Additive for reducing particulate matter in emissions from the combustion of diesel fuel and fuel oil, and fuel composition containing the additive

Abstract

The present invention relates to an additive for fuels such as diesel fuel and fuel oil, which are used for various types of diesel engines and boilers respectively, and the additive contains a suitable ratio of metal oxide catalyst, organic nitrate and dispersant, and can improve the combustion efficiency, thereby reducing the formation of particulate matter and lowering the fuel consumption.

Description

Technical Field

[0001] The present invention relates to an additive for fuels such as diesel fuel and fuel oil, which are used in diesel engines and boilers for civil and industrial purposes respectively, and the additive can be used to reduce particulate emissions and fuel consumption. Background Art

[0002] Diesel fuel and fuel oil are fuels widely used in various fields from automobiles to civil or industrial heating.

[0003] For simplicity, hereinafter, only the use of diesel fuel in internal combustion engines (diesel cycle engines) will be mentioned. However, it should be understood that the content described can equally extend to any use of diesel fuel and fuel oil in which the combustion process generates emissions.

[0004] In recent years, the technological development of alternative internal combustion engines has been closely related to the urgent need to ensure the increasingly rational use of natural energy while limiting the environmental pollution caused by its exploitation. This requires the introduction of substantial technological improvements to the engine, which thus affects spark ignition engines (i.e., gasoline engines) and compression ignition engines (i.e., diesel engines) in different ways. Therefore, relative technological innovations, although arising from the same need, follow completely different paths.

[0005] The different ways to solve these problems stem from the different trends of the combustion process in gasoline engines compared to diesel engines.

[0006] Different from what happens in gasoline engines, in diesel engines, the charge formation process occurs in the form of very small fuel droplets, which burn under conditions of high excess air because the latter reaches a high temperature during the compression stage.

[0007] Although very small droplet sizes with a diameter of one hundredth of a millimeter are achieved through very high injection pressures (up to 2300 atmospheres), the process of their distribution in the combustion chamber is very uneven. As a result, there are such regions in the combustion chamber where, even in the presence of a considerable excess of air, the oxidation process of diesel fuel only occurs partially.

[0008] The nuclei of fuel particles that have not reached the oxidation process (simultaneously under two conditions of high temperature and lack of oxygen) undergo complex cracking phenomena (pyrolysis), which substantially changes their original chemo-physical structure.

[0009] This phenomenon is generally considered to be the main cause of the formation of those characteristic material particles emitted in the exhaust of diesel engines. Although they are commonly referred to as soot or carbon black, these characteristic material particles are essentially carbonaceous and are technically defined as "particulate matter". In the context of "particulate matter", the PM10 fraction consisting of particles with an average diameter of less than 10 micrometers is particularly harmful, and these particles contain approximately 75% of benzo[a]pyrene, acenaphthene, anthracene, phenanthrene, and higher homologues of polycyclic aromatic hydrocarbons that have been shown to have carcinogenic activity.

[0010] Despite the high value of the dosing ratio and the considerable efforts made to improve the efficiency of the combustion process, the carbonaceous particulate matter that causes smoke always exists in the exhaust of diesel engines to a greater or lesser extent. This not only clearly demonstrates the poor energy utilization rate of the fuel but also is the cause of considerable environmental degradation and serious health damage.

[0011] Since carbonaceous particulate matter is one of the main harmful emissions of diesel engines, in recent years, the main efforts made by vehicle manufacturers have basically been directed towards reducing this pollutant.

[0012] Historically, the measures taken to reduce carbonaceous particulate matter in the exhaust of diesel engines have basically consisted of the following interventions: a) directly intervening in the combustion process in the engine to prevent the formation of pollutants; b) applying combustion gas treatment devices to convert harmful substances into harmless products; c) changing the fuel composition.

[0013] The measures implemented to improve the efficiency of the combustion process belong to the interventions of category a) because the incompleteness of this process is the main cause of the formation of PM10 particulate matter.

[0014] On the other hand, the combustion gas treatment devices applied to the exhaust of diesel engines belong to the interventions of category b). The combustion gas treatment devices are called "particle traps", which filter and eliminate the carbonaceous particles formed in the engine during the combustion process.

