Experimental Investigation on the Characteristics and on the Reproducibility of the Flow issuing from a High-Pressure Direct-Injection Nozzle 1999-01-3655

This paper presents an investigation on the experimental determination of some characteristics of the flow issuing from a swirl injector dedicated to direct-injection spark-ignited engines. The reproducibility, from one injection to another, of the temporal evolution of the liquid flow characteristics during the opening of the injector was investigated. This was achieved by using a high-speed film camera set at 8,000 images/s. The resulting visualizations allowed us to measure the evolution of the penetration length and velocity as well as of the liquid cone angle. It was found that the spray produced is a low momentum spray whose penetration length and velocity are small. The good reproducibility of the temporal evolution of the liquid flow characteristics has been obtained, except for the liquid cone angle during the opening stage. A fast-shutter video camera was also used to make images of the early development of the issuing liquid flow. These images were analyzed by a tomographic deconvolution technique that allowed us to get an information on the flow structure. It was found that this image analyzing procedure provided interesting quantitative results. For instance, as soon as 0.35 ms after the injection command, i.e., 0.05 ms after the very beginning of the liquid exit, the issuing liquid flow whose penetration length is equal to 5 mm, already shows an hollow structure 0.7 mm downstream the nozzle. Furthermore, the results obtained here indicate a rapid development of the flow inside the nozzle as well as outside (up to 3 mm) and the reduced influence of the opening stage.