Nonlinear thermoacoustic instability investigation on ammonia-hydrogen combustion in a longitudinal combustor with double-ring inlets

Abstract

The greenhouse effect induced by the combustion of hydrocarbon fuel is an urgent environmental problem. Ammonia gas, as a renewable energy with a high proportion of hydrogen content, can achieve zero CO2 emission. In order to ignite ammonia and obtain continual flame, a partial premix entry condition of NH3/H2/O2 with double-ring inlets is adopted. The RNG k-ε model and EDC model are used to analyse the self-excited oscillation and the total heat release. After the numerical results and experimental data are validated, the following aspects are investigated: (1) total mass flow rate; (2) mass fraction of hydrogen; (3) mass flow ratio of inlets; and (4) the temperature of the heat exchanger. The results are compared with the traditional single-ring structure under the same condition. It is found that the exothermic heat of double-ring structure increases by 98.7% on average. The frequency of intermittent oscillation increases with the decrease in HN3 proportion. When pure hydrogen is passed through the outer ring, the combustion limit can be greatly expanded even if the inlet mass fraction of hydrogen is very small. This study contributes to provide an alternative method to enhance ammonia combustion and improve its flammability limit.