Novel control of supersonic combustion instability via weakly coupled identical oscillators induced by multi-injector design

This study presents a passive control method for suppressing supersonic combustion instability by strategically modifying fuel injector arrangements. Experimental results show that conventional multi-injector configurations behave as weakly coupled identical oscillators, whose synchronization drives large-amplitude combustion oscillations. By implementing a staggered injector geometry to introduce controlled phase differences between oscillators, we achieve a 47.1 % reduction in pressure oscillation amplitude (from 40.1 % to 21.2 %) and a 53.6 % suppression of flame front oscillations (from 22.4 % to 10.4 %), while expanding the ignition boundary by 25 % (equivalence ratio reduced from 0.48 to 0.36). The control mechanism relies on periodic generation and migration of localized recirculation zones, establishing dynamically stable combustion regions. High-speed schlieren imaging and CH* chemiluminescence analysis confirm that the modified injector arrangement disrupts oscillator synchronization while improving fuel-air mixing. This approach provides combustion chamber designers with a new geometric degree of freedom for instability control, offering quantifiable performance benefits without requiring active systems. The findings, supported by coupled oscillator theory, are applicable to multi-injector propulsion systems including scramjets, gas turbines, and rocket engines.