Investigation of the Piston Bowl Shape Effect on the Diesel Spray Development

Abstract

The combustion in a diesel engine is a very complex process. Even more when compared to a gasoline engine where the combustion is triggered using spark plugs, since the diesel engine depends on the auto ignition of the fuel-air mixture. This auto ignition phenomenon depends on many variables, especially on the fuel-air mixing condition and this makes the piston bowl geometry an important role on the combustion characteristics of diesel engines. Each piston bowl design was tailored to work well under certain specific conditions. The usage of biomass diesel mixtures in diesel engines increases the fuel viscosity and requires that the piston bowl geometry is carefully studied. The objective of this study is to compare the effect of certain piston bowl shapes, namely the Flat Bottom to the diesel spray development. Simulations were done using the ANSYS FLUENT 16.1 computational fluid dynamics (CFD) software. The simulation was performed on different injection pressures of 40 and 100 MPa, with the ambient temperature in the combustion chamber that is holding the piston at 500 and 900 K. Results showed that if the pressure and ambient temperature increase, the spray cone angle increases. In addition, the geometry shape of the piston bowl makes the spray to head downward after the wall impingement to the bottom section and prevents spillage of fuel over the piston bowl.