Fuels are substances that release plenty of heat energy on burning.
The conditions favorable for the complete combustion of different fuels:
• The solid fuels must be dry. • Liquid fuels must evaporate easily.
The ignition temperature should be attained.
• Sufficient oxygen must be available for burning
Combustion of fuels
• Fuels burn with the help of oxygen. • Generally complete combustion is a reaction in which fuels react
intensively with oxygen, producing carbon dioxide, steam, heat and light. • If sufficient oxygen is not available, the rate of combustion
decreases. • If oxygen is not sufficient, large quantities of carbon monoxide, soot and a little of carbon dioxide will be formed. This type of burning is
partial combustion.
Pollution test is conducted to know whether the components in the gases released from the vehicle exceeded the permissible limits.
Fossil fuels:
Fossil fuels are formed by the transformation of plants and animals that went under the earth’s crust millions of years ago. The transformation took
place in the absence of air under high pressure and high temperature • Coal, petroleum and natural gases are fossil fuels. They are not replenished
or renewed in proportion to their consumption. Hence, they are nonrenewable energy sources

• Coal is the most abundant fossil fuel on the earth. The main component of
coal is carbon.
Based on the carbon content, it is classified into four groups as peat, lignite,
anthracite and bituminous coal.
When coal is distilled in the absence of air, the substances obtained are
ammonia, coal gas, coal tar and coke.
• We make liquefied natural gas (LNG) and compressed natural gas (CNG)
from the natural gas obtained along with petroleum. The main component of all these is methane. These are used as fuels in vehicles, industries and
thermal power stations.
The importance of LNG is that natural gas can be liquefied and transported to distant places conveniently. It can again be converted into gaseous form
at atmospheric temperature and distributed through pipe lines. • The full form of LPG is liquefied petroleum gas. This is a colourless,
odourless gas obtained through the fractional distillation of petroleum.
Domestic LPG produces an odour since ethyl mercaptan is added as an indicator to detect gas leakage. The main constituent of LPG is butane.
• From ancient times, we have been using firewood, dried cow dung etc., as
fuel. Since these fuels are obtained from plants and animals, they are known as bio-waste or biomass.
The burning of such bio-wastes will be partial combustion.
• When bio waste is deposited in a biogas plant in the absence of oxygen,
biogas is formed by the action of bacteria. Its main constituents are methane and carbon dioxide.

The slurry discharged from the biogas plant is good manure. • When biomass is converted into biogas, not only a fuel of greater calorific
value is obtained but the atmospheric pollution is also minimised.
Calorific value
• The amount of heat liberated by the complete combustion of 1 kg of fuel
is its calorific value. Its unit is kilojoule/kilogram.

Some fuels and their calorific values:
150000 kJ/kg
50000 kJ/kg
Dried cow dung
6000 – 8000 kJ/kg
55000 kJ/kg
30000 – 40000 kJ/kg
25000 – 33000 kJ/kg
45000 kJ/kg
50000 kJ/kg
Hydrogen and hydrogen fuel cell
• Hydrogen is a fuel with the highest calorific value. This is highly
inflammable and explosive in nature. So it is difficult to store and transport it. We make use of hydrogen fuel cell to produce electricity by combining hydrogen and oxygen.
The properties that a good fuel:

Should be easily available. Should be of low cost.
Should have a high calorific value

.Should cause minimum atmospheric pollution on combustion.
• Should be easily storable. • A liquid fuel must not evaporate quickly at ordinary temperatures
Electrical energy:
Electrical energy is the most important form of energy. Its speciality is that it can easily be converted into many other forms. Power stations are the centres where electricity is produced on a large scale
for distribution.
The mechanical energy required for running power generators is made available in different ways. Power stations can be classified based on the
nature of the source providing the energy required to operate the generator. • Flowing water – hydroelectric power stations
Water stored at a height is allowed to flow down through a penstock pipe. The energy of the flowing water is used to rotate the turbine and electricity
is generated. Such power stations are established at Pallivasal, Moolamattom, etc., in Kerala. The energy change taking place here is: Potential energy – Kinetic energy – Mechanical energy – Electrical energy.
• Fuels like coal, naphtha, lignite, etc., are ignited. The heat energy thus
liberated is used to convert water into steam at high temperature and pressure. The energy of steam is used to rotate the turbines to generate
electricity. • Such power stations are established at Neyveli, Kayamkulam , etc.

