Low speed pre-ignition (LSPI) is a limiting phenomenon for several of the technologies being pursued as part of the low carbon agenda. To achieve maximum power density and efficiency engines are being downsized and turbocharged, while Direct- injection technologies are becoming ever more prominent. All changes that increase the propensity of LSPI. The low speed-high load operation envelope is limited due to LSPI. Hydrogen engines are also being explored, however, with such a low minimum enthalpy of ignition, LSPI is a major limitation to thermal efficiency. Several techniques are utilized in this study to investigate physical and physio-chemical aspects of lubricant initiated LSPI. Where possible attempts have been to validate methodologies or directional alignment with published data. The basis of the methodologies used is a validated 1D predictive combustion model of a single cylinder GTDI engine, that was used to provide simulation boundary conditions.
The study comprises of two parts; the first part of the study investigates the likelihood of hydrocarbon components within the lubricant causing LSPI. All aspects of hydrocarbons will be investigated including hydrodynamics behaviour between ring-liner, transport from crevice volume to combustion chamber, evaporation and reaction/heat release. A justification is provided for why lubricant hydrocarbons demonstrate ignition in rapid compression machines but not in engines.
The second part of the study investigates the behaviour of Ca and Mg based lubricant detergents inside an engine environment. With the use of a single particle ignition model a corroborated explanation is offered as to why LSPI occurs with Ca and not Mg. A sensitivity study is completed to assess how deviations in the assumed boundary conditions impact the time of ignition. The predicted heat release from a Ca particle is then represented inside a static air-fuel volume to observe the nature of heat propagation. Finally, the paper combines findings from the hydrocarbon and detergent studies to postulate a novel theory for why LSPI occurs at an appropriate timing to subsequently cause Mega Knock.