WO1999032584A1

WO1999032584A1 - Ignition improved fuels

Info

Publication number: WO1999032584A1
Application number: PCT/EP1998/008131
Authority: WO
Inventors: Johannes Jacobus De Groot; Andreas Herman Hogt; John Meijer
Original assignee: Akzo Nobel N.V.
Priority date: 1997-12-22
Filing date: 1998-12-14
Publication date: 1999-07-01
Also published as: BR9814373A; NZ505170A; CA2315683A1; CN1121479C; CN1283218A; ID25464A; ZA9811722B; AU2271399A; JP2001527124A; PL341331A1; EP1042433A1; HUP0100654A2; TR200001920T2

Abstract

A fuel is presented which is doped with 0.01-10 % by weight of cyclic ketone peroxide(s), characterized in that it comprises from 0.01 to 10 percent by weight of cyclic ketone peroxides of formula (I) wherein R1-R6 are independently selected from the group consisting of hydrogen, C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 aralkyl, and C7-C20 alkaryl, which groups may include linear or branched alkyl moieties; and each of R1-R6 may optionally be substituted with one or more groups selected from hydroxy, alkoxy, linear or branched alkyl, aryloxy, ester, carboxy, nitrile, and amido, with the proviso that said peroxides make up at least 35 % by weight of all peroxides in the fuel, to reduce the emission of pollutants when the fuel is used in a combustion engine. Also the process to make such fuels is presented.

Description

IGNITION IMPROVED FUELS

The invention relates to fuels with improved ignition characteristics comprising one or more ketone peroxides, as well as to a process to prepare such fuels.

The use of peroxides in fuels has long been common knowledge. Back in the 1940s US 2,378,341 disclosed the use of a peroxide of a hydrocarbon having at least one aliphatic tertiary carbon atom, the peroxy radical in said peroxide connecting two tertiary carbon atoms, while Ind. Enq. Chem., Vol. 41 , No. 8, pp. 1679-1682 disclosed the use of di-tert-butyl peroxide and 2,2-bis(tert- butylperoxy)butane for the purpose of improving the ignition of diesel fuels. Also, FR-B-862,070 disclosed a very hazardous process which is conducted at undesired low temperatures to make polymeric ketone peroxides from mixtures of aliphatic ketones, and their use in fuel. The products are said to have improved solubility in the fuel and a low crystallization temperature. FR-B-862,974 discloses the production of certain cyclic ketone peroxides and their use in diesel fuel to improve the ignition characteristics. In 1961 , US 3,003,000 disclosed ketone peroxides and oligomeric ketone peroxides, a process to make them, and their generic use in, inter alia, diesel fuels. The process also yields some cyclic ketone peroxide by-products. These by-products are present in the oligomeric ketone peroxides in trace amounts. Also, the use in diesel fuel formulations is not exemplified. US 3,116,300 (published in 1963) discloses dimeric cyclic ketone peroxides, viz. the product formed when two ketone molecules are reacted.

Ignition improvers are desired for use in hydrocarbon distillates and residue- containing oils that are useful as fuels for combustion engines except for their ignition characteristics. Usually, such fuels suffer from a too long ignition lag, i.e., the time between the injection of the fuel into the zone of combustion, as in directly injected engines such as diesel engines, and the moment the fuel ignites, or the time between the activation of external ignition sources, such as spark plugs, and the moment the fuel ignites. As a result, poor combustion efficiency and rough engine operation are observed, with all attendant adverse consequences. The term improved ignition, therefore, means that in combustion engines fuel is burned with improved efficiency, which usually is obvious from the higher cetane number of the fuel and the reduced emission of pollutants upon combustion of the fuel in said engine. As is well-known, the use of diesel fuel with improved ignition can result in reductions of the hydrocarbon, carbon monoxide, NOx, and particulate matter (soot) emissions. Depending on the type of fuel and the type and quantity of ignition improver used, reductions of 40% of said emissions are quite feasible.