[0015] The PM10 particle trap usually consists of a porous ceramic substrate having a plurality of parallel channels that are alternately closed and opened at the ends, and the particulate matter is deposited on the walls of the channels by filtration. To prevent the material accumulated in the carrier from generating excessive backpressure in the engine exhaust, and the consequent power loss and increased fuel consumption, the operation of the trap always includes a particle elimination cycle ("cleaning" phase), also called the "regeneration process", during which the particulate matter is burned and converted into carbon dioxide and water through appropriate technical measures.

[0016] Interventions of type c) include supplementing the fuel with an emulsion or using an additive containing an oxidation catalyst. For example, EP1 307 531 describes an additive for diesel fuel and fuel oil, the additive comprising a mixed metal oxidation catalyst based on iron, cerium, calcium, at least one organic nitrate ester, and a dispersant.

[0017] However, as generally indicated above, the solutions provided so far for eliminating particulate matter from exhaust gases still have certain application limitations. In particular, in intervention a) mentioned above, the chemo-physical characteristics of the fuel in the heterogeneous phase pose an insurmountable limitation to the increase in reactivity and thus to the efficiency of the engine. In the case of the relevant interventions of type b), from an economic point of view, the construction of the combustion gas treatment device has so far proven to be too expensive, making large-scale use unthinkable. Finally, supplementing the fuel does not always result in a satisfactory reduction of particulate matter, and in the case where the additive contains a metal oxidation catalyst, it leads to the formation of metal oxides, although to a lesser extent, but still a source. The use of the additive also greatly increases the risk of engine or burner corrosion. Finally, due to the instability of the additive, the supplemented fuel may form deposits, which may decompose or form precipitates over time, thus precluding the possibility of directly supplementing the fuel downstream at the production site before transportation and use.

[0018] On the other hand, the increasingly strict national and EU anti-smog regulations are making the need for an effective solution to reduce pollutants in the exhaust gases of diesel engines ever more urgent, and the regulations are becoming increasingly stringent.

[0019] Therefore, there is an urgent need to find a solution to limit the emissions of pollutants from the exhaust gases of diesel engines, even in the face of these regulations. Summary of the Invention

[0020] The Applicant has now found that the use of a diesel engine fuel additive (diesel fuel) composed of a metal catalyst improves the combustion efficiency, thereby significantly reducing the generation of particulate matter and lowering the fuel consumption, and provides many other advantages over the additives of the prior art. The metal catalyst comprises a binary mixture of specific and suitable ratios of iron salts and cerium salts, an organic nitrate ester, and a dispersant.

[0021] In particular, in its first aspect, the present invention relates to an additive for diesel fuel and fuel oil, the additive comprising:

[0022] A) an oxidation catalyst in an amount of 2% to 12% by weight relative to the sum of components A), B), and C), the oxidation catalyst comprising a salt mixture of at least one iron salt and at least one cerium salt;

[0023] B) at least one organic nitrate in an amount of 82% to 92% by weight, relative to the sum of components A), B) and C);

[0024] C) at least one dispersant in an amount of 6% to 16% by weight, relative to the sum of components A), B) and C).

[0025] This additive is not only particularly effective in reducing particulate matter emissions, but has also proven useful at every stage of the combustion process, thus achieving better cleanliness in the so-called low-temperature zone, as well as a sharp reduction in fouling due to the reduction of residues and unburned carbonaceous substances in the cylinders and exhaust manifolds, thereby obtaining better heat exchange conditions.

[0026] Furthermore, due to the reduced content of oxidation catalysts, the additive according to the invention allows for reduced emissions while using a smaller amount of metals, resulting in fewer metal oxides being formed and thus allowing for less fouling of the particulate system.

[0027] Finally, the additive according to the invention unexpectedly shows a high chemical-physical stability over time, which allows it to be used even far upstream in the product chain, immediately downstream of the production site, at the stage before transportation. This has the advantage of not causing problems during storage and allows the manufacturer to sell fuels that do not require additive replenishment before use by the user.

[0028] In yet another aspect, the present invention further relates to a fuel composition comprising a fuel and an additive according to the first aspect of the present invention, wherein the fuel is selected from the group consisting of diesel fuel and fuel oil.

[0029] The advantages of the fuel composition according to the present invention are evident from the characteristics of the additive according to the first aspect of the present invention and are not repeated herein.

