**Abstract**

Biodiesels are the promising sources of alternative energy. Combustion phenomenon of blended biodiesels differs to those of diesel due to changes in physio-chemical properties. Experimental investigations are costly and timeconsuming process, whereas mathematical modeling of the reactive flows is involved. This chapter deals with combustion simulations on four-stroke singlecylinder direct injection compression ignition engine running at a constant speed of 1500 rpm, injection timing of 25° BTDC with diesel and 20% blend of Jatropha biodiesel. Standard finite volume method of computational fluid dynamics (CFD) is capable of simulating two-phase engine flows by solving three-dimensional Navier– Stokes equations with k-ε turbulence model. Combustion simulations have been carried out for half-cycle by considering the two strokes compression and expansion at zero load condition. The model mesh consists of 557,558 elements with 526,808 nodes. Fuel injection begins at 725° and continues till 748° of the crank angle. Charge motion within the cylinder, turbulent kinetic energy, peak pressure, penetration length, and apparent heat release rate are analyzed with respect to the crank angle for diesel and its B-20 Jatropha blend. Experimental data supports the simulation results. B-20 Jatropha blend possesses similar characteristics of diesel and serves as an alternative to diesel.

**Keywords:** combustion, simulation, crank angle, compression, fuel spray
