Note: Descriptions are shown in the official language in which they were submitted.
CA 02483200 2010-05-05
Diesel fuel compositions
This invention relates to diesel fuel compositions,
their preparation and their use in diesel engines, and to
the use of certain types of fuel in diesel fuel
compositions.
Typical diesel fuels comprise liquid hydrocarbon
middle distillate fuel oils having boiling points from
about 150 to 400 C. Examples of such fuels include the
reaction products of Fischer-Tropsch methane condensation
processes, for example the process known as Shell Middle
Distillate Synthesis (van der Burgt et al, "The Shell
Middle Distillate Synthesis Process", paper delivered at
the 5th Synfuels Worldwide Symposium, Washington DC,
November 1985; see also the November 1989 publication of
the same title from Shell International Petroleum Company
- Ltd, London, UK). These Fischer-Tropsch derived gas oils
are low in undesirable fuel components such as sulphur,
nitrogen and aromatics and tend to lead to lower vehicle
emissions. They are typically blended with other diesel
base fuels, for instance petroleum derived gas oils, at
concentrations of for instance from 10 to 30% w/w, to
modify the base fuel properties.
. Compression-ignition (diesel) engines running on
conventional diesel fuels can suffer from the build up of
combustion related deposits in their fuel injection
systems, in particular in the injector nozzles. This
injector fouling can impair engine performance. To reduce
fouling, a detergent-containing additive may be included in
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the fuel, or the proportion of heavier components in the
fuel may be adjusted so as to lower its endpoint.
It has now been found that Fischer-Tropsch derived
fuels can themselves contribute to a reduction in, and/or
reversal of, injector fouling. A fuel composition
containing such components can therefore be used to help
maintain and/or improve engine cleanliness.
According to a first aspect of the present invention
there is provided the use of a Fischer-Tropsch derived gas
oil in.a diesel fuel composition, for the purpose of
reducing subsequent combustion related deposits in a diesel
engine into which the fuel composition is introduced.
The Fischer-Tropsch derived gas oil may instead or in
addition be used for the purpose of removing previously
incurred combustion related deposits (ie, to "clean up" the
engine).
In the context of the present invention, "reducing"
includes complete prevention and "removing" embraces both
complete and partial removal. "Use" of the Fischer-Tropsch
derived gas oil in a fuel composition means incorporating
the fuel into the composition, typically as a blend (ie, a
physical mixture) with one or more other fuels,
conveniently before the composition is introduced into the
engine.
The Fischer-Tropsch derived gas oil should be suitable
for use as a diesel fuel. Its components (or the majority,
for instance 95% w/w or greater, thereof) should therefore
have boiling points within the typical diesel fuel ("gas
oil") range, ie, from about 150 to 400 C or from 170 to
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370 C. It will suitably have a 90% w/w distillation
temperature of from 300 to 370 C.
By "Fischer-Tropsch derived" is meant that the fuel
is, or derives from, a synthesis product of a Fischer-
Tropsch condensation process. The Fischer-Tropsch reaction
converts carbon monoxide and hydrogen into longer chain,
usually paraffinic, hydrocarbons:
n(CO + 2H2) = (-CH2-)n + nH2O + heat,
in the presence of an appropriate catalyst and typically at
elevated temperatures (eg, 125 to 300 C, preferably 175 to
250 C) and/or pressures (eg, 5 to 100 bar, preferably 12 to
50 bar). Hydrogen:carbon monoxide ratios other than 2:1
may be employed if desired.
A gas oil product may be obtained directly from this
reaction, or indirectly for instance by fractionation of a
Fischer-Tropsch synthesis product or from a hydrotreated
Fischer-Tropsch synthesis product. Hydrotreatment can
involve hydrocracking to adjust the boiling range (see, eg,
GB-B-2077289 and EP-A-0147873) and/or hydroisomerisation
which can improve cold flow properties by increasing the
proportion of branched paraffins. EP-A-0583836 describes a
two-step hydrotreatment process in which a Fischer-Tropsch
synthesis product is firstly subjected to hydroconversion
under conditions such that it undergoes substantially no
isomerisation or hydrocracking (this hydrogenates the
olefinic and oxygen-containing components), and then at
least part of the resultant product is hydroconverted under
conditions such that hydrocracking and isomerisation occur
to yield a substantially paraffinic hydrocarbon fuel. The
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desired gas oil fraction(s) may subsequently be isolated
for instance by distillation.
