Learning Objectives

At the end of this chapter, student will be able to:

List requirements of aviation fuel

Differentiate the type of aviation fuel

Describe the properties/characteristics of fuel

Understand the function of additive in fuel

Understand the Fuel Discipline

Aviation fuel is a liquid containing chemical energy.

The chemical energy is released as heat energy through combustion.

Finally the heat energy is converted to mechanical energy by the engine.

Gasoline and kerosene are the two most widely used aviation fuels.

Gasoline is piston engine fuel and kerosene is jet engine fuel.

Be capable of being pumped and flow easily under all operating conditions.

Enable engine starting at all ground conditions and gives satisfactory relighting characteristics.

Give efficient combustion under all conditions.

Have as high a calorific value as possible.

Be resistant to fungus growth

Have low freezing point

Produce minimum corrosive affects on the combustion system or the turbine blades.

Produce minimal corrosive effects on the fuel system components.

Provide adequate lubrication for the moving parts of the fuel system.

Reduce fire risks to a minimum.

Have low emissions

Distilled from crude oil by fractional distillation.

Each different product has a distinct boiling temperature.

Each product is boiled off or separated from the crude oil as it is heated to increasingly higher temperatures.

Gasoline boils at a relatively low temperature

Heavier fractions become turbine engine fuel, diesel fuel, and furnace oil.

Consists almost entirely of hydrogen and carbon compound

Has impurities in the form of sulfur and dissolved water

Volatility

The tendency of a liquid substance to vaporize under given conditions

If a gasoline vaporize

too fast; fuel lines may become filled with vapour and cause decreased fuel flow/ vapour lock.

too slow; it can result in hard starting, slow warm up, poor acceleration, uneven fuel distribution to cylinders.

Vapour pressure is a major factor in the susceptibility of a fuel to vapour lock.

The Reid vapor pressure test gives a gasoline's tendency to vapour lock.

Refined to have a vapor pressure be between 5.5 psi and 7.0 psi at 100F

Limited to a maximum of 7 psi to minimize the tendency to vapour lock at high altitudes.

Sample of the fuel is sealed in a "bomb" equipped with a pressure gauge.

The apparatus is then immersed in a constant temperature bath and the indicated pressure is noted.

The higher the vapour pressure, the more susceptible to vapor lock

Carburetor icing is also related to volatility

When fuel changes from liquid to vapour, it extracts heat from its surroundings

More volatile the fuel, the more rapid the heat extraction and it can freeze the water vapor in the incoming air

The icing condition is most severe in temperatures ranging

from 30F to 40F (-1C to +4C) outside air temperature, but may occur at much higher temperatures.

Aromatic hydrocarbons added to increase the rich mixture performance rating of the fuel, known as aromatic fuels.

Can swell some types of hoses and other rubber parts

Aromatic-resistant hoses and rubber parts have been used.

Used in high horsepower, reciprocating engines used on military and large transport category aircraft.

These aircraft are disappearing from the active fleet, and this type of fuel is no longer available.

Detonation is the explosive, uncontrolled burning of the fuel-air charge.

Occurs when the fuel burns unevenly or explosively because of excessive temperature or pressure in the cylinder.

Rather than smoothly pushing the piston down, detonation slams against the cylinder walls and the piston.

The pressure wave hits the piston like a hammer, often damaging the piston, connecting rods, and bearings.

Often heard as a knock in the engine hence also known as engine knocking

Causes high cylinder head temperatures, and if allowed to continue, can melt engine components.

The potential for engine overheating is greatest under the following conditions: Use of fuel grade lower than recommended

Takeoff with an engine that is above or very near the maximum allowable temperature

Operation at high rpm and low airspeed

Extended operations above 75 percent power with an extremely lean mixture

Combustion is precisely timed in a properly functioning ignition system.

In contrast, preignition is when the fuel/air mixture ignites too soon.

Caused by hot spots in the cylinder.

When preignition exists, an engine may continue to operate even though the ignition has been turned off.

Preignition and detonation often occur simultaneously, and one may cause the other.

Aviation gasoline is formulated to burn smoothly without detonating

Fuels are numerically graded according to their ability to resist detonation.

The higher the number, the more resistant the fuel is to detonation.

The most common grading system is octane rating.

The octane number assigned to a fuel compares the anti-knock properties of that fuel to a mixture of iso-octane

(C8H18) and normal heptane(C7H16)

For example, grade 80 fuel has the same anti-knock properties as a mixture of 80% iso-octane and 20% heptane.

100 Octane fuel has the same anti-knock properties as pure iso-octane gasoline.

Engines having high compression ratios and/or high

horsepower output require higher octane fuel.

Tetraethyl lead (TEL) added to increase anti-detonation properties

TEL increases the critical pressure and temperature of a fuel.

TEL can raise the anti-detonation characteristics from 80 to the 100 octane level and higher.

TEL also forms corrosive compounds in the combustion chamber.

Ethylene dibromide and tricresyl phosphate, must be added so that the TEL does not leave solid deposits in the combustion chamber.

References to octane characteristics above 100 percent iso-octane are made by referencing the anti-detonation properties of the fuel to a mixture of pure iso-octane and specific quantities of TEL.

