JPH05214351A - Fuel composition - Google Patents

Abstract

PURPOSE: To provide a fuel compositions prepd. by adding an org. nitrate combustion improver and a tert. alkyl peroxyalkanoate into a hydrocarbon middle distillate fuel with a specified sulfur content and to reduce the amt. of atmospheric pollutants generated on combustion.

CONSTITUTION: The objective fuel composition is obtained by adding (A) at least one org. nitrate combustion improver consisting of a nitrate of an unsubstd. or substd. aliph. or cyclic aliph. alcohol (e.g. cyclopentyl nitrate, etc.), and (B) at least one tert. alkyl peroxyalkanoate of the formula (wherein R is a 4-8c tert. alkyl; R' is a 1-24C hydrocarbon) (e.g. t-butyl peroxyacetate, etc.), or a tert.-alkyl peroxybenzoate (e.g. tert.-butyl peroxybenzoate, etc.), to a main part consists of hydrocarbon middle distillate fuels having a sulfur content less than 500 ppm and dissolving to reduce the amt. of atmospheric pollutants generated on combustion of the fuels.

COPYRIGHT: (C)1993,JPO

Description

Detailed Description of the Invention

The present invention relates to environmental preservation. More particularly, the present invention relates to fuel compositions and methods that reduce air pollution that normally occurs in the operation of engines or combustors with middle distillate fuel.

The importance and desirability of reducing pollutant emissions into the atmosphere is well understood. Among the pollutants sought to be reduced are nitrogen oxides (“NO _x ”), carbon monoxide, unburned hydrocarbons, and particulates.

The present invention is, inter alia, of major parts 500
a small amount of (i) at least one organic nitrate which comprises a hydrocarbon-based middle distillate fuel having a sulfur content of less than ppm and which reduces the emissions dissolved therein. Atmosphere during operation of an engine or other combustion device operating with a combustion improver and (ii) a fuel composition characterized in that it comprises at least one tertiary alkylperoxyalkanoate or peroxybenzoate. may reduce the amount of the NO _X or CO or unburned hydrocarbons released into, is accompanied by the discovery that. In fact, by using the fuel composition it is possible to reduce the amount of two and possibly all three of the pollutants (NO _x , CO and unburned hydrocarbons) emitted by a diesel engine. I found out that Moreover, this important and highly desirable objective is achieved, which can thus be achieved without the disadvantage of increasing undesired particulate emissions. This is a unique finding, because the available experimental evidence and mechanistic theory of combustion shows that if NO _x is reduced, the amount of particulate matter increases and vice versa. Because it is.

Accordingly, the present invention, in one of its embodiments, comprises a major portion of less than 500 ppm (preferably 100 ppm).
ppm or less, most preferably 60 ppm or less), comprising a hydrocarbon-based middle distillate fuel, wherein said fuel has a small amount that reduces the emissions dissolved therein. (I) at least one organic nitrate combustion improver and (ii) formula

[0005]

[Chemical 3] Wherein R is a tertiary alkyl group having 4 to 8 carbon atoms and R'is a hydrocarbon group having 1 to 24 carbon atoms. A fuel composition comprising a trialkylperoxyalkanoate or a peroxybenzoate.

As used in the description below and in the appended claims, the term "hydrocarbon-based" means a middle distillate fuel consisting predominantly or wholly of petroleum-derived fuels by any of the conventional processing operations. ing. These finished fuels are also suitably desulfurized, suitably derived from small amounts of non-hydrocarbon fuels or blending components such as alcohols or similar materials, and / or tar sands, shale oil or coal. Boiling range (ie 1
A small amount of auxiliary liquid fuel having a temperature of 60 to 370 ° C.) may be included. When using the blend consisting of the desulfurization auxiliary liquid fuel and the hydrocarbon middle distillate fuel, it is necessary to keep the sulfur content of the total blend below 500 ppm.

In another embodiment of the invention, the invention comprises:
Provided is an improvement in a combustion process in which a hydrocarbon-based middle distillate fuel is subjected to combustion in the presence of air. The improvement is less than 500 ppm (preferably 100 ppm or less, most preferably 60 pp as fuel used in the above method.
(i) at least one organic nitrate combustion improver and a formula (ii) having a sulfur content of less than or equal to m) and reducing the emissions dissolved therein.