Other post-synthesis treatments, such as
polymerisation, alkylation, distillation, cracking-
decarboxylation, isomerisation and hydroreforming, may be
employed to modify the properties of Fischer-Tropsch
condensation products, as described for instance in
US-A-4125566 and US-A-4478955.
Typical catalysts for the Fischer-Tropsch synthesis of
paraffinic hydrocarbons comprise, as the catalytically
active component, a metal from Group VIII of the periodic
table, 'in particular ruthenium, iron, cobalt or nickel.
Suitable such catalysts are described for instance in
EP-A-0583836-(pages 3 and 4).
An example of a Fischer-Tropsch based process is the
SMDS (Shell Middle Distillate Synthesis) described in "The
Shell Middle Distillate Synthesis Process", van der Burgt
et al (supra). This process produces middle distillate
range products by conversion of a natural gas (primarily
methane) derived synthesis gas into a heavy long-chain
hydrocarbon (paraffin) wax which can then be hydroconverted
and fractionated to produce liquid transport fuels such as
the gas oils useable in diesel fuel compositions. A
version of the SMDS process, utilising a fixed-bed reactor
for the catalytic conversion step, is currently in use in
Bintulu, Malaysia and its products have been used in
petroleum derived gas oil blends in commercially available
automotive fuels.
Gas oils prepared by the SMDS process are commercially
available for instance from the Royal Dutch/Shell Group of
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Companies. Further examples of Fischer-Tropsch derived gas
oils are described in EP-A-0583836, EP-A-1101813,
wO-A-97/14768, WO-A-97/14769, WO-A-00/20534, WO-A-00/20535,
WO-A-00/11116, WO-A-00/11117, WO-A-01/83406, WO-A-01/83641,
WO-A-01/83647, WO-A-01/83648 and US-A-6204426.
Suitably, in accordance with the present invention,
the Fischer-Tropsch derived gas oil will consist of at'
least 70% w/w, preferably at least 80% w/w, more preferably
at least 90% w/w, most preferably at least 95% w/w, of
paraffinic components, preferably iso- and linear
paraffins. The weight ratio of iso-paraffins to normal
paraffins will suitably be greater than 0.3 and may be up
to 12; suitably it is from 2 to 6. The actual value for
this ratio will be determined, in part, by the
hydroconversion process used to prepare the gas oil from
the Fischer-Tropsch synthesis product. Some cyclic
paraffins may also be present.
By virtue of the Fischer-Tropsch process, a Fischer-
Tropsch derived gas oil has essentially no, or undetectable
levels of, sulphur and nitrogen. Compounds containing
these heteroatoms tend to act as poisons for Fischer-
Tropsch catalysts and are therefore removed from the
synthesis gas feed. Further, the process as usually
operated produces no or virtually no aromatic components..
The aromatics content of a Fischer-Tropsch gas oil, as
determined by ASTM D 4629, will typically be below 1% w/w,
preferably below 0.5% w/w and more preferably below 0.1%
w/w.
The Fischer-Tropsch derived gas oil used in the
present invention will typically have a density from 0.76
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to 0.79 g/cm3 at 15 C; a cetane number (ASTM D613) greater
than 70, suitably from 74 to 85; a kinematic viscosity from
2.0 to 4.5, preferably from 2.5 to 4.0, more preferably
from 2.9 to 3.7, centistokes at 40 C; and a sulphur content
of 5 ppmw (parts per million by weight) or less.
Preferably it is a product prepared by a Fischer-
Tropsch methane condensation reaction using a
hydrogen/carbon monoxide ratio of less than 2.5, preferably
less than 1.75, more preferably from 0.4 to 1.5, and
ideally using a cobalt containing catalyst. Suitably it
will have been obtained from a hydrocracked Fischer-Tropsch
synthesis product (for instance as described in
GB-B-2077289 and/or EP-A-0147873), or more preferably a
product from a two-stage hydroconversion process such as
that described in EP-A-0583836 (see above). In the latter
case, preferred features of the hydroconversion process may
be as disclosed at pages 4 to 6, and in the examples, of
EP-A-0583836.
The level of combustion related deposits in a diesel
engine maybe measured in its fuel injection system, with
reference to the degree of fouling of the injector nozzles.
