# Patent

## Title
Method and composition for reduction of combustion chamber deposits

## Abstract

The present invention provides a diesel fuel oil composition comprising a base fuel which contains normal paraffin compounds having a carbon number of 20 or more at 4.0 wt % or less, has a specific carbon number distribution in the high-boiling normal paraffin compounds, contains sulfur at 0.05 wt % or less, and is incorporated with 0.01 to 0.1 wt % of an FI and 0.002 to 0.1 wt % of lubricity improver.

## Background
1. Field of Industrial Utililzation

This invention relates to a new diesel fuel oil composition, more particularly the composition characterized by base fuel which contains a specific content of normal paraffin compounds having a carbon number of 20 or more, has a specific carbon number distribution in the high-boiling normal paraffin compounds, contains sulfur at 0.05 wt % or less, and is incorporated with a flow improver (FI) and lubricity improver.

2. Prior Art

Diesel engines are widely used for various purposes, e.g., for driving automobiles, ships and construction machines, and are still spreading further. As a result, fuel for diesel engines is increasingly in demand, and becoming heavier to satisfy the increased demands, because straight-run diesel fuel oil is distilled deeper and/or blended with heavier fractions. This is accompanied by several problems, e.g., deteriorated fluidity at low temperature (i.e., increased pour point and/or cold flow plugging point). It is anticipated, therefore, that several engine troubles, e.g., plugging of fuel passage or fuel filter, may occur regionally in a normal temperature range at which the engine is operated in some districts. The other concerns are increased nitrogen oxide and particulate matter emissions, which further aggravate environmental pollution.

Several measures against deteriorated fluidity of diesel fuel oils at low temperature have been proposed to provide fuel oils having adequate pour point and cold flow plugging point (CFPP) properties for temperature conditions, in particular in cold districts. These measures include limitation on end point of straight-run diesel oil, limitation on use of heavier fractions as the blending stocks, use of lighter blending stocks, and use of adequate additives, e.g., fluidity improver, including pour point depressant and FI, to improve fluidity at low temperature. For example, Japanese Laid-open Patent application No. 8-157839 discloses fuel oil composition characterized by base fuel which contains normal paraffin compounds at 15 wt % or less, normal paraffin compounds having a carbon number of 20 or more at 1.2 wt % or less, and sulfur at 0.15 wt % or less, as the composition serviceable in cold districts, high in density, sufficiently low in pour point and allowing the engine to produce a high power.

Japanese Laid-open Patent application No. 7-331261 discloses a diesel fuel oil composition composed of diesel oil having an end point in a range from 320.degree. C. to 340.degree. C., incorporated with 0.1 to 2.0 vol % of a fraction containing normal paraffin compounds having a carbon number of 26 to 31 and 100 to 600 ppm of an ethylene vinyl acetate-based additive to improve fluidity at low temperature. This composition is aimed at abatement of particulate emissions from a diesel engine and improvement of low-temperature fluidity, measured by CFPP.

Limitation on end point of straight-run diesel oil and limitation on use of heavier fractions as the blending stocks to secure low-temperature fluidity of diesel fuel oils provide a good pour point, but are difficult to provide a good CFPP. Moreover, these approaches contribute little to increasing diesel fuel oil supplies. Blending diesel fuel oil with a lighter fraction decreases flash point and also decreases engine output. Use of an additive, such as pour point depressant or FI, involves some problems. For example, a pour point depressant, although decreasing pour point, will not decrease CFPP. An FI, on the other hand, although generally decreasing pour point and CFPP, may not efficiently decrease CFPP, depending on type of stock for base fuel which constitutes diesel fuel oil or distillation properties of base fuel.

The techniques to abate emissions, e.g., nitrogen oxides and particulate matter, from diesel engines have been also developed from various angles. These include improvement of combustion chamber shapes, installation of exhaust gas recycle (EGR) systems, catalytic converters and particulate filter systems, and improvement of diesel fuel oils and lubricants. None of these, however, brings satisfactory results in terms of abatement effect, economic efficiency or stability for extended periods. An EGR system, which is considered to be one of efficient means, recycles part of exhaust gases into the intake air stream. However, this approach causes various problems, e.g., decreased durability and reliability of the engine, deterioration of the lubricant, increased particulate matter emissions and decreased engine output, because exhaust gases contain sulfate ions and particulate matter. These problems will be further aggravated, when an EGR system is installed for a direct injection diesel engine which is required to operate under a high load. Sulfate ions are derived from sulfur contained in diesel fuel oil, and low-sulfur diesel fuel oil containing sulfur at 0.05 wt % or less has now become a social need.