The energy change taking place here is: Chemical energy – Heat energy – Mechanical energy – Electrical energy.
Electrical energy from solar energy:
Solar cell is a means for converting solar energy into electrical energy.
This is a p-n junction diode. When solar energy falls on N side of a solar cell, a small electric current is obtained due to the flow of electrons to P region from N region. This phenomenon is the photovoltaic effect. It is the electrical energy thus obtained that is stored in batteries and used whenever necessary.
Solar panel:
The voltage and current obtained from a solar cell is insignificant. A large
number of solar cells are suitably assembled to form a solar panel. The electric current obtained from a large number of such cells can be stored in
a battery and used as and when it is needed. • Solar panel is used extensively in lighting street lamps. They are used to
meet the energy requirement of artificial satellites. • Nowadays solar photo voltaic (SPV) power plants capable of producing
electricity of thousands of kilowatts are in use.
The solar powerplant at the International Airport in Nedumbassery is an example.
The specialties of a solar cooker:
• A box with blackened interior
• A glass cover for the box • A mirror outside the box
Solar Water Heater:
Solar water heater, solar cooker etc., are devices that make direct use of
solar heat radiations.• Hot water required for hospitals and hotels for cooking food, and for
washing vessels in houses etc., can be produced using solar water heater.

Solar Thermal Power Plant
• Solar thermal power plant generates electricity using solar energy.
Concave reflectors are used to focus the sun’s rays on the blackened pipes filled with water. As a result, water boils and vaporises. The steam rotates
the steam turbine, so that the generator attached to the turbine is activated.
About 10 such solar power plants are functioning in India, the majority of which are in Rajasthan.
Energy from wind
• Wind energy is a form of energy that is both environment friendly and
• Electricity is obtained by turning the turbine of generator using the wind
power. Icrc production of clectricity docs not incur any recurring expenditure. But it has certain limitations. This can be established only at those places where wind is available for most time of the year. We may
require storage systems to u se electricity when there is no wind.

About 2 hectares of land is needed for the production of one megawatt power. The expense to establish a wind mill is very high and that for repairing it in the event of damages caused by heavy rain, cyclones, heat etc., is also very high
Energy from sea
Two third of the surface of the Earth is sea. Hence ocean is a major source of energy. Sea waves, high tide, heat from the ocean etc., are the phenomena that we can make use of while producing energy from sea.

Tidal Energy
Tidal energy is not exploited in Kerala since the rise in water due to high
tide is less than a metre.
Energy from waves
We can operate a generator by turning the turbine by using the power of sea waves. In India also such methods for the production of electricity from
sca waves are in operation on an experimental basis.
Ocean thermal energy
The surface of ocean is relatively hot due to solar radiations. But the
temperature will be very low at the deep levels. • Ocean Thermal Energy Conversion Plants (OTEC) produce energy,
making use of this difference in temperature. • The temperature of the surface of ocean and the regions at 2 m depth will
vary by more than 20 K in temperature. • The heat at the surface boils volatile liquids like ammonia. Using the gas
obtained, turbine is rotated. The cold water at the bottom liquefies the gas
again. By the continuous action of this we get electrical energy.
Geo thermal energy
Though the surface of the earth has cooled down making it habitable, the interior is still in the molten form. Magma, which is at a higher temperature, comes out of the core through its softer regions. Such places
are known as hot spots. Underground water at this place receives heat energy from the hotspot and is converted into steam. This steam, which is
confined to the region between rocks, is brought out by drilling pipes through the rocks. Using this steam, turbine is rotated to produce electricity.

