Diesel fuel oil composition

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.

DETAILED DESCRIPTION OF THE PRESENT INVENTION 
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. 
DESCRIPTION OF THE INVENTION 
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&lt;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&lt;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: 
(1) the diesel fuel oil composition, wherein a [B/C] ratio is 0.07 to 0.20, 
(2) the diesel fuel oil composition, wherein active ingredient of the FI is 
ethylene glycol ester-based compound, or ethylene-vinyl acetate-based 
copolymer, 
(3) the diesel fuel oil composition of (1), wherein the active ingredient 
of the FI is ethylene glycol ester-based compound, or ethylene-vinyl 
acetate-based copolymer, 
(4) the diesel fuel oil composition, wherein content of the active 
component for the FI is 0.03 to 0.07 wt %, 
(5) the diesel fuel oil composition of one of (1) to (3), wherein content 
of the active component for the FI is 0.03 to 0.07 wt %, 
(6) the diesel fuel oil composition, wherein the active component for the 
lubricity improver is an ester-based compound, 
(7) the diesel fuel oil composition of one of (1) to (5), wherein the 
active component for the lubricity improver is an ester-based compound, 
(8) the diesel fuel oil composition, wherein content of the active 
component for the lubricity improver is 0.005 to 0.05 wt %, and 
(9) diesel fuel oil composition of one of (1) to (7), wherein content of 
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&lt;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&lt;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&lt;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. 
TABLE 1 
__________________________________________________________________________ 
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 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
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.

EXAMPLES AND COMATIVE EXAMPLES 
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. 
TABLE 3 
__________________________________________________________________________ 
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 
__________________________________________________________________________ 
TABLE 4 
__________________________________________________________________________ 
COMATIVE 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. 
TABLE 5 
______________________________________ 
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&lt;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.