Kristin Fletcher, R&D Scientist at Afton Chemical presented the challenges facing the automotive industry with the phenomena of Low Speed Pre-Ignition (LSPI). She discussed the current legislative challenges facing car manufacturers and new technology that is able to meet those challenges. In addition, she reviewed relevant findings available in the literature demonstrating fuel and lubricant impacts on the frequency of LSPI produced in a test engine.

1. The Impact of Low Speed Pre-Ignition on Next
Generation Engine Oils
Kristin Fletcher
Ashu Gupta
Greg Guinther
KSTLE 2014

2. Who We Are!
Fuel
Additives
Gasoline Performance
Diesel Performance
Lubricity
Cetane Improvers
Combustion Improvers
Octane Improver
Finished Fuel Additives
Engine Oil
Additives
Passenger Car Motor
Oils
HD Diesel Oils
Medium Speed Diesel
Oil
Viscosity Index
Improvers
Components
Driveline &
Industrial
Transmission Fluids
Automotive Gear
Hydraulic, Tractor
Slideway, Turbine
Metalworking
Industrial Gear
Grease
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3. What I’m Going to Talk about Today
Low Speed Pre-Ignition – LSPI
 Current legislative challenges facing car manufacturers
 Their technology to meet those challenges
 How LSPI affects their technologies
 How LSPI occurs
 Contributing factors towards LSPI
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4. Legislative Challenges: Lower CO2
EU Baseline: 142
EU 2020: 95
US Baseline: 219
US 2025:107
Japan Baseline:131
Japan 2020: 105
China Baseline: 185
China 2015: 167
270
250
230
210
190
170
150
130
110
90
2000 2005 2010 2015 2020 2025
CO2 Emissions Normalised to NEDC (g/km)
EU US-LDV Japan China
1.9%
Annually
3.9%
Annually
2%
Annually
4.7%
Annually
(Source: Mahle Powertrain, UK)
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5. CO2 Enabler
The Downsized Gasoline Engine
Downsizing replaces larger engines with smaller engines
with additional technology
 Typically a turbocharger and direct fuel injection
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6. CO2 Enabler
The Downsized Gasoline Engine
(Graphs Source: Mahle Powertrain, UK)
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7. CO2 Enabler
The Downsized Gasoline Engine
2.0 litre N/A high-speed engine
MAHLE 1.2 litre D/S engine
0 1000 2000 3000 4000 5000 6000 7000 8000
Engine Speed [rev/min]
(Graphs Source: Mahle Powertrain, UK)
Corrected Torque [Nm]
300
250
200
150
100
50
0
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8. CO2 Enabler
The Downsized Gasoline Engine
Downsizing replaces larger engines with smaller engines with
additional technology
 Typically a turbocharger and direct fuel injection
Downsized engines in conjunction with suitable transmission
design give additional fuel economy gains through
Downspeeding
Downsizing & Downspeeding achieve fuel economy by
 Having fewer and smaller parts leading to less heat loss and friction
 Direct injection gives a cooling effect to allow high levels of
turbocharging
 Downspeeding lowers engine friction and pumping losses
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9. CO2 Enabler
The Downsized Gasoline Engine
(Graphs Source: Mahle Powertrain, UK)
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10. How Does this Link to LSPI?
Unfortunately, the most fuel efficient area for the
engine is also the area where it is most susceptible
to LSPI
LSPI
RISK
(Graph Source: Mahle Powertrain, UK)
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11. How Does this Link to LSPI?
Unfortunately, the most fuel efficient area for the
engine is also the area where it is most susceptible
to LSPI
As a result car manufacturers have to tune their
engines to avoid LSPI in the affected area
Typically achieved by injecting more fuel than
necessary – with detrimental effects on fuel economy
Therefore LSPI is a limiting factor of fuel
economy / CO2 reduction
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12. The Effect of Auto-Ignition / LSPI
(Picture Source: Southwest Research Institute, Tx)
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13. The Effect of Auto-Ignition / LSPI
(Graph Source: Southwest Research Institute, Tx)
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14. The Effect of Auto-Ignition / LSPI
(Pictures Source: Southwest Research Institute, Tx)
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15. What Could be Causing This?
Surface hot spots – LSPI imaging does not show auto-ignition
starting from just one point on the surface of the
engine [Zadeh et al., Dahnz et al, Palaveev et al.]
(Source: Copyright SAE 2014,
2011-01—0340, Zadeh et al)
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16. What Could be Causing This?
Surface hot spots – LSPI imaging does not show auto-ignition
starting from just one point on the surface of the
engine [Zadeh et al., Dahnz et al, Palaveev et al.]
LSPI does not lead to ‘run-away’ pre-ignition
LSPI increases with lower coolant temperature – contrary
to surface pre-ignition or knock
May be due to deposits / particles in the combustion
chamber soaked with fuel and oil and hot enough to start
combustion
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17. Proposed Mechanisms for Preignition
Possible Mechanisms
Release of Oil-Fuel Droplet
from Piston Crevice which
Auto-Ignites
Combustion Chamber
Deposits or Particles which
Initiate a Flame
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18. The Oil Droplet Theory
Droplets of lubricant and fuel mixed together enter
the combustion chamber
The inclusion of lubricant lowers the auto-ignition
temperature of the droplet [Amann et al., SAE 2012-01-1140]
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19. Fuel and Lubricant Mixing
AIR IN
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20. Combustible Fuel
& Air Mixture
Auto-Ignition
Velocity
Accel.