[0008]

[Chemical 4] Wherein R is a tertiary alkyl group having 4 to 8 carbon atoms and R'is an aliphatic or aromatic hydrocarbon group having 1 to 24 carbon atoms. A hydrocarbon-based middle distillate fuel having at least one tertiary alkylperoxyalkanoate or peroxybenzoate is provided, and the organic nitrate combustion improver is nitric acid of an unsubstituted or substituted aliphatic or cycloaliphatic alcohol. Consisting of, consisting of.

Yet another embodiment of the present invention provides an improvement in hydrocarbon-based middle distillate fuel production. The improvement is such that the sulfur content of the fuel is less than 500 ppm (preferably 100 ppm or less, most preferably 6 ppm or less).
After controlling or reducing the level to below 0 ppm), the resulting fuel with this reduced sulfur content,
(I) at least one organic nitrate combustion improver and (ii) formula

[0010]

[Chemical 5] Wherein R is a tertiary alkyl group having 4 to 8 carbon atoms and R'is an aliphatic or aromatic hydrocarbon group having 1 to 24 carbon atoms. Blending with at least one tertiary alkyl peroxyalkanoate or peroxybenzoate, and wherein the organic nitrate combustion improver comprises a nitrate ester of an unsubstituted or substituted aliphatic or cycloaliphatic alcohol.

An additional embodiment of the invention involves improvements in the operation of motor vehicles and aircraft operating on middle distillate fuel. The improvement is less than 500 ppm (preferably 100 ppm or less, most preferably 60 ppm or less).
(i) at least one organic nitrate combustion improver and a formula (ii) having a sulfur content of (ppm or less) and dissolved therein.

[0012]

[Chemical 6] Wherein R is a tertiary alkyl group having 4 to 8 carbon atoms and R'is an aliphatic or aromatic hydrocarbon group having 1 to 24 carbon atoms. A hydrocarbon-based middle distillate fuel, characterized by having at least one tertiary alkylperoxyalkanoate or peroxybenzoate, is supplied to a vehicle or aircraft, and the organic nitrate combustion improver is unsubstituted or substituted. It consists of a nitrate of an aliphatic or cycloaliphatic alcohol.

According to a particularly preferred embodiment of the present invention, a small amount of (i) at least one fuel soluble organic nitrate combustion improver which reduces emissions and (ii) a formula

[0014]

[Chemical 7] Wherein R is a tertiary alkyl group having 4 to 8 carbon atoms and R'is an aliphatic or aromatic hydrocarbon group having 1 to 24 carbon atoms. Less than 500 ppm, preferably containing at least one tertiary alkyl peroxyalkanoate or peroxybenzoate, and wherein the organic nitrate combustion improver consists of a nitrate ester of an unsubstituted or substituted aliphatic or cycloaliphatic alcohol. Is 100 ppm
Or less, most preferably less than 60 ppm) and has a 10% boiling point (ASTM D-86) of 15
A hydrocarbon-based middle distillate fuel in the range of 4-230 ° C. The above fuel compositions tend to emit particularly low levels of NO _x when burned. While not wishing to be limited in scope by theoretical considerations, one explanation for such highly desirable performance is that fuels with higher 10% boiling point cause the combustion to slow down, and The result is a higher peak temperature that increases the amount of NO _x produced.

The above and other specific examples are set forth in the following description and appended claims.

The hydrocarbon-based fuel used in the practice of the present invention generally comprises a mixture of hydrocarbons having a distillation range of about 160-370 ° C. The fuels are often referred to as "middle distillate fuels" because they consist of fractions that distill off after gasoline. The fuel includes diesel fuel, burner fuel, kerosene, gas oil, jet fuel and gas turbine engine fuel.

The preferred middle distillate fuel has the following distillation profile:

[0018]

[Table 1]

It is characterized by having

Diesel fuels having a net octane number (ie cetane number without any cetane improvers such as organic nitrates) in the range of 30 to 60 are preferred. Particularly preferred are those having a cetane number in the range of 40 to 50.

