Engine Fuel Systems Part 1 - Aircraft Gas Turbine Engines #19

Summary

The script delves into the engine fuel system of aircraft, detailing its components and functions. It explains how the system receives low-pressure fuel from the airframe tanks, increases pressure for combustion, and includes mechanisms like booster pumps, low-pressure fuel pumps, oil coolers, and fuel heaters to ensure efficient and safe operation. The focus is on the intricacies of the fuel control unit, which adjusts fuel flow according to various engine requirements, highlighting the importance of components like the high-pressure fuel pump and the hydro-mechanical fuel control systems.

Takeaways

• 🛩️ The engine fuel system is a critical part of the aircraft's fuel supply, receiving low-pressure fuel from the airframe fuel system and increasing it to a usable pressure for the engine.
• 🔧 The booster pumps in the wing and center tanks pass fuel to the engine through non-return valves, ensuring a continuous supply even if the engine fire control handle is activated.
• 🔄 The low-pressure fuel system can be used to shut off the fuel supply for maintenance or in case of engine fire, but it takes longer to shut down the engine compared to using high-pressure fuel.
• 🚫 The low-pressure fuel system contains a significant amount of fuel in the pipeline, which can maintain supply to the burners for some time, unlike the high-pressure system.
• 🔧 The low-pressure fuel pump, also known as the backing pump, supports the fuel supply to the engine in case of booster pump failure and helps prevent cavitation in the high-pressure pump.
• 🔥 A fuel cooled oil cooler is used in most gas turbine engines to cool the oil and heat the fuel, preventing ice crystal formation that could block the fuel system.
• 🛠️ The oil feed line to the fuel cooled oil cooler includes a pressure maintaining valve to ensure oil leaks into the fuel system rather than fuel into the oil system in case of a leak, avoiding potential hazards.
• 🌡️ The fuel heater works with the fuel cool oil cooler to maintain a predetermined fuel temperature, using a Verna therm thermal actuator sensitive to temperature changes.
• 📏 The flow meter measures the instantaneous fuel flow and can totalize the amount of fuel used, with two types in use on large jet aircraft: the vane type and the mass flow measuring type.
• 🛡️ The fuel pressure is sensed after the low-pressure fuel filter, which protects sensitive control components from dirt or contamination, and is indicated on the flight deck for monitoring.
• ⚙️ The high-pressure fuel pump, driven by the engine accessory gearbox, uses a plunger or spur gear type design to supply the necessary fuel flow, with the output controlled by a servo piston from the fuel control unit.

Q & A

What are the two main sections of the aircraft's fuel system?

The two main sections of the aircraft's fuel system are the airframe fuel system and the engine fuel system.

What is the primary function of the engine fuel system?

The primary function of the engine fuel system is to receive low pressure fuel supply from the aircraft fuel tanks, increase the fuel pressure to a value usable by the fuel nozzles in the combustion chamber, and control the volume of fuel into the engine to meet its requirements.

What is the role of booster pumps in the airframe fuel system?

Booster pumps in the airframe fuel system are responsible for passing fuel through non-return valves to the engine via the low-pressure fuel supply.

How can the low-pressure fuel be used in the event of a fire or component removal?

The low-pressure fuel can be used to shut off the supply to the engine automatically if the engine fire control handle is activated or to facilitate the removal of a fuel system component by stopping the fuel supply.

What is the purpose of the low-pressure fuel pump in the engine fuel system?

The low-pressure fuel pump, sometimes called the backing pump, is used to back up the fuel supply to the engine in case of a failure of both booster pumps in the wing tanks and to minimize the chance of cavitation at the inlet of the high-pressure pump.

What is the function of a fuel cooled oil cooler in gas turbine engines?

A fuel cooled oil cooler serves the dual purpose of cooling the oil and heating the fuel, which helps to eliminate the formation of ice crystals that may block components downstream in the fuel system.

How does the pressure maintaining valve in the oil feed line to the fuel cooled oil cooler work?

The pressure maintaining valve keeps the oil pressure in the cooler higher than the fuel pressure, ensuring that if an internal leak occurs, the oil leaks into the fuel system rather than the fuel leaking into the oil system.

What is the purpose of the fuel heater in the fuel system?

The fuel heater assists in warming the fuel to eliminate ice crystals and maintain a predetermined fuel temperature through the use of compressed bleed air.

What are the two types of flow meters used on large jet aircraft?

The two types of flow meters used on large jet aircraft are the vane type and the mass flow measuring type.

How does the high-pressure fuel pump function in the engine fuel system?

The high-pressure fuel pump, which can be of different types such as plunger or spur gear type, is fitted and driven by the engine accessory gearbox and is responsible for supplying fuel under high pressure to the outlet.

