Page 43 - Fuels & Lubes International 2013 - Quarter 3

43 FUELS & LUBES INTERNATIONAL Quarter Three 2013
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Interestingly, it’s been shown that
lubricating oil composition and properties
could play a role in inducing LSPI. At the SAE
Asian Steering Committee Colloquia, held
in conjunction with the 19th Annual Fuels &
Lubes Asia Conference in March in Bangkok,
Satoshi Hirano, chief of engine oil development
at Toyota Motor Corp.’s Engine Division,
discussed the latest research on LSPI.
LSPI Phenomenon
The latest turbocharged DI-SI engines
have led to better torque values at lower engine
speeds, as compared to the conventional
naturally aspirated or even turbocharged
gasoline engines. These features make the DI-SI
engines more efficient and less polluting. This
can be seen from the adjacent graph, which
shows the Brake Mean Effective Pressure
(BMEP) vs. Engine Speed.
Hirano explained a theory that has been
put forward regarding the lubricant-induced
occurrence of LSPI. As per the theory, oil
droplets escape through the piston top land
crevice area and get vaporized since the
temperature inside the combustion chamber
is very high due to the presence of compressed
air. These vapors then ignite spontaneously due
to high temperature and in turn they ignite the
fuel by providing the necessary heat to initiate
combustion before the spark plug could
actually do so at the pre-determined time and
crank angle, leading to the phenomenon of
pre-ignition.
Toyota and Nippon Soken, a research
institute funded by Denso Corp. and Toyota,
carried out tests to study LSPI using a
turbocharged direct ignition L4 engine and
a premium grade gasoline available in Japan.
Basically the test consisted of running the
engine at 4,000 rpm to remove any deposits.
The rpm was then reduced to 1,800 to check
for the LSPI phenomenon by measuring the
frequency of its occurrence in one hour. In this
test, the engine control was tuned to make LSPI
occur more frequently intentionally to evaluate
lubricating oil response.
These tests were used to determine the
effects of lubricating base oil and detergent
additives in the engine oil. The researchers
used different quantities of calcium (Ca),
phosphorous in the form of Zinc Di-Alkyl-
Dithio-Phosphate (ZnDTP), molybdenum as
Molybdenum Di-Thio Carbamate (MoDTC)
and phenolic antioxidants (Phenolic-AO).
ILSAC GF-5 type oils were used as the baseline.
The amount of these additives was varied.
The bove-menti ned experiment was used to
study the variations in LSPI frequency under
different conditions. The tests were also checked
statistically and results showed that they had
good repeatability.
Calcium showed the most dominating
effects on LSPI frequency as increased calcium
detergent raised LSPI frequency, Hirano said.
In fact, the impact was so strong that raising
the percentage of Ca from 0.1 to 0.2% increased
LSPI frequency by a factor of three. However,
further increase to 0.3% had an insignificant
effect on LSPI frequency.
Molybdenum and phosphorus on the other
hand, showed good suppression abilities as the
LSPI frequency decreased when these elements
were increased. At values of 0.07% and 0.15% by
mass of MoDTC and ZnDTP respectively, LSPI
disappeared. The contribution of Phenolic AO
was not found to have any significant effect on
LSPI frequency in any manner.
The tests also confirmed the substantial
decrease in LSPI frequency without the
detergent. Experiments were conducted on
GF-5 oils and two samples were compared, with
and without detergent, which showed that in
the case of the sample without detergent, the
LSPI frequency was substantially lower than the
oil sample with detergent.
Toyota researchers carried out further tests
to confirm whether the hypothesis of oil droplet
evaporation and ignition occurred mainly due
有趣的是，滑润油成份和性质在引发LSPI中
起着一定的作用。在三月于孟买与第十九届燃
料油与润滑油年会同时举办的SAE亚洲指导委
员会对话中，丰田汽车发动机部门发动机油开
发主管Satoshi Hirano讨论了有关LSPI的最新
研究成果。
LSPI现象
与常规的自然吸气式甚至增压式汽油机相
比，最新的增压DI-SI发动机在低速时扭矩更
大。这些特征使得DI-SI发动机效率更高，污染
更少。这从边上的图中可以看出，图中显示了制
动有效压力中值与发动机速度的对比。
针对由润滑油引发的LSPI，Hirano提出了
一个理论。根据该理论，由于燃烧室内空气被压
缩，温度很高，油滴从活塞顶部裂隙处逃离后蒸
发。在火花塞达到预定的时间和曲轴角度点火
之前，这些蒸汽由于高温而自燃，从而提供最初
燃烧所必须的热量点燃燃料，导致了提前点火
的现象。
由电装（Denso Corp.）和丰田资助的研究
机构丰田和日本总研电气（Nippon Soken）进
行了研究LSPI的试验，它们使用了增压直喷L4
发动机和日本销售的高质量汽油。试验中发动
机以4000RPM的速度运行，以消除任何积碳。
然后把转速降到1800RPM，通过测量一小时内
发生的次数来检查提前点火的现象。在试验中，
Source: 2012-01-1615, Published 09/10/2012, Copyright © 2012 SAE International
doi:10.4271/2012-01-1615, saefuel.saejournals.org