In the present work a constant-pressure flow facility able to reach 15 MPa ambient pressure and 1000K ambient temperature has been employed to carry out experimental studies of the combustion process at Diesel-like conditions. The objective is to characterize the influence of boundary conditions on OH* and broadband chemiluminiscence intensity generated by the fuel combustion for passenger car and heavy duty diesel injectors. Three nozzle types were investigated: a spray B nozzle (diameter of 90um) and two heavy duty application nozzles (diameter of 194 um and 228 um respectively). The results showed that nozzle size have a substantial impact on the ignition event, affecting the premixed phase of the combustion and the ignition location. Concerning OH, for the small nozzle geometry (Spray B) the ECN standard methodology was applied; meanwhile, for bigger nozzles a different processing method is proposed based on intensity threshold criteria. The effect of the nozzle size changed the combustion development in such way that the image processing methodology had to be customized, since the determination of the peak in the normalized intensity curve recommended by ECN was indistinguishable. For ECN nozzle geometry cases, the liquid length is shorter than the location of the ignition, with a phase transition in between. Nevertheless, for the bigger size nozzles the range of values obtained for Lift off Length are shorter than Liquid Length; therefore, there is a Liquid-Vapor-flame interaction in this region. This is an important fact that should be taken into account for the combustion process understanding and for further CFD models implementation. Finally, thanks to the broad range of tested conditions, the results have been analyzed statistically and empirical correlations were obtained.