All language subtitles for [SubtitleTools.com] 28. Hệ thống nhiên liệu - chủng loại nhiên liệu-en-US

In this lesson, we will examine
the properties of the various

fuels used in aircraft engines.

Aircraft piston engines use
gasoline and gas turbine engines

kerosene.

Both of these fuels are produced
from crude oil.

In simple terms, the required
fuel is extracted from the crude

oil by a distillation process.

The oil is boiled in a furnace
and then the oil vapour is

cooled in a distillation column.

The various hydrocarbons in the
oil all have different boiling

points, so they condense out of
the vapour and are tapped off at

different points in the column.

The heavy oils condense out
first and are collected near the

bottom.

The process then continues up
through the tower, with kerosene

and gasoline, which are
relatively light and volatile,

being taken out near the top.

The specification from ideal
fuel for either a gas turbine

engine or a piston engine
include the following main

requirements.

It should flow easily under all
operating conditions.

It should have complete
combustion under all conditions.

It needs to have a high
calorific value.

The calorific value is a measure
of the amount of heat released

during its combustion.

It is measured in British
thermal units per pound or

kilojoules per kilogram.

It should be non corrosive.

There should be no damage to the
engine from combustion

byproducts.

The fuel should present a low
fire hazard.

Engines should start easily and
the fuel must be able to

lubricate the moving parts of
the fuel pumps and other

components in the system.

In practice, the cost of
satisfying all these criteria is

prohibitive and therefore
compromises have to be made.

Piston engined aircraft use
gasoline fuels grouped under the

title Aviation Gasoline or
Avgas.

Aviation gasoline is
manufactured to conform with the

exacting specifications that are
issued in the United Kingdom by

the UK Aviation Fuels Committee
on behalf of the Defence

Material Standardisation
Committee.

The specification number for
gasoline is Defence Standard or

DEF Stan 91-90.

Aviation gasoline is graded by
octane rating.

The octane rating of a fuel is a
measure of the fuel's resistance

to detonation when subjected to
high temperature and pressure.

A fuel's octane rating is
checked in a test engine with

the fuel air mixture weak and
with it rich.

This gives the fuel 2 octane
ratings.

The weak figure is used in the
fuel's name.

So for instance, Avgas 100 is a
100 octane fuel when the mixture

is weak, but a 130 octane when
the mixture is rich.

These two octane ratings are
known together as the fuel's

performance number or index.

So avgas 100 has a performance
index of one hundred 130.

High performance engines with
high compression ratios require

high octane fuel.

Engines with lower compression
ratios can use lower octane

fuel.

The grades of aviation gasoline
currently authorized and

available are avgas 100 and
avgas 100.

LL Afgas has a freezing point in
the region of -58°C and a

flashpoint, which is the
temperature at which the fuel

vapour will ignite in contact
with a flame of -40°C or colder.

It has a specific gravity of
0.72 at 15°C.

Specific gravity is important as
fuel is delivered by volume, but

pilots need to know its mass or
weight as the energy available

from the fuel is dependent on
its mass, not its volume.

Afgas 100 is coloured green and
has a performance number of one

hundred 130.

Avgas 100 LL has the same
performance number as Avgas 100,

but it has a lower lead content.

It is coloured blue.

MO gas or motor gasoline can
sometimes be used in certain

airframe engine combinations,
but only under the conditions

specified in Civil Aviation
Authority Airworthiness notices

#9898A98B and 98C.

Because of the higher volatility
and water content of MO gas,

carburettor icing and vapour
locking are much more likely to

occur if this fuel is used.

The subjects of carburetor icing
and vapour locking are covered

in detail in the Piston Engine
Series of Lessons.

Information and advice on the
use of mogas can be found in the

CAA Safety Sense leaflet #4B.

Diesel piston engines use AVTA.

This fuel is described in the
Gas Turbine Engine Fuel section.

Gas turbine engineed aircraft
use kerosene fuels.

These are heavier and less
volatile than gasoline fuels.

They are placed between gasoline
and diesel fuel in the

distillation process.