Sulfur contained in a diesel fuel oil can be reduced by refining, in particular catalytic hydrogenation, of the base fuel. This, however, is accompanied by decreased lubricity of diesel fuel oil itself, and will damage the fuel injection device of the engine. It is known that wear of the injection pump notably increases as sulfur content decreases from 0.2 wt %.

Various attempts have been done to improve lubricity of low-sulfur diesel fuel oils. For example, Japanese Laid-open Patent application No. 8-291292 discloses a diesel fuel oil composition which contains sulfur at 0.01 to 0.05 wt %, and (A) an ester of a nitrogen compound having hydroxide group and straight-chain saturated fatty acid, and (B) 15 to 2000 mg/l of at least one type of polymer selected from the group consisting of the polymers from monomers of olefin compounds, ethylenic unsaturated alkyl carboxylates and saturated aliphatic vinyl compounds. It is claimed that this composition exhibits good lubricity in spite of very low sulfur content, improved low-temperature fluidity and no deterioration of exhaust gases without causing troubles at the fuel injection pump in the diesel engine.

These prior-art techniques, however, give diesel fuel oils of insufficient low-temperature fluidity and lubricity, and are also economically unsatisfactory. Therefore, they can rarely give diesel fuel oil compositions showing good CFPP and lubricity, while containing sulfur at 0.05 wt % or less.

It is an object of the present invention to provide a diesel fuel oil composition showing good CFPP and lubricity, and containing sulfur at 0.05 wt % or less by improving the prior-art techniques.

It has been discovered that good CFPP and lubricity can be secured when the base fuel containing sulfur at 0.05 wt % or less satisfies the relationships of 0<A.ltoreq.4.00 (wt %) (wherein, A is content, based on all normal paraffin compounds present in the base fuel of normal paraffin compounds having a carbon number of 20 or more), and 0.04.ltoreq.[B/C].ltoreq.0.40 (wherein, B is content of normal paraffin compounds having a carbon number of n+5, C is content of normal paraffin compounds having a carbon number of n; [B/C] is average B/C ratio; and (n) is an integer when total content of normal paraffin compounds having a carbon number of (n) or more account for 3.0 wt % of total content of the normal paraffin compounds in the base fuel), and is incorporated with 0.01 to 0.10 wt % of an FI and 0.002 to 0.1 wt % of a lubricity improver, reaching the present invention.

The present invention provides a diesel fuel oil composition characterized by base fuel satisfying the relationships 0<A.ltoreq.4.00 wt % (wherein A is content, based on all normal paraffin compounds presenting the base fuel, of normal paraffin compounds having a carbon number of 20 or more) and 0.04.ltoreq.[B/C].ltoreq.0.40, containing sulfur at 0.05 wt % or less, and being incorporated with 0.01 to 0.10 wt % of an FI and 0.002 to 0.1 wt % of a lubricity improver.

The present invention, relating to the above diesel fuel oil composition, includes the following preferred embodiments: ethylene glycol ester-based compound, or ethylene-vinyl acetate-based copolymer, of the FI is ethylene glycol ester-based compound, or ethylene-vinyl acetate-based copolymer, component for the FI is 0.03 to 0.07 wt %, of the active component for the FI is 0.03 to 0.07 wt %, lubricity improver is an ester-based compound, active component for the lubricity improver is an ester-based compound, component for the lubricity improver is 0.005 to 0.05 wt %, and the active component for the lubricity improver is 0.005 to 0.05 wt %.

The present invention is described below in detail. The diesel fuel oil composition of the present invention is characterized by base fuel which contains a specific content of A, has a specific [B/C] ratio, contains sulfur at 0.05 wt % or less, and is incorporated with 0.01 to 0.10 wt % of an FI and 0.002 to 0.1 wt % of a lubricity improver.

The base fuel for the present invention mainly comprises a mineral oil, having a flash point of 40.degree. C. or higher and 90% distillation temperature of 360.degree. C. or lower. The mineral oil for the present invention is a petroleum fraction, including a petroleum fraction obtained by atmospheric distillation of crude oil, and petroleum fraction obtained by atmospheric or vacuum distillation of crude oil and refined by an adequate process, e.g., hydrogenation, hydrocracking, catalytic cracking and a combination thereof. These petroleum fractions can be used individually or in combination. The base fuel component other than petroleum fraction includes vegetable oil, e.g., soybean, coconut and rape oil and animal oil e.g., whale and fish oil.

