The mixture formation process in diesel engines consists of injection by which fuel is divided into small droplets, heating and evaporation of fuel, and mixing of fuel droplets and air in the combustion chamber. In other words, the shape and position of combustion chamber, fuel injection and air motion play a crucial role in the formation of mixture. Thus, many studies have been carried out in order to improve the mixing performance of fuel and air in the cylinder and improve combustion efficiency.
However, it was not fully taken into account that mass flow rate of intake air could be reduced when air swirl intensity was increased, while changing the inlet channel profile and the helical spiral shroud (HSS) shape of the intake valve. In addition, some attempts have been made to increase the air swirl and turbulent kinetic energy (TKE) by changing the shape of combustion chamber, but little study has been focused on improving the in-cylinder airflow characteristics by changing the eccentricity of combustion chamber.
Sin Mun Hak, a researcher at the Faculty of Mechanical Science and Technology, investigated the variation of in-cylinder swirl intensity and TKE depending on the eccentricity of combustion chamber. To this end, he conducted simulations of six series of eccentric combustion chambers.
The results showed that the air swirl intensity and turbulent kinetic energy in the combustion chamber increases as the y-axis eccentricity of combustion chamber is placed on the eccentric direction of injector and the x-axis eccentricity increases gradually from the centre of cylinder to the direction of injector. It was also shown that when the eccentricity is too large, there will be a drop in the fuel spray jet velocity or airflow separation in the region of mixture formation, resulting in a gradual increase in power and torque and then a decrease over a certain limit.
For more information, please refer to his paper “Effect of Combustion Chamber Eccentricity on In-Cylinder Air Flow and Combustion Process in Direct Injection Diesel Engine” in “Proceedings of KUTIC-2025”.