Degree of nozzle fouling may be assessed in a number of
ways, for instance visually, by measuring the mass of
deposits in a fouled nozzle or by measuring the fluid flow
(for instance, fuel flow or more preferably air flow)
properties of the fouled nozzle relative to those of the
clean nozzle.
An appropriate test might for example determine the
degree of nozzle fouling (conveniently in the form of a
percentage injector fouling index) under steady state
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conditions in a suitable diesel engine, for instance based
on the change in air flow rate through one or more of the
nozzles as a result of using the fuel composition.
Conveniently the results are averaged over all of the
injector nozzles of the engine. A suitable test protocol,
using an indirect injection diesel engine, is described
below in connection with the experimental examples. The
CEC standard test method F-23-T-00, which again involves
injector nozzle air flow measurements, may also be used to
assess engine fouling.
The invention may be applicable where the fuel
composition is used or intended to be used in a direct
injection diesel engine, for example of the rotary pump,
in-line pump, unit pump, electronic unit injector or common
rail type, or in an indirect injection diesel engine. The
fuel composition may be suitable for use in heavy and/or
light duty diesel engines.
The amount of the Fischer-Tropsch derived gas oil used
may be from 0.5 to 100% w/w of the overall diesel fuel
composition, suitably from 1 to 60% w/w, preferably from 5
to 50% w/w, more preferably from 10 to 30% w/w. It may be
desirable for the composition to contain 8% w/w or greater,
more preferably 10% w/w or greater, most preferably 20% w/w
or greater, of the Fischer-Tropsch gas oil.
Other fuel components of the composition may be diesel
fuels of conventional type, typically comprising liquid
hydrocarbon middle distillate fuel oils, for instance
petroleum derived gas oils. Such fuel components will
typically have boiling points within the usual diesel range
of 150 to 400 C, depending on grade and use.
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The diesel fuel composition may, in order to achieve a
reduction and/or removal of engine deposits, consist
essentially of the Fischer-Tropsch derived gas oil - in
other words it may contain a major proportion (by which is
meant preferably 99% w/w or more of the fuel composition,
more preferably 99.5% w/w or more, most preferably
99.8% w/w or more, even up to 100% w/w) of the Fischer-
Tropsch derived gas oil, optionally with a minor proportion
of one or more diesel fuel additives such as are known in
the art but with no other diesel fuels.
The overall fuel composition preferably has a low or
ultra low sulphur content, for instance at most 1000 ppmw
(parts per million by weight), preferably no more than 500
ppmw, most preferably no more than 100 or 50 or even 10
ppmw. It preferably has a cetane number (ASTM D613) from
40 to 85, more preferably from 45 to 75. Its'density will
typically be from 0.75 to 0.9 g/cm3, preferably from 0.8 to
0.85 g/cm3, at 15 C.
The Fischer-Tropsch derived gas oil may in particular
be used to enhance the performance of a fuel or fuel blend
which would otherwise cause relatively high levels of
combustion related deposits, for instance a fuel having a
relatively high endpoint and/or containing relatively high
levels of aromatic components, and/or of a fuel or blend
25, which causes, after three hours' engine running, a
reduction in the achievable air flow rate through one or
more of the engine nozzles of greater than 35 or 40 or 45%
for instance measured using the test protocol described
below.
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Although in general the diesel fuel composition may or
may not contain additives, it is preferred that it includes
a detergent, since this may enhance the cleaning effect of
the Fischer-Tropsch derived gas oil. The first aspect of
the present invention may therefore involve the use of both
a Fischer-Tropsch derived gas oil and a detergent, in a
diesel fuel composition, for the purpose of reducing
subsequent combustion related deposits in a diesel engine
into which the fuel composition is introduced and/or for
the purpose of removing previously incurred combustion
related deposits.
By "detergent" is meant an agent (suitably a
surfactant) which can act to remove, and/or to prevent the
build up of, combustion related deposits within the engine,
in particular in the fuel injection system such as in the
injector nozzles. Such materials are sometimes referred to
as dispersant additives.
The Fischer-Tropsch derived gas oil, or alternatively
the combination of the Fischer-Tropsch derived gas oil and
the detergent, is preferably included in the fuel
composition at a concentration sufficient to achieve a
reduction in engine fouling (measured for instance as
outlined above) of at least 5%, preferably at least 8%,'
more preferably at least 10%, most preferably at least 20%,
as compared to that which results from using (under the
same or'comparable conditions) the same fuel composition
but without the Fischer-Tropsch gas oil. Alternatively the
reduction may be relative to the degree of engine fouling
which results from the use (under the same or comparable
conditions) of a fuel composition containing no, or less
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than 1% w/w, Fischer-Tropsch derived fuels and no, or less
than 50 or even 20 ppmw of, detergent.
