Fuel-Injection Systems
The
fuel-injection system has many advantages over a conventional carburetor
system. There is less danger of induction system icing, since the drop
in temperature due to fuel vaporization takes place in or near the
cylinder. Acceleration is also improved because of the positive action
of the injection system. In addition, fuel injection improves fuel
distribution. This reduces the overheating of individual cylinders often
caused by variation in mixture due to uneven distribution. The
fuel-injection system also gives better fuel economy than a system in
which the mixture to most cylinders must be richer than necessary so
that the cylinder with the leanest mixture operates properly.
fuel-injection system has many advantages over a conventional carburetor
system. There is less danger of induction system icing, since the drop
in temperature due to fuel vaporization takes place in or near the
cylinder. Acceleration is also improved because of the positive action
of the injection system. In addition, fuel injection improves fuel
distribution. This reduces the overheating of individual cylinders often
caused by variation in mixture due to uneven distribution. The
fuel-injection system also gives better fuel economy than a system in
which the mixture to most cylinders must be richer than necessary so
that the cylinder with the leanest mixture operates properly.
Fuel-injection
systems vary in their details of construction, arrangement, and
operation. The Bendix and Continental fuel-injection systems are
discussed in this section. They are described to provide an
understanding of the operating principles involved.
systems vary in their details of construction, arrangement, and
operation. The Bendix and Continental fuel-injection systems are
discussed in this section. They are described to provide an
understanding of the operating principles involved.
Bendix/Precision Fuel-Injection System
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 which measures engine air consumption and uses
airflow forces to control fuel flow to the engine. The fuel distribution
system to the individual cylinders is obtained by the use of a fuel
flow divider and air bleed nozzles.
inline stem-type regulator injection system (RSA) series consists of an
injector, flow divider, and fuel discharge nozzle. It is a
continuous-flow system which measures engine air consumption and uses
airflow forces to control fuel flow to the engine. The fuel distribution
system to the individual cylinders is obtained by the use of a fuel
flow divider and air bleed nozzles.
Fuel Injector
The fuel injector assembly consists of:
- An airflow section,
- A regulator section, and
- A fuel metering section. Some fuel injectors are equipped with an automatic mixture control unit.
Airflow Section
 |
| Figure 1 |
The airflow consumption of the engine is measured by sensing impact pressure and venturi throat pressure in the throttle
body. These pressures are vented to the two sides of an air diaphragm. A
cutaway view of the airflow measuring section is shown in Figure 1.
Movement of the throttle valve causes a change in engine air
consumption. This results in a change in the air velocity in the
venturi. When airflow through the engine increases, the pressure on the
left of the diaphragm is lowered due to the drop in pressure at the
venturi throat. [Figure
2] As a result, the diaphragm moves to the left, opening the ball
valve. Contributing to this force is the impact pressure that is picked
up by the impact tubes.
body. These pressures are vented to the two sides of an air diaphragm. A
cutaway view of the airflow measuring section is shown in Figure 1.
Movement of the throttle valve causes a change in engine air
consumption. This results in a change in the air velocity in the
venturi. When airflow through the engine increases, the pressure on the
left of the diaphragm is lowered due to the drop in pressure at the
venturi throat. [Figure
2] As a result, the diaphragm moves to the left, opening the ball
valve. Contributing to this force is the impact pressure that is picked
up by the impact tubes.
 |
| Figure 2 |
 |
| Figure 3 |
[Figure 3] This
pressure differential is referred to as the “air metering force.” This
force is accomplished by channeling the impact and venturi suction
pressures to opposite sides of a diaphragm. The difference between these
two pressures becomes a usable force that is equal to the area of the
diaphragm times the pressure difference.
pressure differential is referred to as the “air metering force.” This
force is accomplished by channeling the impact and venturi suction
pressures to opposite sides of a diaphragm. The difference between these
two pressures becomes a usable 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. Fuel inlet pressure is applied to one side of the fuel diaphragm
and metered fuel pressure is applied to the other side. The differential
pressure across the fuel diaphragm is called the fuel metering force.
