Lubricant-Oil-Induced Pre-ignition Phenomena in Modern Gasoline Engines: Using Experimental Data and Numerical Chemistry to Develop a Practical Correlation

Recent research on thermal reciprocating engines has focused on the influence of lubricant oil on the combustion process, which can lead to highly undesired super-knock events. Low-Speed Pre-Ignition (LSPI) events severely limit the further development of Direct Injection Spark Ignition Engines (DISI), preventing high efficiencies from being achieved. However, there is still a lack of knowledge about the fundamental mechanisms leading to LSPI, due to the complex phenomena involved and the interaction between lubricant oil and fuel. Understanding how the presence of lubricant oil traces affects gasoline chemical reactivity is an essential step for performing successful numerical simulations aimed at predicting the onset of LSPI phenomena. Reaction mechanisms able to predict oil-fuel interaction have been proposed, but they are computationally demanding. A simple analytical correlation was proposed to predict variations of gasoline ignition delay induced by the presence of lubricant oil, at different temperatures. Such a correlation was developed by taking into account both experimental data available in the literature and numerical simulations employing the “GasLube” reaction mechanism, developed for iso-Octane/n-Hexadecane mixtures. Operating conditions representative of those of typical turbocharged DISI engines were considered for the validation. The proposed correlation makes possible to accurately derive the ignition delay of gasoline/lubricant oil mixtures directly from the values related to pure iso-Octane (gasoline surrogate), avoiding the use of dedicated reaction mechanisms, and thus saving computational time.