provide large benefits:

In turbo/boosted DI engines Cooling power associated with ethanol’s high LHE Ethanol’s combustion properties But need to address compatibility.p y

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Data Gaps and Research Suggestionsp gg

Available public data on the influence of fuel octane number on engine performance and efficiency is limited and does noton engine performance and efficiency is limited and does not allow a robust numerical estimate of the benefits for all engine types and operating conditions.D t i ti l l li it d d DI T b h d Data is particularly limited on modern DI -Turbocharged engines and on new emerging designs like sequential turbo DI engines that can offer high torque even at low RPM, as

ll ll b i b iwell as on small bore size turbo-engines. A large amount of data is available at manufacturers that is

currently not in the public domain. The development of a data y p pbase with manufacturer co-operation can allow more detailed and specific analysis of all parameters affecting the octane to efficiency relationship.y p

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Research Suggestions (cont’d.)gg ( )

• Controlled testing of modern DI-Turbo engines of different bore sizes and of sequential turbo designsdifferent bore sizes and of sequential turbo designs emerging in the market can provide a forward look of the effects of octane number in the coming decades.

• The effects of high volumetric content ethanol blends like E30 or E50 on optimized turbo-DI engine performance appear to be highly beneficial and worthy of more studyappear to be highly beneficial and worthy of more study.

• Data from European auto-manufacturer studies that are unpublished may provide some early insight into structuring such public studies.

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