Despite the time lapse since the invention of ketone peroxides, they have not found any commercial use as an ignition improver. On the contrary, the presently used commercial products to improve the ignition of (diesel) fuels are di-tert-butyl peroxide and 2-ethylhexyl nitrate, as taught by Chemtech, 8-97, pp. 38-41. However, these products suffer from various disadvantages. Nitrates may lead to NOx formation upon combustion, while di-tert-butyl peroxide has a low flash-point and high volatility, which can lead to various safety hazards. Nor do most peroxides possess long-term (thermal) stability in diesel fuels. Especially at higher temperatures such as can be encountered in fuel systems, decreased thermal stability can lead to gum formation or other degradation of the fuel. Also, the decomposition products of peroxides generally are (partly) alcoholic in nature, which tends to increase the undesired water uptake by the fuel. Furthermore, most of the peroxides used thus far suffer from a relatively low active matter content. Also, the price/performance ratio of most peroxides stands in the way of their being widely introduced into (diesel) fuels. In this respect it is noted that the unsatisfactory performance of dimeric cyclic ketone peroxides as disclosed in, for instance, FR-B-862,974 is considered to lead to an unacceptable price/performance ratio of these products. Furthermore, the dimeric structure of conventional cyclic ketone peroxides may present a safety hazard, due to the volatility and the low flash point of such products. In consequence, there still is a need for fuels with improved characteristics.

Surprisingly, some of the peroxide compositions disclosed in WO 96/03397 were found to be very suitable for improving the ignition characteristics of fuels. WO 96/03397 relates to numerous formulations of cyclic ketone peroxides, as described below, comprising a variety of phlegmatizers. However, this patent application does not disclose or suggest the use of cyclic ketone peroxides in fuels. A comparison between the cyclic ketone peroxides of WO 96/03397 that perform well and the cyclic ketone peroxides according to, for example, FR-B- 862,974 showed that the surprising performance is related to the nature of the cyclic ketone peroxide that is used. Therefore, the invention resides in the proper selection of the ketone peroxide used to improve the fuel.

The fuel according to the invention is characterized in that it comprises from 0.001 to 10 percent by weight of one or more cyclic ketone peroxides selected from the group of peroxides represented by formula I:

(I) wherein R R₃, and R₅ are independently selected from the group consisting of hydrogen, C_rC₂₀ alkyl, C₃-C₂₀ cycloalkyl, C₆-C₂₀ aryl, C₇-C₂₀ aralkyl, and C₇-C₂₀ alkaryl, which groups may include linear or branched alkyl moieties, and R₂, R₄, and R₆ are independently selected from the group consisting of hydrogen, C₂- C₂₀ alkyl, C₃-C₂₀ cycloalkyl, C₆-C₂₀ aryl, C₇-C₂₀ aralkyl, and C₇-C₂₀ alkaryl, which groups may include linear or branched alkyl moieties; and each of R R₆ may optionally be substituted with one or more groups selected from hydroxy, alkoxy, linear or branched alkyl, aryloxy, ester, carboxy, nitrile, and amido, with the proviso that said peroxides make up at least 35% by weight of all cyclic ketone peroxides in the fuel.

The improved fuels according to the invention do not suffer from most of the disadvantages mentioned above. More specifically, it was found that the use of the cyclic ketone peroxides of formula I results in fuels with an exceptionally good performance with respect to ignition timing and the correlated cetane number, good miscibility, good chemical stability, i.e. resistance to oxygen, acids, and metal oxides such as rust, and good compatibility with other parts of the fuel system, such as metals, rubber fittings, gaskets, and hoses.