[0030] However, the applicant has also found that the specific compositional characteristics of the additive according to the present invention make it effective even at low concentrations, thus also making its use economically advantageous.

[0031] In still other aspects, the present invention relates to the use of an additive according to the first aspect of the present invention for improving the combustion efficiency of diesel fuel in a diesel engine and fuel oil for a boiler, and to a method for improving the combustion efficiency of a fuel selected from diesel fuel and fuel oil, the method comprising the step of adding an additive according to the present invention to the fuel.

[0032] In addition to the other advantages already emphasized above, the characteristics and advantages of the present invention will be detailed in the following description. Detailed Description

[0033] In its first aspect, the present invention relates to an additive for diesel fuel and fuel oil, the additive comprising:

[0034] A) 2% to 12% by weight, relative to the sum of components A), B) and C), of an oxidation catalyst comprising a salt mixture of at least one iron salt and at least one cerium salt;

[0035] B) 82% to 92% by weight, relative to the sum of components A), B) and C), of at least one organic nitrate;

[0036] C) 6% to 16% by weight, relative to the sum of components A), B) and C), of at least one dispersant.

[0037] This additive is not only particularly effective in reducing particulate matter emissions, but also proves useful for facilitating every stage of the combustion process, thus obtaining better cleanliness in the so-called low-temperature zone, as well as a sharp reduction in fouling due to the reduction of residues and unburned carbonaceous substances in the cylinders and exhaust manifolds, thereby obtaining better heat exchange conditions.

[0038] Furthermore, due to the reduced content of the oxidation catalyst, the additive according to the invention allows for reduced emissions while using a smaller amount of metal, thus resulting in fewer metal oxides being formed and therefore allowing for less fouling of the particulate system.

[0039] Finally, the additive according to the invention unexpectedly shows a high chemical-physical stability over time, which allows it to be used even far upstream in the product chain, immediately downstream of the production site, at the stage before transportation. This has the advantage of not causing problems during storage and allows the manufacturer to sell fuels that do not require the addition of additives before use by the user.

[0040] In the context of the present specification and the appended claims, unless otherwise indicated, all numerical quantities indicating amounts, parameters, percentages, etc. are considered in any case to be preceded by the term "about". Furthermore, all ranges of numerical quantities include all possible combinations of the maximum and minimum values and all possible intermediate ranges, as well as those indicated below.

[0041] The present invention may exhibit one or more of its aspects or one or more of the preferred features reported below, which may be combined with each other according to the application requirements.

[0042] Preferably, in the oxidation catalyst A), the at least one iron salt and the at least one cerium salt are salts of an acid selected from the group consisting of:

[0043] (I) R-COOH, wherein R is a straight-chain or branched-chain, saturated or unsaturated C7 -C 17 An aliphatic group or a C 5 -C 12 alicyclic group, and

[0044]

[0045] wherein R' is H or a straight-chain or branched-chain, saturated or unsaturated C 1 -C 12 aliphatic group, and n is an integer from 1 to 5.

[0046] Preferably, the iron salt is an acid of formula (I), wherein R is a straight-chain saturated C 17 aliphatic group, the cerium salt is an acid of formula (II), wherein R' is a straight-chain saturated C 12 aliphatic group, and n is an integer equal to 1.

[0047] The acids of formula (I) and (II) may also be present in natural products as a mixture.

[0048] Preferably, the content of cerium in the oxidation catalyst A), expressed as the weight percentage of metallic cerium relative to the total weight of the catalyst, is from 0.1% to 1.2%, more preferably from 0.2% to 1%, and even more preferably from 0.3% to 0.8%.

[0049] Preferably, the content of iron in the oxidation catalyst A), expressed as the weight percentage of metallic iron relative to the total weight of the catalyst, is from 0.1% to 1.2%, more preferably from 0.2% to 1%, and even more preferably from 0.3% to 0.8%.

[0050] In a preferred embodiment of the present invention, the content of metals in the oxidation catalyst A), expressed as the weight percentages of metallic iron and cerium relative to the total weight of the catalyst, is 0.1% to 1.2% of cerium and 0.1% to 1.2% of iron, more preferably 0.2% to 1% of cerium and 0.2% to 1% of iron, and even more preferably 0.3% to 0.8% of cerium and 0.3% to 0.8% of iron.

