http://www.infineuminsight.com/insight/jun-2017/lspi-and-lubricant-auto-ignition
Detergent chemistry
The effect of calcium and magnesium based detergents on LSPI has already been the subject of Infineum studies. Calcium-based detergents have been shown to strongly promote LSPI while magnesium-based detergents appeared to have nearly no effect on LSPI. However, various calcium and magnesium concentrations have been observed to have no statistically measurable difference in the IQT for gaseous fuel/oil/air auto-ignition.
Peroxide was mixed with oil in order to focus the IQT auto-ignition study on the branching and the propagation chain of the combustion process. This addition of peroxide increased the reactivity but again showed no sensitivity to calcium or magnesium content. These results seem to indicate that the calcium does not play a role either in the initiation or the branching chemistry reactions of the oil auto-ignition in the gaseous phase.
Base stock selection
The largest impact on auto-ignition measured with the IQT came as a result of the general chemical composition of the base stock. In this test, different quality base stocks were added to the fuel samples.
Base stock choice has a significant impact on auto-ignition
The IQT tests highlighted that the propensity for auto-ignition increased from Group I to Group IV. We also noted that some Group V formulations are very resistant to auto-ignition (no auto-ignition promotion effect compared to pure fuel), which may be interesting for LSPI-resistant formulations.
Conclusions
LSPI is an extremely complex phenomenon including multiple intricate couplings, combustion being only one of these elements. However, many questions remain unanswered, in particular why calcium has an LSPI-promoting effect while magnesium does not. Perhaps further modification of the IQT to allow solid-phase auto-ignition (auto-ignition catalysed by a solid deposit) may help to answer this question.
Meanwhile, this experiment has enabled us to better understand the role of the base stock in LSPI mechanisms. Depending on the specific engine operating conditions and the type of LSPI, base stock selection could be a significant factor in the formulation of LSPI-resistant lubricants.
Not the first study I've read suggesting Grpll and lll being better than GrplV at keeping LSPI at bay. Sounds like a good case for synthetic blends (i.e., Ford's Motorcraft recommendation for some Ecoboost). This is a perplexing issue indeed.
Base stock choice has a significant impact on auto-ignition
The IQT tests highlighted that the propensity for auto-ignition increased from Group I to Group IV. We also noted that some Group V formulations are very resistant to auto-ignition (no auto-ignition promotion effect compared to pure fuel), which may be interesting for LSPI-resistant formulations.
Conclusions
LSPI is an extremely complex phenomenon including multiple intricate couplings, combustion being only one of these elements. However, many questions remain unanswered, in particular why calcium has an LSPI-promoting effect while magnesium does not. Perhaps further modification of the IQT to allow solid-phase auto-ignition (auto-ignition catalysed by a solid deposit) may help to answer this question.
Meanwhile, this experiment has enabled us to better understand the role of the base stock in LSPI mechanisms. Depending on the specific engine operating conditions and the type of LSPI, base stock selection could be a significant factor in the formulation of LSPI-resistant lubricants.
Not the first study I've read suggesting Grpll and lll being better than GrplV at keeping LSPI at bay. Sounds like a good case for synthetic blends (i.e., Ford's Motorcraft recommendation for some Ecoboost). This is a perplexing issue indeed.