Preferably, the cyclic ketone peroxides according to the invention consist of oxygen, carbon, and hydrogen atoms, so as to avoid an adverse effect on the NO_x emission upon combustion of the fuel into which they are incorporated. More preferably, the cyclic ketone peroxides according to formula I are derived from at least one ketone with a molecular weight greater than acetone, such that the total number of carbon atoms of the molecule is greater than 6. The use of such ketones of higher molecular weight will have a positive effect on the solubility of said cyclic ketone peroxide in a fuel and was found to more effective as an ignition improver, based on the amount of active oxygen added. Preferably, a ketone with at least 4 carbon atoms, more preferably with at least 5 carbon atoms, is used to produce the cyclic ketone peroxide used according to the invention. Also, the total number of carbon atoms in the cyclic ketone peroxide according to the invention preferably is less than 40, more preferably less than 30, and most preferably less than 25. Otherwise the molecular weight will be too high, necessitating a high dosing level of the peroxide to the fuel, which is economically unattractive. Incidentally, it is noted that if mixtures of ketones comprising acetone are used, then some undesired dimeric and trimeric acetone peroxides will be formed. Such cyclic acetone peroxides can precipitate at lower temperatures when used in a fuel, particularly in a diesel fuel, and thus may necessitate a further purification step. Hence also the use of acetone in mixtures of ketones is undesired. Furthermore, although mixtures of ketones can be used to make the cyclic ketone peroxides according to the invention, it is preferred that just one ketone is used, such that R₁=R₃=R₅ and R₂=R₄=R₆. Such cyclic ketone peroxides are, inter alia, more easily produced and less prone to changes in composition due to changing process conditions. Hence, the quality of the ignition improvers thus formed is more easily controlled.

The ignition time improving cyclic ketone peroxide(s) preferably is/are present in such an amount that the self-ignition time of treated fuel is shorter in a model test as described below than the self-ignition time of untreated fuel. More preferably, a reduction of the self-ignition time by more than 10% is observed at 270°C in said test. Even more preferably, the reduction of the self-ignition time is more than 25% at this test temperature. Most preferred is a reduction of at least 50% of the self-ignition time at 270°C.

Preferably, one or more of the cyclic ketone peroxides according to formula I are present in the final fuel formulation in an amount of between 0.025 and 5 percent by weight (% w/w). Most preferred is a concentration of cyclic peroxide of formula I in the fuel of between 0.05 and 2.5% w/w. Less peroxide will not result in any noticeable improvement of the ignition characteristics of the fuel, whereas a higher amount may prove to be unsafe or uneconomical.

The term fuels, as used throughout this document, is meant to encompass all hydrocarbon distillates and residue-containing oils for use in combustion engines and which distill between the kerosene fraction and the lubricating oil fraction of petroleum. The fuel may comprise the usual additives, such as anti- foam agents, injector cleaning agents, drying agents, cloud point depressants, also known as anti-gel agents, algea control agents, lubricants, dyes, and oxidation inhibitors, but may also comprise further ignition improving or combustion improving additives, provided that such additives do not adversely affect the storage stability of the final fuel composition according to the invention. A preferred fuel is diesel fuel.

In a second embodiment, the invention relates to a process to make the ignition improved fuels. To this end, an appropriate cyclic ketone peroxide composition is combined with a fuel, or else the cyclic ketone peroxide is produced directly in said fuel.

The cyclic ketone peroxide(s) can be produced as described in WO 96/03397. It is disclosed there how by changing the reaction conditions, the composition of the resulting cyclic ketone peroxide can be controlled. The trimeric cyclic ketone peroxides according to formula I preferably are formed when mild reaction conditions are chosen, e.g. by lowering the amount of acid used in the process, lowering the temperature, reacting for a short period of time, and/or dosing the hydrogen peroxide and the acid at the same time. Furthermore, the production of the trimeric compound is favoured when less water is used in the reaction, probably because less trimeric compound is hydrolyzed to the dimeric compound. The exact conditions will depend on the type of ketone that is used and the concentration of the various reactants. However, the skilled person will have no problem in determining which process conditions are to be selected for producing the cyclic ketone peroxides as used in the invention. Preferably, however, the process temperature ranges from 0-80°C, more preferably 5- 60°C, and most preferably 20-45°C to allow for a cost-efficient process.

