Module 1. Classification of Farm Power Sources
Module 2. Classification of IC Engines & Therm...
Module 3. Performance Characteristics
Module 4. Engine Components
Module 5. Engine Operating System
Module 6.:Engine Fuel System
Module 7. Engine Governor
Module 8. Engine Cooling & Lubrication system
Module 9. Engine Ignition System
LESSON 19. FUEL PROPERTIES
It is the property of fluid/liquid that resists the force which makes the liquid/fluid to flow. It is measured by the instrument known as viscometer in which the time required by certain volume of fluid to flow is measured under stated conditions. It affects the spray pattern of fuel in the combustion chamber. Low viscosity produces a fine mist, whereas high viscosity leads to coarse atomization.
19.2 Octane number
It is a standard used for determining the knock characteristics of fuels (petrol) and it refers to the percentage by volume of iso-octane (C8H18) in a mixture of iso-octane and normal heptane (C7H16). Fuel knock is prevented by the fuel’s ability not to self ignite in the combustion process.
19.3 Cetane number
It is the measure of fuel property in which it is measured that how easily and fast the fuel (diesel) is ignited when reaches into the engine combustion chamber/cylinder. A cetane number rating is obtained by comparing the fuel with cetane, a colourless liquid hydrocarbon, which has excellent ignition qualities and is rated as 100. The percentage of cetane in a mixture of cetane (C16H34) and α (alpha) methyl naphthalene (C11H16) is called cetane number. The higher the cetane number the shorter the lag between the instant fuel enters the combustion chamber and the instant it begins to burn. The commercial diesel fuels have got cetane varying from 30 to 60.
19.4 Carbon residue
Carbon residue refers to matter left after combustion is an indication of the amount of combustion chamber deposits when the fuel is burnt in the engine combustion chamber/cylinder. It varies from 0.15 to 0.35% on weight basis and its permissible limit depends upon the engine characteristics. This property is more critical in small high speed engines than in large, low speed engines.
19.5 Sulphur content
The presence of sulphur in high quantity in the fuel is not desirable as it increases the wear of engine components specifically, the piston rings and the cylinder walls. It also causes the formation of hard coatings on the piston and oil sludge in the engine crankcase. The sulphur in fuel after burning combines with the water to form corrosive acids which further damages the finished surfaces. Sulphur content varies from 0.5 to 2% on weight basis.
19.6 Gum content
Gum in the fuels is formed by the polymerization of some unsaturated hydrocarbons. To have good quality of fuel, the gum content should be minimum.