Calorific value is a measure of energy. One calorie is the amount of energy needed to raise the temperature of one cubic centimeter of water by one degree Celsius. The American measuring systems evaluates energy content in terms of British thermal units (Btu). One Btu is the amount energy needed to raise the temperature of one pound of water by 1 degree Fahrenheit. When you purchase diesel fuel, its calorific value tells you how much energy your dollars are buying. This may help you choose among different sources of the fuel. It can also help you decide which type of heating unit or vehicle to buy -- diesel, gasoline, electric, gas, solar or hydrogen-- based on the fuel source with the most economical calorific value.
Understand the difference between high and low energy content. The high value refers to the total energy stored in a substance, such as diesel fuel. Low energy content reflects the amount of energy the fuel loses because of the steam generated when the fuel burns.
Calculate high calorific values. The high value for Diesel No. 2 is 137,380 Btu per gallon. Because a Btu is equivalent to about 252 calories, the high calorific values for Diesel No. 2 is 252 calories per Btu times 137,380 Btu per gallon, or approximately 34.620 million calories per gallon. Divide by the number of cubic centimeters in a gallon, 3,785.4, to find the high value of 9,145.7 calories per cubic centimeter.
Calculate low calorific values. Diesel No. 2's low calorific value is 128,450 Btu per gallon. Plugging in the same conversion factors, the low value is 252 calories per Btu times 128,450 Btu per gallon divided by 3,785.4 cubic centimeters per gallon, or 8,551.1 calories per cubic centimeter.
Calculate the high and low calorific values for biodiesel. The high energy content for B100 biodiesel -- made up entirely of biological sources -- is 127,960 Btu per gallon. The low energy content value is 119,550 Btu per gallon. You can plug these numbers into the equation (calories per Btu x Btu per gallon / cubic centimeters per gallon) to find the calorific value in a single cubic centimeter of B100 biodiesel.
Different diesel fuel blends have different calorific values. You must adjust your calculations for the exact formulation you are using.
The factor 252 that converts Btu to calories automatically adjusts for the change from Fahrenheit to Celsius.
Local conditions can affect the actual calorific values measured. These conditions include temperature, pressure, measuring device and amount of impurities in the fuel.
You may see energy content expressed in other units, such as Joules, You will have to look up proper conversion factors to translate from one system to another.