Comparison of Homogeneous, Stratified and High-Squish Stratified Combustion in a Direct-Injected Two-Stroke Engine

Gasoline direct injection (GDI) two-stroke engine technology has been developed for use in snowmobile applications. Applying GDI to a two-stroke engine significantly reduces emissions of unburned hydrocarbons and improves fuel economy by reducing the short circuiting of fuel that occurs in conventional carbureted two-stroke engines. The GDI design allows for two different modes of combustion, stratified and homogeneous. Stratified combustion is typically used during idle and light to moderate loads at low engine speeds while homogeneous combustion is used at moderate to high loads and medium to high engine speeds. This work presents the process and results of determining which mode of combustion provides better fuel economy during cruise point operation, and where the transition from stratified to homogeneous combustion should occur in snowmobile operation. Results are also presented regarding the effects of increased squish velocity on the brake specific fuel consumption and torque output during stratified operation. Results show that homogeneous calibration is the superior mode of combustion for the cruise points of a snowmobile.