The diesel fuel oil composition of the present invention satisfies the relationship 0<A.ltoreq.4.00 (wt %) (wherein, A is content, based on all normal paraffin compounds present in the base fuel, of normal paraffin compounds having a carbon number of 20 or more). A diesel fuel oil composition may cause engine troubles, e.g., plugging of the fuel passage or fuel filter, when its base fuel contains normal paraffin compounds having a carbon number of 20 or more (hereinafter referred to as (n-C.sub.20 +)) at above 4.00 wt %, as ambient temperature decreases, because the normal paraffin compounds will separate out.

The diesel fuel oil composition of the present invention also satisfies the relationship 0.04.ltoreq.[B/C].ltoreq.0.40. Assuming that the component A in the base fuel accounts for 3.0 wt % of the total normal paraffin components of the base fuel, the average of the (n-C.sub.25)/(n-C.sub.20), (n-C.sub.26)/(n-C.sub.21), (n-C.sub.27)/(n-C.sub.22) . . . ratios consecutively calculated is in a range from 0.04 to 0.40, inclusive. When [B/C] is below 0.04, some of the normal paraffin compounds in the base fuel may separate out as large planar crystals as ambient temperature decreases, even when the relationship 0<A.ltoreq.4.00 (wt %) is satisfied, to easily cause plugging of the fuel filter. In other words, such a base fuel has an excessively high CFPP. The similar troubles will occur, when [B/C] exceeds 0.40. [B/C] is preferably in a range from 0.07 to 0.20, inclusive. The base fuel shows a good CFPP, even when ambient temperature decreases, when it satisfies the relationships 0<A.ltoreq.4.00 (wt %) and 0.04.ltoreq.[B/C].ltoreq.0.40.

The component A of the base fuel for the present invention can be selected from adequate petroleum fractions of different normal paraffin content. These petroleum fractions include petroleum fractions obtained by atmospheric distillation of crudes of different normal paraffin content, and petroleum fractions obtained by atmospheric or vacuum distillation of crude(s) and refined by an adequate process, e.g., solvent dewaxing and catalytic dewaxing. [B/C] of the base fuel can be adjusted by controlling extent of rectification for the distillation operation. [B/C] increases as extent of rectification decreases. The above petroleum fractions can be used individually or in combination to adjust A and [B/C] levels for the base fuel for the present invention. The above petroleum fractures can be used individually or in combination to adjust the component A content and [B/C] levels for the base fuel for the present invention.

The FI useful for the present invention can be selected from the known ones. These include ethylene glycol ester-based compounds, ethylene-vinyl acetate copolymers, ethylene alkylacrylate-based copolymers, chlorinated polyethylene, polyalkyl acrylate, and alkenyl succinamide-based compounds. The preferable one is an ethylene glycol ester-based compound. An FI dosage below 0.01 wt % may not satisfactorily decrease CFPP, and above 0.1 wt % is not economical, because CFPP will not decrease as much as increased dosage. The preferable FI dosage is 0.03 to 0.07 wt %. The above FI's may be used individually or in combination.

The lubricity improver useful for the present invention can be selected from the known ones. These include fatty acids, e.g., stearic, linolic and oleic acid, and esters, e.g., those of the above fatty acids and polyalcohol, e.g., glycerin. The preferable one is an ester. A lubricity improver dosage below 0.002 wt % may not satisfactorily improve lubricity, and above 0.1 wt % is not economical, because lubricity will not be improved as much as increased dosage. The preferable lubricity improver dosage is 0.005 to 0.05 wt %. The above lubricity improvers may be used individually or in combination.

The diesel fuel oil composition of the present invention may be incorporated with other known additives for fuel oil, so long as its performance is not damaged. These additives include cetane improver, oxidation inhibitor, metal passivator, detergent, corrosion inhibitor, pour point depressant, de-icer, bactericide, combustion promoter, antistatic agent, and coloring agent. A general dosage of the additive is 0.1 to 0.5 wt % in the case of pour point depressant, although not limited to this level. One or more of these additives may be used for the present invention, as required.