What are the two types of hydro-mechanical fuel control systems used in gas turbine engines?

The two types of hydro-mechanical fuel control systems used in gas turbine engines are the pressure control system and the proportional flow control system, with the latter being more popular due to its compactness and insensitivity to flow variations downstream of the throttle.

Outlines

00:00

🛩 Engine Fuel System Mechanics

The first paragraph delves into the engine fuel system's role in managing fuel supply for aircraft engines. It explains how the system receives low-pressure fuel from the airframe's tanks and increases the pressure to meet combustion chamber requirements. Key components such as booster pumps, non-return valves, and low-pressure fuel pumps are highlighted, with a focus on their functions in maintaining fuel pressure and preventing cavitation. The paragraph also discusses the importance of the fuel cooled oil cooler in preventing ice crystal formation and the role of the fuel heater and flow meter in maintaining fuel temperature and measuring fuel flow. Additionally, it touches on the significance of the low-pressure fuel in emergency shutdowns and the use of filters to protect sensitive engine components.

05:03

📏 Types and Functions of Fuel Flow Meters

The second paragraph provides an in-depth look at the two types of fuel flow meters used in large jet aircraft: the vane type and the mass flow measuring type. The vane type, found in older systems, measures the volume of fuel flow and is described as less accurate. In contrast, the mass flow type offers greater precision, within a 1% margin of error, by measuring the mass flow rate. This type uses an impeller and drum with magnets that interact with pickup coils to translate angular displacement into a mass flow rate. The paragraph also covers the importance of fuel temperature and pressure sensing for system monitoring and the various types of high-pressure fuel pumps, including plunger and spur gear types, and their roles in the fuel control system. The hydro mechanical fuel control systems, specifically the pressure control and proportional flow control systems, are also discussed, with a focus on the latter's advantages in compactness and insensitivity to flow variations.

Keywords

💡Engine Fuel System

The engine fuel system is a critical component of an aircraft's fuel management infrastructure. It is responsible for receiving low-pressure fuel from the airframe fuel system and increasing the pressure to a level suitable for the combustion chamber's fuel nozzles. This system ensures that the fuel supply meets the engine's operational requirements, as described in the script when it mentions how the 'engine fuel system increases the fuel pressure' and 'controls a volume of fuel into the engine.'

💡Booster Pumps

Booster pumps are located in the wing and center tanks of the airframe fuel system and play a vital role in passing fuel through non-return valves to the engine. They are part of the low-pressure fuel subsystem and are crucial for maintaining fuel flow. The script refers to them when explaining the initial stage of fuel delivery, stating that 'the booster pumps... pass fuel through non-return valves to the engine via the low-pressure fuel.'

💡Low-Pressure Fuel

Low-pressure fuel is the initial stage of fuel supply that is electrically operated and can be automatically shut off in case of an engine fire, as mentioned in the script. It is used to shut off the fuel supply to the engine for maintenance or in emergency situations, highlighting its importance in safety and operational control.

💡High-Pressure Fuel

High-pressure fuel is essential for the efficient operation of the engine, as it is used to shut down the engine quickly when necessary. The script contrasts it with low-pressure fuel, stating that 'using the low-pressure fuel to shut down the engine... will mean that the engine will take much longer to shut down.' This distinction is important for understanding the different roles and responses of the fuel system under various conditions.

💡Low Pressure Fuel Pump

Also known as the backing pump, the low pressure fuel pump supports the fuel supply to the engine, particularly in the event of booster pump failure. It helps maintain positive pressure and minimize the chance of cavitation at the inlet of the high-pressure pump, as described in the script where it states that the 'low pressure fuel pump... will attempt to back up the fuel supply to the engine.'

💡Fuel Cooled Oil Cooler

The fuel cooled oil cooler serves a dual purpose in gas turbine engines: it cools the oil and heats the fuel, preventing the formation of ice crystals that could obstruct the fuel system. The script explains its function, noting that 'the oil cooler... eliminates the formation of ice crystals which may block components downstream in the fuel system.'

💡Fuel Heater

The fuel heater is an essential component for warming the fuel and preventing ice crystal formation, ensuring smooth operation of the fuel system. It works in conjunction with the fuel cool oil cooler, as mentioned in the script: 'the fuel heater... uses compressed bleed air to warm the fuel to automatically maintain a predetermined fuel temperature.'

💡Fuel Flow Meter

The fuel flow meter measures the rate of fuel flow, which can be crucial for monitoring and managing fuel consumption. The script describes two types of flow meters used in large jet aircraft: 'the vane type and the mass flow measuring type,' with the latter being more accurate and providing a direct measure of mass flow rate.