Organic nitrate combustion improvers (often also known as ignition improvers) consist of nitrates of unsubstituted or substituted aliphatic or cycloaliphatic alcohols which may be mono- or polyhydric. Suitable organic nitrates have up to 10 carbon atoms, preferably 2
Unsubstituted or substituted alkyl or cycloalkyl nitrates having 10 carbon atoms. The alkyl group may be either linear or branched (or a mixture of linear and branched alkyl groups). Specific examples of nitrate compounds suitable for use in the present invention include, but are not limited to, the following: methyl nitrate, ethyl nitrate, n-propyl nitrate, isopropyl nitrate, allyl nitrate, N-Butyl nitrate, isobutyl nitrate, s-butyl nitrate, t-butyl nitrate, n-amyl nitrate, isoamyl nitrate, 2-amyl nitrate, 3-amyl nitrate, t-amyl nitrate, n-hexyl nitrate, n-heptyl nitrate , S-heptyl nitrate, n-octyl nitrate, 2-nitric acid
Ethylhexyl, s-octyl nitrate, n-nonyl nitrate,
N-decyl nitrate, cyclopentyl nitrate, cyclohexyl nitrate, methylcyclohexyl nitrate and isopropylcyclohexyl nitrate. Also suitable are nitrate esters of alkoxy-substituted aliphatic alcohols such as 2-ethoxyethyl nitrate, 2- (2-ethoxy-ethoxy) ethyl nitrate, 1-methoxypropyl-2.
-Nitrates and 4-ethoxybutyl nitrate, as well as nitrates of diols, such as 1,6-hexamethylene dinitrate. Preferred are alkyl nitrates having 5 to 10 carbon atoms, most particularly mixtures of primary amyl nitrates, primary hexyl nitrates, and octyl nitrates such as 2-ethylhexyl nitrate. ..

As is well known, nitrate esters are usually prepared by mixed acid nitration of appropriate alcohols or diols. A mixture of nitric acid and sulfuric acid is generally used for this purpose. Another method for making nitrate esters involves reacting an alkyl halide or cycloalkyl with silver nitrate.

The concentration of the nitrate ester component in this fuel is
It can be varied within a relatively wide range provided that the amount used in combination with at least one tertiary alkyl peroxyalkanoate or peroxybenzoate is at least sufficient to result in a reduction in emissions. And Generally speaking, the amount of nitrate ester used is 250 per million parts by weight of this fuel.
It falls within the range of organic nitrates consisting of ˜10,000 parts by weight. A suitable concentration is typically 5 per million parts of fuel.
It is in the range of 00 to 2000 copies.

The tertiary alkyl peroxyalkanoates or peroxybenzoates used in the practice of this invention have at least 6 carbon atoms in the molecule, and preferably the tertiary alkyl. Base,
That is, R has from 4 to 8 carbon atoms, and a hydrocarbon group, that is, R'is an essentially saturated aliphatic hydrocarbon group or an unsubstituted aromatic group. These tertiary alkyl peroxyalkanoates or peroxybenzoates can be used alone with the nitrate ester component or with the nitrate ester component.
More than one alkanoate or benzoate compound may be used. Illustrative peroxyesters include t-butyl peroxyacetate, t-butyl peroxybutyrate,
T-Butyl peroxycaproate, t-butyl peroxyheptanoate, t-butyl peroxycaprylate, t-butyl peroxydecanoate, t-butyl peroxide decanoate
Butyl, t-butyl peroxytetradecanoate, t-butyl peroxyhexadecanoate, t-butyl peroxyoctadecanoate, t-butyl peroxyeicosanoate,
T-butyl peroxytetracosanoate, t-butyl peroxyhexadecenoate, t-butyl peroxyoctadecenoate
Butyl, t-butyl peroxy-2-methylcaproate, t-butyl peroxy-3-methylcaproate, t-butyl peroxy-2-ethylcaproate, t-butyl peroxy-2-octylcaprylate, peroxy-
T-Butyl 2,7-dimethylcaprylate, t-butyl peroxybenzoate, and the tertiary alkyl group is t-amyl, 1,1,2-trimethylpropyl, 1,1,3,3
Included are similar compounds such as tetra-methyl-butyl and the like.

The base fuel typically contains 100 to 50,000, preferably 500 to 2,000 parts (ppm) of a tertiary alkylperoxyalkanoate or peroxybenzoate component per million parts by weight of the base fuel. There is. The above amounts, when combined with essentially similar amounts of organic nitrate combustion improvers, typically operate under similar conditions with similar fuel compositions without the emission reduction additives of the present invention. Sufficient to reduce diesel emissions over that produced by similar engines.

Other additives may also be included in the fuel composition of the present invention provided they do not adversely affect the emission reductions that can be achieved in the practice of the present invention. .. Therefore, components such as organic peroxides and hydroperoxides, corrosion inhibitors, antioxidants, rust inhibitors, detergents and dispersants, friction modifiers, demulsifiers, dyes, inert diluents, and similar materials. May be used.