The two main types of gas
turbine fuel in use in civilian

aircraft are aviation turbine
fuel or AVATAR, and aviation

turbine gasoline or AVTAG.

As with aviation gasoline in the
United Kingdom, the

specifications for these fuels
are issued by the UK Aviation

Fuels Committee on behalf of the
Defence Material Standardization

Committee.

There are two grades of AVATAR
in use.

Jet A1 is used in Europe and
most of the rest of the world,

whilst Jet A is used in the
United States of America.

Jet A1 is a kerosene type fuel
with a nominal specific gravity

of 0.8 at 15°C.

It has a flashpoint of 38.7°C
and a waxing point of -50°C.

Waxing is explained later in the
lesson.

Jet A is a similar type of fuel
to Jet A1, but it has a waxing

point of -40°C.

Gas turbine fuels are not dyed
for identification.

They retain their natural
colour, which can range between

what is termed as water clear to
a straw yellow.

Avtag is known in Civil Aviation
as Jet B.

It is not generally used in
civilian aircraft.

It is a gasoline and kerosene
mix with a nominal specific

gravity of 0.77 at 15°C.

It has a flashpoint of -20° and
a waxing point of -60°C.

Because of the very low waxing
point, it may be found in use at

a small number of civil
airfields in very cold climates.

If a fuel sample is placed in a
clear glass container and

swirled vigorously and the
sample appears cloudy or hazy,

then there could be one of two
reasons for this.

If the cloudiness appears to
rise quite rapidly towards the

top of the sample, then air is
present.

But if the cloud falls quite
slowly towards the bottom of the

sample, then water is present in
the fuel.

Having said that, a cloudy
appearance usually indicates the

presence of water.

A certain amount of water is
present in all fuel.

The water which is dissolved in
the fuel gives rise to a number

of fuel system problems.

As an aircraft climbs to
altitude, the fuel is cooled and

the amount of dissolved water it
can hold is reduced.

Water droplets form, and as the
temperature is further reduced,

the droplets turn to ice
crystals which can block fuel

system components such as
filters.

A microbiological fungus called
Cladosporium resinae is present

in all turbine fuels.

This fungus grows rapidly in the
presence of water to form long

green filaments, which can block
fuel system components.

The waste products of the fungus
are corrosive, especially to

fuel tank sealing substances.

The inclusion of a fuel system
icing inhibitor or FSII in the

fuel will help to overcome these
problems.

The inhibitor in common use
inhibits the ability of the

water in the fuel to freeze and
acts as a pesticide which

******* the growth of the fungus
in the fuel.

Jet A1 has FSII, but Jet A does
not.

As we have already said, water
is always present in fuel.

The amount will vary according
to the efficiency of the

manufacturer's quality control
and the preventative measures

taken during storage and
transfer.

Further measures can be taken to
minimize water accretion once

the fuel has been transferred to
the aircraft tanks.

If the fuel can be allowed to
settle after replenishment, then

the water droplets, being
heavier than the fuel, will fall

to the bottom of the tank can
then be drained off through the

water drain valve, which is
situated in a sump in the lowest

part of the fuel tank.

Once the fuel is in the aircraft
tanks, the main source of water

contamination is the atmosphere
that remains within the tank.

If the tanks are topped up to
full, then the atmosphere is

excluded together with the
moisture it contains, thus

minimizing the likelihood that
fuel will be contaminated.

Caution is required here.

Filling up the tanks may prove
an embarrassment later if the

ambient temperature rises as the
fuel in the tanks will expand

and there is a danger it may
spill out of the vent system.

Filling the fuel tanks may also
incur a performance penalty as

the aircraft may be too heavy to
take off with the required

passenger or cargo load and some
fuel may have to be removed as a

further precaution in order to
prevent any ice crystals

blocking fuel filters and jets,
the fuel may be passed through a

fuel heater located on the
engine which uses hot air from

the engine compressor to remove
any ice crystals which may have

formed in the fuel when it's
cooler than 0°C.

Some systems utilize a fuel
cooled oil cooler as well as or

instead of a fuel heater.

