Liquid fuels based on hydrocarbon feedstock represent one of the most important commodities. That’s why their production and global distribution involve many different aspects and standardized processes worth considering. The huge amounts of fuels that are produced and consumed require a common understanding of quality which can be supported by means of digital density measurement.
Learn about the most important facts concerning fuel quality control in this easy-to-read article:
Trade of goods: mass to volume conversion
For the international trade of goods it is crucial to precisely know the fuel density or more specifically its apparent density which represents weight by volume. When large quantities of fuel products are traded, it is not possible to measure the weight of e.g. a whole tanker although the weight of the product is used for invoicing. However, the volume of such a tanker is known and hence the relation of weight to volume (equals apparent density) can be used to calculate the desired parameter (weight) based on the known parameter (volume).
This, of course, also works the other way round, when a fuel truck is weighed on a weighbridge before and after it was filled with fuel. This deviation can then be used to calculate the filled volume thanks to the known apparent density measured by a digital density meter.
Fuel density is an important fuel property used for the description of the product and to calculate further fuel characteristics.
Sample handling: coping with volatile components
Refined fuels such as diesel, gasoline, or jet fuel contain a considerable amount (more than 150 different hydrocarbons in total) of volatile components; so-called ‘light end hydrocarbons’. As with any other liquid containing dissolved gases, the solubility coefficient mainly depends on temperature and pressure. Therefore, care needs to be taken during handling of such liquids. To prevent a loss of volatile components, the fuel should be kept at low temperatures (which increases the solubility) and/or stored in closed containers with only a minimum headspace. This ensures that a measured density reading – which describes the total amount of various contained hydrocarbons – is correct. Further, this guarantees comparability if the same sample is measured at different locations, times, etc.
International comparability: API conversion
Throughout the past 170 years of fuel history common practices have become standardized differently in different regions. Because density greatly depends on temperature, it is required to report density values at a covenant temperature. To cope with different measuring temperatures the so-called API conversion was developed. This allows you to perform measurements at any desired temperature (which can be higher than the reporting temperature in the case of crude oil or lower in the case of jet fuel) and to convert the measured density afterwards to the density at a defined reference temperature. This saves time and paves the way to international comparability. Modern digital density meters, of course, measure at the desired measuring temperature and fully automatically convert the density reading to the density at a desired reference temperature.
Diversity of fuel density measurement: from quick on-site checks to fully automated lab results
For quick product characterization outdoors and in the field, portable and mobile density meters provide great assistance, especially when the time is too limited for time-consuming traditional measuring methods such as pycnometers. Such measurements are often suitable to identify a product when it does not require the highest precision but the need for quick results may be much more present.
However, very precise density measurements are needed once a liquid fuel is purchased or sold.
The need for precise density measurements occurs in many different situations on a daily basis at refineries, so the number of measurements performed is very high. Fortunately, modern digital density meters can be fully automated for 24/7 operation and are much more precise than the time-consuming traditional measuring method using hydrometers.
Standards and regulations: ASTM compliance
The various digital density meters also have to be standardized to make sure that two independent parties that check the fuel density of the same liquid but at different locations use a comparable measuring method. For fuel density, digital density measurement is basically covered by two standards: ASTM D7777 and ASTM D4052. ASTM D7777 describes the use of portable density meters and requires a precision of 1 kg/m³ whereas ASTM D4052 covers fuel density measurements by means of digital density meters in the lab and requires a precision of 0.1 kg/m³; it further describes how measuring errors such as gas bubbles in the liquid can be detected by means of physical or optical methods.
Fuel density is an important quality parameter of diesel, gasoline, or jet fuel and, considering the nature of these fuels, their quality control with modern digital density meters can be very easy when appropriate handling is applied. Consider the advice above, make use of API conversion, and stick to regulations described in internationally relevant standards for a professional participation in the fuel industries.
If you have any questions about this topic, please don’t hesitate to contact us or simply add a comment below. We’ll get back to you.