Most of the previous studies investigated the axial cylindrical interface PMBs to stabilize the premixed flames. Very few studies reported in the radial outward flow porous media burner . In the radial flow configuration, the cylinder surface area increases with its radius and its velocity distribution is inversely proportional to the radius. As the flow travels through the porous media, it accelerates and is able to find a location at which it tends to stabilize as the kinematic balance between the burning velocity and the fresh mixture velocity is equal. Accordingly, radial PMBs offer a wider range of flame stability and power modulation rates compared to cylindrical axial burners, which are only dynamically balanced in a narrow range of flow rates. The present study utilizes a graded SiC Voronai-based lattice porous structure with a linear pore density. The objective of the present study is to enhance the NH3/H2/air flame stabilization mechanism and pollutant emissions in the radial inward flow direction for various porus media structures.
An Investigation into the Combustion Characteristics of Ammonia inside a Radial Porous Media Burner
The current research aims to explore the potential of porous media burners (PMBs) to enhance the combustion characteristics of unconventional fuels, specifically focusing on ammonia (NH3). Ammonia is a carbon-free fuel that has gained interest as an energy source. Its combustion encounters significant issues like high ignition energy, low flame speed, poor combustion stability, and high NOx, unburnt NH3 and H2 emissions. The porous media enhance the heat, momentum, and mass transfer leading to an increase in the burning speed and improved stabilization of premixed flames, counteracting the poor combustion characteristics of NH3. Advancements in additive manufacturing technology have allowed the design and manufacture of ceramic foams with compact geometries and continuously graded topologies to integrate into micro-gas turbines. The present study establishes a radial inward PMB to stabilize NH3/air flames in various porous media geometry under atmospheric conditions. The flammability limits of the burner are measured with 30% by volume of hydrogen (H2) added to the fuel stream. Infrared imaging is acquired to analyze flame stabilization within a solid matrix. The qualitative images display the flame front propagation in relation to the fuel air mixture, demonstrating geometric benefit of the porous media. Temperature and emissison measurements are reported for various equivalence ratios and mass flow rates. In addition, exhaust emission NO and unburned H2 are discussed in detail.
A lab-scale combustor with mixtures of NH3/H2/Air is examined in PMB. A schematic of the experimental setup is shown in Fig. This study uses a cylindrical foam block made of SiC porous media with a height of 22 mm, an outer and inner diameter of 60 and 12 mm, respectively. The ceramic foam is graded linearly with 20–10 pores per inch (PPI) in a voronois lattice structure with an approximate porosity of 0.85. The foam block is placed horizontally with an insulating material on both sides to place the inline direction of the combustor. The combustor is designed in such a way that the inlet mixture is supplied through the outer circumference of cylindrical foam. The combustion stabilizes inside the solid matrix, with the geometrical advantage of altering the inlet air mixture velocity. An array of mass flow controllers regulates the reactant mixture of an operating condition. The experiments are conducted with the initial mixture at room temperature and the reactor is held at atmospheric pressure. An NI cDAQ control system consisting of four thermocouples is used to instrument the experimental setup. The temperatures of the exhaust and just upstream of the PIM are recorded. A gas analyzer (Testo -340) setup is incorporated into the system to characterize the O2 and NOx emissions. Using gas chromatography, the unburnt H2 is reported for the NH3/H2/Air mixture. The reported emissions are repeated twice for each condition, with an uncertainty of ±10%.
SiC-Voronoi based lattice structure
Acquisition:
- Temperature: (T_(g,exhaust)– Exhuast, T_(s,inlet)– PIM outer surface)
- Emissions: NO (Testo 340 Gas Analyzer) , H_2 (Gas Chromatography)
- IR Imaging: No gaseous emissions (NB -2085±5 nm), TELOPS
Emission of solid matrix reveals the flame front propagation relative to fuel/air mixture.
Measurement of NO, H_2 and exhaust temperature (T_g) as a function of X_(NH_3 ), for a mass flux m = 0.10 kg m^(-2) s^(-1).
- Potential of PMBs as a practical solution for NH_3 fueled furnaces and gas turbines.
- We demonstrated that this design is suitable to stabilize NH_3/Air and NH_3/H_2 Flames.
- Flame stabilization within solid matrix and flame propagation with fuel mixture reveals the geometrical benefit of radial inward porous media.
- High NO_x in lean, H_2 and NH_3 in rich mixtures encourages to optimize the porous media structures to extend pure NH_3 combustion.
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