Suitable ketones for use in the synthesis of cyclic ketone peroxides as used in the invention include, for example, acetone, acetophenone, methyl-n-amyl ketone, ethylbutyl ketone, ethylpropyl ketone, methylisoamyl ketone, methylheptyl ketone, methylhexyl ketone, ethylamyl ketone, dimethyl ketone, diethylketone, dipropyl ketone, methylethyl ketone, methylisobutyl ketone, methylisopropyl ketone, methyipropyl ketone, methyl-tert-butyl ketone, isobutylheptyl ketone, diisobutyl ketone, 2,4-pentanedione, 2,4-hexanedione, 2,4-heptanedione, 3,5-heptanedione, 3,5-octanedione, 5-methyl-2,4- hexanedione, 2,6-dimethyl-3,5-heptanedione, 2,4-octanedione, 5,5-dimethyl- 2,4-hexanedione, 6-methyl-2,4-heptanedione, 1-phenyl-1 ,3-butanedione, 1- phenyl-1 ,3-pentanedione, 1 ,3-diphenyl-1 ,3-propanedione, 1 -phenyl-2,4- pentanedione, methylbenzyl ketone, phenylmethyl ketone, phenylethyl ketone, and coupling products thereof. Of course, other ketones having appropriate R groups corresponding to the peroxides of formula I can also be employed, as well as mixtures of two or more different ketones.

Examples of preferred peroxides of formula I for use in accordance with the present invention are the cyclic ketone peroxides derived from methyl-n-amyl ketone, ethylbutyl ketone, ethylpropyl ketone, methylheptyl ketone, methylhexyl ketone, ethylamyl ketone, methyipropyl ketone, diethyl ketone, methylethyl ketone, isomers of these ketones, and mixtures thereof. More preferably, the peroxides of formula I are based on at least one ketone selected from the group consisting of methyl-n-amyl ketone, ethylbutyl ketone, ethylpropyl ketone, methylheptyl ketone, methylhexyl ketone, ethylamyl ketone, methyipropyl ketone, diethyl ketone, methylethyl ketone, and one or more isomers of these ketones, such as methyl-isobutyl ketone and methylisopropyl ketone.

The peroxides can be prepared, transported, stored, and applied in any solid or liquid form, but solutions in a non-halogenated liquid phlegmatiser are preferred. These compositions can then be combined with the fuel. It should be noted that certain phlegmatizers may not be suitable for use in all of the ketone peroxide compositions of the present invention. More particularly, in order to obtain a safe composition, the phlegmatizer should have a certain minimum flash point and minimum boiling point relative to the decomposition temperature of the ketone peroxide, such that the phlegmatizer cannot be boiled off leaving a concentrated, unsafe ketone peroxide composition.

Preferred phlegmatizers are selected from the group consisting of hydrocarbons, such as (diesel) fuel, paraffinic and white oils, oxygenated hydrocarbons, such as ethers, aldehydes, epoxides, esters, ketones, alcohols, and organic peroxides, such as linear ketone peroxides and di-tert-butyl peroxide, alkyl nitrates, such as 2-ethylhexyl nitrate, and mixtures thereof. Examples of preferred liquid phlegmatizers for the cyclic ketone peroxides include alkanols, in particular higher aliphatic alkanols, cycloalkanols, alkylene glycols, alkylene glycol monoalkyl ethers, ethers, in particular methyl tert-butyl ether, aldehydes, ketones, epoxides, esters, hydrocarbon solvents, including toluene, xylene, (diesel) fuel, paraffinic oils, and white oils. More preferred liquid phlegmatizers are ethers and hydrocarbons. Most preferably, a fuel is used as the phlegmatiser. A concentrated cyclic ketone peroxide composition is very suitable for further dilution with fuel in order to obtain a fuel comprising an ignition improving amount of said peroxide.

The fuel according to the invention may contain just peroxides of formula I as the ignition improver. However, they may also be combined with other ignition improvers, such as conventional di-tert-butyl peroxide and/or 2-ethylhexyl nitrate. If the peroxides of formula I are used together with other cyclic ketone peroxide ignition improvers, then it is preferred that they make up at least 40% w/w, more preferably at least 45% w/w, more preferably at least 50% w/w, more preferably at least 66% w/w, and even more preferably more than 75% w/w, based on the weight of all cyclic ketone peroxides in the fuel. Most preferred are compositions in which more than 80% w/w of the weight of all cyclic ketone peroxides can be attributed to cyclic ketone peroxides according to formula I, because the ignition properties of such fuels is most efficiently improved. If only cyclic ketone peroxides consisting essentially of a mixture of dimeric and trimeric compounds (according to formula I) are used in the fuel, then the indicated preferred ranges show that the ratio of dimeric to trimeric compounds in the fuel is lower than about 2:1 , more preferably lower than about 3:2, more preferably lower than about 5:4, more preferably lower than about 1 :1 , more preferably lower than 1 :2, more preferably lower than about 1 :3, and most preferably lower than about 1 :4.

