Diesel Fuel Compositions And Methods Of Use Thereof (Innospec)

Diesel Fuel Compositions And Methods Of Use Thereof (Innospec)
United States Patent Application 20160152912
Mulqueen; Simon    June 2, 2016
Assignee: Innospec Limited
Abstract
A method of combating internal diesel injector deposits caused by carboxylate residues and/or lacquers in the injectors of a diesel engine, the method comprising combusting in the engine a diesel fuel composition comprising (a) the reaction product of a carboxylic acid-derived acylating agent and an amine and (b) a quaternary ammonium salt additive.
Description
[0001] The present invention relates to methods and uses for improving the performance of diesel engines using fuel additives. In particular the invention relates to additives for diesel fuel compositions for use in diesel engines with high pressure fuel systems.
[0002] Due to consumer demand and legislation, diesel engines have in recent years become much more energy efficient, show improved performance and have reduced emissions.
[0003] These improvements in performance and emissions have been brought about by improvements in the combustion process. To achieve the fuel atomisation necessary for this improved combustion, fuel injection equipment has been developed which uses higher injection pressures and reduced fuel injector nozzle hole diameters. The fuel pressure at the injection nozzle is now commonly in excess of 1500 bar (1.5.times.10.sup.8 Pa). To achieve these pressures the work that must be done on the fuel also increases the temperature of the fuel.
[0004] These high pressures and temperatures can cause degradation of the fuel. Furthermore, the timing, quantity and control of fuel injection has become increasingly precise. This precise fuel metering must be maintained to achieve optimal performance.
[0005] Diesel engines having high pressure fuel systems can include but are not limited to heavy duty diesel engines and smaller passenger car type diesel engines. Heavy duty diesel engines can include very powerful engines such as the MTU series 4000 diesel having 20 cylinder variants designed primarily for ships and power generation with power output up to 4300 kW or engines such as the Renault dXi 7 having 6 cylinders and a power output around 240 kW. A typical passenger car diesel engine is the Peugeot DW10 having 4 cylinders and power output of 100 kW or less depending on the variant.
[0006] In all of the diesel engines relating to this invention, a common feature is a high pressure fuel system. Typically pressures in excess of 1350 bar (1.35.times.10.sup.8 Pa) are used but often pressures of up to 2000 bar (2.times.10.sup.8 Pa) or more may exist.
[0007] Two non-limiting examples of such high pressure fuel systems are: the common rail injection system, in which the fuel is compressed utilizing a high-pressure pump that supplies it to the fuel injection valves through a common rail; and the unit injection system which integrates the high-pressure pump and fuel injection valve in one assembly, achieving the highest possible injection pressures exceeding 2000 bar (2.times.10.sup.8 Pa). In both systems, in pressurizing the fuel, the fuel gets hot, often to temperatures around 100.degree. C., or above.
[0008] In common rail systems, the fuel is stored at high pressure in the central accumulator rail or separate accumulators prior to being delivered to the injectors. Often, some of the heated fuel is returned to the low pressure side of the fuel system or returned to the fuel tank. In unit injection systems the fuel is compressed within the injector in order to generate the high injection pressures. This in turn increases the temperature of the fuel.
[0009] In both systems, fuel is present in the injector body prior to injection where it is heated further due to heat from the combustion chamber. The temperature of the fuel at the tip of the injector can be as high as 250-350.degree. C.
[0010] Thus the fuel is stressed at pressures from 1350 bar (1.35.times.10.sup.8 Pa) to over 2000 bar (2.times.10.sup.8 Pa) and temperatures from around 100.degree. C. to 350.degree. C. prior to injection, sometimes being recirculated back within the fuel system thus increasing the time for which the fuel experiences these conditions.
[0011] A common problem with diesel engines is fouling of the injector, particularly the injector body, and the injector nozzle. Fouling may also occur in the fuel filter. Injector nozzle fouling occurs when the nozzle becomes blocked with deposits from the diesel fuel. Fouling of fuel filters may be related to the recirculation of fuel back to the fuel tank. Deposits increase with degradation of the fuel. Deposits may take the form of carbonaceous coke-like residues, lacquers or sticky or gum-like residues. Diesel fuels become more and more unstable the more they are heated, particularly if heated under pressure. Thus diesel engines having high pressure fuel systems may cause increased fuel degradation. In recent years the need to reduce emissions has led to the continual redesign of injection systems to help meet lower targets. This has led to increasingly complex injectors and lower tolerance to deposits.
