Low-Speed Pre-ignition (LSPI) is an undesirableabnormal combustion phenomenon observed in turbocharged,direct-injection spark-ignition engines and ischaracterized by early heat release, high cylinder pressuresand severe, potentially damaging knock. LSPI has beenstudied for more than a decade and engine design, operatingconditions and fuel and engine oil formulations have all beenidentified as contributing factors. A significant focus onengine oil has led to the establishment of the Sequence IXengine test and the second-generation of GM dexos® oilrequirements, as well as a convergence of engine oil detergentcausality. Conclusions about the effects of fuel on LSPI havebeen more varied, but as part of a recently completed researchconsortium, the LSPI tendency of market fuels with a rangeof properties, including composition, boiling point distribution,ethanol content and particulate matter index (PMI) wereevaluated. Tests were performed in a 2-liter GM LHU engineand each test comprised of at least 24 repeats of a high-load,low-speed, steady-state test segment, with engine boundaryconditions and calibration adjusted to amplify LSPI. Allmarket fuel tests were bracketed by baseline tests and severityadjustments were made to account for changes in enginecondition. It was found that the PMI and certain boilingpoints correlated the best with the frequency of LSPI events.In addition, decreased LSPI severity, quantified by the peakto-peak knock values, was found to correspond with increasedoctane numbers and higher ethanol content of the market fuels.
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