.More preferably, the Fischer-Tropsch derived gas oil,
or alternatively the combination of the Fischer-Tropsch
derived gas oil and the detergent, is included at a
concentration sufficient to remove, at least partially,
combustion related deposits which have built up in the
engine's fuel injection system, in particular in the
injector nozzles, during a previous period of running using
another diesel fuel (typically a fuel containing no, or
less than 1% w/w, Fischer-Tropsch derived fuels and no, or
less than 50 or even 20 ppmw of, detergent), when the
engine is subsequently run on the Fischer-Tropsch fuel
containing composition. This concentration is preferably
sufficient to remove at least 5% of the previously incurred
injector deposits (measured for instance as described
above), more preferably at least 10%, most preferably at
least 15 or 20 or 25 or 30%.
The removal' of combustion related deposits may be
achieved by running the engine on the Fischer-Tropsch fuel
containing composition for instance for the same period of
time as that during which the deposits accumulated,'or more
preferably for 75%, yet more preferably 50% or even 40% or
30%, of the period of deposit accumulation, conveniently
under comparable conditions. Ideally at least partial
removal of combustion related deposits is achieved by
running the engine on the Fischer-Tropsch fuel containing
composition for five hours or less, preferably for three
hours or less, more preferably for two hours or less.
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Where the fuel composition includes a detergent,
preferred concentrations lie in the range 20 to 500 ppmw
active matter detergent based on the overall fuel
composition, more preferably 40 to 500 ppmw, most
preferably 40 to 300 ppmw or 100 to 300 ppmw or 150 to 300
ppmw. In the case of most commercially available detergent
containing diesel fuel additives, this may mean that the
additive is incorporated at levels higher than the standard
recommended single treat rate, for example between 1.2 and
3 times, preferably between 1.,5 and 2.5 times, such as
about twice the standard single treat rate. 'Lower
detergent levels (for example, corresponding to, between 0.5
and 1.2 times, preferably the same as, the standard single
treat rate) may however be used to help reduce or prevent
further engine fouling and/or power loss.
Examples of detergents suitable for use in accordance
with the present invention include polyolefin substituted
succinimides or succinamides of polyamines, for instance
polyisobutylene succinimides or polyisobutylene amine
succinamides, aliphatic amines, Mannich bases or amines and
polyolefin (eg,polyisobutylene) maleic anhydrides.
Succinimide dispersant additives are described for example
in GB-A-960493, EP-A-0147240, EP-A-0482253, EP-A-0613938,
EP-A-0557561 and WO-A-98/42808. Particularly preferred are
polyolefin substituted succinimides such as polyisobutylene
succinimides.
Detergent-containing diesel fuel additives are known
and commercially available, for instance from Infineum (eg,
F7661 and F7685) and Octel (eg, OMA 4130D).
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The fuel composition may contain other components in
addition to the Fischer-Tropsch derived fuel and if
applicable the detergent. Typically such components will
be incorporated in fuel additives, for instance in
combination with a detergent. Examples are lubricity
enhancers such as EC 832 and PARADYNETM (ex Infineum),
HITECTM E580 (ex Ethyl Corporation) and VEKTRONTM 6010 (ex
Infineum) and amide-based additives such as those available
from the Lubrizol Chemical Company, for instance LZ 539 C;
dehazers, eg, alkoxylated phenol formaldehyde polymers such
as those commercially available as NALCOTM EC5462A (formerly
7D07) (ex Nalco), and TOLADTM 2683 (ex Petrolite); anti-
foaming agents (eg, the polyether-modified polysiloxanes
commercially available as TEGOPRENTM 5851 and Q 25907 (ex
Dow Corning), SAGTM TP-325 (ex OSi) and RHODORSILTM (ex Rhone
Poulenc)); ignition improvers (cetane improvers) (eg, 2-
ethylhexyl nitrate (EHN), cyclohexyl nitrate, di-tert-butyl
peroxide and those disclosed in US-4208190 at column 2,
line 27 to column 3, line 21); anti-rust agents (eg, that
sold commercially by Rhein Chemie, Mannheim, Germany as
"RC 4801", a propane-1, 2-diol semi-ester of tetrapropenyl
succinic acid, or polyhydric alcohol esters of a succinic
acid derivative, the succinic acid derivative having on at
least one of its alpha-carbon atoms an unsubstituted or
substituted aliphatic hydrocarbon group containing from 20
to 500 carbon, atoms, eg, the pentaerythritol diester of
polyisobutylene-substituted succinic acid); corrosion
inhibitors; reodorants; anti-wear additives; anti-oxidants
(eg, phenolics such as 2,6-di-tert-butylphenol, or
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phenylenediamines such as N,N'-di-sec-butyl-p-
phenylenediamine); and metal deactivators.
