The combustion chamber of a jet engine is where the well-known, powerful “bang!” is produced. Fuel mixes with the air that comes from the compressor and ignites, which is what produces this loud sound.. Large quantities of fuel are burned within the combustion chamber, which is supplied by fuel spray nozzles. Heat is released to cause an expansion of the air within, as well as accelerating it for a stream of heated gas. Maximum heat release and minimum pressure loss is required.
The combustion chamber experiences a very high rise in temperature; just how much of an increase in temperature is determined by the amount of fuel within the chamber. In our J85 engines, the exit temperature of the combustion chamber can reach temperatures up to 1,000 °C! A maximum temperature allowance is determined by the material used for the chamber, turbine blades, and nozzles. The combustion chamber must be able to maintain a stable and efficient combustion over a varying range of engine operating conditions since the temperature of the mixed gas determines the engine’s thrust. Our jet racing applications make combustion temperatures even hotter. To manage that, we go to Florida Tech’s Center for Advanced Coatings where we can take advantage of ceramic coatings that provide resistance to extreme heat.
J85 general electric engines contain an annular combustion chamber, which means that its combustion takes place in a full 360 degrees around the engine. This makes for a more uniform combustion. Annular combustion chambers typically have a more consistent exit temperature as well. As mentioned before, a minimum pressure drop is desired within the combustion chamber, and annular combustors have the lowest pressure drop of all the types of combustion chambers, making them very efficient. These aspects make it one of the most commonly used types of combustion chamber.
The exit of the combustion chamber is the hottest region of the engine, therefore a material that is able to withstand these high temperatures needs to be used. Inconel is typically the material of choice because of its thermal properties. It is high strength and corrosion resistant as well. Also, it is quite easily fabricated, making it convenient for manipulation into complex shapes.
Next stop on our journey through a jet engine will be the turbine section. If you haven’t already, watch my video about the combustion section, and stay tuned for the next vlog and blog about the turbine section!
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