Fluid cokers are widely used in the petroleum industry but limited research has been reported for optimizing their feed injector systems. in the present work, the effect of variation in the two-phase flow, with respect to impact on atomization for the range of nominal commercial operating conditions for the feed system, was investigated. A commercial scale injector was assembled and air-water flow dynamics through the assembly was examined to understand the effect of small variation in the mass ratio of gas to liquid on injector operation. The air-to-liquid mass ratio (ALR) is typically used to correlate results for this type of water spray testing. In terms of droplet size and spray dispersion, the measured and observed effects for change in the type of flow were correlated with the resulting atomization efficiency. A fall-scale test system was made of clear Plexiglas pipe to allow observation of the flow. Operating conditions for the tests were in the range of nominal commercial operation. Intermittent or slug flow and dispersed bubble (DB) flow regimes were observed in the transparent injector assembly for the range of conditions studied. In the present research, small changes in the gas flow rate through the spray injector system were demonstrated to alter the two-phase flow structure and subsequent atomization significantly. This change could be encountered in commercial operations where there is a malfunction such as a partially plugged nozzle. Experimental results from this work were applied to selecting optimal operating conditions for commercial operation. From this, criteria for droplet size and spray dispersion were selected for increased efficiency of coker operation. In general, dispersed bubble flow was determined to provide better atomization and dispersion of the spray and thereby potentially improve coker efficiency. Another aspect of this research was to develop a signal analysis method to analyze pulsation patterns measured for the two-phase flow passing through the injector feed system. This analysis allowed qualification of the two-phase flow type and was investigated as a tool for an on-line monitoring tool of the commercial spray injector system. Crown Copyright