The investigation on the influence of swirl induced piston on the diesel engine characteristics powered using papaya biodiesel blends was studied. Papaya oil biodiesel, extracted from papaya seed, was blended by volume ratio of 25:75, 50:50, 75:25, and 100:0 with diesel and tested in a diesel engine. The fuel properties of the biodiesel blends were tested and a detailed fuel characterization was performed to analyze their feasibility as a partial substitute fuel. The experimental research study using a standard piston revealed that the B25 blend (25% papaya seed biodiesel, 75% diesel) shows Brake Thermal Efficiency (BTE) close to that of sole diesel. In order to improve the engine performance and pollutant emission for the B25 blend, a slight modification on the piston bowl geometry was introduced. Based on this, six helical holes with diameters Φ2, Φ2.5, Φ3, and Φ3.5 were drilled on four different piston crown surfaces to enhance the swirl ratio and turbulence. A numerical investigation was performed initially with modified piston geometries to understand the fundamental effects of swirl air motion due to piston modification. The numerical investigation results show that Φ2.5 mm hole size piston produces better swirl motion with increased uniform swirl velocity. The turbulent kinetic energy for the modified piston was higher compared to convention piston due to swirl enhancement. With this justification, investigation of the B25 blend was performed experimentally with three different pistons having six helical holes of size Φ2, Φ2.5, and Φ3 mm respectively. The experimental results showed improved engine characteristics for Φ2.5 mm hole piston due to swirl enhancement as indicated in the numerical study. The BTE with Φ2.5 mm hole piston for the B25 blend was 5.6% higher when compared to the conventional piston for diesel fuel. On the other hand, exhaust emissions such as HC, CO & Smoke are decreased with Φ2.5 mm hole piston for B25 blend by 17.9%, 30.5%, and 11.6% when compared to the conventional piston for diesel fuel.