Numerical Simulation to Understand the Cause and Sequence of LSPI Phenomena and Suggestion of CaO Mechanism in Highly Boosted SI Combustion in Low Speed Range 2015-01-0755

The authors investigated the reasons of how a preignition occurs in a highly boosted gasoline engine. Based on the authors' experimental results, theoretical investigations on the processes of how a particle of oil or solid comes out into the cylinder and how a preignition occurs from the particle. As a result, many factors, such as the in-cylinder temperature, the pressure, the equivalence ratio and the component of additives in the lubricating oil were found to affect the processes. Especially, CaCO₃ included in an oil as an additive may be changed to CaO by heating during the expansion and exhaust strokes. Thereafter, CaO will be converted into CaCO₃ again by absorbing CO₂ during the intake and compression strokes. As this change is an exothermic reaction, the temperature of CaCO₃ particle increases over 1000K of the chemical equilibrium temperature determined by the CO₂ partial pressure. The possibility of a preignition due to particles including CaCO₃ particles is numerically simulated comparing with the experimental results.