The fuel pressure shown on the ball side of the fuel diaphragm is the
pressure after the fuel has passed through the fuel strainer and the
manual mixture control rotary plate and is referred to as metered fuel
pressure. Fuel inlet pressure is applied to the opposite side of the
fuel diaphragm. The ball valve attached to the fuel diaphragm controls
the orifice opening and fuel flow through the forces placed on it.
[Figure 4]
section consists of a fuel diaphragm that opposes the air metering
force. Fuel inlet pressure is applied to one side of the fuel diaphragm
and metered fuel pressure is applied to the other side. The differential
pressure across the fuel diaphragm is called the fuel metering force.
The fuel pressure shown on the ball side of the fuel diaphragm is the
pressure after the fuel has passed through the fuel strainer and the
manual mixture control rotary plate and is referred to as metered fuel
pressure. Fuel inlet pressure is applied to the opposite side of the
fuel diaphragm. The ball valve attached to the fuel diaphragm controls
the orifice opening and fuel flow through the forces placed on it.
[Figure 4]
 |
| Figure 4 |
The distance
the ball valve opens is determined by the difference between the
pressures acting on the diaphragms. This difference in pressure is
proportional to the airflow through the injector. Thus, the volume of
airflow determines the rate of fuel flow.
the ball valve opens is determined by the difference between the
pressures acting on the diaphragms. This difference in pressure 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
insufficient to accomplish consistent regulation of the fuel. A
constant-head idle spring is incorporated to provide a constant fuel
differential pressure. This allows an adequate final flow in the idle
range.
settings, the difference in pressure created by the venturi is
insufficient to accomplish consistent regulation of the fuel. A
constant-head idle spring is incorporated to provide a constant fuel
differential pressure. This allows an adequate final flow in the idle
range.
Fuel Metering Section
 |
| Figure 5 |
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 5] 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.
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 5] 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.
 |
| Figure 6 |
The purpose of
the fuel metering section is to meter and control the fuel flow to the
flow divider. [Figure 6] 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.
the fuel metering section is to meter and control the fuel flow to the
flow divider. [Figure 6] 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.
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.
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.
 |
| Figure 7 |
Referring to
the diagram in Figure 7, 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
8] 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.
the diagram in Figure 7, 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
8] 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 8 |
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.
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.
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.
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
 |
| Figure 9 |
The fuel
discharge nozzles are of the air bleed configuration. There is one
nozzle for each cylinder located in the cylinder head. [Figure 9] 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
discharge nozzles are of the air bleed configuration. There is one
nozzle for each cylinder located in the cylinder head. [Figure 9] 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.
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.
Continental/TCM Fuel-Injection System
The Continental
fuel-injection system injects fuel into the intake valve port in each
cylinder head. [Figure 10] 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.
fuel-injection system injects fuel into the intake valve port in each
cylinder head. [Figure 10] 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 10 |
Fuel-Injection Pump
 |
| Figure 11 |
The fuel pump
is a positive-displacement, rotary-vane type with a splined shaft for
connection to the accessory drive system of the engine. [Figure 11] A
spring-loaded, diaphragm-type relief valve is provided. The relief valve
diaphragm chamber is vented to atmospheric pressure. A sectional view
of a fuel-injection pump is shown in Figure 12.
is a positive-displacement, rotary-vane type with a splined shaft for
connection to the accessory drive system of the engine. [Figure 11] A
spring-loaded, diaphragm-type relief valve is provided. The relief valve
diaphragm chamber is vented to atmospheric pressure. A sectional view
of a fuel-injection pump is shown in Figure 12.