💡Fuel Filter

Fuel filters are the first line of defense against dirt or contamination that could damage sensitive control components. The script specifies that 'the pressure fuel filter is the first line of defense protecting the delicate control components... from the effects of dirt or contamination.'

💡High-Pressure Fuel Pump

The high-pressure fuel pump is a key component driven by the engine accessory gearbox and is responsible for supplying the necessary fuel pressure for engine operation. The script describes it as 'fitted to and driven by the engine accessory gearbox,' and it is crucial for maintaining the correct fuel pressure for efficient engine performance.

💡Fuel Control Unit

The fuel control unit is responsible for managing the fuel flow according to the engine's needs, adjusting for various factors such as air intake pressure and engine acceleration. The script describes two types of hydro mechanical fuel control systems, with the 'proportional flow control system' being more popular due to its compactness and insensitivity to flow variations.

Highlights

The engine fuel system is a critical component that increases fuel pressure and controls fuel volume to meet engine requirements.

The booster pumps in the wing and center tanks pass fuel through non-return valves to the engine via the low-pressure fuel system.

Low-pressure fuel can be used to shut off the engine automatically in case of an engine fire or for maintenance purposes.

The low-pressure fuel pump, also known as the backing pump, supports the fuel supply in case of booster pump failure.

A fuel cooled oil cooler is used to prevent ice crystal formation in the fuel system, ensuring smooth operation.

The oil cooler has a pressure maintaining valve to prevent oil from leaking into the fuel system, avoiding potential hazards.

The fuel heater and fuel cool oil cooler work together to maintain a predetermined fuel temperature using compressed bleed air.

A Verna therm thermal actuator is used for automatic temperature control in the fuel system.

The pressure fuel filter protects sensitive control components from dirt and contamination.

Flow meters measure instantaneous fuel flow and can integrate total fuel usage, with two types being the vane type and mass flow measuring type.

The fuel temperature and pressure are monitored for system performance and safety.

The high-pressure fuel pump is driven by the engine accessory gearbox and is crucial for fuel flow regulation.

Plunger type pumps are used in high-pressure fuel pumps for their ability to control fuel flow based on engine demand.

Spur gear type fuel pumps offer a simpler and lighter construction compared to plunger type pumps.

The fuel control unit is central to managing fuel flow, adjusting for various engine conditions and requirements.

Hydro mechanical fuel control systems, including pressure control and proportional flow control systems, are still widely used.

The proportional flow control system is preferred for its compact design and insensitivity to flow variations downstream of the throttle.

The fuel control unit incorporates various devices to adjust fuel flow for air intake pressure, engine acceleration, and exhaust gas temperature control.