To avoid safety hazards, it is preferred that the cyclic ketone peroxide composition used to make up the claimed fuels is not essentially pure cyclic ketone peroxide. More preferably, the compositions comprise less than 99% w/w, more preferably less than 90% w/w, and even more preferably less than 85% w/w of cyclic ketone peroxide, all based on the weight of the total formulation. Most preferably, the cyclic ketone peroxide composition that is used to make fuels according to the invention comprises less than 75% w/w of cyclic ketone peroxide, based on the weight of the total composition.

Alternatively, the cyclic ketone peroxides can be prepared in a fuel, which can be the fuel the ignition characteristics of which are to be improved, in the desired concentration of between 0.01 and 10% w/w. To this end, the conventional reactants and catalyst(s) are introduced into untreated fuel and reacted. Subsequently, the ignition improved fuel is separated from contaminants and process water, optionally washed, and optionally dried, all in a conventional manner. In this preparation, the streams to be processed are quite large in volume, but the handling of a peroxide concentrate can be avoided.

The invention is elucidated by the following examples. Examples

Materials used: Isopar® M hydrocarbon phlegmatizer ex Exxon Chemical Cyclic-MEKP-1 cyclic methyl-ethyl-ketone peroxide (41% w/w in Isopar M) ex Akzo Nobel 93% trimeric, 7% dimeric compounds (GC area%)

Cyclic-MEKP-2 cyclic methyl-ethyl-ketone peroxide (29.7% w/w in Diesel 1) ex Akzo Nobel 85% trimeric, 15% dimeric compounds (GC area%)

2-EHN 2-ethylhexyl nitrate (97%) ex Aldrich Trigonox® B di-tert-butyl peroxide ex Akzo Nobel DF-0 Low sulfur Diesel #2 ex Octel with a boiling range of 163- 370°C, a flash point of 51.6-65.5°C (D-93), and an auto- ignition temperature of 257°C (E-659).

Procedure

The performance of ignition improvers in the process according to the invention was evaluated by means of the following screening method:

• mixing the ignition improver in the specified amount with the diesel fuel at room temperature,

• injecting a sample of 100 μl or 250 μl by means of a syringe into an apparatus according to DIN 51794, which is controlled at a temperature of 270°C, and measuring the time that elapses before the sample ignites.

Alternatively, the cetane number of the fuel is measured according to method ASTM D-613. The active oxygen content of the peroxides and fuels was analyzed by means of conventional analytical techniques such as iodometric titration and gas chromatographic analysis. More specifically, linear ketone peroxides were analyzed by means of method Jo/97.3 and the total amount of active oxygen was analyzed by means of method Jo/97.2. The ratio of dimeric to trimeric ketone peroxide was analyzed by means of method GC 97.8. These methods are available upon request from Akzo Nobel.

Predominantly trimeric cyclic methylisobutyl ketone peroxide to be used as a fuel additive was produced by adding 97.1 g of hydrogen peroxide (70%) to a stirred mixture of 200 g of methylisobutyl ketone, 100 g of Isopar® M, and 196 g of sulfuric acid (50%) over a period of 20 minutes, under a temperature of 20- 25°C. The mixture was then stirred for another 3 hours at 40°C and for 18 hours at 30°C. The organic phase was separated, washed with water and caustic and sulfite solutions, respectively, and dried over magnesium sulfate dihydrate. This process resulted in 235 g of an organic liquid with a total active oxygen content of 2.14%, of which 2.07% was cyclic methylisobutyl ketone peroxide and less than 0.07% was linear methylisobutyl ketone peroxide. The ratio of dimeric to trimeric cyclic compounds was 12:88 GC area%.

