LESSON 18. FUEL PROPERTIES

Engine needs to run on fuel of high quality to produce maximum work output. Several fuel properties have been identified and defined as following.

i) Heat value or Calorific value

ii) Specific gravity

iii) Volatility

iv) Flash point

v) Fire point

vi) Pour point

vii) Viscosity

viii) Octane number

ix) Cetane number

x) Carbon residue

xi) Sulphur content

xii) Gum content

18.1 Heat value or Calorific value

It is the indicative of heat energy being produced by the fuel when it is burnt inside the cylinder/combustion chamber of an engine. It is expressed in J/kg of fuel and is measured in the device which is known as calorimeter. The impurities in the fuel leads to decrease in its heat value.

18.2 Specific gravity

It is expressed as the ratio of the density of fuel to the density of water. The specific gravity affects the fuel atomization in the nozzles and spray penetration/injection in the engine cylinder/combustion chamber. Fuels which are relatively heavier have usually greater heat value. The specific gravity is measured by the hydrometer.

18.3 Volatility

It is the property of the fuel to get converted into vapours on burning at a specific temperature. The volatility is measured by means of distillation. In diesel fuel, volatility is indicated by 90%  distillation temperature (temperature at which 90% of the fuel is distilled off). Lower volatility in fuels leads to increase in carbon deposits, smoke content and also wear of engine components.

18.4 Flash point

It is the temperature at which the fuel must be heated to get flammable vapours and is driven off to ignite when brought into contact with the flame.

18.5 Fire point

It is the higher temperature at which the vapours will continue to burn after being ignitied. Generally, the fire point is 100 to 210 C higher than the flash point and it is the indicator of fire hazards. The lower the flash point, the greater is the fire hazard. In general, the flash point should be high enough to avoid producing flammable vapours.

18.6 Pour point

It is the temperature  at which the fuel becomes insoluble to pevent flow under specified conditions. In cold weather conditions, this becomes very important parameter as wax crystals start forming even when temperature is slightly over the pour point. A higher pour point implies that in cold weather the fuel will not flow easily through the filters and fuel system and also the atomization/spray characteristics are affected.

Last modified: Wednesday, 29 January 2014, 5:36 AM