Fuel enters at
the swirl well of the vapor separator. Here, vapor is separated by a
swirling motion so that only liquid fuel is delivered to the pump. The
vapor is drawn from the top center of the swirl well by a small pressure
jet of fuel and is directed into the vapor return line. This line
carries the vapor back to the fuel tank.
the swirl well of the vapor separator. Here, vapor is separated by a
swirling motion so that only liquid fuel is delivered to the pump. The
vapor is drawn from the top center of the swirl well by a small pressure
jet of fuel and is directed into the vapor return line. This line
carries the vapor back to the fuel tank.
 |
| Figure 12 |
Ignoring the
effect of altitude or ambient air conditions, the use of a
positive-displacement, engine-driven pump means that changes in engine
speed affect total pump flow proportionally. Since the pump provides
greater capacity than is required by the engine, a recirculation path is
required. By arranging a calibrated orifice and relief valve in this
path, the pump delivery pressure is also maintained in proportion to
engine speed. These provisions assure proper pump pressure and fuel
delivery for all engine operating speeds.
effect of altitude or ambient air conditions, the use of a
positive-displacement, engine-driven pump means that changes in engine
speed affect total pump flow proportionally. Since the pump provides
greater capacity than is required by the engine, a recirculation path is
required. By arranging a calibrated orifice and relief valve in this
path, the pump delivery pressure is also maintained in proportion to
engine speed. These provisions assure proper pump pressure and fuel
delivery for all engine operating speeds.
A check valve
is provided so that boost pump pressure to the system can bypass the
engine-driven pump for starting. This feature also suppresses vapor
formation under high ambient temperatures of the fuel, and permits use
of the auxiliary pump as a source of fuel pressure in the event of
engine-driven pump failure.
is provided so that boost pump pressure to the system can bypass the
engine-driven pump for starting. This feature also suppresses vapor
formation under high ambient temperatures of the fuel, and permits use
of the auxiliary pump as a source of fuel pressure in the event of
engine-driven pump failure.
Fuel/Air Control Unit
 |
| Figure 13 |
The function of
the fuel/air control assembly is to control engine air intake and to
set the metered fuel pressure for proper fuel/air ratio. The air
throttle is mounted at the manifold inlet and its butterfly valve,
positioned by the throttle control in the aircraft, controls the flow of
air to the engine. [Figure 13]
the fuel/air control assembly is to control engine air intake and to
set the metered fuel pressure for proper fuel/air ratio. The air
throttle is mounted at the manifold inlet and its butterfly valve,
positioned by the throttle control in the aircraft, controls the flow of
air to the engine. [Figure 13]
The air
throttle assembly is an aluminum casting which contains the shaft and
butterfly-valve assembly. The casting bore size is tailored to the
engine size, and no venturi or other restriction is used.
throttle assembly is an aluminum casting which contains the shaft and
butterfly-valve assembly. The casting bore size is tailored to the
engine size, and no venturi or other restriction is used.
Fuel Control Assembly
The fuel
control body is made of bronze for best bearing action with the
stainless steel valves. Its central bore contains a metering valve at
one end and a mixture control valve at the other end. Each stainless
steel rotary valve includes a groove which forms a fuel chamber.
control body is made of bronze for best bearing action with the
stainless steel valves. Its central bore contains a metering valve at
one end and a mixture control valve at the other end. Each stainless
steel rotary valve includes a groove which forms a fuel chamber.
Fuel enters the
control unit through a strainer and passes to the metering valve.
[Figure 14] This rotary valve has a cam-shaped edge on the outer part of
the end face. The position of the cam at the fuel delivery port
controls the fuel passed to the manifold valve and the nozzles. The fuel
return port connects to the return passage of the center metering plug.
The alignment of the mixture control valve with this passage determines
the amount of fuel returned to the fuel pump.
control unit through a strainer and passes to the metering valve.
[Figure 14] This rotary valve has a cam-shaped edge on the outer part of
the end face. The position of the cam at the fuel delivery port
controls the fuel passed to the manifold valve and the nozzles. The fuel
return port connects to the return passage of the center metering plug.
