If someone told you that jet fuel was made of old fish, you would probably think they were half-baked.

In fact, the poor old fish have been pressure-cooked for hundreds of millions of years.

They have been in the cooker for so long that they have turned liquid.

This liquid is called crude oil and it is used to make petrol, diesel and jet fuel.

We use the fish analogy a bit loosely, so here is the story in more detail.

Cooked fish

Hundreds of millions of years ago the atmosphere was rich in the greenhouse gases carbon dioxide (CO2). Warm, shallow seas heaved with life. As the marine organisms grew and then died, they formed sea beds full of carbon-rich organic material (i.e. plankton and fish).

Over millions of years, these became buried deep under the ground. After millions of years under intense heat and pressure, the carbon rich material converted into a liquid called crude oil. Most of the crude oil came to the surface and was lost. However, some of it was trapped.

Crude Oil

Crude oil is extracted from deep below the ground in oil fields. Oil fields are found all over the world, but most are in the Middle East. The oil is flowing fast these days, about 90 million barrels a day. However, experts speak of 'peak oil,' the point at the reserves as so depleted that the remaining oil is increasingly costly to extract. Problems can occur on oil fields including uncontrolled spills. In the rollover picture, oil workers struggle to shut off an oil well head that has been damaged. Crude oil is toxic. It harms human health as well the environment. However, it is very useful.

Around the world in a big ship

Crude oil is transported around the world to oil refineries in huge ships called oil tankers. Sometimes oil tankers sink, causing massive local environmental disasters.

In the rollover picture, the oil tanker Prestige breaks up off the coast of Spain in 2002, spilling 64,000 tons of fuel oil. The estimated cost of the clean-up operation was 2.5 billion Euros. Furthermore, as late as March 2004, oil was continuing to leak from the hull of the ship and floating to the surface from 4,000 metres below.

Turning oil into fuels

The crude oil is taken to oil refineries where it is heated and separated into a variety of components to form petrol, diesel, kerosene, bitumen and other petroleum hydrocarbons. The largest  oil refineries in the world are in the Middle East and America.

Major oil installations are vulnerable to fire and increasingly to terrorist attack. The rollover picture shows the accidental fire at UK oil storage facility Buncefield in 2005. This fire poured 177,000 tons of greenhouse emissions into the sky. 

Jet engines

One of the outputs from an oil refinery is kerosene. A refined version of kerosene is used to power jet engines. This is called Jet-A1 or just jet fuel. In the jet engine the kerosene is burnt in the prescence of oxygen, releasing heat.

As the burning fuel expands, it forces hot gases out of the rear, forming thrust and driving the plane forward. When burnt, the hydrogen and carbon in the kerosene combine with oxygen from the atmosphere to form water and the greenhouse gas carbon dioxide (CO2).

Jet engine exhaust

The thrust produced by the expanding gases in the jet engine push the plane forward while the movement of air across the plane's wings produces lift.

This lift allows the plane to gain altitude. In  most instances, the plane flys upwards to escape the turbulent weather systems found low in the atmosphere, aiming for the calm air in the lower stratosphere, about ten kilometers above the earth.

Jet Fuel

According to the Air Transport Action Group, over 200 billion litres of jet fuel are consumed every year. Jet fuel is made of kerosene which is extracted from crude oil in an oil refinery. In the refinery, crude oil is heated and the various components seperate.

In very simple terms, kerosene is made of hydrocarbon molecules consisting of a chain of about 15 carbon atoms, with hydrogen atoms around the outside. The atoms in the molecule are all held together with 'energy bonds'. Energy is release when the bonds between the carbon-carbon and the carbon-hydrogen is broken. The energy is released as heat, this makes the exhaust gas expand and this is blasted out the back of the jet engine forming thrust that moves the plane forward.

Graphic left shows a 'cracking chamber' in which crude oil is seperated into various grades of fossil fuels, including kerosene to be used as jet fuel.

Graphics below show the molecular components of the fuel and the exhaust.

In the graphics left and below the blue 'O' represents oxygen, the green 'H' is hydrogen, the black 'C' is carbon and the red dash is the energy bond that keeps atoms joined in to the clusters known as molecules.

For exery molecule of kerosene that is burned, 22 molecules of oxygen are needed. Air containing the oxygen is bought into into combustion chamber of the jet engine, and fuel is added. When the fuel/oxygen mixture burns, the resulting hot gases expand in volume and pass out the back of the engine, forming thrust.

The exhaust gases include 15 molecules of carbon di-oxide and 16 molecules of water vapour. Both carbon di oxide and water vapour are greenhouse gases.

In the lower stratosphere, where the airliners fly, the air is very cold. Sometimes, the moisture in the hot wet exhaust condenses and the water becomes visible as a while line behind the jet. This is called a condensation trial or a 'contrail'.

If you though that filling your car was tiresome, it takes over 26,000 litres to fill a Boeing 737-800 from empty.

Pictured here is a fuel tanker about to refuel a Boeing 737-800 at Townsville airport.

This truck holds about 18,000 litres of Jet-A1 so you would need one and a half tankers like this to fill a Boeing 737 from empty.

Jet A1 Material Safety Data Sheet.