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INTRODUCTION
This section briefly describes the main features of fuels.
Energy from the Sun is converted into chemical energy by photosynthesis. But, as we know,
when we burn dried plants or wood, producing energy in the form of heat and light, we are
releasing the Sun’s energy originally stored in that plant or in that wood through
photosynthesis. We know that, in most of the world today, wood is not the main source of
fuel. We generally use natural gas or oil in our homes, and we use mainly oil and coal to heat
the water to produce the steam to drive the turbines for our huge power generation systems.
These fuels - coal, oil, and natural gas - are often referred to as fossil fuels.
The various types of fuels (like liquid, solid and gaseous fuels) that are available depend on
various factors such as costs, availability, storage, handling, pollution and landed boilers,
furnaces and other combustion equipments.
The knowledge of the fuel properties helps in selecting the right fuel for the right purpose and
for the efficient use of the fuel. Laboratory tests are generally used for assessing the nature
and quality of fuels.
2 TYPE OF FUELS
This section describes types of fuels: solid, liquid, and gaseous.
2.1 Liquid Fuels
Liquid fuels like furnace oil and LSHS (low sulphur heavy stock) are predominantly used in
industrial applications. The various properties of liquid fuels are given below.
2.1.1 Density
Density is defined as the ratio of the mass of the fuel to the volume of the fuel at a reference
temperature of 15°C. Density is measured by an instrument called a hydrometer. The
knowledge of density is useful for quantitative calculations and assessing ignition qualities.
The unit of density is kg/m3.
2.1.2 Specific gravity
This is defined as the ratio of the weight of a given volume of oil to the weight of the same
volume of water at a given temperature. The density of fuel, relative to water, is called
specific gravity. The specific gravity of water is defined as 1. Since specific gravity is a ratio,
it has no units. The measurement of specific gravity is generally made by a hydrometer.
Specific gravity is used in calculations involving weights and volumes.
Viscosity
The viscosity of a fluid is a measure of its internal resistance to flow. Viscosity depends on
the temperature and decreases as the temperature increases. Any numerical value for
viscosity has no meaning unless the temperature is also specified. Viscosity is measured in
Stokes / Centistokes. Sometimes viscosity is also quoted in Engler, Saybolt or Redwood.
Each type of oil has its own temperature - viscosity relationship. The measurement of
viscosity is made with an instrument called a Viscometer.
Viscosity is the most important characteristic in the storage and use of fuel oil. It influences
the degree of pre-heating required for handling, storage and satisfactory atomization. If the
oil is too viscous, it may become difficult to pump, hard to light the burner, and difficult to
handle. Poor atomization may result in the formation of carbon deposits on the burner tips or
on the walls. Therefore pre-heating is necessary for proper atomization.
2.1.4 Flash Point
The flash point of a fuel is the lowest temperature at which the fuel can be heated so that the
vapour gives off flashes momentarily when an open flame is passed over it. The flash point
for furnace oil is 66 0C.
2.1.5 Pour Point
The pour point of a fuel is the lowest temperature at which it will pour or flow when cooled
under prescribed conditions. It is a very rough indication of the lowest temperature at which
fuel oil is ready to be pumped.