It’s Not Only What Comes Out, but How: A Detailed Explanation of Exhaust Systems

Exhaust systems are undoubtedly the bowels of any vehicle, automobile, or aircraft. The main function of the exhaust system is to allow for the smooth propulsion of gas emission from an engine out to its surrounding environment. This allows for proper gas exchange to take place in order to optimize fuel usage and energy output. In theory, this function could be performed by any metal tubing that leads from the engine to the tailpipe, however, there are many other requirements that must be considered in order for an exhaust system to function effectively. According to Federal Aviation Association (FAA) regulations, the exhaust system of an aircraft must be able to withstand high temperatures, corrosion, vibration and inertia loads, and must have means for flexibility in addition to performing its typical roles.

A structural aspect that must be put into consideration in designing an exhaust system is the maintenance of back pressure. The engine propels outward, creating a pressure that flows out. However, if there are too many bends, or if the piping of the exhaust system is too small, then the air pressure could build up in the opposite direction of the exhaust system, creating what is known as “back pressure”. The higher the back pressure, the more energy is needed for the exhaust to expel the gases outward. If the back pressure is higher that of the exhaust system, then the back pressure completely cancels out the exhaust and nothing gets expelled. To prevent this, exhaust pipes need to be wide enough and allow for optimal air flow. If pipes are too wide, not enough pressure will be built up, and the air will move too slowly.

Another consideration for a properly functioning exhaust system would be the routing of the exhaust pipes. Commercial aircraft exhaust can reach temperatures of 2000?, which can melt the cowling and other parts of the engines. The exhaust pipes must be designed in a way that is clear from areas that are unable to withstand such temperatures. The cowling around the engine may need adjustment in order to allow for adequate room for proper routing. However, it should also be noted that there will be a large difference between top temperatures of commercial planes and experimental builds.

Although not as important, you should be mindful of how much noise your aircraft creates. The sudden expulsion of air from any source can result in an audible sound, whether that be flatulence or exhaust. The engine is the lifeline of an aircraft, but the process of carrying away gas from the engine system can result in very loud sounds. This is why zero emission cars, such as any of the Tesla automobiles, create little to no sound when in use. Loud noise can be a distraction for pilots and pose as an overall safety concern. Unfortunately, the sound created from an aircraft is largely influenced by the structure of the exhaust system.

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