The specific mixtures of iso-octane and TEL are assigned arbitrary octane numbers above 100.

TEL also lubricates the engine valves. 100LL has 2 milliliters of TEL per gallon

For environmental purposes, AVGAS with no TEL is sought for the aviation fleet of the future.

Performance numbers are also used to characterize the anti-detonation characteristics of fuel.

Consists of two numbers (e.g., 80/87, 100/130) in which higher numbers indicate a higher resistance to detonation.

The first number indicates the octane rating of the fuel in a lean fuel-air mixture, and the second number indicates the octane rating of the fuel in a rich mixture

To avoid confusion and to minimize errors in handling , common practice is to designate the different grades by the lean mixture performance numbers only.

The color code for the aviation gasoline currently available is as follows: 80 Red

100 Green

100LL Blue

EU Labelling (Symbol)

Flame

St Andrews Cross

Dead tree and fish

Physical and Chemical Properties

Colour - Blue

Odour - Gasoline

Density at 15C - 725 kg/ m3

Boiling Point - 35C

Flash Point - -40C

Aviation Gasoline (avgas)

Protection and Safety

Personal Contact

Wear face visor or goggles

Avoid skin contact

Clean protective clothing

Respiratory Protection

Solvent Properties

Indicates contamination with another product or a loss of fuel quality.

May be caused by a chemical reaction that has weakened the dye component.

This color change itself may not affect the quality of the fuel, but if one has occurred, determine the cause before releasing the aircraft for flight.

1. Marking of the Hose

A color band not less than one foot wide is painted adjacent to the fitting on each end of the hose used to dispense fuel.

The bands completely encircle the hose and the name and grade of the product is stenciled longitudinally in one-inch letters over the color band.

2. Marking on the fuel trucks and hydrant carts:

Fuel trucks and hydrant carts are marked with large fuel identification decals on each side of the tank or body and have a small decal on the dash board.

The fixed ring around both the dome covers and hydrant box lids are also painted in accordance with the color code.

3. Marking and coding system

Marking and coding system has been adopted to identify the various airport fuel handling facilities and equipment, according to the kind and grade of fuel they contain.

all aviation gasoline are identified by name, using white letters on a red background.

In contrast, turbine fuels are identified by white letters on a black background.

The markings for fuel installations and fuelling vehicles is a single blue band followed by a red rectangle, with AVGAS 100LL written in white.

.

AVGAS

White letter 1 high

Filler cap in the center

12 diameter RED Circle Around the cap

Aircraft gas turbine engines are designed to operate on a distillate fuel, commonly called jet fuel.

Jet fuels are also composed of hydrocarbons with a little more carbon and a higher sulfur content than gasoline.

Inhibitors may be added to reduce corrosion, oxidation, and the growth of microbes or bacteria.

Anti-icing additives are also added.

Turbine engines can operate for limited periods on aviation gasoline.

Prolonged use of leaded avgas forms tetraethyl lead deposits on turbine blades and decreases engine efficiency.

Turbine engine manufacturers specify the conditions under which gasoline can be used in their engines, and these instructions should be strictly followed.

Reciprocating engines will not operate on turbine fuel. Jet fuel should never be put into a piston engine aircraft.

There are four main types of turbine engine fuel.

Jet A1

Jet A

Jet B

JP 5.

Density

Freezing point.

Jet A1 -52.6 F (-47 C)

Jet A -40 F (-40 C)

Jet B -58 F (-50 C)

JP 5 -51 F (-46 C)

Physical and Chemical Properties JET A-1 (FSII)

Colour - clear/colourless

Odour - kerosene

Boiling Point - 156C

Flash Point - 38C

EU Labelling (Symbol)

St Andrews Cross

Dead tree and fish

Aviation Kerosene (AVTUR)

Protection and Safety

Personal Contact

Wear face visor or goggles

Avoid skin contact

Clean protective clothing

Respiratory Protection

Solvent Properties

Identification Markings (JET A1)

The fuel grade identification markings for fuel installations and fuelling vehicles for JET A1 is two black bands followed by a black rectangle, with JET A-1 written in white.

.

.

JET A-1

.

AVTUR

12 BLACK SQUARE

Fuel symbol

Types of Fuel

MOGAS Motor Gasoline Airworthiness Notice No 98 A, B & C authorises the use of MOGAS under strict conditions for

Light Aircraft

DIESEL Diesel Fuel Some modern Light Aircraft have now been designed with new engines, certified for the use of Jet fuel

and Diesel.

JET A A kerosene type fuel with a freezing point of around -40C.

Available only in the USA.

JET A1

FSII

(AVTUR)

A kerosene type fuel with a freezing point of around -

47C.(UK additive AL48)

Types of Fuel

JP8 (AVTUR-FSII) A kerosene type fuel with a freezing point of

around -50C.

JET B (AVTAG) A wide cut gasoline with a freezing point of

around -50C.

JP4 (AVTAG FSII) A wide cut gasoline with a freezing point of

around -58C.

JP5 (AVCAT) A high flash point kerosene mainly utilised for

the Royal Navy and ship borne activities.

