Combustion Science and Technology, Vol.192, No.1, 62-77, 2020
A Mixture Fraction-Based Model and Axial Thermal Positions for Buoyancy/Momentum-Controlled Jet Diffusion Flames
This study investigated the axial distributions of temperature and radiation output in buoyancy- and momentum-controlled jet diffusion flames, both theoretically and experimentally. An equation based on mixture fraction theory was constructed to analyze the axial stoichiometric positions and the soot production regions. For a given fuel flow rate, compared with the buoyance-controlled flames, the thermal positions of the momentum-controlled flames exhibited a greater upward shift due to a lower virtual origin. Furthermore, with increasing fuel flow rate, for both flames, the majority of the soot particles had greater velocities after the smoke point and thus persisted above the oxidation zone. As such, the position of maximum radiation output shifted above that of the maximum temperature. After the lift-off of momentumcontrolled flames, the maximum temperature position appeared at a greater height due to increased propagation speed, while the reduced soot residence time lowered the maximum radiation output position. Finally, the maximum radiation output position approached the maximum temperature position.