Unless otherwise stated, the (active matter)
concentration of each such additional component in the
overall fuel composition is preferably up to 1% w/w, more
preferably in the range from 5 to 1000 ppmw, advantageously
from 75 to 300 ppmw, such as from 95 to 150 ppmw.
It is particularly preferred that a lubricity enhancer
be included in the fuel composition, especially when it has
a low (eg, 500 ppmw or less) sulphur content. The
lubricity enhancer is. conveniently present at a
concentration from 50 to 1000 ppmw, preferably from 100 to
1000 ppmw, based on the overall fuel composition.
The (active matter) concentration of any dehazer in
the fuel composition will preferably be in the-range from 1
to 20 ppmw, more preferably from 1 to 15 ppmw, still more
preferably from 1 to 10 ppmw and advantageously from 1 to 5
ppmw. The (active matter) concentration of any ignition
improver present will preferably be 600 ppmw or less, more
preferably 500 ppmw or less, conveniently from 300 to 500
ppmw.
A second aspect of the present invention provides a
method of operating a diesel engine, and/or a vehicle which
is driven by a diesel engine, which method involves
introducing into a combustion chamber of the engine a
diesel fuel composition incorporating a Fischer-Tropsch
derived gas oil, and optionally-also a detergent, for the
purpose of reducing subsequent combustion related deposits
in the engine and/or removing previously incurred
combustion related deposits in the engine.
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Preferred features of the second aspect of the
invention, for instance regarding the engine type, the
nature of the diesel fuel composition, the nature and
concentration of the Fischer-Tropsch derived gas oil and if
present the detergent, as well as of other components of
the fuel composition, and the ways in which engine fouling
may be assessed, may all be as described above in
connection with the first aspect.
According to a third aspect of the invention, there is
provided a diesel fuel composition which includes a major
proportion of a fuel or fuel blend for an internal
combustion engine of the compression ignition type, wherein
the fuel or fuel blend comprises at least 30% w/w of a
Fischer-Tropsch derived gas oil, preferably at least 40%
w/w, more preferably at least 50% w/w, most preferably at
least 60% w/w. The fuel or.fuel blend may comprise up to
100% w/w of the Fischer-Tropsch derived gas oil, preferably
up to 95% w/w, more preferably up to 90% w/w, most
preferably up to 80% w/w or 70% w/w.
This fuel composition preferably also contains a minor
proportion of a detergent-containing additive. By "minor
proportion" is meant preferably less than 1% w/w of the
fuel composition, more preferably less than 0.5% w/w (5000
ppmw) and most preferably less than 0.2% w/w (2000 ppmw);
references to "major proportion" may be construed
accordingly.
As described above, in accordance with the present
invention a fuel or fuel blend may be additivated
(additive-containing) or unadditivated (additive-free). If
additivated, it will contain a minor proportion of one or
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more additives, in particular a detergent containing
additive. Such additives may be added at various stages
during the production of the fuel composition; those added
at the refinery for example might be selected from anti-
static agents, pipeline drag reducers, flow improvers (eg,
ethylene/vinyl acetate copolymers or acrylate/maleic
anhydride copolymers) and wax anti-settling agents (eg,
those commercially available under the Trade Marks
"PARAFLOW" (eg, PARAFLOWTM 450, ex Infineum), "OCTEL" (eg,
OCTELTM W 5000, ex Octel) and "DODIFLOW" (eg, DODIFLOWTM v
3958, ex Hoechst).
In accordance with a fourth aspect of the invention,
there is provided a method of operating a diesel engine,
and/or a vehicle which is driven by a diesel engine, which
method involves introducing into a combustion chamber of
the engine a diesel fuel composition according to the third
aspect.