The diesel fuel oil composition of the present invention may be also incorporated with one or more types of oxygenated compounds so long as its performance is not damaged. These compounds include alcohols, e.g., methanol, ethanol, isopropanol, n-butanol, isobutanol, tert-butanol, amyl alcohol, isoamyl alcohol n-octanol, 2-ethyl hexanol, n-heptyl alcohol, tridecyl alcohol, cyclohexanol and methyl cyclohexanol; ethers, e.g., methyl tert-butyl ether and ethyl tert-butyl ether; dialkyl phthalates, e.g., diethyl phthalate, dipropyl phthalate and dibutyl phthalate; glycol-ether compounds, e.g., ethylene glycol monoisobutyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol monoisobutyl ether, diethylene glycol dimethyl ether, triethylene glycol mono-n-butyl ether, triethylene glycol dimethyl ether, propylene glycol monomethyl ether acetate and dipropylene glycol mono-n-butyl ether; hydroxyl amine compounds; and diketones, e.g., acetyl acetone. A general dosage of the oxygenated compound is 1 to 15 wt %, although not limited to this level.

The present invention is described in more detail by the embodiments presented below, which by no means limit the present invention. The following base fuels, FI's and lubricity improver were used for Examples and Comparative Examples. Measurements of CFPP, A and [B/C] are also described.

(1) Base Fuel

A total of 16 types of base fuels were used. Their properties are given in Tables 1 and 2. __________________________________________________________________________ Base Oil A    B    C    D    E    F    G    H __________________________________________________________________________ Density (g/cm.sup.3) 0.8369 0.8338 0.8248 0.8461 0.8365 0.8370 0.8262 0.8377 Flash Point (.degree. C.) 70   68   69   69   75   73   71   70 Distillation (.degree. C.) Initial Boiling Point 176.0 182.0 161.5 224.0 216.0 208.0 180.0 171.0 10%       222.5 220.5 212.5 260.0 254.0 248.0 221.5 230.5 50%       287.5 279.0 279.0 294.0 287.0 287.0 274.5 280.0 90%       346.0 345.0 342.5 340.0 330.0 334.0 328.5 343.0 End Point 376.5 377.0 374.0 365.0 353.0 357.0 357.0 372.0 Sulfur Content (wt %) 0.04 0.05 0.03 0.04 0.03 0.04 0.04 0.03 Cloud Point (.degree. C.) -4   -3   -4   -2   1    1    -2   -2 CFPP (.degree. C.) -5   -4   -4   -3   -2   0    -3   -3 Pour Point (.degree. C.) -7.5 -5   -7.5 -2.5 0    0    -2.5 -5 A (wt %)  2.78 3.03 2.82 3.05 3.80 3.45 4.46 1.06 [B/C]     0.092 0.089 0.089 0.054 0.045 0.434 0.027 0.354 __________________________________________________________________________ __________________________________________________________________________ Base Oil I    J    K    L    M    N    O    P __________________________________________________________________________ Density (g/cm.sup.3) 0.8350 0.8369 0.8403 0.8425 0.8139 0.8255 0.8355 0.8348 Flash Point (.degree. C.) 68   69   69   71   75   73   75   72 Distillation (.degree. C.) Initial Boiling Point 175.0 172.0 146.5 139.0 194.5 167.0 170.0 172.5 10%       228.5 230.0 218.0 222.0 225.5 228.0 230.0 232.5 50%       278.5 279.5 276.0 280.0 265.5 273.0 280.0 281.5 90%       345.5 344.0 334.0 334.5 312.0 324.0 246.0 350.0 End Point 376.0 373.0 361.5 361.0 329.0 346.0 376.0 375.0 Sulfur Content (wt %) 0.04 0.03 0.03 0.04 0.03 0.03 0.05 0.04 Cloud Point (.degree. C.) -2   -2   -1   -1   -5   -4   -1   0 CFPP (.degree. C.) -3   -3   -3   -3   -6   -5   -2   -2 Pour Point (.degree. C.) -5   -5   -5   -5   -7.5 -5.0 -2.5 -2.5 A (wt %)  0.92 1.02 3.61 3.92 0.90 1.57 3.35 4.72 [B/C]     0.154 0.248 0.086 0.100 0    0    0.460 0.320 __________________________________________________________________________

(2) FI

An ethylene glycol ester-based FI (ECA9911, produced by Exxon Chemical) and ethylene-vinyl acetate-based FI (PF240, produced by Exxon Chemical) were used.

