The Fuel Injection System of an Aircraft

Posted on November 8, 2021 James Hinds Aircraft

Across all piston-powered aircraft, the two primary fuel systems are the carburetor and fuel-injection system. While most general aviation aircraft initially relied on carburetor systems, fuel-injection systems have quickly risen in popularity in past years. The fuel-injection system holds various advantages over its counterpart, its benefits ranging from increased safety to improved performance. As a result, fuel-injection systems can be beneficial for many pilots depending on their needs. In this blog, we will discuss the design and functionality of the fuel injection system, allowing you to better understand how they work and provide fuel for flight.

While there are variations of fuel-injection systems that differ in design based on their manufacturer, the standard assembly consists of an airflow, regulator, and fuel metering section. In regard to the airflow section, engine airflow consumption can be measured with the use of impact and venturi throat pressure sensors that are present within the throttle body. Both pressure types will flow into an air diaphragm, and adjustments in air consumption are determined by the movement of the throttle valve. As a result of such processes, the air velocity within the venturi will change. Impact pressure is also picked up by impact tubes.

Within the regulator section of the fuel-injection system, a fuel diaphragm acts to oppose air metering forces. While fuel inlet pressure acts against one side of the diaphragm, metered fuel pressure acts against the other. Metered fuel pressure is typically generated after the fuel has moved through the fuel strainer and manual mixture control rotary plate. The resulting differential pressure that is exhibited across the diaphragm is referred to as the fuel metering force. As both pressures act against the diaphragm, their difference will determine the degree at which the ball valve opens. The difference in air pressure is also always proportional to the air that flows through the injector, and as a result, airflow volume directly determines fuel flow rates. While in the idle range with low power settings, a constant-head idle spring is implemented to ensure constant fuel differential pressure.

The fuel metering section is directly connected to the air metering section, and it comprises an inlet fuel strainer, manual mixture control valve, idle valve, and the main metering jet. While the idle and throttle valve are interconnected by an external adjustable link, some models will also implement a power enrichment jet as well. As all parts work together, the fuel metering section is capable of metering and managing fuel flow delivery to the flow divider. To control how rich or lean fuel is, adjustments are made to the manual mixture control valve with the use of a lever. Additionally, idle speed and idle mixture can both be managed externally for the means of catering to various engine requirements.

Alongside such sections, fuel-injection systems also contain other various parts such as fuel discharge nozzles, fuel-injection pumps, the fuel/air control unit, fuel manifold valve, fuel discharge nozzle, and much more. While fuel-injection systems surpass carburetors in terms of improved acceleration, better fuel distribution, and safety, they still face wear and tear that necessitates regular maintenance. At ASAP AM Spares, we are your sourcing solution for top quality fuel-injection system parts and other aircraft components that you require.

ASAP AM Spares is a leading supplier of components for the fuel injection system of an aircraft and other aviation parts, all of which are offered with competitive pricing and rapid lead-times. Take the time to explore our ever-expanding part catalogs at your leisure, and you may request quotes for your comparisons with ease through the submission of a completed RFQ form. At ASAP AM Spares, we are more than just a dependable distributor; we are your strategic sourcing partner for all your operational needs. 

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