Diesel fuel cold behavior

In Europe, the classification of diesel fuels according to cold behavior is shown in Tables 5.13 and 5.14. The products are divided into ten classes, six for temperate climates, four for arctic zones. 

Hydrocracking makes very good quality diesel fuels concerning the cetane number, cold behavior, stability, and sulfur content. However this type of stock is only available in limited quantities since the process is still not widely used owing essentially to its high cost. 

It is mainly in cold behavior that the specifications differ between bome-heating oil and diesel fuel. In winter diesel fuel must have cloud points of -5 to -8°C, CFPPs from -15 to -18°C and pour points from -18 to 21°C according to whether the type of product is conventional or for severe cold. For home-heating oil the specifications are the same for all seasons. The required values are -l-2°C, -4°C and -9°C, which do not present particular problems in refining. 

The most important point in the use of diesel fuel is its cold temperature behavior. The subject has been addressed previously because it directly affects the engine operation in winter conditions. 

It should be noted finally that adding gasoline to diesel fuel which was sometimes recommended in the past to improve cold behavior conflicts with the flash point specifications and presents a serious safety problem owing to the presence of a flammable mixture in the fuel tank airspace. Adding a kerosene that begins to boil at 150°C does not have the Scune disadvantage from this point of view. 

Additives for Improving the Cold Behavior of Diesel Fuel (Coley, 1989)... 

The nature of these paraffins and their concentration in diesel fuel affect the three temperatures that characterize the cold behavior. The cloud point is the temperature at which crystals of paraffins appear when the temperature is lowered. The cold filter pluming point is defined as the temperature under which a suspension no ionger flows through a standard filter. Finally, the pour point is the temperature below which the diesel fuel no longer flows by simple gravity in a standard tube. These three temperatures are defined by regulations and the refiner has three types of additives to improve the quality of the diesel fuel of winter. 

Although lubricant base stocks have been subjected to dewaxing processes, they still contain large amounts of paraffins that result in a high pour point for the oil. In the paragraph on the cold behavior of diesel fuels, additives were mentioned that modify the paraffin crystalline system and oppose the precipitation of solids. 

Botros, M. G. 1997. Enhancing the Cold Flow Behavior of Diesel Fuels. In SAE Spec. Publ. SP-1302, Gasoline and Diesel Fuel Performance and Additives. Warrendale PA Society of Automotive Engineers (Paper No. 972899). 

The pour point (ASTM D-97, IP 15) is the lowest temperature at which the fuel oil will flow under specified conditions. The maximum and minimum pour point temperatures provide a temperature window where a petroleum product, depending on its thermal history, might appear in the liquid as well as the solid state. Pour point data can be used to supplement other measurements of cold flow behavior, and the data are particularly useful for the screening of the effect of wax interaction modifiers on the flow behavior of petroleum. The pour point should not be confused with the freezing point, which is an index of the lowest temperature at which the crude oil will flow under specified conditions. Test methods (ASTM D-2386, ASTM D-5901, ASTM D-5972, IP 434, IP 435) for the freezing point are not usually applicable to fuel oil but are more applicable to diesel fuel and aviation fuel. 

Anti-oxidation Cetane improvement Dispersion Anti-icing Detergent Metal passivation Corrosion inhibition Cold-flow improvement Minimize oxidation and gum formation during storage Increase cetane number Improve behavior in fuel injectors Minimize ice formation during cold weather Control deposition of carbon in the engine Deactivate trace metals that can accelerate oxidation Minimize rust throughout the diesel fuel supply chain Improve flow characteristics in cold weather... 

This section shows how DSC and thermomicroscopy can be used to study the cold flow behavior of two biodiesels (palm oil methyl ester (MEl) and rapeseed oil methyl ester (ME2)) and their blends with a conventional diesel fuel (DF). The impact of a cold flow improver on the quantity and size of crystals is also presented. 

The chemical composition of a fuel is very complex and generally a lot of additives are added in order to improve some properties such as viscosity, oxidative stability, cold flow behavior, cetane number, color or smell etc. The impact on fuel properties of a complex mixture of miscellaneous additives is not always very well known. It has been already shown that it can bring a positive or negative synergy. Therefore, DSC and P-DSC can be very useful in evaluating with high accuracy and in a reasonable time the impact of a package of additives on the oxidative stability or the cold flow behavior of an alternative or conventional diesel fuel. 

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