Have you ever flown on a Boeing 787? If not, you may have seen one in a photo like the one at the top of this post. If you've ever looked at the engine of the 787, you may have noticed a spiked look to the back of the engine. You might have also noticed this feature is absent from any other aircraft except the newest 747-8 models. So why are these on the newest Boeing planes?
These features are called chevrons and were developed with the assistance of NASA. In order to understand what they are for, we must first have a basic understanding of exhaust gasses and airplane engines.
After air is ingested at the front of the engine and compressed through a number of compression stages, the air is combined with fuel and ignited in the combustion stage of the engine. Once the mixture is ignited, it quickly heats, expands and exits out the back through the turbine stage. Exhaust gases help power the engine and keep it running. After the turbine stage, the hot gases exit the engine all together and mix with the ambient air.
As the hot gases mix with surrounding cold air, the air experiences rapid temperature shifts. These shifts in temperature as the gases abruptly mix, can cause significant amounts of noise. Reducing this noise is a major step in reducing engine noise as a whole. Airports have tighter and tighter noise regulations to meet and solving this problem can help keep noise pollution down around major airports.
Enter the engine chevron.
With design assistance from NASA, these engine chevrons were developed to help spread out the gas mixing process. Spreading the mixing process out over a larger area means that the gases don't see as much of a sudden temperature change. This helps significantly reduce engine noise on both the 787 and the brand new 747-8.
These new features will make customers happy on board as well as those people in surrounding communities. Making such a small addition to the engine cowling seems like a minor thing, but the impact is quite large. Boeing has had such great success with this engine design that new aircraft being developed by Boeing in the commercial field all seem to have this new feature. This includes the new 777x and 737Max, it looks to be here to stay, and luckily it's visually pleasing as well.