Fuel &
Air
Crevice
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21. The Deposit Mechanism
Suggests that deposits may flake off, heat up by the
exhaust gases and survive the gas-exchange process and
induce thermal ignition in the next cycle
Mechanism consistent with
 Fuel sensitivity (aromatic content and T90)
 Lubricant sensitivity (basestock quality, additives)
 High-speed visual images
SAE 2014-01-1218
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22. Why are These Engines Sensitive to LSPI?
Spray direction – direct injection engines allows
fuel onto cylinder walls
Side mounted injectors are worst [Zadeh et al., SAE 2011-
01-1140]
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23. Why are These Engines Sensitive to LSPI?
Spray direction – direct injection engines allows
fuel onto cylinder walls
Side mounted injectors are worst [Zadeh et al., SAE 2011-
01-1140]
Boost pressure – increases combustion chamber
temperature [Zadeh et al., SAE 2011-01-1140]
Engine speed – lower engine speeds allow more
time for the reactive fuel-oil mixture to auto-ignite
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24. Influence of Fuel Composition
RON and MON are not the best indicators for LSPI
resistance [Dahnz et al., SAE 2010-01-0355]
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25. Influence of Fuel Composition
RON and MON are not the best indicators for LSPI
resistance [Dahnz et al., SAE 2010-01-0355]
Less volatile and older fuel can increase LSPI as a
larger fraction remains with the lubricant on the
cylinder wall
High Aromatic content can increase LSPI - even
though aromatics are commonly used to achieve
octane [Amann et al., SAE 2012-01-1140]
Oxygenate content may reduce LSPI – due to their
low boiling point, requires further research
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26. Influence of Base Oil
Takeuchi et al. [SAE 2012-01-1615] evaluated different
base stocks in a prototype engine
 Found higher group numbers correlated with lower LSPI
frequency
(Source: Copyright SAE 2014,
2012-01—1615, Takeuchi et al.)
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27. Influence of Lubricant Additives
Calcium
Higher calcium levels correlate with higher LSPI
frequency [Takeuchi et al., 2012-01-1615, Hirano et al., 2013-01-2569]
(Source: Copyright SAE 2014,
(Source: Copyright SAE 2014, 2013-01-2569, Hirano et al.)
2012-01—1615, Takeuchi et al.)
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28. Influence of Lubricant Additives
Phosphorous and Molybdenum
Increasing molybdenum and phosphorus (through
ZDDP) levels decreased LSPI frequency [Takeuchi et al.,
2012-01-1615]
(Source both graphs: Copyright SAE 2014,
2012-01—1615, Takeuchi et al.)
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29. Lubricant Physical Properties
Takeuchi et al. [SAE 2012-01-1615] also evaluated
lubricant volatility using the Noack test
 There was no clear correlation between lubricant volatility and
LSPI
(Source: Copyright SAE 2014,
2012-01—1615, Takeuchi et al.)
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30. Lubricant Physical Properties
Takeuchi et al. [SAE 2012-01-1615] also evaluated
lubricant oxidative reactivity inferred by auto-ignition
temperature
 There was a clear
correlation between
oxidative characteristic
and frequency of LSPI
DSC = differential scanning
calorimeter
(Source: Copyright SAE 2014,
2012-01—1615, Takeuchi et al.)
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31. Wear Metals and Older Oils
Hirano et al. [SAE 2013-01-2569] also looked at lubricant
effects
 Simulated the impact of wear metals using iron and copper
• Found that in their presence LSPI frequency increased
 Similar to Takeuchi, also found that used oil may have higher LSPI
frequency
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32. Lubricants Require Holistic Formulation
Chain Wear
LSPI
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33. LSPI Lube Industry Tests Under Development
 ILSAC GF-6
• Ford 2.0L 4-cyl Ecoboost
 GM dexos1TM Gen II
• GM 2.0L 4-cyl Ecotec
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34. Afton’s Approach: Technology Driven Solutions
Afton are conducting a range of research/testing
programs in-house
 Fundamental / Basic research for improved understanding of LSPI
 Internal engine testing to support research is underway
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35. Afton’s Approach: Technology Driven Solutions
Afton are conducting a range of research/testing
programs in-house
 Fundamental / Basic research for improved understanding of LSPI
 Internal engine testing to support research is underway
Commercially available GF-5 technologies 5W-20 using
Group II base oils used as the baseline for LSPI tests
 Afton understands key drivers of LSPI performance
We are using optimal formulation strategies to develop Technology
Driven Solutions
Afton actively involved in the Preignition Prevention
Program (P3) - a joint program with Southwest Research
Institute, OEMs and other oil industry partners
 Characterizing the LSPI phenomenon
 Developing test conditions and platforms
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36. Summary of the Problem
OEMs
 Employ sub-optimal engine calibration to reduce LSPI risk
• Fuel enrichment, exhaust gas recirculation
 Sacrifice fuel economy
 Stronger engine components – higher cost and weight (degrading CO2)
Fuels
 Fuel characteristics appear to influence LSPI
 Current fuel specifications are not sufficient to capture LSPI
performance
Lubricants
 Industry developing tests to measure tendency for LSPI
 Optimal formulation strategies will be used to reduce risk of LSPI
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37. Conclusions
Downsized engines will only become more prevalent
in mature and emerging markets
Fuels and lubricants work together with the engine
as a system
Their combined performance is crucial to enable the
engine to realize its full potential
We must balance this new demand against the
existing requirements through the use of
relevant industry tests
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38. Acknowledgements
Many thanks to our technical partners who contributed to this
presentation
The Southwest Research Institute