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FUEL USED IN IC ENGINES

An article on fossil fuels

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Internal Combustion Engines are the generators of the energy mainly used for transportation. Almost more than 90% of the total IC Engines run on fossil fuels or different derivatives of petroleum.

IC Engines are a kind of open cycle heat engine where heat is supplied to the engine by the combustion of working fluids thus releasing huge amount of energy due to the combustion processes of the working fluids. Combustible working fluids are called fuels.

The natural petroleum oil is the largest single source of internal combustion engine fuels. Petrol and Diesel are the most used among them. The boiling point of petrol is 30C to 200C and that of diesel oil is from 200C to 375C.

Fuels of most of the IC Engines are the derivatives of Petroleum like gasoline, diesel oil, kerosene, jet fuel etc. All of these fuels are produced during the fractional distillation of Petroleum Oil obtained from crudes from oil wells.

The fuels used in the IC Engines are designed to satisfy the performance requirements of the engine system in which they are used. As a result the fuels must have certain
(i) physical,
(ii) chemical and
(iii) combustion properties.

Following are the some characteristics a fuel must have in order to produce the desirable output to the engine performance.

(i) A fuel must have a large energy density to be capable to release huge amount of energy during its combustion in side the combustion chamber.

(ii) A fuel must posses a good combustion quality to produce large amount of energy in smooth way.

(iii) A fuel must have high thermal stability or pre-ignition may occur.

(iv) A fuel must show a low deposit forming tendency else gum formation and other deposit forming processes will hamper the combustion process.

(v) A fuel must be non-toxic, easy to handle and storage.

CRUDE PETROLEUM OIL:

Petroleum or oftenly referred as "Crude Oil" is a naturally occuring inflammable mixtures of liquid and mud and it contains a complex mixture of different hydrocarbons of various moleculer weights. It is mainly recovered through a process called "Oil Drilling".

Oil Wells & Gas Wells:

An oil well produces mainly crude oil with some natural gas dissolved in it. In contrast a gas well produces natural gases although it may contain heavier hydrocarbons like pentane, hexane or hepthane in gaseous state due to the extreme pressure and temperature inside the well, but at surface conditions condensation starts and forms "Natural Gas Condensate" or simply known as Condensate.

COMPOSITIONS OF CRUDE WELL:

Basically, crude well is the muddy mixtures of different hydrocarbons of different moleculer weights. Alkanes, Cyclo-alkanes or napthenes, aromatics. It contains nitrogen, oxygen, sulfur and phosphorous. It may also contains metallic compounds too.

Four different types of hydrocarbon molecules appear in crude oil. The relative percentages are widely varied from oil to oil. They are:
i) Paraffins (alkanes, CnH2n+2),
ii) Olefins (alkenes, CnH2n),
iii) Napthenes (cyclo-alkanes, CnH2n),
iv) Aromatics (having benzene ring, CnH2n-6).

It is then refined by fractional distillation in oil refinery to obtain a large number of consumer products, from petrol or gasoline, diesel to kerosene, heavy oil, fuel oil, asphalt, chemical reagents, plastics etc.

Most of the derivatives of the petroleum have been used as fuel or heating purpose. The major products of a petroleum refinery are:

(i) Gasoline,
(ii) Kerosene,
(iii) Diesel Oil,
(iv) Fuel oil,
(v) Heavy Oil,
(vi) Lubricating Oil,
(vii) Asphalts

As the demands for gasoline, kerosene/ jet fuel and diesel oil are maximum, refineries around the world have started to convert heavy fuels and other higher hydrocarbons into gasoline, kerosene and diesel oil. To perform this, refineries have adopted several thermo-chemical processes those can convert high moleculer weight hydrocarbons into lighter ones by breaking them.

GENERAL REFINERY PROCESSES:

In order to meet the high demands for gasoline and other lighter products, oil refineries have adopted several useful thermo-chemical processes which break the long chain hydrocarbons into lighter ones like gasoline.

CRACKING:

One of the most important processes to convert high moleculer weight hydrocarbons into lighter ones is called Cracking. Cracking basically breaks the carbon long chains into several fragmented short chain hydrocarbons.

THERMAL CRACKING:

Large hydrocarbons are thermally unstable, hence whenever they are sufficiently heated to an elevated high temperature and pressure, they breakdown into smaller, lower boiling point hydrocarbons. The process of thermal decomposition is called cracking.


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