Hydrogen-blended fuels: Nonlinear flame dynamics and safe operation limits

This paper presents a two-part study on laminar hydrogen-blend flames in a micromix combustion test rig . The first part of the study focuses on the nonlinear dynamics of the flame, which is modelled by the G-equation. The laminar flame speed and the amplitude of convected velocity perturbations are the key parameters. Both have a marked effect on the travel times associated with the convected perturbations. These travel times are quantified and represented as functions of the laminar flame speed and the perturbation amplitude. The second part of the study considers a combustion test rig with the hydrogen-blend flame considered in the first part. A Green’s function approach is used to calculate the complex eigenfrequencies of the complete combustion system. The key parameters are the hydrogen concentration, equivalence ratio and amplitude of velocity fluctuations . The following regions are identified in this 3-D parameter space: regions of thermoacoustic instability , stable limit cycles and flame flashback. This information gives the safe operation limits. • Laminar flame dynamics is always nonlinear, even at very low amplitudes. • Flames are effectively shortened by high-amplitude excitation. • Stability analysis for micromix combustion rig is made with Green’s function approach. • Increase in hydrogen concentration reduces risk of instability.