Enlargement of Auto-Ignition Regions by Applying a Stratified Charge Concept

The auto-ignition attracts researchers as an ultimate combustion method that could simultaneously reduce fuel consumption and NOx emissions. The authors have studied auto-ignition combustion in the two-stroke gasoline engines aiming at vehicle engine applications. However, our attempts were in an impasse with the onset of irregular combustion in the lower speed and the extremely lower load range. As a solution for this problem, this paper proposes a new auto-ignition concept, i.e. Stratified Charge Auto-Ignition (SCAI), which focuses on the thermal distribution and mixture formation in the combustion chamber. Visualization of the direct injection spray formation was conducted first, and then a combustion chamber design was determined by using a CFD simulation, so as to form a mixture at the hottest spot in the combustion chamber. As a result, the auto-ignition regions were remarkably enlarged toward the lower speed and lower load, and the HC emissions decreased by 20% while the fuel consumption and NOx emissions remained in the same level with those of the conventional Homogeneous Charge Auto-Ignition (HCAI).