Unlike hydrocarbon fuel, hydrogen is 'green' and attracting more and more attentions in energy and propulsion sectors due to the zero emission of CO and CO 2 . By applying numerical simulations, we explore the physics of how a hydrogen-burnt flame can sustain pulsating combustion and its impact on the thermodynamic properties of a standing-wave combustor. We also explain how implementing a heat exchanger can mitigate such pulsating combustion. The dynamic interactions of the unsteady flow-flame-acoustics-heater are examined by varying the mass flow rate ṁ H2 and the heating bands' surface temperature T H . The frequency and amplitude of the pulsating combustion are shown to depend strongly on ṁ H2 . In addition, varying T H is shown to lead to not only the molar fraction of the combustion species being changed but also the flame-sustained pulsating oscillations being mitigated somehow. Finally, nonlinearity is observed and identified in the unsteady flow velocity and the two heat sources.
Unlike hydrocarbon fuel, ammonia is a carbon-free and renewable energy source. It is also regarded as one of the potential energy carriers. However, ammonia combustion for power generation is not well studied under micro-scale conditions, especially concerning nitrogen oxides (NO x ) emission. For this, thermal performances and NO emission characteristics of premixed ammonia/oxygen combustion are numerically investigated on a micro-planar combustor. The effects of 1) the equivalence ratio ϕ, 2) inlet temperature T in and 3) inlet pressure P in are examined. The outer wall mean temperature (OWMT) is found to vary non-monotonically as the mixture varies from lean to rich conditions, with the peak occurring at ϕ = 0.9 mainly due to the optimal heat transfer performance. However, a low ϕ could lead to the high nitric oxides (NO) concentrations because of the high flame temperature as well as O atom concentrations. Up to 75.5% of NO reduction could be achieved, as ϕ is optimized. Furthermore, increasing T in is shown to be associated with a low OWMT and NO concentration. In addition, varying P in is shown to lead to not only OWMT being changed but also NO formation being mitigated. The decrease in NO concentration for high P in is mostly attributable to the short residence time of high flame temperature in the channel and low OH concentrations. This work reveals that optimizing the operating thermodynamic parameters is an effective means to reduce NO emissions and improve thermal performances.
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