Study on High Liquid Pressure Internal Mixing Prefilming Airblast Atomization

The objective of the present investigation is to provide better understanding of the hybrid atomization process in an effort to support the development of fuel injectors for future high performance / low emissions gas turbine combustors. A specially designed atomizer that incorporated two swirling air streams, and a prefilming device located upstream of the atomizer exit section was tested under a combined hybrid airblast and high liquid pressure mode. The experiments focused on evaluating the effects of several operating parameters, in particular the air / liquid ratio, on the atomization quality. The results demonstrated that, to accurately determine the role of the air / liquid ratio in the atomization process, the effects of liquid injection velocity and the relative air–liquid velocity need to be separated from that of the air / liquid ratio. Two approaches were used in the present investigation to deduce the actual effect of the air / liquid ratio: first, by reducing the air swirler flow areas, and second, by increasing the number of liquid injection holes. Both approaches enabled changing the air / liquid ratio without changing the air or liquid velocities. The atomization results indicate that changes in swirler flow area produce a stronger effect of the air / liquid ratio than that when liquid hole number was changed. For fixed air / liquid ratio, better atomization quality was achieved when both levels of air flow and liquid flow were high compared to when both flow rates were low. Also, the atomizer demonstrated a continuous improvement in atomization quality under very high air pressure drop, indicating a better utilization of the air kinetic energy over conventional airblast atomizers. The other important observation was that the dependency of the atomization process on air velocity was not constant, but rather changed with liquid pressure, air flow rate, and air pressure drop.