A fifth aspect of the invention provides a process for
the preparation of a diesel fuel composition, such as a
composition according to the third aspect, which process
involves blending a Fischer-Tropsch derived gas oil with a
non Fischer-Tropsch derived diesel fuel, optionally
together with a detergent. Again the blending is ideally
carried out with the aim of reducing subsequent combustion
related deposits in a diesel engine into which the fuel
composition is introduced and/or for the purpose of
removing previously incurred combustion related deposits in
the engine.
The discovery that Fischer-Tropsch gas oils can at
least partly remove existing engine deposits may be put to
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use in the "clean-up" of a fouled engine. Thus, according
to a sixth aspect of the present invention, there is
provided the use of a Fischer-Tropsch derived gas oil,
and/or of a fuel composition containing a Fischet-Tropsch
derived gas oil, to clean (ie, to remove combustion related
deposits from)- the fuel injection system of a diesel
engine. "Use" in this way means running the engine, or a
part thereof such as its fuel injection system, on the gas
oil or fuel composition for a period of time sufficient to
effect at least partial removal of the combustion related
deposits. It need not necessarily involve driving the
vehicle.
A Fischer-Tropsch derived gas oil, or a fuel
composition containing such a gas oil, may therefore in
accordance with the invention be packaged together with
instructions for its use to clean a diesel engine in the
manner described above.
The sixth aspect of the invention also encompasses a
method of cleaning the fuel injection system of a diesel
engine, by introducing into a combustion chamber of the
engine a Fischer-Tropsch derived gas. oil and/or a fuel
composition containing a Fischer-Tropsch derived gas oil.
Preferred features of the third to the sixth aspects
of the invention, for instance regarding the nature and
concentrations of the Fischer-Tropsch derived gas oil, any
detergent. present and any other fuel components and
additives present, may be as described above in connection
with the first and second aspects of the invention.
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According to a seventh aspect, the present invention
provides a method for assessing the performance of a
candidate diesel fuel composition, comprising the steps of:
1) measuring the level of combustion related deposits in
a diesel engine running on a "standard" diesel fuel
composition, which "standard" fuel composition contains no,
or less than 10. w/w of, Fischer-Tropsch derived gas oils;
2) subjecting the engine to a first test cycle running on
the standard fuel composition;
3) measuring the level of combustion related deposits in
the engine after the first test cycle;
4) calculating the increase in deposits during the first
test cycle;
5) subjecting the engine to a second test cycle running
on the candidate diesel fuel composition;
6) measuring the level of combustion related deposits in
the engine after the second test cycle;
7) calculating the increase in deposits (if any) during
the second test cycle; and
8) if applicable, calculating the extent of removal of
deposits during the second test cycle.
The "standard" fuel composition suitably contains no,
or less than 50 or even 20 ppmw, active matter detergent.
It is suitably a low or ultra low sulphur diesel fuel, as
described above, and is preferably unadditivated.
The level of combustion related deposits may be
measured by assessing the degree of fouling of the injector
nozzles in the fuel injection system of the engine, as
described above.
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The test cycles involve running-the engine on the
relevant fuel composition for a given period of time and/or
for a given number of miles. The tests may be conducted on
the engine alone or driving a vehicle - in the latter case
they may be conducted under simulated driving conditions
(such as using a chassis dynamometer) or involve regular
road driving (preferably under urban as opposed to motorway
conditions). The engine running and/or driving conditions
should be the same or comparable for both the first and the
second test cycles.
By way of example, the duration of the first test
cycle should be sufficient to cause a significant, and at
least detectable, build up of combustion related deposits
compared to that measured in step 1 of the test. A typical
first test cycle might last from 1 to 5 hours, preferably 2
hours or more, more preferably 3 hours or more.
An appropriate duration for the second test cycle is
typically from 10 to 100%, preferably from 50 to 100%, most
suitably 100%, of that of the first test cycle. It may in
cases be 80% or -75% or even 50% or less of the duration of
the first test cycle. For assessing reductions in (as
opposed to removal of) combustion related deposits, it may
be up to 120% or 150% or even 200% of the duration of the
first test cycle.
The engine used for.the test may for instance be an
indirect injection diesel engine, such as a VolkswagenT"'
PassatTM engine, for instance the PassatTM AAZ 1.9 TD engine.