Example 1

Diesel fuel DF0 was mixed with sufficient cyclic-MEKP-1 to give a 1 % w/w concentration of cyclic ketone peroxide in the diesel fuel.

Both the 100 μl and the 250 μl sample, when tested as described above, ignited after 3.0 seconds. The cetane number of the ignition improved fuel was greater than 73.7. Comparative Examples A-D

Example 1 was repeated, except that no or other conventional ignition improvers were used. The compounds used, their concentration in the diesel fuel, and the results of the tests are incorporated into the following table.

n.d. = not determined

Example B was repeated using 0.787% w/w of 2-EHN and diesel 2. The ignition improved fuel (cetane number about 61) was evaluated according to Conradson test ASTM-D189. When converted to equivalent values for the Ramsbottom residue test, 0.2% w/w of carbon deposits was formed.

Comparative Examples E-G

The Examples 1 , 3, and 5 of FR-862 974 were reworked as Comparative Examples E-G, respectively, except that Example 5 was not reworked in a continuous but in a discontinuous fashion.

The dissolution and performance of the cyclic acetone peroxide of Comparative

Example E in fuel was unsatisfactory.

The cyclic butanone peroxides of Comparative Examples F and G contained 90 and 76% (GC area%) of dimeric butanone peroxide and 10 and 24% (GC area%) of trimeric butanone peroxide, based on the GC area of cyclic ketone peroxides. Examples 2-7 and Comparative Examples H-J

Using three types of diesel fuel, various ketone peroxides were evaluated for their influence on the cetane number. In Examples 2-6 cyclic-MEKP-2 was used as an ignition fuel improver, while in Example 7 the cyclic methylisobutyl ketone peroxide as prepared above was used. In Comparative Example H, no ketone peroxide was used, in Comparative Example I Butanox®M50 ex Akzo Nobel, a predominantly linear methylethyl ketone peroxide, was used, while in Comparative Example J, Trigonox®233 ex Akzo Nobel, a predominantly linear methylisobutyl ketone peroxide, was used.

LGO = light gas oil LCO = light cycling oil

Obviously, on an equal active oxygen basis, the cyclic ketone peroxides of the higher ketones are more efficient at improving the cetane number.

Also, the product of Example 6 in diesel 2 was evaluated according to Conradson test ASTM-D189. When converted to equivalent values for the Ramsbottom residue test, 0.05% w/w of carbon deposits was formed, which is much better than the result obtained in Comparative Example B.

Example 8

A fuel according to the invention was prepared by adding 19.4 g of hydrogen peroxide to a stirred mixture of 27 g of diesel 1 , 28.8 g of methylethyl ketone peroxide, and 14.0 g of sulfuric acid over a period of 20 minutes, while maintaining a temperature of about 20°C. The mixture was then stirred for another 90 minutes at 20°C, and the two layers were separated. The organic layer was washed with 25 g of a 6% w/w solution of sodium hydrogen carbonate, dried over magnesium sulfate dihydrate, and filtered. The product contained predominantly cyclic methylethyl ketone peroxide with a ratio of dimeric/trimeric compounds of 13:87 GC area%.

Example 9 and Comparative Example K In order to demonstrate the differences in effect of dimeric and trimeric cyclic ketone peroxides when used as a fuel ignition improver, a diesel fuel was doped with 0.595% w/w of cyclic methylethyl ketone peroxide. In Example 9, a product was used with a ratio of dimeric/trimeric compounds of 5.6:94.4 (GC area%), while in Comparative Example K this ratio was 98.6:1.4 (GC area%). The cetane number of the untreated fuel was 54.7. The cetane number of the fuel of Example 9 was 69.3. The cetane number of the fuels of Comparative Example K was 64.7.