Transcripts

the entire system which stalls carries

and controls the fuel supply for the

engines can be divided into two sections

the airframe fuel system

at the engine fuel system

here we'll look specifically at the

engine fuel system which receives the

low pressure fuel supply from the

aircraft fuel tanks which are part of

the airframe fuel system

the engine fuel system increases the

fuel pressure to a value that the fuel

nozzles in the combustion chamber can

use

and then controls a volume of fuel into

the engine so that it conforms to the

engine's requirements

the engine fuel system consists of a

number of components which will now

describe in more detail

the booster pumps which are situated in

the wing and center tanks of the

airframe fuel system pass fuel through

non-return valves to the engine via the

low pressure fuel

the low-pressure fuel is

electrically operated it can be shut

automatically if the engine fire control

handle is activated

if a component of the fuel system needs

to be removed for whatever purposes the

low-pressure fuel can be used to

shut off the supply of fuel to the

engine to facilitate the removal

if the high-pressure fuel cannot be

used to shut down the engine for

whatever reason as an alternative the

low-pressure fuel can be used to

stop the engine however using the

low-pressure fuel to shut down the

engine instead of the high-pressure fuel

will mean that the engine will take

much longer to shut down this is because

the pipeline between the low pressure

fuel and the engine contains a

considerable amount of fuel which will

maintain the supply to the burners for

some time whereas in the case of the

high pressure fuel very little fuel

is contained in the pipeline between

aids and the combustion chambers

after it's passed through the low

pressure fuel cocked the fuel then

enters the engine fuel system and is

delivered to the low pressure fuel pump

the low pressure fuel pump is sometimes

called the backing pump because it will

attempt to back up the fuel supply to

the engine in the event of failure of

both of the booster pumps in the wing

tanks

pressure fuel pump is used to supply

positive fuel pressure directly to the

high-pressure pump by maintaining a

positive pressure the low pressure pump

minimizes the chance of cavitation

occurring at the inlet of a

high-pressure pump

the low pressure fuel pump is driven by

the engines accessory gearbox which

itself is driven by the high pressure

compressor shaft

a fuel cooled oil cooler is fitted in

the majority of gas turbine engine

installations the oil cooler serves the

double purpose of cooling the oil and

also heating the fuel

by raising the temperature of the fuel

the oil cooler eliminates the formation

of ice crystals which may block

components downstream in the fuel system

the oil feed line to the fuel cooled oil

cooler incorporates a pressure

maintaining valve this valve keeps the

oil pressure in the cooler higher than

the fuel pressure if the oil cooler does

develop an internal leak then the fact

that the oil pressure is higher than the

fuel pressure will ensure that the oil

leaks into the fuel system rather than

the fuel leaking into the oil system

which could be very dangerous

the fuel heater assists in the warming

of the fuel and thus the elimination of

ice crystals the fuel heater working in

conjunction with the fuel cool oil

cooler uses compressed breed air to warm

the fuel to automatically maintain a

predetermined fuel temperature

the automatic temperature control can be

achieved by the action of a Verna therm

thermal actuator the thermal actuator

incorporates a material which is

sensitive to temperature change this is

used to open or close a valve which

regulates the entry of hot air into the

fuel heater from the engine compressor

pressure fuel filter is the first line

of defense protecting the delicate

control components within the high

pressure fuel pump and the fuel control

unit from the effects of dirt or

contamination

the low-pressure filter is usually a

replaceable paper filter element which

is capable of filtering out particles

larger than 50 to 100 microns

the flow meter measures the

instantaneous fuel flow in gallons per

hour kilograms per hour or pounds per

hour the flow meter may also include an

integrating system which can add the

total amount of fuel used

are basically two types of flow meter in

use on large jet aircraft they are the

vane type and the mass flow measuring

type

the vein type of fuel flow meter which

is fitted to older aircraft systems is

designed to measure volume of flow

the flowmeter consists of a vein which

is moved against the force of a

restraining spring by the volume of fuel

flowing past it this system is not too

accurate

the mass flow type of instrument can be

accurate to within plus or minus 1% fuel

flowing through the instrument rotates

both the drum and a spring mounted

impeller which have magnets fixed to

them

sense by pickup coils which translate

the difference in angular displacement

between the magnets into a mass flow

rate

you

the fuel temperature is sensed as the

fuel leaves of your heater

fuel temperature is indicated on the

flight deck to allow system monitoring

you

the fuel pressure is sensed as the fuel

leaves the low-pressure fuel filter

fuel no pressure may be indicated by

either an LP fuel warning light all the

activation of warnings on the eye cash

or ECAM depending on aircraft type

you

a high pressure fuel pump is fitted to

and driven by the engine accessory

gearbox the engine accessory gearbox

itself is driven by the high-pressure

compressor shaft

I pressure fuel pump Illustrated is

representative of one type of pump

employed its a plunger type pump it can

be used as a single unit if the volume

of fuel required is not too great but in

larger engines two units can be driven

together to supply a greater fuel flow

several plungers are fitted on a rotor

assembly

against a stationary camp late which

causes them to reciprocate within the

balls that contain them on the rotor

assembly

the distance that the plungers move

during this reciprocating action is

dictated by the angle of inclination of

the cam plate here we see the camp eight

angled so that the plungers stay in the

same position in their balls as the

rotor drives them round

now the camp blade angle is such that

the springs force the plungers to their

maximum stroke when they are at the top

of the cam plate sucking fuel into the

pores

and the kemplay forces the plungers to

their minimum stroke when they are at

the bottom of the cam plate forcing fuel

under pressure to the outlet of the pump

the angle of inclination of the camp

rate is controlled by a servo piston

which itself is controlled from the fuel

control unit

systems incorporate a fuel filter into

the output of the high pressure fuel

pump to prevent very fine particles

entering the extremely small passageways

inside the fuel control unit the fuel

filter is composed of a number of wire

mesh green disks

the spur gear type fuel pump is simpler

and lighter in construction and the

plunger type fuel pump and like the

plunger type pump the spur gear type

pump is driven by the accessory gearbox

the output of the spur gear type pump is

directly proportional to its rotational

speed

the fuel control unit controls the fuel

flow to the

for every thrust setting

there are two types of hydro mechanical

fuel control systems still used on gas

turbine engines they are the pressure

control system and the proportional flow

control system the proportional flow

control system is the more popular of

the two types because it is more compact

than the pressure control system and

it's not sensitive to the effect of flow

variations that occur downstream of the

throttle

the proportional flow control system is

the type we'll use to describe the

individual parts of a fuel control unit

various devices within the fuel control

unit are used to adjust the fuel flow to

cater for variations in air intake

pressure engine acceleration control

exhaust gas temperature rpm limiting and

compress the delivery pressure