The.test may be conducted on only a part of the engine (eg,
the fuel injection system) or on a simulated engine or
engine part.
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The assessment method of the invention is particularly
applicable to a candidate diesel fuel composition which
incorporates a Fischer-Tropsch derived gas oil, more
particularly to one which also incorporates a detergent.
The method may therefore be used to identify and/or
evaluate fuel compositions according to the third aspect of
the invention.
The method may also be used to assess the performance
of a diesel engine, and/or to assess the performance of a
fuel injection system for use in a diesel engine, and/or to
assess the performance of a vehicle driven by a diesel
engine.
An eighth aspect of the present invention provides a
diesel fuel composition which, when used as the candidate
fuel composition in the assessment method of the seventh
aspect, leads to removal of at least 5%, preferably at
least 10% or 15% or 20% or 25% or 30%, of the combustion
related deposits accumulated in the engine prior to step 5
of the test, when the duration of the second test cycle is
the same as or less than, more preferably 80% or 75% or
even 50% or less of, the duration of the first test cycle,
and the duration of the first test cycle is preferably at
least 2 hours, more preferably 3 hours or more.
Such a fuel composition ideally contains, in
accordance with the present invention, a Fischer-Tropsch
derived gas oil, preferably together with a detergent.
The present invention will be further understood from
the following examples, which illustrate the effects of
using Fischer-Tropsch derived gas oils in diesel fuel
compositions, on the degree of fuel injector fouling.
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General
The two fuels used in the tests were a .petroleum
derived low sulphur diesel fuel Fl and a Fischer-Tropsch
(SMDS) derived gas oil F2, both alone and in blends
containing varying proportions of the two. Their
properties are shown in Table A.
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Table A
Fuel property Test method F1 F2
Density @ 15 C (g/cm3) IP 365/ASTM 0.8403 0.7842
D4052
Distillation IP 123/ASTM D86
IBP ( C) 180.0 212.5
10% 220.0 248
20% 237.0 264
30% 251.5 277.5
40% 264.0 290.5
50% 276.0 300.5
60% 288.0 309
70% 301.0 316
80% 316.5 327
90% 338.0 332
95% 355.0 339
FBP 364.5 344
Cetane number ASTM D613 52.9, 54.0
Jul '00
Cetane index IP 364/84 52.3 78.0
Cetane index IP 380/94 52.7 93.7
Kinematic viscosity @ IP 71/ASTM D445 3.020 3.467
40 C (centistokes)
Cloud point ( C) IP 219 -9 1
Cold filter plugging IP 309 -26 -2
point ( C)
Sulphur (WDXRF) (ppmw) ASTM D2622 280 <5
Carbon (% w/w) 85.1
Hydrogen (% w/w) 15.1
Calorific value (cal
(IT) /g)
Gross 11170
Net 10405
HPLC aromatics (% w/w) IP 391 (mod)
Mono 22.4 <0.1
Di 3.9 <0.1
Tri 0.3 <0.1
Total 26.6 <0.1
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The gas oil F2 had been obtained from a Fischer-
Tropsch (SMDS) synthesis product via a two-stage
hydroconversion process analogous to that described in
EP-A-0583836.
In the Example 3 tests, a commercially available
detergent-containing additive A was added to the fuels and
fuel blends. Additive A is a detergency additive available
from Infineum which passes the Cummins L10 heavy duty
detergency test and contains inter alia a detergent, a
lubricity additive, an anti-foam agent and a corrosion
inhibitor. It was. added at a concentration of 842 ppmw
(double its standard treat rate); this resulted in an
active matter detergent concentration of greater than 100
ppmw in the additivated fuel/blend.
The performance of the fuels and blends in an indirect
'injection (IDI) diesel engine was tested according to the
following protocol, which assesses the degree of injector
nozzle fouling under steady state conditions.
Injector fouling test protocol
The engine used was a VolkswagenTM PassatTM AAZ 1.9 TD
indirect injection diesel engine having the following
specification:
Bore x stroke: 79.5 x 95.5 mm
No. of cylinders: 4 in line
Swept volume: 1.896 litres
Maximum rated power: 75 kW @ 4200 r/min
Maximum rated torque: 140 Nm @ 2400 - 3400 r/min
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Engine features: turbocharger and EGR with
electronic control;
oxidation catalyst
EGR system: blanked off at turbo outlet.
