We investigated the effects of injection parameters such as injection pressure, ambient pressure, and ambient temperature on spray characteristics. We calculated the turbulence occurring point ($t_c$), defined as the time required to generate a vortex, and the deceleration point ($t_b$), defined as the time when spray penetration begins to decelerate, to elucidate the breakup mechanism of the test injectors. The spray velocity coefficient ($C_v$) was obtained to evaluate the spray characteristics. As the ambient pressure increases in the case of a slit injector, $C_v$ decreases. We investigated the effects of nozzle tip shape according to injection pressure, ambient pressure, and fuel properties on spray characteristics and provide a $C_v$ value of 0.38 for the swirl injector with a spray angle of $60^{circ}$ and the slit injector under atmospheric conditions. The value of $C_v$ in the case of a slit injector was reduced by increasing the ambient pressure. Our results suggest that $C_v$ of a swirl injector is constant regardless of changes in ambient pressure, injection pressure, and fuel properties. On the other hand, $C_v$ of a slit injector is altered by changes in ambient pressure.