The fuel cooled oil cooler uses
the hot engine oil to warm the

fuel and in doing so produces
the added benefit of cooling the

oil.

A number of additives may be
blended into the fuel either at

the refinery or the airfield to
improve the operating ability of

the fuel.

A lubricity agent is added to
the fuel to reduce wear in

moving parts of the fuel system
Components.

Static dissipator additives
partially eliminate the hazards

of static electricity generated
by the movement of fuel through

modern fuel transfer systems.

This would otherwise be a
particular problem with the high

flow rates generated during
refuelling and de fuelling.

Corrosion inhibitors protect
ferrous metals in fuel handling

systems such as pipelines and
storage tanks from corrosion.

Certain of these corrosion
inhibitors improve the

lubricating qualities of some
gas turbine engine fuels.

Metal deactivators suppress the
tendency which some metals,

particularly copper, have to
cause the fuel to oxidize.

We are now going to talk about
fuel waxing.

This is something that happens
to fuel when it is extremely

cold.

Do not confuse this with the
water in the fuel freezing.

Gas turbine fuel consists of
many hydrocarbons, each with its

own freezing point, so it
doesn't become as solid at one

temperature in the same way that
water does.

As the temperature of the fuel
drops, the heavy hydrocarbons

which have the highest freezing
point freeze 1st and form wax

crystals.

As the temperature drops
further, the hydrocarbons with

slightly lower freezing points
start to solidify, and so on as

the temperature continues to
fall.

The waxing point of a fuel is
the temperature at which wax

crystals begin to form.

Jet A1 has a waxing point of
-50°C, so waxing is only a

problem for aircraft operating
for prolonged periods at high

altitude.

In very low temperatures, the
crystals can clog the fuel

filter and interfere with the
operation of the engine fuel

control unit.

The effects of waxing can be
minimized by the refinery

keeping the heavy hydrocarbons
in the fuel to a low level.

The temperature at which a
liquid boils will reduce as the

pressure on its surface reduces.

As an aircraft climbs, the
pressure on the surface of the

fuel reduces, and with that
reduction comes an increased

likelihood that the fuel will
boil and form vapour in the

pipelines.

The vapour locks that this
effect causes can cut off the

fuel supply to the engine, with
the result that the engine will

stop.

Fuel booster pumps fitted inside
the tanks can help to overcome

this problem by pressurizing the
fuel in the pipelines from the

tank to the engine, pushing fuel
towards the engine rather than

engine driven pumps, sucking
fuel from the tanks and further

reducing the pressure.

Specific gravity, or SG is
defined as the ratio of the

density of a given solid or
liquid substance to the density

of water.

Or to put it more simply, it is
the weight or mass of the liquid

divided by the weight or mass of
an equal volume of water.

So in the example shown here, we
have one gallon of fuel in the

left container and it weighs 8
lbs.

In the right container there is
an equal volume 1 gallon of

water and it weighs 10 lbs.

The specific gravity of the fuel
is then 8 / 10 or 0.8.

Specific gravity has no
dimensions.

The higher the specific gravity
of a fuel, the greater will be

the mass or weight of fuel for a
given volume, and conversely,

the lower the specific gravity,
the less will be the mass or

weight for any given volume.

The specific gravity of fuel
varies inversely with its

temperature, so depending on the
storage conditions, the specific

gravity of the fuel supplied to
an aircraft may be different

from the standard value.

On modern aircraft fuel systems
this usually makes little

difference as fuel in the
aircraft tanks is measured in

mass or weight rather than
volume, with the fuel quantity

measuring system compensating
for changes in fuel specific

gravity.

However, if a high fuel load is
required, it may not be possible

to get sufficient volume of fuel
on board for the required mass

if the specific gravity of the
fuel is low.

That is the end of the lesson.

The tables listing the
characteristics of the various

fuel types are shown on screen.

Remember that ice crystals
formed from water in the fuel

are prevented from blocking the
fuel filter by heating the fuel

upstream of the filter using
either hot air or oil.