Soroush Sheykhbaglou

Ammonia stands out as a promising zero-carbon fuel and an efficient hydrogen carrier, offering great promise for industrial applications in gas turbines and boilers. However, different combustion modes significantly influence the flame structure and combustion characteristics of ammonia. In this study, two distinct fuel injection strategies were employed in a model combustor: ammonia and methane, under fully premixed and dual-flame combustion modes. Numerical simulations were performed to analyze the flame structure, velocity fields, and temperature distribution, complemented by planar flow field, flame OH* chemiluminescence, and NO emission measurements. Findings reveal that with an increasing NH₃ ratio, the flame front becomes more elongated with more pronounced temperature fluctuations at the swirler exit. Particularly, at 50% NH₃, a significant reduction in flame temperature is observed, notably at a height of 30 mm from the burner. For dual flames, the reaction NH₂ + O ↔ HNO + H was less significant compared to its effect in premixed flames, whereas the H + O₂ ↔ O + OH reaction demonstrated the highest sensitivity coefficient. An increase in the NH₃ ratio correspondingly led to a reduction in NO consumption reaction rates, heightening the sensitivity coefficient for NO inhibition, and providing critical insights into ammonia combustion optimization.

Micropower generation and micropropulsion are two emerging fields where micro‐ and miniature‐scale combustors are anticipated to play a significant role. Today, there is a growing interest in combustion‐based direct energy conversion modules such as thermoelectric and thermophotovoltaic micropower generators. In this study, the effects of swirl addition to fuel flow and airflow on combustor operational envelope, flame blowout limit, combustion efficiency, exhaust gas temperature, mean outer wall temperature, emitter efficiency, and normalized temperature standard deviation of a miniature‐scale (mesoscale) combustor are studied under various equivalence ratios. The findings demonstrate that swirling flows improve the flame blowout limit and operational envelope of the combustor; however, this improvement is more significant for airflow swirl. Besides simultaneous swirling flows of fuel and air result in the highest blowout limit. Additionally, it has been shown that swirl addition improves combustion efficiency and causes a significant amount of heat to be generated, which raises the temperature of the exhaust gas, the mean outer wall temperature, and the emitter efficiency. Furthermore, mean outer wall temperature and emitter efficiency have the highest values for simultaneous swirling flows of fuel and air. It is also observed that increasing the fuel flow swirl number generally lessens the normalized temperature standard deviation (NTSD) and consequently improves the combustor wall temperature uniformity, while for the airflow swirl case, a swirler with 30° vane angle for airstream has a lower NTSD than a 45° vane angle swirler. The results obtained in this study provide useful information for designing a combustion‐based direct energy conversion module.

In this paper, the effects of coaxial airflow swirl number on blow-out limit, flame characteristics, and emission performance of non-premixed methane/air and n-butane/air flames in a miniature-scale swirl burner are investigated experimentally. Swirl numbers ranging from 0 to 0.72 have been chosen to be examined. It was observed that increasing the vane angle does not increase the blow-out limit monotonically and a swirler with 30 ° vane angle ( 0.50 swirl number) results in the greatest blow-out limit. Besides, it was found out that methane outperforms n-butane in the blow-out limit at the same fuel flow rates. The intermittency distribution approach was used to determine flame properties such as lift-off height, length, and width. It was found that the lift-off variation with coaxial airflow Reynolds number at the specified fuel flow rates yields an inverted V-shape for S _n ≥ 0.50. The tip of these plots indicates the airflow rate at which the swirl shows its influence, and after this point, the lift-off height begins to decrease. It was also observed that the airflow related to this point decreases with an increase in the swirl number at a certain fuel flow rate. Furthermore, the results revealed that at high airflow rates, the flame width rises as the swirl number increases. Also, raising the swirl number and airflow Reynolds number reduced the flame length. It was also observed that n-butane/air flames have longer and wider flames than methane/air flames. Additionally, adding swirl to the airflow rate typically reduces N O x and CO concentrations and n-butane/air flames exhibit lower levels of N O x and higher levels of CO than methane/air flames under the same operating conditions.

Recent advances in small power-consuming electric devices have increased the demand for appropriate, compact, rapidly rechargeable, lightweight, and long-lived power sources with higher energy densities. Hydrocarbon fuels are capable of providing high specific energy density, so combustion-based power generators have received increasing attention as an interesting alternative to batteries. In this study, a small power generation system using a miniature-scale swirl burner, two thermoelectric generators (TEGs), a heat medium, and two water blocks as heat sink has been developed. Various swirl strengths ranging from 0 to 1 are studied to find the optimum swirl number (vane angle) for the blow-out limit. The swirl number related to the greatest stable region is found 0.5 which is associated with the 30 ° vane angle for the 3D printed axial swirlers. Because normal-butane is easily liquified and stored, and is in the gas phase at room temperature and atmospheric pressure, it is chosen as the fuel. This paper examines the effect of three thermal input powers of 194 , 291 , and 388 W along with various airflow rates on the performance of the power generation system at the 30 ° vane angle swirler. The results show that about 3 min is needed for our system to reach a steady power output. Moreover, it is observed that the maximum output power is found at the load resistance of R load = 3 Ω for studied operating conditions. Besides, it is shown that by considering the airflow rate fixed, the power output of the system increases with an increase in the fuel flow rate (thermal input power). Furthermore, a maximum power output of 17.2 W is obtained for the fuel flow rate and an airflow rate of 0.200 slpm ( ≈ 388 W ) and 2.7 slpm , respectively, which corresponds to a conversion efficiency of about 4.5 % at R = 3 Ω load resistance.