Compositional inhomogeneities as a source of indirect combustion noise

TL;DR

This paper theoretically investigates how compositional inhomogeneities in combustion gases generate indirect noise, extending nozzle theory to multi-component mixtures and highlighting conditions where compositional noise surpasses entropy noise.

Contribution

It introduces a chemical potential function into compact nozzle theory for multi-component gases and derives transfer functions for different flow regimes.

Findings

Compositional noise depends on local mixture composition.

It can exceed entropy noise in fuel-lean and supercritical flows.

Implications for designing low-emission combustors.

Abstract

The generation of indirect combustion noise by compositional inhomogeneities is examined theoretically. For this, the compact nozzle theory of~\cite{MARBLE_CANDEL_JSV1977} is extended to a multi-component gas mixture, and the chemical potential function is introduced as an additional acoustic source mechanism. Transfer functions for subcritical and supercritical nozzle flows are derived and the contribution of compositional noise is compared to entropy noise and direct noise by considering an idealized nozzle downstream of the combustor exit. It is shown that compositional noise is dependent on the local mixture composition and can exceed entropy noise for fuel-lean conditions and supercritical nozzle flows. This suggests that the compositional indirect noise requires potential consideration with the implementation of low-emission combustors.