Nuclear fission
Nuclear fission is the process by which the nuclei of greater mass are split into lighter nuclei, using neutrons. The mass of small nuclei formed is less than that of parent nucleus. It means that there is loss of matter during such a splitting. The matter that is lost is converted into energy. According to Einstein’s equation E = mc, even if the matter converted is very small, the energy produced will be very large. Uncontrolled fission will end in a huge explosion. This is the process that takes place in an atom bomb.
Nuclear fusion
Nuclear fusion is the process in which lighter nuclei are combined to form heavier ones. In this process the matter lost is converted into energy. You know that energy is produced in the stars and the Sun in this way. This is the principle used for making a hydrogen bomb. The scientific world has not yet been able to produce energy commercially by controlled nuclear fusion.
There are power stations to control fission reaction and produce electricity. They are known as thermal power stations.
Nuclear reactor is a system that converts nuclear energy into electrical energy.
Enriched uranium is the fuel used in nuclear reactors. India has developed the indigenous technology of using carbide fuel in nuclear reactors. The power Station at Kalpakkam in Tamilnadu makes use of such a reactor. Dangerous radioactive radiations and products are also formed in nuclear reactions.
Nuclear Power stations
Using nuclear energy water is converted to steam at a high temperature and pressure. The force of steam is used to turn the turbines to generate electrical energy.Such power stations are established at Tarapur, Kalpakkam, Kota, and Koodamkulam.
Energy change taking place here is: Nuclear energy – Heat energy – Mechanical energy – Electrical energy

Nuclear Pollution

The pollution caused by the presence of radioactive substances and radiations in water, air and environment is known as nuclear pollution.
The nuclear decomposition of polluted materials results in the dangerous pollutions. As a result of nuclear decomposition alpha, beta and gamma radiations spread out. Density of polluting substance, the type of radiation, proximity of pollution to physical organs etc., are the factors that determine the probability of danger. Nuclear hazards can be artificial or natural.
• Cosmic rays from outer space • Radiations from radioactive materials on the Earth

The use of radioactive isotopes in the medical field.
• Wastes from nuclear reactors.
Precautions to face nuclear hazards
Shift out to safe places (Concrete buildings, buildings constructed using
bricks etc.)
Strictly follow the directions from the concerned authoritics
Observe the symbols showing the nuclear radiations and behave
accordingly. • Reduce the density of population in places likely to experience nuclear
hazards.If necessary, consume potassium iodide tablets or take food rich in iodine.

Renewable Sources of energy:
The natural sources of energy obtained from sunlight, wind, rain, high tide
etc. can be replenished. Hence these are examples for renewable sources
of energy. They do not pollute the environment. • Petroleum, coal, natural gases, nuclear energy etc., are non-renewable
sources. They are harmful to the environment as well.
Green Energy:
Green energy is the energy produced from natural sources that does not cause environmental pollution. All the energy produced from renewable
sources belong to this category. The renewable sources like solar energy,
wind energy, energy from waves and energy from biomass are considered as green energy. This is also referred to as clean energy. But thc cncrgy produced from nonrcncwable sources such as petrolcum and coal, and the nuclear energy are named brown energy. These are sources which cause environmental problems including global warming.
Green Energy:
Solar cells, tidal energy, hydroelectric power, windmills.
Brown Energy
atomic reactors, diesel engines, thermal power stations

Energy crisis:
Energy crisis is the consequence of increasing demand but decreasing
Reducing energy crisis:• Judicious utilisation of energy. • Maximum utilisation of solar energy
Minimising the wastage of water. • Making use of public transportation as far as possible.
Construction and beautifying of houses and roads in a scientific manner. • Controlling of the street lamps with LDR (Light Dependent Resistor). • Timely maintenance of machines. • Limiting the size of newly constructed buildings.
• Ensuring of maximum efficiency of the machines used.
The devices that can be used at home to reduce energy consumption.
Hot box
• Pressure cooker • Energy efficient oven
The local activities that can be taken up to spread social awareness:
• Poster publicity
• Jatha (procession)
LDR is a variable resistor that works based on the intensity of light.

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