(3) Lubricity Improver

A lubricity improver with ester-based compound as the active ingredient (PDN655, produced by Exxon Chemical) was used.

(4) Measurement of CFPP

CFPP was measured as per JIS K-2288.

(5) Measurement of "A"

Content of an individual normal paraffin compound in each base fuel was measured by gas chromatography using an analyzer (GC-6AM, produced by Shimadzu), where each sample was passed through a capillary column (inner diameter: 0.25 mm, length: 15 m, impregnated with methyl silicon to a thickness of 0.1 .mu.m) at 50.degree. C. to 350.degree. C. "A" is defined as total content of normal paraffin compounds having a carbon number of 20 or more.

(6) Measurement of [B/C]

Content of an individual normal paraffin compound in each base fuel was measured by gas chromatography. Content of the normal paraffin compound having the largest carbon number, and contents of the normal paraffin compounds having smaller carbon numbers are calculated consecutively, where (n) is defined as the integer when total content of normal paraffin compounds having a carbon number of (n) or more account for 3.0 wt % of total content of the normal paraffin compounds in the base fuel. Next, (content of normal paraffin compounds having a carbon number of (n+5))/(content of normal paraffin compounds having a carbon number of (n)) ratios are calculated, and the average is taken as [B/C]. The same gas chromatography as that for measurement of "A" was used.

The base fuel samples shown in Tables 1 and 2 were used to prepare the fuel oil samples shown in Tables 3 and 4, to measure CFPP levels and lubricity of the base fuels. The results are given in Tables 3 and 4. Method to determine lubricity is described later. __________________________________________________________________________ EXAMPLES 1   2   3   4   5   6   7   8   9 __________________________________________________________________________ Base fuel A   99.95 Base fuel B       99.95 Base fuel C           99.948 Base fuel D               99.95 Base fuel H                   99.97 Base fuel I                       99.97 Base fuel J                           99.97 Base fuel K                               99.968 Base fuel L                                   99.97 Dosage of FI .cndot. ECA9911 0.04 0.04 0.04 0.04 --  --  --  --  -- .cndot. PF240 --  --  --  --  0.02 0.02 0.02 0.02 0.02 Dosage of lubricity improver .cndot. PDN655 0.010 0.010 0.012 0.010 0.010 0.010 0.010 0.012 0.010 Properties of base fuel Sulfur content (wt %) 0.04 0.05 0.03 0.04 0.03 0.04 0.03 0.03 0.04 A (wt %)      2.78 3.03 2.82 3.05 1.06 0.92 1.02 3.61 3.92 [B/C]         0.092 0.089 0.089 0.054 0.354 0.154 0.248 0.086 0.100 Properties and performances of fuel oil CFPP (.degree. C.) (1) Base fuel -5  -4  -4  -3  -3  -3  -3  -3  -3 (incorporated with no FI) (2) Fuel oil  -16 -13 -14 -9  -12 -12 -12 -11 -9 (incorporated with an FI) (3) Difference in CFPP 11  9   10  6   9   9   9   8   6 [(1) - (2)] Lubricity of fuel oil Wear scar diameter (.mu.m) 416 411 418 421 410 408 415 421 416 __________________________________________________________________________ __________________________________________________________________________ COMPARATIVE EXAMPLES 1   2   3   4   5   6   7   8   9   10  11 __________________________________________________________________________ Fuel oil compositions (wt %) Base fuel A  99.99 99.96 Base fuel E          99.92 Base fuel F              99.953 Base fuel G                  99.91 Base fuel H                      99.99 99.98 Base fuel M                              99.90 Base fuel N                                  99.968 Base fuel O                                      99.973 Base fuel P                                          99.93 Dosage of FI .cndot. ECA9911 0   0.04 0   0.04 0.04 --  --  --  --  --  -- .cndot. PF240 --  --  --  --  --  0   0.02 0.02 0.02 0.02 0.02 Dosage of lubricity improver .cndot. PDN655 0.010 0   0.080 0.007 0.050 0.010 0   0.080 0.012 0.007 0.050 Properties of base fuel Sulfur content (wt %) 0.04 0.04 0.03 0.04 0.04 0.03 0.03 0.03 0.03 0.05 0.04 A (wt %)     2.78 2.78 3.80 3.45 4.46 1.06 1.06 0.90 1.57 3.35 4.72 [B/C]        0.092 0.092 0.045 0.434 0.027 0.354 0.354 0   0   0.460 0.320 Properties and performances of fuel oil CFPP (.degree. C.) (1) Base fuel (incorporated -5  -5  -2  0   -3  -3  -3  -6  -5  -2  -2 with no FI) (2) Fuel oil (incorporated -5  -15 -2  0   -4  -4  -12 -7  -6  -3  -3 with an FI) (3) Difference in CFPP 0   10  0   0   1   1   9   1   1   1   1 [(1) - (2)] Lubricity of fuel oil Wear scar diameter (.mu.m) 418 547 418 406 403 425 552 401 418 428 406 __________________________________________________________________________