[0012] The problem of injector fouling may occur when using any type of diesel fuels. However, some fuels may be particularly prone to cause fouling or fouling may occur more quickly when these fuels are used. For example, fuels containing biodiesel and those containing metallic species may lead to increased deposits.
[0013] When injectors become blocked or partially blocked, the delivery of fuel is less efficient and there is poor mixing of the fuel with the air. Over time this leads to a loss in power of the engine and increased exhaust emissions and poor fuel economy.
[0014] Deposits are known to occur in the spray channels of the injector, leading to reduced flow and power loss. As the size of the injector nozzle hole is reduced, the relative impact of deposit build up becomes more significant. Deposits are also known to occur at the injector tip. Here they affect the fuel spray pattern and cause less effective combustion and associated higher emissions and increased fuel consumption.
[0015] In addition to these "external" injector deposits in the nozzle hole and at the injector tip which lead to reduced flow and power loss, deposits may occur within the injector body causing further problems. These deposits may be referred to as internal diesel injector deposits (or IDIDs). IDIDs occur form further up inside the injector on the critical moving parts. They can hinder the movement of these parts affecting the timing and quantity of fuel injection. Since modern diesel engines operate under very precise conditions these deposits can have a significant impact on performance.
[0016] IDIDs cause a number of problems, including power loss and reduced fuel economy due to less than optimal fuel metering and combustion. Initially the user may experience cold start problems and/or rough engine running. These deposits can lead to more serious injector sticking. This occurs when the deposits stop parts of the injector from moving and thus the injector stops working. When several or all of the injectors stick the engine may fail completely.
[0017] The present inventors have studied these internal diesel injector deposits and have found that they contain a number of components. However they believe that the presence of lacquers and/or carboxylate residues lead to injector sticking.
[0018] Lacquers are varnish-like deposits which are insoluble in fuel and common organic solvents. Some occurrences of lacquers have been found by analysis to contain amide functionality and it has been suggested that they form due to the presence of low molecular weight amide containing species in the fuel.
[0019] Carboxylate residues may be present from a number of sources. By carboxylate residues we mean to refer to salts of carboxylic acids. These may be short chain carboxylic acids but more commonly long chain fatty acid residues are present. The carboxylic residues may be present as ammonium and/or metal salts. Both carboxylic acids and metals may be present in diesel fuel from a number of sources. Carboxylic acids are commonly added into fuel as lubricity additives and/or corrosion inhibitors; they may occur due to oxidation of the fuel and may form during the combustion process; residual fatty acids may be present in the fatty acid methyl esters included as biodiesel; and they may also be present as byproducts in other additives. Derivatives of fatty acids may also be present and these may react or decompose to form carboxylic acids.
[0020] Various metals may be present in fuel compositions. This may be due to contamination of the fuel during manufacture, storage, transport or use or due to contamination of fuel additives. Metal species may also be added to fuels deliberately. For example transition metals are sometimes added as fuel borne catalysts to improve the performance of diesel particulate filters.
[0021] The present inventors believe that one of the causes of injector sticking occurs when metal or ammonium species react with carboxylic acid species in the fuel. One example of injector sticking has arisen due to sodium contamination of the fuel. Sodium contamination may occur for a number of reasons. For example sodium hydroxide may be used in a washing step in the hydrodesulfurisation process and could lead to contamination. Sodium may also be present due to the use of sodium-containing corrosion inhibitors in pipelines. Another example can arise from the presence of calcium from for example interaction with or contamination with a lubricant or from calcium chloride used in salt drying processes in refineries. Other metal contamination may occur for example during transportation due to water bottoms.
[0022] Metal contamination of diesel fuel and the resultant formation of carboxylate salts is believed to be a major cause of injector sticking. The formation of lacquers is yet another major cause of injector sticking.
[0023] One approach to combatting IDIDs and injector sticking resulting from carboxylate salts is to try to eliminate the source of metal contamination and/or carboxylic acids or to try to ensure that particularly problematic carboxylic acids are eliminated. This has not been entirely successful, and there is a need for additives to provide control of IDIDs.
[0024] Deposit control additives are often included in fuel to combat deposits in the injector nozzle or at the injector tip. These may be referred to herein as "external injector deposits". Additives are also used to control deposits on vehicle fuel filters. However additives which have been found to be useful to control "external deposits" and fuel filter deposits have not been found to be effective at controlling IDIDs. A challenge for the additive formulator is to file provide more effective detergents.
