Controlling LSPI is essential The drive to improve fuel economy means we can expect smaller, turbocharged, gasoline direct injected engines to be deployed more widely in all the key markets of the world in the coming years - making them increasingly susceptible to LSPI. Engineering solutions that have been shown to inhibit the occurrence of LSPI, such as the use of cooled exhaust gas recirculation, increased crevice volume, higher oil ring tension and chamfered piston heads can be implemented by OEMs. However, these solutions are not without drawbacks, including sacrifices in on-the-road fuel economy through timed engine management strategies, increased weight and/or increased material costs.
Optimal test conditions and data are key In Infineum’s view, the key step in investigating the fuel and lubricant effects of LSPI is to define a precise and repeatable method for collecting and analyzing the data. However, the disruptive nature and random occurrence of LSPI means this is not an easy task.
To examine the impact of different lubricant formulations, Infineum devised a test program using a General Motors engine, which was run on an industry standard fuel at Southwest Research Institute.
The study focused on stationary engine test equipment configured to deliberately generate LSPI events, and on the development of a statistically rigorous method to measure and quantify the data generated. Using this approach, consistent results have been obtained across the six test engines chosen.
The LSPI test consists of six segments: four at higher speed and load conditions, and two at lower speed and load conditions. All speeds were 2,000 rpm or lower to simulate the conditions that would generate sufficient LSPI events, while causing minimal damage to the engine and instrumentation.
A reference oil is run between every four or five test lubricants to confirm the efficacy of the approach and set the stage for a statistical study of the effects of various lubricant chemistries. Over the testing period the most frequently used reference oil generated more than 31,000 LSPI events. This data was used to quantify the precision of the engine test and allowed rigorous interpretation of the data.
LSPI research continues In Infineum’s view there is a sizable prize for the additive and lubricant suppliers who can minimise LSPI with a well formulated lubricant for a given fuel.
We will be continuing to explore this statistically rigorous approach to measuring and quantifying LSPI data, examining how it is being used to not only investigate the key effects of the lubricant, but also to identify the components that can quench or exacerbate LSPI.
Properties of the Reference Oil
We will also look at how this statistical approach can be refined for another engine platform that will be part of the upcoming ILSAC GF-6 engine oil standard.
LINK
www.infineuminsight.com
Infineum LSPI Test Conditions
Each LSPI test consists of four runs of 150,000 cycles and, for each cycle, data is collected at 0.5° crank angle resolution to provide adequate combustion analysis without creating an exceptionally large data file. The data consists of peak pressure, crank angle at 2% mass fraction burned, cycle number and engine cylinder.
At the end of each four hour run, approximately five gigabytes of measured and calculated data is generated for analysis.
The Infineum definition of LSPI in this study is outliers of peak pressure and/or crank angle at 2% mass fraction burned that exceed 4.7 standard deviations. Also, an LSPI event is one in which there are more than three ‘normal’ cycles both before and after each event.
LUBE MAGAZINE NO.134 AUGUST 2016
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