| Frequently Asked Questions |
| What Is The Composition Of Air? |
Oxygen 20.9%
Nitrogen 78.08%
Argon 0.934%
Carbon Dioxide 0.033% |
| These gases make up 99.99 % of the air
the other ‘trace’ gases make up the balance. |
| What Are The Properties Of These Gases? |
| Oxygen is a reactive gas. Oxygen supports
combustion. The higher the % of oxygen available the easier
it is for materials, such as fuels, to ignite and burn. |
| Nitrogen is a non reactive gas. Nitrogen
will not support combustion. The higher the % of Nitrogen
available the more difficult it is to for materials, such
as fuels, to ignite and burn. |
| Argon is a non reactive gas. Argon is
used for many purposes in industry such as welding to prevent
oxidation. |
| Carbon Dioxide is a non reactive gas.
It is also the major ‘Green House’ gas. Carbon
Dioxide is often used as a fire extinguishant. |
| What Is Nitrogen Blanketing? |
| Nitrogen blanketing is the use of a
Nitrogen atmosphere to prevent oxidation. This can be as
pure nitrogen for example in food packaging, extending the
life of packaged foods, or in high concentration to prevent
the ignition of material such as fuels and their vapours
stored in tanks. |
| Why Is Nitrogen Blanketing Needed For
Fuel Tanks? |
| To ignite a fuel the mixture of air
to fuel must be correct. Too much or too little fuel and
nothing will happen. This air / fuel mixture, known as the
stoichiometric ratio, is calculated using the known concentration
of oxygen in the air, i.e. 20.9%. |
| As fuel is used from a tank air is allowed
to enter the tank to prevent the formation of a vacuum. At
several points during the emptying of the tank the combination
of temperature, oxygen concentration and vapour formation
will yield the correct conditions for explosive ignition
to occur. All that is required is a source of ignition. This
source could be electrical, mechanical or thermal. |
| To prevent the possibility of explosive
ignition within fuel tanks the volumetric concentration of
oxygen must be lowered. Detailed studies of this subject
have been made within the aerospace industry and the accepted
concentration of oxygen at which ignition can not occur has
been established as 12%. Therefore if the oxygen content
of the gas within the fuel tank is 12% or less, Nitrogen
87% or more, explosive ignition and combustion can not occur. |
| How Do We Change The Oxygen Concentration? |
| We can add pure Nitrogen from a stored
gas supply to the air entering the fuel tank; this would
change the relative concentrations as dictated by the flow
of Nitrogen. |
| We can create a gas with the correct
composition, 10-11% Oxygen, and only allow this gas to enter
the tank as the fuel is used. |
| Making pure Nitrogen is costly and the
equipment heavy. The pure Nitrogen gas would also have to
be stored in heavy pressure vessels and the use of high pressure
pipes and regulators would be required. |
| We can use the ASTEK NBS™ which
is lightweight, low pressure and produces the exact gas that
we require. |
| How Does The ASTEK NBS™ Work? |
| The system is based on drawing normal
atmospheric air through a specially treated and patented
hollow fibre gas separation membrane that separates the air
into an oxygen rich fraction and an inert nitrogen rich fraction.
The nitrogen rich air, which would only contain 11% oxygen
instead of the 21% oxygen in normal air, is fed to the fuel
tank. As the fuel level drops inside the fuel tank, nitrogen
rich air is continually drawn into the tank so as to form
a permanent blanket of inert air over the fuel. |
| The system does not store nitrogen on
board the vehicle and no pressure vessels are involved. Only
a small pump is required for operation and the system pressure
is a mere 450mbar below atmospheric. |
| The lightweight nitrogen blanketing
device is derived from a system developed to provide an inert
atmosphere inside the fuel tanks of large passenger aircraft. |
| A typical automotive unit would weigh
around 1 kilo and be around 350mm long by 60mm in diameter.
The precise size of the unit is dependant on the fuel capacity
of the vehicle to which the system is fitted; the size quoted
above would be adequate for a large passenger car or SUV. |
| The membrane units are cylindrical and
the housings can be constructed in Aluminium alloy or composite
materials such as carbon fibre where unit weight is critical. |
| The patented membrane system has been
designed to produce specific gas mixtures at low pressures
and is therefore the safest and most efficient unit available. |
| Why Fit Such A System To A Racing Car? |
| The fuel systems used on race cars resemble
those employed in the aerospace industry in many ways. The
electrical fuel pumps are usually mounted inside the fuel
tank and run submerged in fuel. The electrical wiring and
pump units themselves offer the potential for electrical
arcing as an ignition source. |
| Race cars are also subjected to violent
high energy accidents, tanks can be ruptured by high energy
intrusion of nearby mechanical components. |
| The motor sport industry constantly
strives to improve safety; there can be no practical reason
not to improve the safety of the fuel system by using the ASTEK NBS™ on all race vehicles. There is no real performance penalty
with the fitting of the ASTEK NBS™. |
| Why Fit Such A System To A Road Car? |
| Many of the reasons for Race Car use
apply to road vehicles. Again safety must be paramount. The
systems can be fitted easily and present no problems with
vehicle operation. |
| There are many well documented instances
of fuel tank explosions on road cars. |
| Where Else Can The ASTEK NBS™ Be Used? |
Aircraft fuel tanks
Boat fuel tanks
Ship fuel tanks
Filling station tanks
Fuel storage depots
Gas tanks
Flammable process tanks |
| There are many potential uses for the
ASTEK NBS™ system wherever there is risk of explosive ignition. |
| NBS is a trade mark of Applied Sciences Technology Corp, Nassau, Bahamas |
