How Does an Aircraft Exhaust System Affect Engine Performance?
For the most part, any engine– piston or jet– is really just an air pump. By “air pump” we mean it takes air in and compresses it. With the addition of fuel and a subsequent ignition, the expanding air pushes down a piston or is perhaps jetted out the back.
How does an aircraft’s exhaust system affect its engine performance? A well-maintained and well-cleaned aircraft exhaust system not just ensures the engine operates at peak power and efficiency, it also greatly contributes to the overall safe and smooth operation of the aircraft.
Pressure Ratios Simplified
Pressure ratios account for power and efficiency.
Generally speaking, this simply means that the higher the pressure ratio, the better the engine performance.
Of course, other factors come into play such as engine size and weight, and how much fuel is consumed during operation. For modern civilian engines, pressure rations typically range between 40 and 55 to 1.
Can the current integrity and state of an aircraft’s exhaust system affect pressure ratio?
Yes, it can. Any obstruction to the exit of hot air from an engine results in a decrease in the pressure ratio, affecting power and efficiency as well.
More on Aircraft Exhaust Systems
As opposed to simpler automobile exhaust systems, aircraft exhaust systems perform two important functions. First, it vents exhaust gases away from the engine and fuselage while reducing noise. Secondly, the aircraft exhaust system indirectly supplies cabin and carburetor heat.
Now, aircraft exhaust systems are constantly exposed to very high temperatures, sometimes in excess of 1200 to 1400 degrees Fahrenheit. In addition, hydrocarbon fuels continuously burn throughout the system, leaving corrosive residue that can accumulate and damage components throughout.
It is for this reason that aircraft technicians take extra care in looking for signs of greater-than-usual deterioration or even blockages during engine and exhaust inspections.
Not only can faulty exhaust systems lead to poorer engine performance, they can also increase the risk of carbon monoxide poisoning, fire, or other accidents from system leaks.
In reciprocating aircraft engines, there are two general types of exhaust systems:
- Short stack systems. This type of exhaust system is generally used on non–supercharged engines and low-powered engines where noise level is not too overpowering.
- Collector systems. This type of exhaust system is used on most larger non–supercharged engines and on all turbo–supercharged engines and installations. The system improves nacelle streamlining, as well easier maintenance in the nacelle area.
On turbo–supercharged engines, the exhaust gases must be collected to drive the turbine compressor of the supercharger.
These systems are built with exhaust headers, emptying hot exhaust gases into a common collector ring with only one outlet. The combustion gases are then vented through a tailpipe into the supercharger, thus driving the turbine.
So, while in a collector-type system, you have an increase of back pressure from the exhaust system, you do get a larger gain in horsepower from turbo–supercharging.
Meanwhile with a short stack-type system, the setup is more relatively simple. Removal and installation would consist of removing and fastening the hold-down nuts and clamping components. Also, on most modern aircraft, short stack systems have a rather limited use.
A Final Word
At great heights where the density of air is much less compared to the that on the ground, most aircraft use highly compressed air and fuel mixtures for the engines to provide high efficiency.
A supercharger or turbocharger is used to compress the incoming air before being injected into the engine compartment. Taking its power from the exhaust, the turbocharger is nothing but an air compressor, with its blades rotating using the exhaust from the engine.
For this reason, the optimum function of the engine depends on the quality of the exhaust. And while modern-day aviation tech is quite advanced as it is, there is always a need for cleaner exhaust systems to further improve engine performance and efficiency.