[0051] Preferably, in the oxidation catalyst A), the weight ratio between cerium and iron is from 0.8 to 1.2, more preferably from 0.9 to 1.1, and most preferably about 1.

[0052] Preferably, the organic nitrate B) of the additive according to the present invention is selected from the group consisting of n-pentyl nitrate, isopentyl nitrate, and isooctyl nitrate (i.e., 2-ethylhexyl nitrate), and binary or ternary mixtures thereof. The preferred nitrate is isooctyl nitrate.

[0053] Preferably, dispersant C) is selected from alkylamines, alkylamides, alkylarylamines, and alkylarylamides and mixtures thereof. A particularly preferred dispersant C) according to the present invention is an alkylamide and an alkylamine having an aliphatic chain with C 10 -C 24 aliphatic chains.

[0054] Dispersant C) generally results in an increase in the activity of (A)+(B). A particularly high synergistic effect is obtained by adding a dispersion product based on polyolefinamine or alkylarylamine and an olefin-alkyl ester copolymer to a mixture of an organic nitrate and a metal catalyst as described above. Products suitable for carrying out the present invention are, for example, those sold on the market under the name Wax Anti-Settling Agent (WASA).

[0055] In addition to the essential components indicated above, the additive according to the present invention may contain and generally contains small amounts of reagents suitable for improving specific aspects of the mixture, such as oxidation stability, corrosion inhibition, lubricity, and foaming (defoaming) of the fuel.

[0056] Preferably, the additive according to the present invention does not contain calcium salts. In fact, the applicant has unexpectedly found that the addition of calcium salts may lead to the formation of precipitates in diesel fuel, thereby deteriorating its properties over time and reducing the stability of the supplementary diesel fuel.

[0057] Preferably, in the additive according to the present invention, the content of oxidation catalyst A) is 3% to 12% by weight, more preferably 3% to 9% by weight, and most preferably it is equal to about 5% by weight.

[0058] Preferably, in the additive according to the present invention, the content of organic nitrate B) is 82% to 91% by weight, more preferably 84% to 90% by weight, and most preferably it is equal to about 86% by weight.

[0059] Preferably, in the additive according to the present invention, the content of dispersant C) is 6% to 15% by weight, more preferably 7% to 13% by weight, and most preferably it is equal to about 9% by weight.

[0060] In a preferred embodiment of the present invention, in the additive according to the present invention, relative to the total weight of the additive, the content of the oxidation catalyst A) is 3% to 12% (by weight), the content of the organic nitrate B) is 82% to 91% (by weight), and the content of the dispersant C) is 6% to 15% (by weight); more preferably, relative to the total weight of the additive, the content of the oxidation catalyst A) is 3% to 9% (by weight), the content of the organic nitrate B) is 84% to 90% (by weight), and the content of the dispersant C) is 7% to 13% (by weight); and most preferably, relative to the total weight of the additive, the content of the oxidation catalyst A) is equal to about 5% (by weight), the content of the organic nitrate B) is equal to about 86% (by weight), and the content of the dispersant C) is equal to about 9% (by weight).

[0061] The additive according to the present invention is suitable for any diesel engine fuel or any boiler fuel oil for civil and industrial purposes.

[0062] In yet another aspect, the present invention also relates to a fuel composition comprising a fuel and at least one additive according to the first aspect of the present invention, wherein the fuel is selected from the group consisting of diesel fuel and fuel oil.

[0063] Due to the characteristics of the additive according to the first aspect of the present invention, the advantages of the fuel composition according to the present invention are obvious and will not be repeated herein.

[0064] However, the applicant has also found that the specific compositional characteristics of the additive according to the present invention make it effective even at low concentrations, thus also making its use economically advantageous.

[0065] Preferably, the additive according to the present invention can be added to the fuel in an amount of 1 to 10 g / l of fuel, more preferably in an amount of 1 to 5 g / l of fuel, and even more preferably in an amount equal to about 2 g / l of fuel, thereby allowing an effective reduction of particulate matter to be obtained.

