Thermoacoustic Stabilization of a Sequential Combustor with Ultra-low-power Nanosecond Repetitively Pulsed Discharges

TL;DR

This paper demonstrates that low-power nanosecond pulsed plasma discharges can effectively suppress thermoacoustic instabilities in a sequential combustor, offering a promising active control method for enhancing combustor stability and operational range.

Contribution

It introduces a novel active control approach using nanosecond pulsed discharges to stabilize a sequential combustor, a method not previously demonstrated at such low power levels.

Findings

Plasma power of 1.1 W can stabilize the combustor thermoacoustically.

The plasma actuation influences flame dynamics and emissions.

Optimal plasma parameters depend on combustor operating conditions.

Abstract

This study demonstrates the stabilization of a sequential combustor with Nanosecond Repetitively Pulsed Discharges (NRPD). A constant pressure sequential combustor offers key advantages compared to a conventional combustor, in particular, a higher fuel flexibility and a wider operational range. However, thermoacoustic instabilities remain a barrier to further widen the operational range of these combustors. Passive control strategies to suppress these instabilities, such as Helmholtz dampers, have been used in some industrial systems thanks to their simplicity in terms of implementation. Active control strategies are however not found in practical combustors, mainly due to the lack of robust actuators able to operate in harsh conditions with sufficient control authority. In this study, we demonstrate that thermoacoustic instabilities can be suppressed by using a non-equilibrium plasma produced with NRPD in a lab-scale atmospheric sequential combustor operated at 73.4 kW of thermal power. We employ continuous NRPD forcing to influence the combustion process in the sequential combustor. The two governing parameters are the pulse repetition frequency (PRF) and the plasma generator voltage. We examine the effect of both parameters on the acoustic amplitude, the NO emissions, and the flame centre of mass. We observe that for some operating conditions, with plasma power of 1.1 W, which is about 1.5$\times$ $10^{-3}$ percent of the thermal power of the flames, the combustor can be thermoacoustically stabilized. This finding motivates further research on the optimization of the plasma parameters as a function of the thermoacoustic properties of the combustor where it is applied. This study is a pioneering effort in controlling the thermoacoustic stability of turbulent flames with plasma discharges at such low power compared to the thermal power of the sequential combustor.