What is Calorific Value of a fuel ?
Calorific Value is defined as the quantity of heat produced for the quantity of fuel used by the combustion. This has to be done at normal conditions, i.e., at constant temperature and constant pressure. The temperature and pressure must be constant at zero degrees on the centigrade scale and 1,013 mbar respectively.
When a combustion process takes place, the heat gets released and water vapor too. When a fuel is burned, heat is released. This water vapor can be used to calculate the quantity of heat produced and it is known as Calorific value of a fuel.
Calorific value is also known as Heating values. There are two calorific values. They are Higher Calorific Value and Lower Calorific value. Higher calorific value is also known as Gross calorific value or GCV. Lower calorific value is also known as Net calorific value or NCV. Higher calorific value represents that the water vapor present in the heat can be recovered easily where as lower calorific value represents that the water vapor is contained in the products or the fuel that is under combustion. The units of calorific value are energy/mole of fuel. [ energy/mass of fuel or energy /volume of fuel ].
Calorific value can be determined with the help of a Bomb Calorimeter. A bomb calorimeter consists of a crucible which need to be filled with any type of fuel for which the calorific value has to be measured. The fuel fuel may be any type of fuel but need to be clean without impurities. If there are any impurities present in the crucible, the calorific value obtained will be with errors. The accurate calorific value can be only obtained when the fuel is free of all the types of impurities. We need to make sure that the weight of fuel in the bomb calorimeter, i.e., in the crucible. The next step is to ignite the bomb calorimeter and wait for the result. The bomb calorimeter is made in such a way that water surrounds the crucible. The heat released from the combustion gets absorbed by the surrounding water. The initial temperature and the final temperature of the water is observed and noted with the help of a thermometer.
The calorific value can be determined from the bomb calorimeter by using the heat balance. We usually know that the heat released due to the combustion is equal to heat absorbed by the fluid. The calorific value can be determined the formula. Calorific value is the ratio of water, specific heat, change of temperature and the mass of fuel. It is represented as
Calorific Value = Water * Specific Heat * Change in Temperature / Mass of the Fuel
Bomb Calorimeter is used to measure the calorific value when the fuel is in solid or liquid state.
Boys Calorimeter is used to measure the calorific value when the fuel is in gaseous state. Exact value can never be determined but very close approximate value can be determined.