A high speed acquisition system has been developed with the purpose of studying the behaviour of unsteady liquid fuel jets in a test chamber. The influence of fuel type, injection pressure and chamber conditions are of concern. The working principle of the instrument is based on the backlight photography technique. Instead of a photographic plate, a rectangular matrix built with an array of 300 photodetectors is used. The spatial resolution can be changed by appropriately changing the optics. The time resolution ranges from one microsecond to one millisecond, with a storage capability of 2048 frames. This allows to study liquid jets produced by short, high pressure pulses, that seem to improve the performances of diesel engines and reduce the formation of black smoke. Preliminary tests have been successfully conducted on single shot spray injections of diesel fuel. In particular, spray angle, penetration, and velocity can be easily evaluated.