Flameholders

Flameholders are devices integrated into combustion equipment to stabilize flames in high-velocity flows. They work by creating a region of recirculating hot gases near a solid surface where reactants can mix, preheat, and ignite, enabling a flame to anchor rather than be swept downstream. This stabilization is especially important in gas turbine combustors and other high-speed burners, where the incoming air can easily blow out a flame or force a flashback toward the fuel inlet.

There are several common forms. Bluff-body flameholders use a central block or projection to create a low-velocity recirculation zone behind it, often with attached fins or struts to shape the flow. Vee or wedge flameholders are simpler geometries that also generate an anchoring region. Swirl-type flameholders employ cavities or vanes to induce a vortex, producing a stable recirculation zone and a flame anchor near the surface.

Flameholders are used with various fuels, including natural gas and kerosene, in premixed or diffusion flames. In lean-burn gas turbines, they help maintain stability at high power and low emissions, while in industrial burners they improve ignitability and flamehold at high flow rates. They also help resist flashback by keeping the flame near the flameholder rather than the inlet.

Design considerations include balancing flame stability with pressure loss, accounting for thermal and mechanical stresses, and minimizing erosion from particulates. Materials are typically high-temperature alloys or ceramics, sometimes with protective coatings. Overall, flameholders are a key component for reliable, stable combustion in engines and burners operating under challenging flow conditions.