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Fuels

By Edited Jun 11, 2015 0 0

Fuels covers a wide range of materials, but all fuels can be made to undergo an exothermic reaction to produce heat in useful quantities. Usually the reaction is with oxygen from the atmosphere.

The Law of Conservation of Energy tells us that energy can neither be created, nor destroyed. Energy can only change forms, as in natural gas burning, where chemical energy from the methane and oxygen is released as heat and light energy.

Why do fuels give out heat when they burn?

All fuels are stores of chemical energy that can be easily changed into heat energy would be another definition of a fuel.

Burning is a chemical reaction. In any chemical reaction, bonds are broken initially and then new bonds are formed. Breaking bonds absorbs energy, making new bonds releases energy.

If a reaction gives out a lot of heat we know that more energy is being released by the formation of new bonds than is being used to break the old bonds.

Fuels and Early Human Life

Burning fuels to keep our selves warm has allowed humans to colonize almost all the planet. Without fire we would be still stuck in Africa, because with our lack of bodily hair, or natural subcutaneous fat, we would have frozen to death in European or Asian winters.

Wood was the first fuel that humans burnt for heat and for cooking. It is still the main fuel in many parts of Africa. Wood is a renewable fuel and burning it does not cause extra carbon dioxide in the atmosphere.

Trees remove carbon dioxide from the atmosphere by photosynthesis and lock it up in their wood. When the tree is chopped down and the wood is burned the locked up carbon dioxide returns to the atmosphere.

Charcoal, made from wood was used to smelt iron as long ago as 1200 BC. Without iron and later, steel we would have no motor vehicles, no gears, no pedal cycles. Our technology would still be in the bronze age.

Fossil Fuels

Most of the fuels we use today for home heating and transport are fossil fuels. Fossil fuels were made from the remains of living organisms that lived 300 million years ago. Fossil fuels are being used up, they are not being made any more, therefore, logically, will run out. Coal, oil and natural gas are all fossil fuels.

Burning any fossil fuel releases the carbon dioxide into the atmosphere from the carbon that was locked up in the fuel. This is increasing the percentage of carbon dioxide in the air and is probably linked to global warming.

We have reserves of coal that will last for about 120 years, but burning the coal will release massive quantities of carbon dioxide into the atmosphere, increasing global warming. Coal is totally unsuited as a motor vehicle fuel anyway – Can you imagine your passengers throwing another shovel full of coal into the furnace behind the back seat?

We have about 100 years worth of oil left, but again, burning it releases more carbon dioxide.

Alternatives to Fossil Fuels for Heating

Renewable fuels for heating include wood, wood pellets and electricity made by renewable energy power stations or by your own wind turbine.

Timber is very bulky for the energy that can be obtained from it. It also needs to be dried before it will burn. Cut timber is less than perfectly shaped and is cylindrical in cross-section so it is difficult to store efficiently.

Wood pellets are made from finely ground wood, sawdust. They can be moved by conveyor belts from store to furnace, enabling automated furnace operation. Pellets are still bulky and they must be kept totally dry, which is not easy as they absorb water from the air.

Electricity is a secondary fuel, and if we make electricity using wind turbines or tidal power then that is a good way of replacing fossil fuels in heating our homes.

Domestic wind turbines and photoelectric cells are becoming a real option in the drive to replace fossil fuels. You need to use the electricity you make in batteries and then to feed the current from the batteries through an inverter to change it back to mains voltage.

Hydroelectric power stations have been in use for a long time, these were the first examples of renewable energy, along with windmills.

Alternatives to Fossil Fuels for Transport

Gasoline and diesel are very difficult to replace as motor vehicle fuels. They are so useful because they are liquids, so they can be pumped, and because a litre of oil based fuel can be made to burn to release a lot of useful heat energy.

Propane/butane powered vehicles have been around for quite a while. The gas mixture used as fuel was not taxed, so had a low price compared to gasoline and diesel. The big disadvantages are that these vehicles still release a lot of carbon dioxide into the air and the propane/butane mixture is made from crude oil.

Alcohol, Hydrogen and battery powered vehicles are the only current alternatives to gasoline and diesel for transport use.

Prototype hydrogen and battery powered vehicles have been in operation for about ten years in Europe and North America. Ethanol, common alcohol, was used as a total replacement for gasoline in Brazil decades ago.

The drawbacks of ethanol power include the corrosion effects it has on engines and the tax structure in most countries, which means that another alcohol, methanol, has to be added to it to avoid massive taxation. Methanol causes major corrosion problems.

Hydrogen power is probably the long-term future fuel for transport. Only water vapor is formed when it burns, no carbon dioxide, so no global warming. The main problems relate to safety.

Hydrogen would need to be kept under high pressure, both in the vehicle and at filling stations. High-pressure systems mean expensive high-pressure valves on fuel systems, both in the vehicle and at the pumps at filling stations.

High-pressure gas containment systems need good maintenance for safety. Maintenance is costly and the average driver is thought unlikely to look after the hydrogen fuel system properly.

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