Diesel Fuel With Improved Ignition Characteristics (United States Patent Application 20150284652 Shell Oil)

Diesel Fuel With Improved Ignition Characteristics (United States Patent Application 20150284652 Shell Oil)
October 8, 2015
Applicant: Shell Oil Company
Abstract
Diheterocyclo diazene dicarboxamides have been found to effectively reduce the ignition delay and/or as effective cetane number improvers in diesel fuels and is suitable for use in modern engines.
FIELD OF THE INVENTION
[0002] The present invention relates to diesel fuels having improved ignition characteristics, more particularly to diesel fuels with enhanced cetane numbers.
BACKGROUND OF THE INVENTION
[0003] The cetane number of a fuel composition is a measure of its ease of ignition and combustion. With a lower cetane number fuel a compression ignition (diesel) engine tends to be more difficult to start and may run more noisily when cold; conversely a fuel of higher cetane number tends to impart easier cold starting, to lower engine noise, to alleviate white smoke ("cold smoke") caused by incomplete combustion.
[0004] There is a general preference, therefore, for a diesel fuel composition to have a high cetane number, a preference which has become stronger as emissions legislation grows increasingly stringent, and as such automotive diesel specifications generally stipulate a minimum cetane number. To this end, many diesel fuel compositions contain ignition improvers, also known as cetane boost additives or cetane (number) improvers/enhancers, to ensure compliance with such specifications and generally to improve the combustion characteristics of the fuel.
[0005] Further, thermal stability is an important attribute of diesel fuel quality because of its function as a heat transfer fluid. Poor thermal stability, for example, may result in premature fuel filter plugging.
[0006] Currently, the most commonly used diesel fuel ignition improver is 2-ethylhexyl nitrate (2-EHN), which operates by shortening the ignition delay of a fuel to which it is added. However, 2-EHN can potentially have an adverse effect on the thermal stability of a fuel as it forms free radicals on decomposition at relatively low temperatures. 2-EHN begins to decompose at about 43.degree. C. at atmospheric pressure. Poor thermal stability also results in an increase in the products of instability reactions, such as gums, lacquers and other insoluble species. These products can block engine filters and foul fuel injectors and valves, and consequently can result in loss of engine efficiency or emissions control.
[0007] 2-EHN can also be difficult to store in concentrated form as it tends to decompose, and so is prone to forming potentially explosive mixtures. Furthermore, it has been noted that 2-EHN functions most effectively under mild engine conditions.
[0008] These disadvantages mean that it would be generally desirable to replace 2-EHN, whilst at the same time maintaining acceptable combustion properties.
SUMMARY OF THE INVENTION
[0009] It has now been found that diheterocyclo diazene dicarboxamide compounds can serve to reduce the ignition delay and/or as effective cetane number improvers in diesel fuels, while being more stable to decomposition than 2-EHN.
[0010] Accordingly, in an embodiment, there is provided a composition comprising a diesel base fuel and at least one diheterocyclo diazene dicarboxamide.
[0011] The diheterocyclo diazene dicarboxamides have been found to effectively reduce the ignition delay and/or as effective cetane number improvers in diesel fuels and are suitable for use in modern engines.
[0012] Still yet another aspect of the invention relates to a method of operating a compression ignition engine and/or a vehicle which is powered by such an engine, which method involves introducing into a combustion chamber of the engine a diesel fuel composition containing at least one diheterocyclo diazene dicarboxamide.
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