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DEFINITION : By
motor gasoline is meant a mixture of the lighter fractions of petroleum composed of
hydrocarbons having boiling points in the range approximately 30 0C
to 215 0C. Straighfluidizet run stream from Crude Distillation Unit (CDU) and cracked stream from
d
Catalytic Cracker Unit (FCCU) with the above boiling range are blended to obtain required
quality Motor Gasoline. It may contain small quantities of chemical e.g. tetraethyl lead,
etc. added to improve its performance.
NOMENCLATURE
Motor spirit,
Petrol and Gasoline are different nomenclatures for the same product. Motor spirit is of
British origin while Gasoline is of American origin.
END USE
Normally used
as a fuel for spark ignition internal combustion engines such as passenger cars, 2
wheelers, 3 wheelers etc.
SPECIFICATIONS
Motor gasoline are currently
marketed meeting Bureau of Indian Standards Specification, IS : 2796-1971, for Motor
Gasoline 87 and 93 Octane. Besides Motor Gasoline (MT 80) is marketed as defense
applications.
OCTANE NUMBER
The most important property of
a gasoline is its Octane Number, (ON), which indicates whether the fuel will knock in an
engine. Knock or "Pink" is the audible explosion (detonation) produced when a
portion of the fuel charge in the cylinder ignites spontaneously ahead of the normal flame
front. All things being equal, knock is a direct function of the fuel alone, some fuels
being more prone to it than others. It is determined in the CFR (Co-operative Fuel
Research) engine and is defined as the percentage of iso-octane, arbitrarily
given an
O.N. of 100, in a blen with normal heptane (O.N.=0) which matches the fuel under
examination.
Motor gasoline is normally rated in the CFR engines under two sets of
conditions which differ in severity. The Research or F.1 method gives a rating more
applicable to operation under mild conditions, while the Motor or F.2 method may be a
better criterion when operating at higher speeds and loads.
The higher the compression
ration of an engine the higher is its thermal efficiency. The limiting compression ration
that can be utilized is set by the anti-knock characteristics of the fuel; thus increasing
of the octane number permits the use of higher compression rations and gives more power,
higher efficiency and lower fuel consumption. However, no advantage is gained by
increasing the octane number beyond that necessary to give knock free performance.
The CFR octane number is a
rating on one particular type of engine under a given set of conditions and cannot by
itself be used to predict the road octane number (RON) of the fuel under varying
conditions of operations. VOLATILITY
The volatility of a Motor
Gasoline is controlled and measured by a laboratory distillation test and by the Reid
vapour pressure determination.
Motor Gasoline have flash
point of less than 23 deg C and as per explosive classification these fall in the category
of Class A Petroleum products.
COLD STARTING
The ease with which an engine
will start from cold has been found to depend on the 10% evaporated temperature and
Reid
Vapour pressure and suitable limits are therefore placed on these two properties.
WARM UP
Whereas under cold conditions
of starting the amount of gasoline which evaporates is of the order of 10%, the amount
which evaporates during the warm-up period averages about 50%, the remainer entering the
cylinders in the form of fine droplets. The volatility criterion generally used to ensure
satisfactory warm up performance is therefore the 50% evaporated temperature.
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