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A flame holder is used inside a rocket, jet, or similar engine to maintain combustion. It creates a small area of reduced activity to prevent high wind from putting the flame out so fuel can steadily combust to generate rapidly expanding air and thrust. A number of factors are incorporated o into flame holder design, especially with sophisticated and expensive engines. Hobbyists occasionally need to make flame holders for projects like home rockets, which have much more forgiving engine tolerances than space shuttles and commercial aircraft.
Classically, the flame holder consists of a cylinder with some air holes in it to allow air to form an eddy. Currents of air moving through the engine swirl around the device, leaving a void in the middle where a flame can burn. As fuel is combusted, it elevates the air temperature around the flame holder. Rapidly heating air expands to generate thrust, while the high heat ignites incoming fuel to keep the engine continually running.
There are some other shapes and designs that may be considered for come applications. One option is a V, with the point of the V facing the direction of inward air flow, or an H design, which provides a slightly different kind of air current. Some aircraft use cavities, where the air flows over the flame while it’s maintained in the base of the cavity. In all cases, a fuel nozzle is located near the air holder to keep up a continuous supply of new fuel for combustion.
Careful calculation of the fuel/air mixture is needed to keep the flame going and maintain the engine’s operating conditions. The air holder helps control the movement of air currents inside a primary engine or afterburner, while fuels are carefully mixed to provide optimum performance. Engines that operate in this way can use high volumes of fuel with each flight in a tradeoff for power and speed. This can be critical for military aircraft or long-haul planes that rely on jet engines.
Problems with flame holder design can lead to the malfunctioning of an engine that may interfere with the performance of the aircraft. Most seriously, there is a risk that the flame in the combustion chamber will go out. If a flameout occurs, the engine can no longer operate until the flame is reignited. A number of measures are used to address this concern, including carefully engineering flame holders and other engine components, and training pilots in how to respond to such situations quickly.