Chemiluminescence as a diagnostic in studying combustion instability in a practical combustor

Abstract

Prediction of combustion instability is essential in reducing development costs of large scale rocket engines. Recently, high fidelity CFD models have shown some ability to represent the stability characteristics of sub-scale experimental combustors. A challenge remains in acquiring experimental measurements of critical combusting flow properties, especially measurements of the unsteady heat addition field, for comparison to models. Previous studies have shown that OH* and CH* emission intensity is a function of pressure, strain rate, equivalence ratio, and turbulence level. Since these flame properties have large variations at all times in an unstable rocket combustor it is difficult to decouple the chemiluminescent emission from all variables except heat release. Emission due to chemiluminescence can, however, be isolated from other flame property variables in a computational model. A detailed chemical kinetics model is used to investigate the relationship between chemiluminescent species and heat release rate of the flame. This predicted relationship is then compared to experimental spectral measurements captured with a fiber optic probe both to check the validity of the model and to provide insight on the ability of the chemiluminescent light emission to indicate heat release in the unstable CVRC flame.

The use of OH* and CH* as heat release markers in combustion dynamics

“…The previous study of this combustor using chemiluminescence relied on the assumption of QSS of the excited species. 45 Although in that study, qualitative similarities in the phase-averaged, volume-integrated OH* emission were observed, some discrepancies remained. Specifically in the results used for the study by Bedard et al, QSS OH* is discernible at locations downstream of the heat release zone throughout the instability cycle, which is contrary to the experimental observations.…”

Injector-coupled transverse instabilities in a multi-element premixed combustor

“…This accounts for the precision and bias uncertainty of the measured pressure, but it does not include possible amplification or attenuation of the measured peak pressure due to the installation of the pressure transducer in a recessed cavity port. 44,45 As reported in Table 1, for Case A-1, the resulting pp−p′/pc is 124%, while for Case B-2, the pp−p′/pc is 5%.…”

“…All HF transducers are installed in a recessed cavity with a port resonance greater than 10 kHz and sampled at 180 kHz. 44,45…”

“…For the purposes of this work, the change in chemiluminescence intensity is assumed to be proportional to the heat release rate from the flame. [46][47][48] Lineof-sight integrated CH* chemiluminescence images are recorded at 75 kHz through a window in one side of the combustion chamber. The field-of-view (FOV), indicated in Figure 1, is 82 mm in the x-direction and 77 mm in the y-direction.…”

Direct Identification of Two Regimes of Metal Particle Combustion using Condense-luminescence

“…In condense-luminescence, the energy released during condensation of gaseous metal nano-oxides is emitted. In chemiluminescence, chemical heat released leads to excitation of a molecule that is further emitted and chemiluminescence could been used as a diagnostic in studying combustion [8]. The principal difference in condense-luminescence is that condensation leads to excitation of a nanoparticle as a whole, which is why the phenomenon deserves a separate name.…”