The model of a jet atomization and spray formation in a diesel engine is presented. The jet is assumed to have a shape of Rankine's ogive body, and the related potential of air flow past the body is applied. The quasi-continuous, high-frequency dispersion from the unstable part of a jet surface caused by hydrodynamic instability of a gradient flow in conjugated (gas-liquid) boundary layers is adopted as an atomization mechanism. The Karman-Pohlhausen technique is used to calculate the conjugated boundary layer thickness distributions at both, air and fuel, sides of the jet surface, as well as the interface velocity. This problem is simplified, making use of the linear approximation of the conjugated velocity profile, which theoretically allow the jet drag coefficient. The main assumptions and numerical scheme of the spray formation are the extensions of the previous model of a drop atomization. The modeling at lower level solves the mechanics of atomization and gives initials to the upper-level modeling of spatial aerodynamics of the evaporating spray generated by the atomizing jet. The evaporating spray ballistics are rendered as multi-velocity equations in dynamic 4-D space, and the CFD method is used to investigate the problem at an early stage. A comprehensive mapping of the droplet-phase and vapor fields in the diesel jet spray is obtained. The transient spatial distributions of the droplet-phase mass and number densities, as well as the vapor density, droplet mean diameters, and polydispersity within the spray are described. Analysis of the calculated data shows the existence of aerodynamic mechanism of fuel-air mixing, which scatters the fuel droplets in the radial traverses of a spray.