[0027] Detroit Diesel on the engine dynamometer
A series of engine tests using the 11.1 liter Series 60 engine showed the advantages that can be achieved with the practice of the present invention. Appendix I of Code of Federal Regulations (7-1-86), Volume 40, Part 86, pp. 810-819, "EPA Engine Dynamometer S for Powerful Diesel Engines"
The system was operated according to the schedule for Heavy-Duty Diesel Engines). In the above test, the first of nine consecutive tests involved the running of the engine with normal DF-2 diesel fuel having a nominal sulfur content in the range 2000-4000 ppm. This test was used as one of two baselines. In the next run, the engine was run with a low sulfur diesel fuel having the following characteristics: Sulfur (ppm) 50 Gravity (API @ 60 degrees F) 34.7 Pour point (degree F) -5 Cloud point (degree F) 8 Copper strip 1 Distillation (degree F) IBP 332 10% 430 50% 532 90% 632 EP 634 Cetane number 44.3 Viscosity (@ 40 ° C, cS) 2.96 3rd and 4th The test used the same low sulfur fuel as above except that a diesel ignition improver consisting of 2-ethylhexyl nitrate was blended therein. In this third test, the concentration was 2000 ppm of the organic nitrate. In the fourth test, 5000p for this fuel
pm of the organic nitrate was included. The fifth was with the other baseline operating with the first regular DF-2 diesel fuel. In the sixth test another additive low sulfur fuel was tested. This fuel contains 1250 ppm of the organic nitrate and 1250 p
A seventh test was conducted using the same low sulfur fuel except that it contained pm peroxyester (t-butyl peroxy-2-ethylcaproate). In the eighth test, different additive low sulfur fuels were tested. In the ninth and final tests, 500 ppm of the organic nitrate and 50
The same fuel was used as in 8 except that it contained 0 ppm of the peroxyester. In all cases, the amounts of NO _x , unburned hydrocarbons (“HC”), carbon monoxide (“CO”) and particulates emitted by this engine were measured and integrated. The results of these tests are summarized in the table below. NO _x, HC, is shown therein with respect to CO and particulates value is expressed as grams per brake horsepower per hour. Therefore, the lower the value, the lower the emission rate and quantity.

[0028]

[Table 2]

In a particularly preferred embodiment of the present invention, the use of fuels having specific boiling characteristics as well as low sulfur levels results in even further reductions in NO _x or particulate emissions. Therefore, using fuels that meet the low sulfur parameters listed above and also have a 10% boiling point (ASTM D-86) in the range of 154-230 ° C., reduces NO _x emissions to very low levels. It becomes possible.
Similarly, a 90% boiling point (ASTM
Use of fuels with D-86)) tends to reduce particulate emissions to particularly low levels. For explanation purposes,
In a series of emissions tests, a Detroit Diesel Corporation series 60 engine was used, which is an 11.1 liter construction and is nominally rated at 320 hp at 1800 rpm. The engine was installed in a powerful transient emission cell equipped with a constant volume sampler (CVS) system. EPA Transient Emmissions
Using a dilution tunnel according to the Cycle Procedure, HC,
CO, NO _x and particulate matter measurements were taken.

In each individual test, the engine was started and then warmed up. Then, it was operated for 20 minutes at the rated speed and load. Checked the rated power. Further, a power test was conducted to plot the engine torque against the speed. These parameters are required as part of the EPA Transient Cycle Procedure. 20 minutes EP after getting this information
Two A transient cycles were performed and engine controls were adjusted to meet the statistical operating limits specified in the above test. After the engine was stopped, it was soaked for 20 minutes. At the end of this soaking period, the warm-up transient cycle (Hot St
NO _x , CO by performing art EPA Transient Cycle)
And the discharge of particulate matter was measured. After soaking for a further 2 minutes, a second discharge amount evaluation was performed. This 2
The results for the eight warm transient cycles were averaged to obtain the final reported value. Whenever refueling, fresh fuel was introduced into the refueling system, new fuel filters were installed, and the fuel lines were flushed.

For each fuel (A to D), the same warmer start E
It was evaluated by the PA transient emission cycle operation. Fuels A, B, and C contain sufficient amounts of nitric acid 2- to increase the nominal cetane number of the individual fuels to 50.
It contained ethylhexyl. The intrinsic cetane number is 49.
Fuel D of 8 was used without any addition.

The physical and chemical property data for the additive-free fuels AD are shown in the table below.

