Characteristics of H₂/air annular jet flames using multiple shear coaxial injectors

抄録

The heat transfer characteristics for the process tubes of a cracking furnace and the combustion chamber wall of a liquid oxygen/gas hydrogen rocket engine, both of which use multiple nozzles, are very important in terms of performance and safety. In order to determine the heat transfer characteristics of the combustion chamber wall, the present study investigates both experimentally and numerically the combustion characteristics of H₂/air annular jet flames using multiple shear coaxial nozzles in a small combustion chamber under normal conditions. Three-dimensional simulations are performed in order to clarify the flame-flame interaction. The standard k-ε model is used as the turbulence model, and so the evaluation of the model for multiple nozzles is also an objective of the present study. Each flame appears as an independent flame until amalgamation, at which point the temperature increases. Further downstream, the high-temperature regions once again merge and form a large flame. At this point, the flame becomes squeezed and the temperature distribution spreads rapidly in the radial direction downstream. The wall heat flux is strongly influenced by the flow characteristics. Heat transport is weak in the near field. The turbulent heat transport downstream is dominant where turbulence is developed, and thus the wall heat flux is increased. An increase in Reynolds number based on the airflow Re_air shifts the peak position of the wall heat flux upstream because the turbulent heat transport is enhanced. The increase in the recess shifts the amalgamation position upstream and shortens the flame length. Spreading of the flame is also suppressed. The temperature decreases downstream. The increase in the recess leads to a reduction in EINOx. Under the present experimental conditions, the numerical method reproduces the combustion characteristics with a high degree of certainty.