Combustion Instabilities of Ultra-Lean Premixed H_2/Air Mixtures by Prechamber Turbulent Jet Ignition

摘要

Unstable combustion was observed in a dual-chamber combustor that mimics heavy-duty gas engines utilizingprechamber jet ignition. Prechamber combustion generated a hot turbulent jet that ignited the ultra-lean H2/a irmixture in the main chamber. Thermoacoustic combustion instability was initiated for main-chamber equivalenceratio,<0.5,and grew severe in the lean-burn regime,0.22<0<0.3.Simultaneous schlieren and OH*chemiluminescence were used to visualize the unstable flame propagation and to characterize the instability. Classicalacoustic resonator analysis and pressure spectra showed the longitudinal mode of acoustic disturbance as the primaryinstability mode for all equivalence ratios. However,a leaner flame was affected more due to stronger couplingbetween heat release and the pressure field perturbation. Transverse and mixed modes were observed at leanconditions,<0.4.A phase-resolved measurement of strain rates along flame edge showed an oscillating strain alongpressure perturbation cycle. To model the instability,3D linearized Euler equations were solved in the frequencydomain coupled with combustion response models. The physical significance of the instability modes and theirbehavior were identified using dynamic mode decomposition. Based on the experimental and modeling results,a mechanism for thermoacoustic instability was proposed for ultra-lean premixed H2/a ir ignition by a hotturbulent jet.