[0033]

TABLE 3 TABLE fuel characteristics hydrocarbon composition (vol%) A B C D aromatic 36.5 28.5 37.6 39.4 Olefins 1.2 1.1 2.2 2.9 saturates 62.3 70.4 60.2 57.7 Carbon (wt%) 86.35 86.49 86.12 87.32 Hydrogen (wt%) 13.15 13.25 12.89 13.35 Nitrogen (ppm) 5.3 285 356 152 Sulfur (ppm) <1 225 219 476 Aniline point (℃) 70.1 60.0 65.4 69.4 Diene content (% by weight) <0.1 0.2 <0.1 <0.1 Viscosity (cSt) @ 40 (℃) 2.99 2.20 3.10 3.53 @ 100 (℃) 1.22 0.97 1.23 1.34 Combustion heat (BTU / lb) 19,593 19,840 19,543 19,672 Boiling range (℃) IBP 170 172 202 218 10% 217 211 234 252 20% 233 222 246 262 262 30 % 249 230 257 271 40% 262 237 267 278 50 50% 274 244 276 284 60% 288 253 286 291 70% 300 263 294 298 80% 314 276 306 306 90 90% 331 297 322 317 195 95% 344 319 338 329 FBP 352 334 353 341 Recovery rate (%) 98.7 98.9 98.6 98.9 Gravity (API degree 34.9 36.1 34.6 34.5 Specific gravity 0.850 0.844 0.852 0.852 Calculated cetane index 48.1 44.0 48.9 51.7 Cetane index 48.5 43.8 48.3 49.7 Cetane number 45.3 39.6 47.7 49.8 In the above table, the following test methods were used: Hydrocarbon composition-ASTM D-1319 Carbon − Carlo-Erba 1106 Hydrogen − Carlo-Erba 1106 Nitrogen − ASTM D-4629 Sulfur − ASTM D-3120 Aniline point − ASTM D-611 Diene content − UOP 326 Viscosity − ASTM D-445 Heat of combustion − ASTM D-2382 Boiling Range-ASTM D-86 Gravity-ASTM D-287 Calculated cetane index-ASTM D-4737 Cetane index-ASTM D-976 Cetane number-ASTM D 613 Determine the sulfur content of hydrocarbon middle distillate fuels or their precursors. Methods for lowering have been reported in the literature,
Otherwise, it is available to engineers in this field. Among the above methods are solvent extraction with reagents such as sulfur dioxide or furfural, sulfuric acid treatment, and hydrodesulfurization methods. Of these, hydrodesulfurization is generally preferred, which includes numerous specific processes and operating conditions applied to various feedstocks. For example, the hydrotreating or hydrotreating of naphtha or gas oil is generally carried out under mild or moderately severe conditions. On the other hand, the removal of sulfur by hydrocracking applied to fraction feeds is usually carried out under more severe operating conditions. Vacuum distillation of bottoms obtained by distillation at atmospheric pressure is yet another method for controlling or reducing the sulfur content of hydrocarbon feedstocks used in the manufacture of hydrocarbon-based middle distillate fuels. Is. For more information on the above method, see "Encyclopedia of Chemical Technology" by Kirk-Othmer.
(Encyclopediaof Chemical Technology), 2nd edition, In
terscience Publishers, 11: 432-445 (1966 Copyright) and references cited therein; Idem., 15
Volume, pages 1-77 and references cited therein; and Ki
rk-Othmer "Encyclopedia of Chemical Technology" (Encyclopedia of C
hemical Technology), Volume 17, 3rd edition, Wiley-Intersci
ence, pp. 183-256 (1982 copyright) and references cited therein;

Another method that can be used involves the treatment of hydrocarbon-based middle distillate fuels with metal desulfurizing agents such as metal sodium or a mixture of sodium and calcium metals.

The present invention can be applied to stationary diesel engines (eg, those used in power generators or pumping stations), and traveling diesel engines (eg, motor vehicles, trucks, road levelers, or prime movers in military vehicles). It is applicable to both driving.

The features and aspects of the present invention are as follows.

1. The main part consists of a hydrocarbon-based middle distillate fuel having a sulfur content of less than 500 ppm, and said fuel has a small amount of (i) at least one of which reduces the emissions dissolved therein. Organic nitrate combustion improver and formula (ii)

[0038]

[Chemical 8] Wherein R is a tertiary alkyl group having 4 to 8 carbon atoms and R'is a hydrocarbon group having 1 to 24 carbon atoms. A fuel composition comprising a trialkyl peroxyalkanoate or peroxybenzoate.

