UNITI Mineral Oil Technology Congress - umtf.de - LSPI - lubricant... · Low speed pre-ignition Turbocharged engine Knocking Natural aspirated engine ... • LSPI synopsis: ... combustion

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LSPI – lubricant formulation effect on fuel

pre-ignition in engines

Presented by: Dr Cecile Pera, Senior Engineer

Performance you can rely on.

UNITI Mineral Oil Technology Congress

Introduction


• LSPI has been studied by researchers for more than a decade

• It happens at low-speed and high-load

• Very sporadic and ‘random’ occurrences

IntroductionWhat do we know about LSPI?

High speed pre-ignition

Turbocharged engineLow speed pre-ignition

Knocking

Natural aspirated engine

Auto ignition

Engine speed (rpm)

To

rqu

e (

Nm

)

October 2014 edition of SRI news

2012-01-1276

IntroductionWhat do we know about LSPI?

Normal

combustion

Knock

Super-knock

Pre-ignition

Spark-timing

Pcy

l

Crank

• Problem exacerbated with high power-density engines (downsizing)

• Contrary to ‘classical knock’, it cannot be eliminated by spark-timing delay

• Contrary to ‘classical knock’, it can instantaneously damage the engine

• Lubricant and its additive package are involved

• Fuel blending and its properties also play a crucial role


Normal

combustion

Knock

Super-knock

Pre-ignition

Spark-timing

Pcy

l

Crank

• LSPI synopsis:• Pre-ignition stage (prior to spark timing)• Slow heat release stage due to flame propagation which is similar to

normal combustion• Super-knock: fast heat release due to large amount of unburnt

mixture auto-igniting in one go

IntroductionDifference between LSPI, pre-ignition and super-knock?

Although sometimes interchangeable,

‘pre-ignition’ and ‘super-knock’ represent

2 different phenomena

– Pre-ignition: combustion of fuel/air mixture

triggered by ‘hot-spot’ prior to the spark

timing

– Super-knock: severe engine knock (fuel

auto-ignition) resulting of in-cylinder

conditions (pressure, temperature)

Contents

• Introduction

• Influencing parameters

• LSPI mechanism – focus on combustion

• LSPI – combustion process

• Ignition Quality Tester (IQT)

• Conclusion


Influencing parameters

Influencing parameters on LSPIOverview

• Many factors can affect LSPI

• Engine hardware design (injection system, piston rings, etc.)

• Engine operating conditions (temperature, pressure, mixture composition,

etc.)

• Gasoline fuel properties

• Deposits

• Lubricant


Influencing parameters on LSPIAdditives

0

2

4

6

8

10

12

14

0

20

40

60

80

100

120

LSP

I e

ven

ts

% Calcium

SwRI HSHL Average GM Engine

ILSAC GF-5

products


0

2

4

6

8

10

12

14

0

20

40

60

80

100

120

LSP

I e

ven

ts

% Magnesium

GM engine

SwRI engine



0

20

40

60

80

100

120

140

160

180

200

LSP

I E

ven

ts

% ZDDP

SwRI engine

Influencing parameters on LSPIBase stocks

Gp I Gp II Gp III PAO PAO(High Visc)

LSP

I fr

eq

ue

ncy

Data from [SAE 2012-01-1615]

Gp I Gp II Gp III PAO PAO(High Visc)

Ign

itio

n f

req

ue

ncy

Data from [SAE 2014-01-1213]

LSP

I e

ven

t

GM engine Ford engine

Gp II Gp III Gp III+ Gp IV Gp V


LSPI mechanism – focus on combustion

Oil film

Injector

Fuel + Oil

Spray

Step 1: pre-ignition

Hot-spot ignition triggered by oil /

additive combustion properties

LSPI mechanism: Proposed synopsis

Fuel liner wetting


Step 2: Following combustion

process

(flame propagation)

Oil film

Injector

Fuel + Oil

Spray




Fuel liner wetting


Step 2: Following combustion

process

(flame propagation)

Oil film

Injector

Fuel + Oil

Spray




Step 3:

Super-knock

(fuel auto-ignition)

•Hardware (small vs large

bore, etc.)

•Operating conditions (spark

timings, etc.)

•Fuel/oil mixture and mixing

– Lube formulation

– Fuel properties

Fuel Liner wetting



LSPI – combustion process

Combustion processWhy is pre-ignition not always followed by super-knock?

