Flow characteristics of natural-gas from an outward-opening nozzle for direct injection engines

In this research article, we present for the first time an experimental investigative study on the flow characteristics of compressed natural-gas (CNG) issued from a direct injector with an outward-opening nozzle operating at a wide range of pressures. High speed schlieren imaging is used to capture the growth of the highly turbulent transient gaseous jet with high spatial and temporal resolution in a quiescent chamber at atmospheric conditions. The existing penetration scaling correlations for gas jets issued from single round nozzles were found to apply to outward-opening nozzle as well. The penetration constant is found to be 1.15 ± 0.05 for fuel pressure ranging from 20 bar to 160 bar. A new method to calculate combined penetration for radially spreading jets such as the one used in this study is presented which can also be used for jets of irregular shape. The data from these tests show that the axial penetration from a 90° conical annular nozzle is roughly about 3 times lower than round nozzles for similar injection and ambient conditions. The lower penetration rate of such annular nozzles can be beneficial for stratified mixture formation in spray-guided direct-injection spark-ignition engines.