[0066] In particular, the applicant has unexpectedly found that at the same use concentration, the additive according to the present invention generally obtains better performance than other similar additives of the prior art (such as the additive according to EP 1 307 531), and thus, if used at a concentration significantly lower than 50% thereof, it may even obtain performance similar to that of the latter. Due to the reduced metal content of the additive according to the present invention, this subsequently results in less metal oxide formation and thus allows less fouling of the particulate system.

[0067] The fuel composition of the present invention may also contain additional additives conventionally used in diesel engine fuels, in the amounts in which they are normally used. For example, the fuel composition of the present invention may contain conventional additives such as additional lubricity and stability enhancers, corrosion inhibitors, etc.

[0068] When mixed with diesel engine fuel, the additive according to the present invention significantly reduces particulate matter in the emissions of diesel engines of motor vehicles, locomotives, ships, earth - moving machinery, and diesel engines used in pumping stations or power generation facilities. The additive according to the present invention can also be used to reduce particulate matter emitted by heating systems fueled by diesel fuel, with the same advantageous results as described above, since the combustion mechanism of diesel fuel in boilers fueled with this fuel is similar to those that control the oxidation process in internal combustion engines, although with a much lower air / fuel ratio.

[0069] In still other aspects, the present invention relates to the use of the additive according to the first aspect of the present invention for improving the combustion efficiency of diesel fuel in diesel engines and fuel oil for boilers, and to a method for improving the combustion efficiency of a fuel selected from diesel fuel and fuel oil, the method comprising the step of adding the additive according to the present invention to the fuel.

[0070] Preferably, in the method for improving fuel combustion efficiency, in the addition step, 1 to 10 g / l, more preferably 1 to 5 g / l, and most preferably about 2 g / l of the at least one additive is added to the fuel.

[0071] The present invention will now be described by means of some examples, which are considered to be non - limiting illustrations for its purpose.

[0072] Experimental section

[0073] Example 1 - Measurement of pollutant emissions and opacity test

[0074] To illustrate the properties of the additive according to the present invention, the emissions of regulated pollutants were measured and a smoke opacity test was conducted in a comparative test, in which the additive according to the present invention was added to a standard reference diesel fuel, and then the results obtained were compared with those obtained only from the standard reference diesel fuel without the additive according to the present invention, and then the percentage change in performance under the same conditions was calculated in order to highlight the improvement obtained by using the additive.

[0075] On an engine dynamometer, using a Cummins C110 D5(6B) engine, the following six different engine power levels were tested:

[0076] Level Power (kW) 6 78 5 64 4 50 3 41 2 27 1 13

[0077] In countries where mandatory on-site testing is provided, the verification of diesel vehicles covers not only the values of regulated pollutants but also the measurement of diesel smoke opacity. Opacity is measured with a special instrument (opacity meter) in which the exhaust gas collected by a probe is conveyed into a measurement chamber; based on the color and density of the gas, the optical path in the chamber undergoes a change; the degree of absorption depends on the opacity. In this embodiment, a TESTO 338 diesel smoke meter ( https: / / www.testo.com / it-IT / testo-338 / p / 0632-3381 ) is used.

[0078] The light attenuation is measured by the instrument as the soot index (FSN) or Bosch index and the mass concentration of soot per unit volume (mg / m 3 ).

[0079] As an additive according to the present invention, a mixture composed as follows is used:

[0080] A) An oxidation catalyst composed of a binary mixture of an iron salt and a cerium salt: for iron, in the form of an acid of formula (I) in which R is a straight-chain saturated C 17 aliphatic group; for cerium, in the form of an acid of formula (II) in which R' is a straight-chain saturated C 12 aliphatic group and n is an integer equal to 1. In the catalyst, the iron content (expressed as the weight percentage of metallic iron relative to the total weight of the catalyst) is 0.4%, and the cerium content (expressed as the weight percentage of metallic cerium relative to the total weight of the catalyst) is 0.4%. Relative to the total weight of the additive, the catalyst is present in the additive in a content equal to 5% by weight;

[0081] B) Relative to the total weight of the additive, isooctyl nitrate with a content equal to 86% by weight;

[0082] C) A commercially available wax anti-settling agent (WASA) (Infineum R715) is used as a dispersant, and its content is equal to 9% by weight relative to the total weight of the additive.

