Effects of recess length on combustion instability in a model chamber with a gas-centered swirl coaxial injector

Abstract

Combustion instability is investigated in a model chamber by changing the recess length of a gas-centered swirl coaxial injector ranging from 0 mm to 20 mm with a 4 mm interval. Effects of recess length on combustion instability are pursued by numerical simulations and experiments and compared with each other. The parameters for evaluation of instability, i.e., damping factor, decay rate, and damping coefficient, are quantified based on numerical and experimental data. The parameters show that acoustic oscillations in the combustor are suppressed relatively more as the recess length of the injector increases. Combustion stability improves more and more with the recess length and then, levels off. Improvement in stability is not appreciable when the recess length is increased further than a critical value. On the other hand, stability increases with equivalence ratio for a lean condition, reaches its maximum, and then, decreases finally for a rich condition. However, injectors with a longer recess length maintain good stability even if the equivalence ratio varies.