AS9120B, ISO 9001:2015, AND FAA AC 0056B ACCREDITED

Aircraft Fuel Injection Systems

Before burning gasoline in an aircraft piston engine, it needs to be vaporized and mixed with oxygen in the right quantities, and this is facilitated by either a carburetor or a fuel injector. In the case of carburetors, a float-type chamber collects and distributes fuel to the induction system. Air speeds up in the manifold, fuel is vaporized and mixed with air before entering the engine, and this fuel-air mixture moves through the induction system to the engine’s cylinders. Finally, the mixture is ignited by spark plugs and power is produced.

Fuel Injection Systems

Within an aircraft fuel injection system, on the other hand, fuel is injected into the cylinders or through the front of the intake valve using a fuel pump. Similar to a carburetor system, the air intake features an alternate air source located within the engine cowling, which is used if the external air source has been obstructed. This alternate source of air is operated automatically and features a backup manual system which can be employed if the automatic feature malfunctions. Generally, fuel injection systems are typically built of six basic components: an engine-driven fuel pump, fuel-air control unit, fuel manifold (distributor), auxiliary fuel pump, discharge nozzles, and fuel pressure/flow indicators.

Fuel-Air Control Unit

To begin, the auxiliary fuel pump provides pressurized fuel to the fuel-air control unit to start the engine for standard or emergency use. Once the engine starts, the fuel pump provides pressurized fuel from the fuel tank to the fuel-air control unit. This unit, which replaces the carburetor, meters fuel and moves it to the fuel manifold valve where it is distributed to various fuel discharge nozzles located in the cylinder head. These nozzles inject the mixture of fuel and air into each cylinder intake port.

Advantages of Fuel Injection Systems

There are several benefits to working with fuel injection systems rather than carburetor-based systems. First, fuel injection systems tend to be less susceptible to icing, which can obstruct the openings to various aircraft systems. In fact, ice accumulation on a carburetor has caused hundreds of aircraft engine failures and crashes. Next, there is better fuel flow, faster throttle response, improved fuel distribution, and enhanced control of the air-fuel mixture. As such, engines become more efficient and easier to start with fuel injection systems. On the other hand, it is difficult to use fuel injection systems when the engine is hot because vapor lock can occur in the steel fuel lines above the engine. More than that, the fuel must be free of debris and contaminants, and there must be a set of fuel return lines or a separate header tank. Despite the increased costs, fuel injection systems are fuel efficient and prolong engine life, which will help you save money on maintenance in the long term and increase engine reliability.


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