[0083] The aforementioned additive is added to diesel fuel in an amount equal to 2 g / l of diesel fuel (the data related thereto is hereinafter referred to as "diesel fuel + additive").

[0084] As a comparison, tests are also carried out on the same diesel fuel without adding the additive according to the present invention (the data related thereto is hereinafter referred to as "diesel fuel"). Then the data is compared by determining the % change in performance between the supplemented diesel fuel according to the present invention and the diesel fuel without additive (the data related thereto is hereinafter referred to as "change"), which is calculated according to the following formula:

[0085] Variation = (Data 柴油燃料 - Data 柴油燃料+添加剂 ) / Data 柴油燃料 ) * 100

[0086] The obtained results are reported in Tables 1 and 2 below.

[0087]

[0088] Table 2 - Opacity Test

[0089]

[0090] a: Values below the instrument detection limit

[0091] From the data analysis of Tables 1 and 2, it is evident that under all test conditions, the additive according to the present invention has proven to be effective in significantly reducing pollutant and particulate matter emissions.

[0092] Example 2 - Comparison with additives according to EP 1 307 531

[0093] To further illustrate the advantages associated with the additive according to the present invention compared to additives of the prior art, a comparative test was conducted between the additive of Example 1 according to the present application ("AddInv", the additive according to the present invention) and an additive having the following composition according to EP 1 307 531 ("AddEP531", the additive according to EP 1 307 531):

[0094] a) A metal oxidation catalyst composed of 5% Ce, 7% Fe, and 2.5% Ca, for Ce in the form of a salt of aliphatic acid C 8 and for Fe as C 18 , and for Ca as dodecylbenzenesulfonic acid. By weight, the catalyst is present in the additive at a content of 10% relative to the total weight of the additive; and

[0095] b) Isooctyl nitrate at a content equal to 70% by weight relative to the total weight of the additive;

[0096] c) Using Para-Flow 412 (Exxon) (50% active substance) as a dispersant, at a content of 20% by weight relative to the total weight of the additive.

[0097] Two additives were added to a standard reference diesel fuel; additive AddInv was added in an amount equal to 2 g / l of diesel fuel, while additive AddEP531 was added in an amount equal to 3.5 g / l of diesel fuel, as taught in the examples of EP 1 307 531. EP 1 307 531 also teaches that 3.5 g / l is the preferred dosage (see paragraph

[0040] of EP 1 307 531 A1).

[0098] The results obtained using the two different additives were then compared with the results obtained using only diesel fuel. Additionally, by comparing the two additives with each other, in order to highlight the improvements obtained by using the additives according to the invention, the percentage change in performance of the two corresponding additives compared to the unsupplemented diesel fuel under the same conditions was calculated according to the formula already used in Example 1:

[0099] Change in diesel fuel = (Data 柴油燃料 - Data 柴油燃料+添加剂 ) / Data 柴油燃料 ) * 100

[0100] And the performance improvement factor of the additive according to the invention compared to the additive according to EP 1 307 531 was further calculated according to the following formula:

[0101] Improvement [%] = ((Change 柴油燃料+AddInv / Change 柴油燃料+AddEP531 ) - 1) * 100

[0102] The tests were carried out on an engine dynamometer using an Isotta Fraschini model V1312 T2 MLL engine with a constant engine power of 50%. Engine fuel consumption and smoke opacity data (FSN scale, mg / m 3 ) were measured and compared.

[0103] The results obtained are reported in Tables 3, 4 and 5 below.

[0104] Table 3 - Test with AddInv

[0105]

[0106] Table 4 - Test with AddEP531

[0107]

[0108] Table 5 - Comparison of AddInv - AddEP5311

[0109]

[0110] It can be seen from the analysis of the data in Tables 3, 4 and 5 that, clearly, in terms of significantly reducing fuel consumption and particulate matter emissions, the additive according to the present invention has proven to be much more effective than the additive according to EP 1 307 531, while pollutant emissions are also significantly reduced, as shown in Example 1, and at the same time a smaller amount of metal is used, thereby also resulting in a significant reduction in the subsequent formation of metal oxides.

