Combined Effects of Engine and Oil Age on Low Speed Pre-Ignition 2019-01-0033
Low speed pre-ignition (LSPI) is a well-established phenomenon that occurs in boosted, direct injection, spark ignition engines. The impact of lubricant formulation has arguably received the most attention, leading to the introduction of the Sequence IX test for LSPI as part of the API SN Plus lubricant service category. This test, as with most other LSPI evaluations, evaluates the performance of fresh oil. A handful of papers have started addressing the effect of both engine and oil age on LSPI during both test-stand and in-vehicle studies. The current paper adds to this body of knowledge by analyzing results from multiple test-bench installations of the GM 2.0L LHU engine platform. For each engine, multiple tests, each comprising of multiple segments of a high load, low speed test point, known to amplify the occurrence of LSPI, were analyzed to investigate the combined effect of oil and engine age on LSPI activity, using a known baseline lubricant.
As previously reported, the average LSPI activity for successive tests shows an overall downward trend as the engine as it ages. The current research revealed that within each of the tests, comprising at least 12 hours or 24 segments, there is a general diminishing trend of LSPI activity. It is believed that this trend is associated with increased levels of fuel dilution and a commensurate reduction in the concentrations of detergent metals, which is known to contribute to LSPI.
A comprehensive statistical analysis was performed to discern segment-to-segment variability - which could be attributed to both oil and engine aging - as well as test-to-test variability – which is predominantly due to engine aging. The analysis was able to separate these effects, as well as the impact of engine-to-engine variability. Some information about the impact of different lubricant formulations on the LSPI activity trends is also presented.
Andre Swarts, Travis Kostan, Vickey Kalaskar
Southwest Research Institute
International Powertrains, Fuels & Lubricants Meeting