Standard Test Method for Heat of Combustion of Liquid Hydrocarbon Fuels by Bomb Calorimeter.
This test method covers the determination of the heat of combustion of liquid hydrocarbon fuels ranging in volatility from that of light distillates to that of residual fuels.
Under normal conditions, this test method is directly applicable to such fuels as gasolines, kerosines, Nos. 1 and 2 fuel oil, Nos. 1-D and 2-D fuel and Nos. 0-GT, 1-GT, and 2-GT gas turbine fuels.
This test method is not as repeatable and not as reproducible as Test Method D4809.
The values stated in SI units are to be regarded as the standard.
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.
The fuel can be either liquid or solid, and contain only the elements carbon, hydrogen, nitrogen, and sulfur. The products of combustion, in oxygen, are gaseous carbon dioxide, nitrogen oxides, sulfur dioxide, and liquid water. In this procedure, 25 Deg C is the initial temperature of the fuel and the oxygen, and the final temperature of the products of combustion.
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.
The fuel can be either liquid or solid, and contain only the elements carbon, hydrogen, oxygen, nitrogen, and sulfur. The products of combustion, in oxygen, are carbon dioxide, nitrogen oxides, sulfur dioxide, and water, all in the gaseous state. In this procedure, the combustion takes place at a constant pressure of 0.1012 MPa (1atm), and 25 Deg C is the initial temperature of the fuel and the oxygen, and the final temperature of the products of combustion.
Summary of Test Method
Heat of combustion is determined in this test method by burning a weighed sample in an oxygen bomb calorimeter under controlled conditions. The heat of combustion is computed from temperature observations before, during, and after combustion, with proper allowance for thermochemical and heat transfer corrections. Either isothermal or adiabatic calorimeter jackets can be used.
Temperatures can be measured in degrees Celsius.
Temperature can be recorded in either degrees Fahrenheit or ohms or other units when using electric thermometers. Use the same units in calculations, including standardization.
Time is expressed in calculations in minutes and decimal fractions thereof. It may be measured in minutes and seconds. Masses are measured in grams and no buoyancy corrections are applied.
Significance and Use
The heat of combustion is a measure of the energy available from a fuel. A knowledge of this value is essential when considering the thermal efficiency of equipment for producing either power or heat.
The heat of combustion is determined by this test method is designated as one of the chemical and physical requirements of both commercial and military turbine fuels and aviation gasoline.
The mass heat of combustion, the heat of combustion per unit mass of fuel, is a critical property of fuels intended for use in weight=limited craft such as airplanes, surface effect vehicles, and hydrofoils. The range of such aircraft between refueling is a direct function of the heat of combustion and density of the fuel.
Benzoic Acid powder must be compressed into a tablet or pellet before weighing. Benzoic Acid pellets for which the heat of combustion has been determined by comparison with the National Bureau of Standards are obtainable commercially for those laboratories not equipped to pellet benzoic acid.
Test Room, Bomb, Calorimeter, Jacket, Thermometers and Accessories.
The room in which the calorimeter is operated must be free from drafts and not subject to any sudden temperature changes. The direct rays of the sun shall not strike the jacket or thermometers. Adequate facilities for lighting, heating, and ventilating shall be provided. Thermostatic control or room temperature and controlled relative humidity are desirable.
The oxygen bomb is to have an internal volume of 350 +- 50ml. All parts are to be constructed of materials which are not affected by the combustion process or products sufficiently to introduce measurable heat input or alteration of end products. If the bomb is lined with platinum or gold, all openings shall be sealed to prevent combustion products from reaching the base metal. The bomb must be designed so that all liquid combustion products can be completely recovered by washing the inner surfaces. There must be no gas leakage during the test. The bomb must be capable of withstanding a hydrostatic pressure test to a gauge pressure of 3000psi (20MPa) at room temperature, without stressing any parts beyond its elastic limit.
The calorimeter vessel shall be made of metal (preferably copper or brass) with a tarnish-resistant coating, and with all outer surfaces highly polished. Its size shall be such that the bomb will be completely immersed in water when the calorimeter is assembled. It shall have a device for stirring the water thoroughly and at a uniform rate, but with minimum heat input. Continuous stirring for 10min shall not raise the calorimeter temperature more than 0.01 Deg C starting with identical temperatures in the calorimeter, room, and jacket. The immersed portion of the stirrer shall be coupled to the outside through a materials of low heat conductivity.
Note - As used in this test method, the term calorimeter designates the bomb, the vessel with stirrer, and the water in which the bomb is immersed.
The calorimeter shall be completely enclosed within a stirred water jacket and supported so that its sides, top and bottom are approximately 10mm from the jacket wall. The jacket can be arranged so as to remain at substantially constant temperature, or with provision for rapidly adjusting the jacket temperature to equal that of the calorimeter for adiabatic operation. It must be constructed so that any water evaporating from the jacket will be maintained for all experiments, including standardization.
Temperatures in the calorimeter and jacket shall be measured with the following thermometers or combinations thereof : Etched Stem, Mercury-in-Glass, ASTM Bomb Calorimeter Thermometer, Beckmann Differential Thermometer, Calorimetric Type Platinum Resistance Thermometer.
A magnifier is required for reading mercury-in-glass thermometers to one tenth of the smallest scale division. This shall have a lens and holder designed so as not to introduce significant errors due to parallax. A Wheatstone bridge and galvanometer capable of measuring resistance of 0.0001 ohm are necessary for use with resistance thermometers.
A watch or other timing device capable of measuring time to 1s is required for use with the isothermal jacket calorimeter.
Non-volatile samples shall be burned in an open crucible of platinum (preferred), quartz or acceptable base metal alloy. Base metal alloy crucibles are acceptable if after a few preliminary firings the weight does not change significantly between tests.
Use a 100mm length of No.34 B & S gauge iron wire or Chrome C resistance wire. Shorter lengths may be used if the same length is employed in all tests, including standardization tests. Platinum wire may be used if the ignition energy is small and reproducible.
A 6 to 16V alternating or direct current is required for ignition purposes with an ammeter or pilot light in the circuit to indicate when the current is flowing. A step-down transformer connected to a 115V 50/60Hz lighting circuit of storage batteries can be used (Warning - The ignition circuit switch shall be of the momentary contact type, normally open, except when held closed by the operator).
Oxygen Purifying Device
Commercial oxygen produced from liquid air can generally be used without purification. Oxygen prepared by electrolysis of water should not be used without purification, as it can contain enough hydrogen to affect results by 1% or more. Combustible impurities can be removed from oxygen by passing it over copper oxide (CuO) at about 500°C.