2. R is a tert-butyl group, the total number of carbon atoms in R'is 1 to 12, and the organic nitrate combustion improver comprises a nitrate ester of an unsubstituted or substituted aliphatic or cycloaliphatic alcohol. The fuel composition according to item 1.

3. The tertiary alkyl peroxyalkanoate is t-butyl peroxyacetate, the tertiary alkyl peroxybenzoate is t-butyl peroxybenzoate, and the organic nitrate combustion improver is essentially The fuel composition according to claim 1, comprising at least one nitric acid ester of a primary alkanol having from 5 to 10 carbon atoms.

4. The organic nitrate combustion improver is
A composition according to claim 3 consisting essentially of a mixture of hexyl nitrate.

5. The base fuel has a net cetane number in the range of 30-60 and the following distillation profile:

[0043]

[Table 4]

The composition of claim 1 having:

6. Comprising supplying to the engine a composition as defined in paragraph 1 and burning in the engine,
A method of reducing the amount of particulate matter in diesel engine exhaust.

7. The fuel used in the above process in a combustion process in which middle distillate fuel is burned in the presence of air, has a small amount of (i) which has a sulfur content of less than 500 ppm and which reduces the emissions dissolved therein. At least one organic nitrate combustion improver and formula (ii)

[0047]

[Chemical 9] Wherein R is a tertiary alkyl group having 4 to 8 carbon atoms and R'is an aliphatic or aromatic hydrocarbon group having 1 to 24 carbon atoms. Comprising supplying a hydrocarbon-based middle distillate fuel having at least one tertiary alkyl peroxyalkanoate or peroxybenzoate, wherein the organic nitrate combustion improver is an unsubstituted or substituted aliphatic or cycloaliphatic A method comprising the nitrate ester of a group alcohol.

8. (I) a major portion of a hydrocarbon-based middle distillate fuel having a sulfur content of 100 ppm or less and a net cetane number in the range of 30-60, and (ii) emissions dissolved therein. (A) at least one nitrate ester of at least one aliphatic or cycloaliphatic alcohol and (b) the formula

[0049]

[Chemical 10] Wherein R is a tertiary alkyl group having 4 to 8 carbon atoms and R'is an aliphatic or aromatic hydrocarbon group having 1 to 24 carbon atoms. 8. The method of claim 7 wherein the combustion is performed in the combustion chamber of a compression ignition engine operating with a diesel fuel composition comprising at least one tertiary alkyl peroxyalkanoate or peroxybenzoate.

9. The organic nitrate combustion improver is
A process according to claim 8 consisting essentially of a nitrate of at least one primary alkanol having 5 to 10 carbon atoms in the molecule.

10. The organic nitrate combustion improver consists essentially of a mixture of primary hexyl nitrate, the tertiary alkyl peroxyalkanoate is t-butyl peroxyacetate, and the tertiary alkyl peroxybenzoate is peroxybenzoic acid. 10. The method of claim 9 which is t-butyl acidate.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Alexander Michael Klenowski Missouri, United States 63125 Saint Louis Provence Drive 3840 B 7748

Claims (3)

[Claims] 1. A main part is characterized in that it comprises a hydrocarbon-based middle distillate fuel having a sulfur content of less than 500 ppm, and said fuel contains a small amount of () which reduces the emissions dissolved therein. i) at least one organic nitrate combustion improver and (ii) a compound of formula Wherein R is a tertiary alkyl group having 4 to 8 carbon atoms and R'is a hydrocarbon group having 1 to 24 carbon atoms. A fuel composition comprising a trialkyl peroxyalkanoate or peroxybenzoate. 2. A method of reducing the amount of particulate matter in a diesel engine exhaust comprising supplying an engine with the composition as defined in claim 1 and combusting in the engine. 3. A combustion method in which middle distillate fuel is burned in the presence of air, the fuel used in said method having a sulfur content of less than 500 ppm and reducing the emission dissolved therein. A small amount of (i) at least one organic nitrate combustion improver and (ii) the formula Wherein R is a tertiary alkyl group having 4 to 8 carbon atoms and R'is an aliphatic or aromatic hydrocarbon group having 1 to 24 carbon atoms. Comprising supplying a hydrocarbon-based middle distillate fuel having at least one tertiary alkyl peroxyalkanoate or peroxybenzoate, wherein the organic nitrate combustion improver is an unsubstituted or substituted aliphatic or cycloaliphatic A process comprising a nitrate of a group alcohol.