Claims

1. An additive for fuel, the additive comprising: A) 2% to 12% by weight, based on the sum of components A), B) and C), of an oxidation catalyst, the oxidation catalyst comprising a salt mixture of at least one iron salt and at least one cerium salt; B) 82% to 92% by weight, based on the sum of components A), B) and C), of at least one organic nitrate; and C) 6% to 16% by weight, based on the sum of components A), B) and C), of at least one dispersant, wherein the dispersant C) is selected from the group consisting of alkylamines, alkylamides, alkylarylamines, alkylaryl amides, or mixtures thereof.

2. The additive according to claim 1, wherein the at least one iron salt and the at least one cerium salt are salts of an acid selected from the group consisting of: (I) R-COOH, where R is a straight-chain or branched, saturated or unsaturated C 7 -C 17 aliphatic group or a C 5 -C 12 alicyclic group, and wherein R’ is H or a straight-chain, branched-chain, saturated or unsaturated C 1 -C 12 aliphatic group, and n is an integer from 1 to 5.

3. The additive according to claim 1, wherein the iron salt is an acid of formula (I), wherein R is a straight-chain saturated C 17 aliphatic group, the cerium salt is an acid of formula (II), wherein R' is a straight-chain saturated C 12 aliphatic group, and n is an integer equal to 1.

4. The additive according to claim 1, wherein the content of metals in the oxidation catalyst A), expressed as the weight percentage of metallic iron and cerium relative to the total weight of the catalyst, is 0.1% to 1.2% of cerium and 0.1% to 1.2% of iron.

5. The additive according to claim 4, wherein the content of metals in the oxidation catalyst A), expressed as the weight percentage of metallic iron and cerium relative to the total weight of the catalyst, is 0.3% to 1% of cerium and 0.3% to 1% of iron.

6. The additive according to claim 1, wherein in the oxidation catalyst A), the weight ratio between cerium and iron is 0.8 to 1.

2.

7. The additive according to claim 1, wherein the organic nitrate B) is selected from the group consisting of amyl nitrate, isoamyl nitrate, isooctyl nitrate, or binary or ternary mixtures thereof.

8. The additive according to claim 7, wherein the organic nitrate B) is isooctyl nitrate.

9. The additive according to claim 1, wherein the dispersant C) is selected from alkylamines and alkylamides having an aliphatic chain with C 10 -C 24 aliphatic chains of alkylamines and alkylamides.

10. The additive according to any one of claims 1 to 9, wherein, relative to the total weight of the additive, the content of the oxidation catalyst A) is 3% to 12% by weight, the content of the organic nitrate B) is 82% to 91% by weight, and the content of the dispersant C) is 6% to 15% by weight.

11. The additive according to any one of claims 1 to 9, wherein, relative to the total weight of the additive, the content of the oxidation catalyst A) is 3% to 9% by weight, the content of the organic nitrate B) is 84% to 90% by weight, and the content of the dispersant C) is 7% to 13% by weight.

12. The additive according to any one of claims 1 to 9, wherein, relative to the total weight of the additive, the content of the oxidation catalyst A) is equal to 5% by weight, the content of the organic nitrate B) is equal to 86% by weight, and the content of the dispersant C) is equal to 9% by weight.

13. A fuel composition, the fuel composition comprising fuel and the additive according to any one of claims 1 to 12, the fuel being selected from the group consisting of diesel fuel and fuel oil.

14. The fuel composition according to claim 13, wherein the content of the additive is 1 to 10 g / l of fuel.

15. The fuel composition according to claim 14, wherein the content of the additive is 1 to 5 g / l of fuel.

16. The fuel composition according to claim 15, wherein the content of the additive is equal to 2 g / l of fuel.

17. Use of the additive according to any one of claims 1 to 12 for increasing the combustion efficiency of diesel fuel in a diesel engine.

18. Use of the additive according to any one of claims 1 to 12 for increasing the combustion efficiency of fuel oil for a boiler.

19. A method for increasing the combustion efficiency of a fuel selected from diesel fuel and fuel oil, the method comprising the step of adding an additive according to any one of claims 1 to 12 to the fuel.

20. The method according to claim 19, wherein in the adding step, 1 to 10 g / l of the additive is added to the fuel.

21. The method according to claim 20, wherein in the adding step, 1 to 5 g / l of the additive is added to the fuel.

22. The method according to claim 21, wherein in the adding step, 2 g / l of the additive is added to the fuel.

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