Fuel-Injection Systems (Part Two)

in Engine Fuel and Fuel Metering Systems

Fuel Metering Section

The fuel metering section is attached to the air metering section and contains an inlet fuel strainer, a manual mixture control valve, an idle valve, and the main metering jet. [Figure 2-34] The idle valve is connected to the throttle valve by means of an external adjustable link. In some injector models, a power enrichment jet is also located in this section. The purpose of the fuel metering section is to meter and control the fuel flow to the flow divider. [Figure 2-35] The manual mixture control valve produces full rich condition 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 individual engine requirements.


Figure 2-34. Fuel metering section of the injector.

Figure 2-34. Fuel metering section of the injector.

Figure 2-35. Fuel inlet and metering.

Figure 2-35. Fuel inlet and metering.

Flow Divider

The metered fuel is delivered from the fuel control unit to a pressurized flow divider. This unit keeps metered fuel under pressure, divides fuel to the various cylinders at all engine speeds, and shuts off the individual nozzle lines when the control is placed in idle cutoff.

Referring to the diagram in Figure 2-36, metered fuel pressure enters the flow divider through a channel that permits fuel to pass through the inside diameter of the flow divider needle. At idle speed, the fuel pressure from the regulator must build up to overcome the spring force applied to the diaphragm and valve assembly. This moves the valve upward until fuel can pass out through the annulus of the valve to the fuel nozzle. [Figure 2-37] Since the regulator meters and delivers a fixed amount of fuel to the flow divider, the valve opens only as far as necessary to pass this amount to the nozzles. At idle, the opening required is very small; the fuel for the individual cylinders is divided at idle by the flow divider.

Figure 2-36. Flow divider.

Figure 2-36. Flow divider.

As fuel flow through the regulator is increased above idle requirements, fuel pressure builds up in the nozzle lines. This pressure fully opens the flow divider valve, and fuel distribution to the engine becomes a function of the discharge nozzles.

Figure 2-37. Flow divider cutaway.

Figure 2-37. Flow divider cutaway.

A fuel pressure gauge, calibrated in pounds per hour fuel flow, can be used as a fuel flow meter with the Bendix RSA injection system. This gauge is connected to the flow divider and senses the pressure being applied to the discharge nozzle. This pressure is in direct proportion to the fuel flow and indicates the engine power output and fuel consumption.

Fuel Discharge Nozzles

The fuel discharge nozzles are of the air bleed configuration. There is one nozzle for each cylinder located in the cylinder head. [Figure 2-38] The nozzle outlet is directed into the intake port. Each nozzle incorporates a calibrated jet. The jet size is determined by the available fuel inlet pressure and the maximum fuel flow required by the engine. The fuel is discharged through this jet into an ambient air pressure chamber within the nozzle assembly. Before entering the individual intake valve chambers, the fuel is mixed with air to aid in atomizing the fuel. Fuel pressure, before the individual nozzles, is in direct proportion to fuel flow; therefore, a simple pressure gauge can be calibrated in fuel flow in gallons per hour and be employed as a flowmeter. Engines modified with turbosuperchargers must use shrouded nozzles. By the use of an air manifold, these nozzles are vented to the injector air inlet pressure.

Figure 2-38. Fuel nozzle assembly.

Figure 2-38. Fuel nozzle assembly.

Continental/TCM Fuel-Injection System

The Continental fuel-injection system injects fuel into the intake valve port in each cylinder head. [Figure 2-39] The system consists of a fuel injector pump, a control unit, a fuel manifold, and a fuel discharge nozzle. It is a continuous-flow type, which controls fuel flow to match engine airflow. The continuous-flow system permits the use of a rotary vane pump which does not require timing to the engine.

Figure 2-39. Continental/TCM Fuel-Injection System.

Figure 2-39. Continental/TCM Fuel-Injection System.