Page 109 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

MODULE 4 : Fuel Supply System (Petrol)

LESSON 29 & 30: Fuel supply system in petrol engine

Gasoline Fuel: properties of Gasoline
fuel - combustion processes

Objectives

At the end of this lesson you shall be able to

• explain Petrol Fuel Supply System
• elaborate properties of Gasoline fuel
• demonstrate Combustion processor.

Gasoline Fuel: properties of Gasoline fuel-combustion processes
Petrol or Gasoline Fuel

It is obtained by fractional distillation or cranking of petroleum. It is the lightest and most volatile liquid fuel. After
refining petrol, desired properties are obtained by adding other desired substances (additives) to it.
mechanic motor vehicle It is used in different types of IC engines, such as cars, scooters, motorcycles, aircraft etc.
It is a mixture of unrefined petrol, paraffin, naphtha and aromatic hydrocarbons. Generally, and highly flammable,
yellow color is distilled and soot. This is hydrogen. Its relative gravity is about 0.73 and calorific value ranges from
42 to 44 mega joules/kg.
Characteristics of Gasoline Fuel Following are the main properties of gasoline fuel
i Volatility: Volatility refers to the ability of petrol to evaporate. Due to this property of fuel, it gets mixed with air
in sufficient quantity for combustion. It blows at 90°C with a vapor pressure of 0.5 to 1.0 cm. This property is
of great benefit when the engine is running, because the vaporized fuel burns easily.
ii Purity: Petrol should be pure i.e. it should not contain dust, dirt, grease and water

iii The sulfur obtained during purification of sulfur: free crude oil should be cleaned as much as possible,
otherwise there is a possibility of rusting in the engine. Only a maximum of 0.1% of it is acceptable in fuel.
iv Due to the amount of gum in adhesion-free petrol. Piston rings and valves etc. start sticking and the manifold
and The jets of the carburetor get blocked. Therefore, there should not be any amount of gum in petrol i.e. it
should be stick-free.
v Anti-knocking quality: This quality of petrol depends on its octane number. Octane The higher the number,
the less knocking the engine will have.
vi Viscosity: This is a physical property of petrol which depends on its rate of flow. The lower the viscosity of the
petrol, the more easily the petrol will flow in the engine.
vii Additive: Some chemical additives are added to petrol to increase the anti-freezing capability of petrol as well
as to increase its combustion capability and to reduce the harmful waste left after combustion. Detergent is
used as an additive to clean critical parts of the engine.
viii Stoichiometric ratio: The ratio of fuel and air required for complete combustion of petrol is called stoichiometric
ratio. For petrol this ratio is 14.7:1 which means that 14.7 liters of air will be required to burn 1 liter of petrol.
ix According to ISA (International Standard Atmosphere) the sea level density is also 1.235 K. Air mixture for the
engine. The air used as fuel in petrol engine is 14.7 kg of air. If the air density in the fuel is low, the mixture
obtained will be a rich mixture and if the air density in the fuel is high, the mixture obtained will be a lean
mixture.

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