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The aim of this study is numerical investigation of a evaporating and non-reacting diesel spray operating in a high pressure and high temperature constant volume combustion chamber, as an essential step in simulation of liquid fuels combustion. To this end, the impact of droplets diameter distribution on estimating two critical characteristic parameter i.e. liquid and vapor penetration lengths is studied using the open-source OpenFOAM code. In order to determine droplets diameter distribution effect, three different distribution ranging from 0.25-100 micron is chosen and the liquid and vapor penetration lengths are individually calculated for each distribution. The results are validated against the experimental data published by Sandia National Laboratory. The results show while the droplets diameter distribution has a remarkable effect on the predicted value of the liquid length, so that leads to overestimate liquid penetration lengths up to more than two times; its effect on the vapor length prediction is negligible. Also assuming a nozzle diameter distribution leads to non-physically increase in the value of liquid length. This non-physically prediction may lead to misleading prediction of spray impingement to piston and the cylinder walls resulting an error in unburnt hydrocarbons concentration as well as the engine efficiency estimation.