Study of Preignition Appearance in a Ultra Super-charged Gasoline Engine

The authors investigated the causes of how a preignition occurs in a highly boosted gasoline engine from both experimental and theoretical viewpoints. As a result, three processes are derived; i) small oil droplets coming out during compression stroke cause autoignition and become the source of preignition, ii) oil droplets coming out during exhaust stroke burn and CaO particle as residue included in oil as an additive becomes the preignition source, and iii) deposits peeled off from the combustion chamber are heated by combustion and become the preignition source in the next engine cycle. Many experimental facts can be adopted to either process. As a result, the reduction of CaCO3 in lubricating oil and preventing oil from coming out into the cylinder are radical solutions to reduce preignitions. Combustion strategy of strong miller cycle and LPEGR were also studied and compared in very high BMEP condition. Finally IMEPg of 3 MPa at 1500 rpm was achieved by using a single cylinder test engine equipped with 2-stage mechanically supercharged intake system.