The fuel-injection system has countless advantages over the conventional carburetor system. For example, fuel-injection systems are less likely to experience induction system icing, since the drop in temperature due to fuel vaporization happens in or near the cylinder. Additionally, acceleration is also improved as a result of the positive action of the injection system.
Fuel-injection systems also improve fuel distribution, which reduces the overheating of the individual cylinders caused by variation in mixture due to uneven distribution. More than that, they also provide better fuel economy than a system wherein the mixture to most cylinders must be richer so that the cylinder with the leanest mixture operates optimally.
In terms of construction, arrangement, and operation, fuel-injection systems vary. For instance, the Bendix inline stem-type regulator injection system (RSA) series consists of an injector, flow divider, and fuel discharge nozzle. It is a continuous-flow system that measures engine air consumption and utilizes airflow forces to streamline fuel flow to the engine. Meanwhile, the fuel distribution system to the individual cylinders is obtained by the implementation of a fuel flow divider and air bleed nozzles.
To better understand the fuel-injection system, we will be covering the RSA series fuel injector assembly’s various sections and components.
Fuel Injector
The fuel injector assembly itself consists of an airflow section, a regulator section, and a fuel metering section. It is important to note that some fuel injectors may be equipped with an automatic mixture control unit.
Airflow Section
The airflow consumption of the engine is measured by the throttle body sensing impact pressure and venturi throat pressure. These pressures are vented into both sides of the air diaphragm. As the throttle valve moves, there is a change in engine air consumption and a change in the air velocity of the venturi as well.
When the airflow in the engine increases, the pressure on the left side of the diaphragm is lowered due to a drop in pressure at the venturi throat. This pressure difference makes the diaphragm move to the left, opening the ball valve.
Adding to this force is the impact pressure that is absorbed by the impact tubes. This pressure differential is called the “air metering force,” and it is acquired by channeling the impact and venturi suction pressures to opposite sides of a diaphragm. The difference between these two pressures is considered a viable force that is equal to the area of the diaphragm times the pressure difference.
Regulator Section
The regulator section consists of a fuel diaphragm that opposes the air metering force. When fuel inlet pressure is applied to one side of the diaphragm, metered fuel pressure is applied to the other. The pressure difference across the fuel diaphragm is referred to as the “fuel metering force.”
The fuel pressure displayed on the ball side of the fuel diaphragm is referred to as metered fuel pressure, and it is the pressure after the fuel has made its way through the fuel strainer and the manual mixture control rotary plate. Meanwhile, the fuel inlet pressure is applied to the opposite side of the fuel diaphragm, and the ball valve attached to the fuel diaphragm controls the valve opening and fuel flow.
Keep in mind that the extent to which the ball valve opens is dictated by the difference between the pressures acting on the diaphragms. This pressure difference is proportional to the airflow through the injector; thus, the volume of airflow determines the rate of fuel flow.
Under low power settings, the difference in pressure created by the venturi is inadequate to achieve consistent regulation of the fuel. Moreover, a constant-head idle spring is implemented to provide a constant fuel differential pressure, allowing ample flow in the idle range.
Fuel Metering Section
The fuel metering section of the injector assembly is affixed to the air metering section and has an inlet fuel strainer, a manual mixture control valve, an idle valve, and the main metering jet. To begin, the idle valve is connected to the throttle valve through the use of an external adjustable link. In some injector models, a power enrichment jet may also be located in this section.
The main function of the fuel metering section is to measure and control the flow of fuel to the flow divider. The manual mixture control valve, on the other hand, produces a richer mixture when the lever is against the rich stop, and a progressively leaner mixture as the lever is moved toward idle cutoff. Both idle speed and idle mixture may be adjusted externally to meet your specific engine requirements.
At this point, the metered fuel moves from the fuel control unit to a pressurized flow divider. The flow divider keeps the metered fuel under pressure, divides the fuel between the various cylinders at all engine speeds, and shuts off the individual nozzle lines when the control is placed in idle cutoff.
At idle speed, the fuel pressure from the regulator must build up to surpass the spring force applied to the diaphragm and valve assembly. This enables the valve to move upward until fuel can exit via the annulus of the valve to the fuel nozzle. With an increase in fuel flow through the regulator, fuel pressure builds up in the nozzle lines, which fully opens the flow divider valve, allowing fuel to go into the engine.
A fuel pressure gauge can be utilized as a fuel flow meter with the Bendix RSA injection system in particular. This gauge can be connected to the flow divider to sense the pressure being applied to the discharge nozzle. This pressure is proportional to the fuel flow and indicates the engine power output as well as fuel consumption.
The fuel discharge nozzles have an air bleed design. Generally, there is one nozzle for each cylinder positioned in the cylinder head and the nozzle outlet is directed into the intake port. Furthermore, each nozzle contains a calibrated jet that disperses fuel into an ambient air pressure chamber within the nozzle assembly. Prior to making its way into the individual intake valve chambers, the fuel is mixed with air to aid in atomizing the fuel. A conventional pressure gauge can be calibrated in fuel flow in gallons per hour and be incorporated as a flowmeter.
Conclusion
Automatize Industrials is a premier distributor of fuel-injector system components, such as pressure gauges, valves, fuel nozzles, and more. With over 2 billion new, used, obsolete, and hard-to-find items in our inventory, customers can fulfill their part requirements with ease. Kickoff the procurement process by requesting a competitive quote on any desired item and see how Automatize Industrials can serve as your strategic sourcing partner. For additional questions, call or email us any time; we are available 24/7x365!
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