Claims

1. Fuel with improved ignition characteristics comprising one or more cyclic ketone peroxides, characterized in that it comprises from 0.01 to 10 percent by weight of one or more cyclic ketone peroxides selected from the group of peroxides represented by formula I:

wherein R_{1 t} R₃, and R₅ are independently selected from the group consisting of hydrogen, C₁-C₂₀ alkyl, C₃-C₂₀ cycloalkyl, C₆-C₂₀ aryl, C₇-C₂₀ aralkyl, and C₇-C₂₀ alkaryl, which groups may include linear or branched alkyl moieties; R₂, R₄, and R₆ are independently selected from the group consisting of hydrogen, C₂-C₂₀ alkyl, C₃-C₂₀ cycloalkyl, C₆-C₂₀ aryl, C₇-C₂₀ aralkyl, and C₇-C₂₀ alkaryl, which groups may include linear or branched alkyl moieties; and each of R Re ^may optionally be substituted with one or more groups selected from hydroxy, alkoxy, linear or branched alkyl, aryloxy, ester, carboxy, nitrile, and amido, with the proviso that said peroxides make up at least 35% by weight of all cyclic ketone peroxides in the fuel.

2. A fuel according to claim 1 , characterized in that the final concentration of the peroxide(s) according to formula I in the fuel is between 0.025 and 5 percent by weight, based on the weight of the total formulation.

3. A fuel according to claim 1 or 2, characterized in that at least one of the cyclic ketone peroxides in the fuel is derived from one or more ketones selected from the group consisting of acetone, methyl-n-amyl ketone, ethylbutyl ketone, ethylpropyl ketone, methylheptyl ketone, methylhexyl ketone, ethylamyl ketone, methyipropyl ketone, diethyl ketone, methylethyl ketone, isomers of these ketones, and mixtures thereof.

4. A fuel according to claim 3, characterized in that it comprises a cyclic ketone peroxide of formula I derived from at least one ketone selected from the group consisting of methyl-n-amyl ketone, ethylbutyl ketone, ethylpropyl ketone, methylheptyl ketone, methylhexyl ketone, ethylamyl ketone, methyipropyl ketone, diethyl ketone, methylethyl ketone, and isomers thereof.

5. A fuel according to claim 4, characterized in that the cyclic ketone peroxide of formula I is derived from one ketone selected from the group consisting of methylbutyl ketone, methyl-n-amyl ketone, ethylbutyl ketone, ethylpropyl ketone, methylheptyl ketone, methylhexyl ketone, ethylamyl ketone, methyipropyl ketone, diethyl ketone, methylethyl ketone, and isomers thereof.

6. A fuel according to any one of claims 1-5, characterized in that the amount of cyclic ketone peroxide of formula I in the fuel is at least 40% by weight, preferably at least 50% by weight, and most preferably more than 80% by weight, based on the weight of all cyclic ketone peroxide in the fuel.

7. A fuel according to any one of claims 1-6, characterized in that the cyclic ketone peroxide of formula I is selected from the group consisting of cyclic methylethyl ketone peroxide, cyclic methylisobutyl ketone peroxide, and cyclic methylisopropyl ketone peroxide.

8. A fuel according to any one of claims 1-7, characterized in that the fuel is a diesel fuel.

9. Process to make an ignition improved fuel according to any one of claims 1- 8, characterized in that a cyclic ketone peroxide composition is combined with a fuel, which cyclic ketone peroxide composition comprises at least 35% by weight, based on the weight of all cyclic ketone peroxides, of one or more cyclic ketone peroxides selected from peroxides represented by formula I and further comprises one or more non-halogenated phlegmatizers selected from the group consisting of hydrocarbons, oxygenated hydrocarbons, alkyl nitrates, and mixtures thereof.

10. A process according to claim 9 wherein a phlegmatizer is used that is selected from the group consisting of alkanols, cycloalkanols, alkylene glycols, alkylene glycol monoalkyl ethers, ethers, aldehydes, ketones, epoxides, esters, hydrocarbons, and mixtures thereof.

11. A process according to claim 10 wherein the phlegmatizer is selected from ethers or hydrocarbons, preferably from hydrocarbon fuels, such as diesel fuels.

12. A process to make an ignition improved fuel according to any one of claims 1-8, characterized in that the cyclic ketone peroxide is produced in the specified concentration in the fuel.

13. Use of a fuel according to any one of claims 1-8 in a combustion engine to reduce the emission of pollutants.