The spray characteristics of fuels greatly influence the emissions from diesel engines. Spray development plays a vital role in improving the combustion and emission characteristics of fuels because it directly affects the air-fuel mixture formation. The spray characteristics of fuels depend mainly on the fuel injection process, fuel density, fuel viscosity, ambient pressure, and temperature. Among these, the effect of fuel injection pressure and fuel viscosity is a very important parameter directly affecting spray structures. This study investigates the effects of viscosity of fuel on pre-heating. The spray characteristics such as spray angle and spray tip penetration in a constant volume chamber under non-evaporating conditions are carried out by Mie scattering techniques and using Image J software. The Weber number, Reynolds number, and air to fluid density ratio dimensionless numbers were used to capture the primary forces including the inertia, surface tension, and aerodynamics. The experiments were carried out for different pre-heat temperatures. For the fuels and temperature-pressure conditions evaluated, the Weber number varies from 3000 to 120 000, the Reynolds number varies from 10 000 to 63 000. The result of the macro analysis shows that an increase in the fuel temperature leads to a decrease in viscosity and density, thereby increasing the spray tip penetration.