The alignment of the mixture control valve with this passage determines
the amount of fuel returned to the fuel pump.
 |
| Figure 14 |
By connecting
the metering valve to the air throttle, the fuel flow is properly
proportioned to airflow for the correct fuel/ air ratio. A control level
is mounted on the mixture control valve shaft and connected to the
cockpit mixture control.
the metering valve to the air throttle, the fuel flow is properly
proportioned to airflow for the correct fuel/ air ratio. A control level
is mounted on the mixture control valve shaft and connected to the
cockpit mixture control.
Fuel Manifold Valve
The fuel
manifold valve contains a fuel inlet, a diaphragm chamber, and outlet
ports for the lines to the individual nozzles. [Figure 15] The
spring-loaded diaphragm operates a valve in the central bore of the
body. Fuel pressure provides the force for moving the diaphragm. The
diaphragm is enclosed by a cover that retains the diaphragm loading
spring. When the valve is down against the lapped seat in the body, the
fuel lines to the cylinders are closed off. The valve is drilled for
passage of fuel from the diaphragm chamber to its base, and a ball valve
is installed within the valve. All incoming fuel must pass through a
fine screen installed in the diaphragm chamber.
manifold valve contains a fuel inlet, a diaphragm chamber, and outlet
ports for the lines to the individual nozzles. [Figure 15] The
spring-loaded diaphragm operates a valve in the central bore of the
body. Fuel pressure provides the force for moving the diaphragm. The
diaphragm is enclosed by a cover that retains the diaphragm loading
spring. When the valve is down against the lapped seat in the body, the
fuel lines to the cylinders are closed off. The valve is drilled for
passage of fuel from the diaphragm chamber to its base, and a ball valve
is installed within the valve. All incoming fuel must pass through a
fine screen installed in the diaphragm chamber.
 |
| Figure 15 |
From the fuel-injection control valve, fuel is delivered to the fuel manifold valve, which provides a central point for
dividing fuel
flow to the individual cylinders. In the fuel manifold valve, a
diaphragm raises or lowers a plunger valve to open or close the
individual cylinder fuel supply ports simultaneously.
flow to the individual cylinders. In the fuel manifold valve, a
diaphragm raises or lowers a plunger valve to open or close the
individual cylinder fuel supply ports simultaneously.
Fuel Discharge Nozzle
The fuel
discharge nozzle is located in the cylinder head with its outlet
directed into the intake port. The nozzle body contains a drilled
central passage with a counterbore at each end. [Figure 16] The lower
end is used as a chamber for fuel/air mixing before the spray leaves the
nozzle. The upper bore contains a removable orifice for calibrating the
nozzles. Nozzles are calibrated in several ranges, and all nozzles
furnished for one engine are of the same range and are identified by a
letter stamped on the hex of the nozzle body.
discharge nozzle is located in the cylinder head with its outlet
directed into the intake port. The nozzle body contains a drilled
central passage with a counterbore at each end. [Figure 16] The lower
end is used as a chamber for fuel/air mixing before the spray leaves the
nozzle. The upper bore contains a removable orifice for calibrating the
nozzles. Nozzles are calibrated in several ranges, and all nozzles
furnished for one engine are of the same range and are identified by a
letter stamped on the hex of the nozzle body.
 |
| Figure 16 |
Drilled radial
holes connect the upper counterbore with the outside of the nozzle body.
These holes enter the counterbore above the orifice and draw air
through a cylindrical screen fitted over the nozzle body. A shield is
press-fitted on the nozzle body and extends over the greater part of the
filter screen, leaving an opening near the bottom. This provides both
mechanical protection and an abrupt change in the direction of airflow
which keeps dirt and foreign material out of the nozzle interior.
holes connect the upper counterbore with the outside of the nozzle body.
These holes enter the counterbore above the orifice and draw air
through a cylindrical screen fitted over the nozzle body. A shield is
press-fitted on the nozzle body and extends over the greater part of the
filter screen, leaving an opening near the bottom. This provides both
mechanical protection and an abrupt change in the direction of airflow
which keeps dirt and foreign material out of the nozzle interior.
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