– Flame propagation development

Auto-ignition

Unburnt

Gas

Flame

propagation

• LSPI synopsis:

– Early auto-ignition

– 2nd auto-ignition(s) or spark event is (are) followed by:

a) Combustion extinction (no flame development)

Normal

combustion

(envelope)

Pre-ignition + flame

propagationPre-ignition

Spark timing

Pcyl

°V




Unburnt

Gas

Flame

propagation

• LSPI synopsis:




b) Flame propagation

Normal

combustion

(envelope)



Spark timing

Pcyl

°V

Flame

fronts



Unburnt

Gas

Flame

propagation

• LSPI synopsis:





Normal

combustion

(envelope)



Spark timing

Pcyl

°V

Flame

fronts

-auto-ignition heat release is too weak

-initiated initial flame kernel is too small

-fuel properties }




• LSPI synopsis:





c) Detonation (succession of auto-ignitions)

Normal

combustion

(envelope)



Spark timing

Pcyl

°V

Super-knockFlame

fronts

Succession

of auto-ignition



• LSPI synopsis:





c) Detonation (succession of auto-ignitions)

Normal

combustion

(envelope)



Spark timing

Pcyl

°V

Super-knockFlame

fronts

Succession

of auto-ignition

- acoustic/combustion coupling

- hardware design


Combustion processCombustion theory: deflagration vs detonation

Sound speed

‘reaction’ front

velocity

�

�ξ =

• Two conditions are needed to initiate a coupling between pressure waves

and the 2nd AI front

– An auto-ignition propagation velocity close to the one of pressure waves (called here ξ)

Combustion processCombustion theory: deflagration vs detonation

Subsonic deflagration = classical flame

propagationSound speed

‘reaction’ front

velocity

Time for maximal

heat releaseTime for pressure wave to go

out from the end gas region

�

�ξ =

��

��ε =

Supersonic reaction wave propagation

Developing and developed detonation

• Two conditions are needed to initiate a coupling between pressure waves

and the 2nd AI front

– An auto-ignition propagation velocity close to the one of pressure waves (called here ξ)

– A smooth gradient in the fresh gases surrounding the initial auto-ignition spot (called

here ε)


IQT – Ignition Quality Tester

Ignition Quality TesterObjectives

• In auto-ignition mechanism, there are two driving mechanisms:

– Creation of radicals through branching reactions which is an important

mechanism for low temperature chemistry

– Run-away due to large heat release and

temperature increase which is more important

for high temperature kinetics

– IQT has the potential to focus on both mechanisms


Ignition Quality TesterPrinciple of measurements

• Either pure oil or mixture of oil and fuel were tested

Injection nozzle

body

ττττig

Injector

displacement

Bomb pressure

EN228 Surrogate

RON 95.0 95.0

MON 85.0 85.0

H/C ratio 1.801 1.801

O/C ratio 0.011 0.011

Density (g/mol) 94.3 94.3

Surrogate

Ignition Quality TesterGasoline surrogate design

Real EN228 Gasoline

Linear

paraffins

Branched

paraffins

Cyclic

paraffins

Aromatics

OlefinsOxgenated

n-Heptane

Isooctane

Cyclohexane

Toluene

CyclohexeneEthanol

Gasoline surrogate has been designed to target auto-ignition properties following methodology defined by Pera and Knop[1,2,3]

[1] Pera and Knop, Fuel 2012 – [2] Knop et al, Combust Flame 2013 – [3] Knop et al Fuel 2014


Ignition Quality TesterResults

50

60

70

80

90

100

10

20

30

40

RO

ND

CN

Mass Oil A in Sur95f

DCN RON (Estimated)

IQT

DCN ↔ RON Correlation

Pure Fuel Fuel + oil

• Various Ca and Mg concentrations showed no statistically measurable

difference in the IQT

• Addition of peroxide increased oil/fuel reactivity but showed again no

sensitivity to the IQT to Ca / Mg content

– This result seems to indicate that Ca does not play a role either in

the initiation or the branching reactions of the oil auto-ignition

in the gaseous phase

DC

N

Mass oil in fuel

Gasoline

Various Ca and /or

Mg concentration



• Largest effect on IQT ignition appears to be the general chemical

identity of the base oil

– Increased hydrocracking as group number increases through Group I

→ Group IV

10

15

20

25

30

35

40

45

Group I Group II Group III Group IV Group V

DC

N

25% mass Oil in

Sur95f

Sur95f

Average

+


Conclusion


• Base oil and additives play a role on LSPI mechanisms subject to test

conditions (hardware, operating conditions, others)

• LSPI mechanism involves intricate sub-mechanisms

– Combustion is one of them

Conclusion

• No discernible impact observed for Ca and Mg additives in the IQT

– No catalytic effect of Ca on auto-ignition in the homogeneous gaseous phase

• Large impact by base oil chemistry (Groups I-V) on auto-ignition in the IQT

– Reactivity ranking is: Gp I < Gp II < Gp III < Gp IV (Gp IV is the one that auto-ignite the more easily)

– Some Gp V base oils are very resistance to auto-ignition

Conclusion

Step 2:

Flame propagation

Oil film

Injector

Fuel + Oil

Spray

Step 1:

pre-ignition

Step 3:

Super-knock

Fuel Liner

wetting


Talk to us at exhibition stand 10

Dr. Cecile Pera, Senior [email protected]

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UNITI Mineral Oil Technology Congress - umtf.de - LSPI - lubricant... · Low speed pre-ignition Turbocharged engine Knocking Natural aspirated engine ... • LSPI synopsis: ... combustion