Cleanliness

Blanks/covers

Jointing compound

Contaminants can include either soluble or insoluble materials or both.

The more common forms of aviation fuel contamination include:

Solids

Water

Surfactants

Microorganisms

Water can be present in two forms:

Dissolved in the fuel

Entrained or suspended in the fuel

Entrained water can be detected by

Naked eye; The finely divided droplets reflect light and high concentration can be seen by dull, hazy or cloudy appearance.

Free water can cause icing in the fuel pump screens, and low pressure filters, or cause engine stoppage.

Fuel can be contaminated by mixing with other grades or types of fuels

By picking up compounds from concentrations in rust and sludge deposits, by additives, or by any of a number of other soluble materials.

The greatest single danger to aircraft safety from contaminated fuels cannot be attributed to solids, exotic microorganisms, surfactants, or even water. It is contamination resulting from human error.

The spores of microbial species e.g. micro fungi

(Cladosporium Resinae), can exist in a dormant state in kerosene fuels in most parts of the world.

The spores but they will propagate when water is present and the temperature is between 25C and 35C.

Cladosporium Resinae

The fungus itself is of a slimy nature and may appear as any colour, varying from white to brown to near black.

In large quantities it possesses an offensive odour.

The fungus causes corrosion, clogged fuel lines/filters, erratic or false fuel quantity indication

Microbiological contamination occurs on the upward facing surfaces of fuel tank.

Additives are fuel-soluble chemicals added in small amounts to enhance or maintain properties important to fuel performance or fuel handling.

Derived from petroleum based raw materials and their function and chemistry are highly specialised.

They produce the desired effect in the parts per million (ppm) concentration range.

JET A-1 contains a static dissipater additive and also has an antioxidant

Antioxidants Oxygen in air dissolved in the fuel attacks reactive compounds

in the fuel and trigger oxidation.

Antioxidants work by interrupting this chain of reactions and prevent:

Formation of peroxides

Peroxides can attack elastomeric fuel system parts

Soluble gums Gums can lead to engine deposits

Insoluble particulates.

Particulates can plug fuel filters

Antioxidants Required in any fuel or fuel blend component that has been

hydrogen treated under the DEF STAN, JET A-1 and US military specifications.

Metal Deactivator Metal deactivators are chelating agents chemical

compounds that form stable complexes with specific metal ions.

More active metals, like copper and zinc, are effective catalysts for oxidation reactions, and degrade fuel thermal stability.

Metal Deactivator

These metals are not used in most jet fuel distribution systems or turbine engine fuel systems.

However, if fuel becomes contaminated with these metals, metal deactivators inhibit their catalytic activity.

The only approved metal deactivator is N, N disalicylidene - 1, 2-propane diamine.

Electrical conductivity/static dissipater

The conductivity of jet fuel presents a potential safety hazard in certain circumstances, additives have been developed that improve the fuels conductivity.

Conductivity additives are often referred to as static dissipater additives SDA.

When the additive is used, the conductivity of the fuel must be between 50 and 450 CU at the point of delivery into the aircraft.

The only additive currently approved for use in jet fuel is

Stadis 450.

Corrosion Inhibitor / Lubricity Improver

The tanks and pipelines of the jet fuel distribution system are constructed primarily of uncoated steel.

Corrosion inhibitors prevent free water and oxygen in the jet fuel from rusting or corroding these structures.

Lubricity additives are used to compensate for the poor lubricity of severely hydro-treated jet fuel.

Corrosion Inhibitor / Lubricity Improver

They contain a polar group that adheres to metal surfaces, forming a thin surface film of the additive.

The film acts as a boundary lubricant when two metal surfaces come in contact.

Both corrosion and lubricity are surface phenomena.

Therefore corrosion inhibitors also improve lubricity.

Icing Problem in Fuel System

Ice crystals can form in fuel tanks and pipelines at the very low temperatures encountered at altitude.

Generally, this ice is formed from water that was dissolved in the fuel when the aircraft was refuelled, but separated from the fuel as the fuel temperature dropped.

Most aircraft have heaters on their main fuel filters to melt any ice that collects, which would otherwise reduce fuel flow.

Fuel System Icing Inhibitor

One commonly used anti-icing additive is Prist, manufactured by PPG Industries.

Prist is added to jet fuel during refueling. It has limited solubility in jet fuel but is completely soluble in water.

When dissolved in water, Prist lowers the water's freezing point.

The water/Prist mixture then stays in a liquid state and passes through fuel lines and filters.

FSII (Fuel System Icing Inhibitor) Contd

In practice, the additive must be injected at a controlled rate into a flowing stream of fuel.

If a fuel containing FSII comes into contact with free water, the additive will be extracted out of the fuel and form a thick, gelatinous phase with the water, which would be unacceptable.

To avoid contact with free water, FSII is usually not added to fuel at a refinery, but at some point in the fuel distribution system.

Biocides Biocides are designed to kill micro organisms, which

may include bacteria and fungi (yeasts and moulds).

Since biocides are toxic, any water removed from a

fuel system that contains biocides must be

disposed of appropriately.