A Study on Effect of Piston Bowl Shape on Engine Performance and Emission Characteristics of a Diesel Engine

Abstract

This paper presents a study on the effect of re-entrant piston bowl configuration on the emissions characteristics and engine performances of a direct injection (DI) diesel engine. In order to meet the emission norms, modern-day diesel engines rely on methods of in-cylinder emission reduction and expensive after treatment device. By using an effective piston bowl shape, one can reduce the in-cylinder emission and the cost increased for the after-treatment device with considerable increase in the engine lifetime. Six piston bowl shapes with various geometric configurations were selected for numerical simulations. Three-dimensional models of the piston bowl shapes and the combustion chamber were created using Pro-E and mesh was generated by using preprocessor ANSYS ICEM CFD. The flow characteristics inside the cylinder with these piston bowls were investigated under steady condition with the RNG k-e turbulent model using ANSYS Fluent. Numerical simulations under isothermal condition were carried out to select an optimum bowl shape. The mass flow boundary condition was used for inlet manifold and the value of this was measured from the experimental test. The CFD results of mean swirl velocity of the engine at different locations inside the combustion chamber were calculated. From the computational results, it was found that the average swirl number is increased from 0.87 (base shape) to 1.74 (modified bowl shape). It is well known that the swirl number is very important to enhance the homogeneity of air/fuel mixture inside the combustion chamber, which in turn improves the combustion efficiency. The experimental results shows that, as compared to the baseline engine 20 % reduced in hydrocarbons (HC) emissions and 24 % reduced in carbon monoxide (CO) for the engine with modified piston bowl shape. However, there is a small amount of reduction in engine performance. It is observed that the brake specific fuel consumption (BSFC) reduced significantly for all load conditions.