Optical measurements of two cylindrical and conical heavy-duty diesel injector nozzels – A comparison of reference diesel, HVO, and RME fuels

•The findings of reactive and inert gas background measurements with two heavy-duty diesel injectors are presented.•It is generally accepted that the injector geometry has a major impact on the jet cone angle, jet cone area, and air-to-fuel ratio.•The cylindrical nozzle exhibits better mixture formation prior to ignition delay, which results in a faster flame initiation.•The flame lift-off length and the ignition time have an influence on the quality of the mixture formation downstream of the spray.