Numerical Study on the Effects of Tumble and Swirl on Combustion and Emission Characteristics of an LPG Direct Injection Engine

Recently, global warming caused by greenhouse gases has been highlighted, so many studies have been carried out for developing eco-friendly products. In the vehicle industry, various techniques have been developed for eco-friendly engines. A previous fuel injection system, injecting fuel at the intake port, had difficulty precisely controlling the air/fuel ratio in the cylinder. Therefore, the fuel injection system has been changed to a direct injection system injecting fuel directly inside the cylinder. Due to concerns about fossil fuel depletion and the instability of oil prices, various alternative fuels are currently becoming popular. Liquefied petroleum gas (LPG) is an alternative fuel that has similar characteristics to gasoline. LPG can be used in gasoline engines without sophisticated modification of the engine. For these reasons, the present work focuses on a numerical investigation of the combustion and emission characteristics of LPG direct injection (LPDI) engines by using tumble and swirl. For conducting the simulation, commercial software STAR-CD ver. 4.26 was used. The study was performed at the minimum spark advance for best torque (MBT) of the stoichiometric excess air ratio (λ = 1.0) and the lean-burn excess air ratio (λ = 1.5) with changes in the intake port geometry to induce in-cylinder flow changes.