This work aims to establish a stable premixed ammonia/air flame in a tangential swirl combustor by employing an ethanol spray to extend the fuel-lean extinction limit of the ammonia flame and reduce pollutant emissions. A Planar Laser Induced Fluorescence (PLIF) system is introduced to acquire the flame structure of this blending system. The results demonstrate that OH radicals originating from the ethanol flame support the ammonia flame, in which fluorescence images are indicated by the NH₂ radicals. Moreover, the lean extinction limit is significantly extended from an equivalence ratio of 0.6 to 0.1. In particular, the addition of a minor quantity of ethanol (3 mL/min) to ammonia flame sustains the blending flame due to the ultralow extinction limit of the ethanol swirl spray flame. However, both experimental data and chemical reaction analysis reveal that an increase in OH radical concentration leads to an elevation in NO_x (nitrogen oxides) concentration. This poses a challenge in balancing the effects of ammonia consumption and NO_x generation in the blending combustion system. Ethanol flames indeed generate active radicals (O, OH, HO₂, etc.) to accelerate ammonia oxidation. However, these active radicals also exacerbate the reaction between NO and NO₂, inhibiting their conversion to N₂. Even so, the objective of achieving clean combustion with low concentrations of both NO_x and unburned NH₃ can still be met under the condition of the total air flow rate 90 L/min and the global equivalence ratio 0.7.

The ignition and combustion of aluminum particles are crucial to achieve optimal energy release in propulsion and power systems within a limited residence time. This study seeks to develop theoretical ignition and combustion models for aluminum particles ranging from 10 nm to 1000 μm under wide pressure ranges of normal to beyond 10 MPa. Firstly, a parametric analysis illustrates that the convective heat transfer and heterogeneous surface reaction are strongly influenced by pressure, which directly affects the ignition process. Accordingly, the ignition delay time can be correlated with pressure through the p^b relationship, with b increasing from –1 to –0.1 as the system transitions from the free molecular regime to the continuum regime. Then, the circuit comparison analysis method was used to interpret an empirical formula capable of predicting the ignition delay time of aluminum particles over a wide range of pressures in N₂, O₂, H₂O, and CO₂ atmospheres. Secondly, an analysis of experimental data indicates that the exponents of pressure dependence in the combustion time of large micron-sized particles and nanoparticles are –0.15 and –0.65, respectively. Further, the dominant combustion mechanism of multiscale aluminum particles was quantitatively demonstrated through the Damköhler number (Da) concept. Results have shown that aluminum combustion is mainly controlled by diffusion as Da > 10, by chemical kinetics when Da ≤ 0.1, and codetermined by both diffusion and chemical kinetics when 0.1 < Da ≤ 10. Finally, an empirical formula was proposed to predict the combustion time of multiscale aluminum particles under high pressure, which showed good agreement with available experimental data.