Measurement of Lubricity

Lubricity was assessed by resistance of fuel oil to wear. Resistance to wear was measured as per JPI-5S-50-97 (gas oil-lubricant oil testing method). Scar diameter (.mu.m) of the wear was determined using a high frequency reciprocating rig (HFRR, produced by PCS) under the conditions shown in Table 5. Scar diameter increases as lubricity of fuel oil decreases. ______________________________________ Liquid Quantity   2 .+-. 0.20 ml Stroke            1 .+-. 0.03 mm Frequency         50 .+-. 1 Hz Liquid Temperature 40 .+-. 2.degree. C. or 60 .+-. 2.degree. C. Load              200 .+-. 1 gf Testing Time      75 .+-. 0.1 Liquid Surface Area 6 .+-. 1 cm.sup.2 ______________________________________

As shown in Table 3, diesel fuel oil exhibits a notably low CFPP of -9 to -16.degree. C., when it comprises a base fuel which contains a specific content of the component A, has a [B/C] value in a specific range, contains sulfur at 0.05 wt % or less, and is incorporated with an adequate FI and lubricity improver. Its CFPP is significantly lower than that of the base fuel by 6 to 11.degree. C. Its resistance to wear is also excellent, showing a wear scar diameter of 408 to 421 .mu.m. By contrast, the samples prepared by Comparative Examples, which do not satisfy the relationship with respect to A or [B/C], has a CFPP value high and virtually unchanged from that of the base fuel, even when incorporated with an FI and lubricity improver, as shown in Table 4. It is also found that diesel fuel oil shows insufficient CFPP or lubricity without FI or lubricity improver, even when its base fuel contains a specific content of the component A and has a [B/C] value in a specific range. It is therefore essential for a diesel fuel oil composition to comprise a base fuel which contains a specific content of the component A, has a [B/C] value in a specific range, contains sulfur at 0.05 wt % or less, and is incorporated with an adequate FI and lubricity improver, in order to exhibit good CFPP and lubricity.

As described above in detail and concretely, the present invention provides a diesel fuel oil composition which exhibits good CFPP and lubricity by incorporating a base fuel satisfying the relationships 0<A.ltoreq.4.00 (wt %) and 0.04.ltoreq.[B/C].ltoreq.0.40 and containing sulfur at 0.05 wt % or less with an adequate FI and lubricity improver.

## Claims

1. A diesel fuel oil composition comprising a base fuel which satisfies the following relationships (1) and (2), contains sulfur at 0.05 wt % or less, and is incorporated with 0.01 to 0.10 wt % of a flow improver and 0.002 to 0.1 wt % of a lubricity improver (based on active component): wherein, A is content, based on all normal paraffin compounds present in the base fuel, of normal paraffin compounds having a carbon number of 20 or more (wt %), and wherein, B is content of normal paraffin compounds having a carbon number of n+5 (wt %), C is content of normal paraffin compounds having a carbon number of n (wt %); [B/C] is average B/C ratio, and (n) is an integer when total content of normal paraffin compounds having a carbon number of (n) or more account for 3.0 wt % of total content of the normal paraffin compounds in the base fuel.

2. The diesel fuel oil composition of claim 1 wherein the [B/C] ratio is 0.07 to 0.20.

3. The diesel fuel oil composition of claim 1 wherein the flow improver content, based on active component, is 0.03 to 0.07 wt %.

4. The diesel fuel oil composition of claim 1 wherein the lubricity improver content, based on active component, is 0.005 to 0.05 wt %.

5. The diesel fuel oil composition of claim 1, 2, 3 or 4 wherein the flow improver is an ethylene glycol ester-based compound or ethylene-vinyl acetate-based copolymer.

6. The diesel fuel oil composition of claim 1, 2, 3 or 4 wherein the lubricity improver is an ester-based compound.