Crude oil properties that are important for refining and transportation include API gravity, vapor pressure, octane number, cetane number, cloud point, pour point, viscosity index, and calorific value. API gravity measures the relative density. Vapor pressure indicates conditions under which bubbles may form. Octane number measures resistance to engine knocking. Cetane number relates to ignition delay in diesel engines. Cloud and pour points indicate temperatures at which wax may precipitate out. Viscosity index characterizes viscosity changes with temperature. Calorific value measures heat energy content. These properties help determine how crudes can be transported and processed into refined products.

1. Petroleum Refining and
Petrochemicals
PET 217
Important Properties of Crude Oil

2. API Gravity
• A specific gravity scale developed by the American Petroleum Institute (API)
for measuring the relative density of various petroleum liquids, expressed in
degrees. API gravity is gradated in degrees on a hydrometer instrument and
was designed so that most values would fall between 10° and 70° API gravity.
The arbitrary formula used to obtain this effect is: API gravity = (141.5/SG
at 60°F) - 131.5, where SG is the specific gravity of the fluid.

3. API Gravity

4. Vapor Pressure

5. Vapor Pressure
• •Vapor Pressure is the pressure exerted by a vapor at a given
temperature in a closed system
• •A liquid with a high vapor pressure is called a volatile liquid•Vapor
Pressure is directly related to temperature
• •Increasing Temperature = Increased Vapor Pressure

6. Vapor Pressure
• The vapor pressure reflects the level of performance of the crude oil at the
time of handling. It also underlines conditions under which bubbles may
probably form and shows where pressure build-ups of escaping light ends
are likely to happen. The measurement of vapor pressure eliminates costly
damage to vessels or pipelines that transport crude oil. In addition, it
provides guidance on how transportation facilities should be constructed to
withstand a worst-case situation.

7. Octane number
• Octane number, also called Antiknock Rating, measure of the ability of a
fuel to resist knocking when ignited in a mixture with air in the cylinder of
an internal-combustion engine. The octane number is determined by
comparing, under standard conditions, the knock intensity of the fuel with
that of blends of two reference fuels: iso-octane, which resists knocking, and
heptane, which knocks readily. The octane number is the percentage by
volume of iso-octane in the iso-octane–heptane mixture that matches the
fuel being tested in a standard test engine. See also knocking.

8. Octane number

9. Knocking
• Knocking, in an internal-combustion engine, sharp sounds caused by
premature combustion of part of the compressed air-fuel mixture in the
cylinder. In a properly functioning engine, the charge burns with the flame
front progressing smoothly from the point of ignition across the combustion
chamber. However, at high compression ratios, depending on the
composition of the fuel, some of the charge may spontaneously ignite ahead
of the flame front and burn in an uncontrolled manner, producing intense
high-frequency pressure waves. These pressure waves force parts of the
engine to vibrate, which produces an audible knock.

10. Engine Knocking

11. Cetane number
• Cetane number (or CN) is an inverse function of a fuel's ignition delay, the
time period between the start of ignition and the first identifiable pressure
increase during combustion of the fuel. In a particular diesel engine, higher
cetane fuels will have shorter ignition delay periods than lower Cetane fuels.
Cetane numbers are only used for the relatively light distillate diesel oils

12. Cetane number
• Generally, diesel engines operate well with a CN from 48 to 50. Fuels with
lower cetane number have longer ignition delays, requiring more time for the
fuel combustion process to be completed. Hence, higher speed diesel engines
operate more effectively with higher cetane number fuels.

13. Benefits of a High Cetane Rating
• A higher cetane number resulting in quicker ignition of the fuel leads to less
non-ignited fuels building up inside the combustion chamber, as well as more
complete fuel combustion. Better fuel combustion and quick ignition leads to
quicker starting for vehicles, as well as an engine that operates more quietly
as only misted fuel is ignited and buildup inside the engine is minimized.
Moreover, fuel efficiency improves with more complete combustion and
harmful emissions are reduced.

14. Cloud Point
• The cloud point represents the temperature at which wax or paraffin begins
to precipitate from a hydrocarbon solution
• In the petroleum industry, cloud point refers to the temperature below
which wax in diesel or biowax in biodiesels forms a cloudy appearance. The
presence of solidified waxes thickens the oil and clogs fuel filters and
injectors in engines. The wax also accumulates on cold surfaces (producing,
for example, pipeline or heat exchanger fouling) and forms an emulsion or
sol with water. Therefore, cloud point indicates the tendency of the oil to
plug filters or small orifices at cold operating temperatures

15. Cloud Point

16. Pour point
• The pour point of a liquid is the temperature below which the liquid loses
its flow characteristics. It is defined as the minimum temperature in which
the oil has the ability to pour or flow

17. Pour point

18. Viscosity index
• The viscosity of lube oil does not give any relevant information unless the
temperature, at which it was measured, is known. Temperature is the most
influential parameter for the viscosity change of oil. For any oil used under
changing temperature conditions, it is important to know the change of
viscosity in relation to the change of temperature. For this purpose, the
viscosity index12 for base stocks and lube oils was developed

19. Viscosity index
• The viscosity index (VI) is an arbitrary, unit-less measure of a fluid's change
in viscosity relative to temperature change. It is mostly used to characterize
the viscosity-temperature behavior of lubricating oils. The lower the VI, the
more the viscosity is affected by changes in temperature. The higher the VI,
the more stable the viscosity remains over temperature fluctuations. The VI
was originally measured on a scale from 0 to 100

20. Viscosity index

21. Viscosity index

22. Calorific value
• Calorific value is the amount of heat energy present in fuel and which is
determined by the complete combustion of specified quantity at constant
pressure and in normal conditions. It is also called calorific power. The unit
of calorific value is kilojoule per kilogram i.e. KJ/Kg.
• The efficiency of fuel or food mainly depends on the calorific value. If the
value is high, its efficiency will also be high. If the value is low, its efficiency
would also decrease. Calorific value is directly proportional to its efficiency.

23. Calorific values
Fuel
Calorific Value Of Fuel(
Approximately)
Cow Dung 8000
Wood 22000
Coal 33000
Biogas 40000
Diesel 45000
kerosene 45000
Petrol 45000
Methane 50000
LPG 55000