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Lab Methods

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Net/Gross Heat of Combustion Bomb Method

  • Method ASTM D240
  • Repeatability .012 MJ / Kg
  • Reproducibility .035 MJ / Kg
  • Blending linear
  • Additive Correction No

This method will provide a measure of how much energy is contained in liquid petroleum hydrocarbons from light distillates to residual fuels. This can be expressed in many types of units including Calories, Joules, BTU, etc.

A thermal calorie is defined as the amount of energy required to warm one gram of air free water one degree Celsius as a result of the complete combustion of the sample. This can be converted to BTU (British Thermal Unit). There are 252 calories in a single BTU. The British Thermal Unit is the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.

This method is reported in two different forms defined below.

Gross heat of combustion, Qg (MJ/kg)—the quantity of energy released when a unit mass of fuel is burned in a constant volume enclosure, with the products being gaseous, other than water that is condensed to the liquid state.

Net heat of combustion, Qn (MJ/kg)—the quantity of energy released when a unit mass of fuel is burned at constant pressure, with all of the products, including water, being gaseous.

This method is performed by placing a weighed piece of sample in an oxygen bomb vessel. This vessel is placed in the instrument where it is immersed in water. The sample is then combusted entirely and the heat given off by the bomb is absorbed by the water. This temperature rise in the water is then converted to one of the energy units and reported.