[0025] It is an aim of the present invention to provide methods and uses which improve the performance of a diesel engine, especially a diesel engine having a high pressure fuel system by preventing or reducing the formation of IDIDs and/or by reducing or removing existing IDIDs. It is a further aim of the invention to provide methods and uses which also provide control of "external injector deposits" and/or fuel filter deposits.
[0026] Reducing or preventing the formation of deposits may be regarded as providing "keep clean" performance. Reducing or removing existing deposits may be regarded as providing "clean up" performance. It is an aim of the present invention to provide "keep clean" and/or "clean up" performance in relation to IDIDs. It is a further aim to also provide "keep clean" and/or "clean up" performance in relation to external injector deposits and/or fuel filter deposits.
[0027] According to a first aspect of the present invention there is provided a method of combating internal diesel injector deposits caused by carboxylate residues and/or lacquers in the injectors of a diesel engine, the method comprising combusting in the engine a diesel fuel composition comprising (a) the reaction product of a carboxylic acid-derived acylating agent and an amine and (b) a quaternary ammonium salt additive.
[0028] According to a second aspect of the present invention there is provided the use of a combination of (a) the reaction product of a carboxylic acid-derived acylating agent and an amine and (b) a quaternary ammonium salt additive to combat internal diesel injector deposits caused by carboxylate residues and/or lacquers in the injectors of a diesel engine.
[0029] Preferred features of the first and second aspects of the present invention will now be described.
[0030] The present invention relates to combating internal diesel injector deposits caused by carboxylate residues and/or lacquers. By combating internal diesel injector deposits we mean to include the prevention of deposit formation, the reduction of deposit formation and/or the removal of existing deposits. Thus combatting IDIDs may refer to providing "keep clean" and/or "clean up" performance.
[0031] The present invention relates to combatting internal diesel injector deposits or IDIDs in the injectors of a diesel engine. This problem typically occurs in modern diesel engines having a high pressure fuel system. Preferably the diesel engine has a fuel injection system which comprises a high pressure fuel injection (HPFI) system. The fuel pressure may be greater than 1350 bar, for example greater than 1500 bar or greater than 2000 bar. Preferably, the diesel engine has fuel injection system which comprises a common rail injection system or a unit injection system for example a piezoelectric injector. The skilled person will have a good knowledge of such engines. In the common rail injection system fuel is compressed utilizing a high-pressure pump that supplies it to the fuel injection valves through a common rail. In the unit injection system the high-pressure pump and fuel injection valve are integrated in one assembly. Preferably, the diesel engine has a fuel injection system which comprises a common rail injection system.
[0032] By carboxylate residues we mean to refer to salts of carboxylic acids. These may be salts of monocarboxylic acids, dicarboxylic acids or polycarboxylic acids. Mixtures of two or more different compounds may be present. The acids may be short-chain carboxylic acids, for example having less than 8 carbon atoms. Suitably the carboxylate residues are salts of mono and/or dicarboxylic acids having from 8 to 40 carbon atoms, preferably 12 to 40, and most preferably 16 to 36 carbon atoms. The acid residues may be saturated or unsaturated. The carboxylate residues are suitably the residues of fatty acids of the type typically found in diesel fuel, for example as lubricity additives, corrosion inhibitors or from fatty acid methyl-esters used as biodiesel.
[0033] The carboxylate residues are present as metal or ammonium salts. Suitably they are present as metal salts. They may be present as transition metal salts, for example copper or zinc salts. Most commonly they are present as alkali metal or alkaline earth metal salts, especially alkali metal salts. They are often present as sodium or calcium salts, and particularly as sodium salts.
[0034] By lacquers we mean to refer to fuel insoluble varnish-like deposits. The reasons for the presence of these deposits is not fully understood but low molecular weight amide-containing species present in fuel additives or reaction products of amines present in the fuel or fuel additives with carboxylic acids as described above have been suggested as a contributing factor.
A method of combating internal diesel injector deposits caused by carboxylate residues and/or lacquers in the injectors of a diesel engine, the method comprising combusting in the engine a diesel fuel composition comprising (a) the reaction product of a carboxylic acid-derived acylating agent and an amine and (b) a quaternary ammonium salt additive.
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