Its fuel injection equipment (BoschTM) had the
following specification:
Injector body: 2FH KCA 275 77
Nozzle type: DNO SD 308
Nozzle needle lift: 0.81 mm (+/- 0.02)
Nozzle pre lift: 0.010 mm (+/- 0.001)
Nozzle opening pressure (1): 150 bar (+8/-0)
Nozzle opening pressure (2): 235 bar (+/10/-0)
Nozzle nut torque: 70 Nm
Leakback test 100 bar down to 70 bar applied
pressure in 10-35 s (new nozzles)
Injection pump: VE No. 0 460 494 314.
The injector blanking plugs used were also BoschTM,
133-9802. High pressure injection pipes were used between
the injection pump and the injectors.
Prior to the start of each test, the four clean
nozzles were air flowed at a needle lift of 0.05 mm, and at
0.1 to 0.8 mm in steps of 0.1 mm, and the results recorded.
The fuel filter was also changed prior to each test, and
the fuel supply bled and the systems returned with 9 litres
of the test fuel or blend.
In order to limit flow variations between tests, steps
were taken to ensure that each nozzle needle remained in
its own nozzle and that the nozzle bodies and needles were
aligned in the same way for each test.
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Each test began with a 20 minute engine warm up cycle,
using the same injectors as for the subsequent deposit
accumulation stage. During the warm up the engine speed
was 1500 r/min (+/- 25 r/min) and the applied torque 25 Nm
(+/- 2.5 Nm).
Once oil and water temperatures had reached 90 C the
engine ramped for 15 seconds to the deposit accumulation
stage, for which the conditions were as follows:
Engine speed: 2000 r/min (+/- 20 r/min)
Torque: 90 Nm (+/- 1.25 Nm)
Duration: 3 hours (+/- 3 minutes)
Oil temp (into cooler): 90 C (+/- 4 C)
Coolant temp (out of engine): 90 C (+/- 4 C)
Fuel pressure to injection pump: 0.35 bar (gauge) (+/- 0.05
bar)
Nominal fuel flow: 5.1 kg/h (85 g/min)
Nominal fuel supplied: 35 litres.
The engine was allowed to stabilise for 5-7 minutes at
these test conditions. A series of manual readings was
taken, including a Bosch smoke measurement. After reaching
test conditions but before starting the test, the engine
was returned to idle and the blow by measured. Test
conditions were then re-established.
The parameters listed in Table B below were recorded
throughout the test.
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Table B
Parameter Nominal end of test value
Engine speed 2000 r/min
Engine torque 90 Nm
Duration 3 hrs
Water outlet temperature 90 C
Oil inlet temperature 90 C
Fuel flow 85-88 g/min
Fuel pressure 0.4 bar
Fuel temperature 30-32 C
Ambient air tempera-ture 25-30 C
Air filter temperature 23-27 C
Inlet manifold temperature 84-88 C
Inlet manifold pressure 1480-1510 mbar
Exhaust temperature (before catalyst) 325-340 C
Exhaust back pressure 1770-1800 mbar
On completion of each test, the injectors were removed
taking care not to disturb or contaminate the deposits on
the nozzle faces. They were dismantled and the nozzles
removed. The nozzle body and needle were dipped separately
in clean n-heptane or another suitable solvent to remove
excess fuel, taking care not to disturb the deposits, and
then allowed to drain prior to drying in an oven at 50 C'
.for a minimum of 1 hour.
The dried nozzles were allowed to cool to ambient
temperature for a minimum of 1 hour. Their air flow was
then measured at needle lifts of 0.05 mm, and at 0.1 to
0.8 mm in steps of 0.1 mm, and the results recorded.
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In order to ensure consistency between nozzle flows a
reference nozzle was also flowed at lifts of 0.1, 0.2 and
0.3 mm before flowing the test nozzles clean and dirty.
The fouling level for each test was assessed by
calculating a "fouling index" from the air flow data. For
each nozzle, fouling numbers Fn were calculated using the
flow rates measured at needle lifts of 0.1, 0.2 and 0.3 mm,
with the nozzles clean and fouled:
Fn = flow clean - flow fouled x 100 %
flow clean
An average fouling number was then calculated for each
nozzle from its three Fn values. The mean fouling index
for the test was the average (mean) of the fouling numbers
Fn from all four nozzles.
Example 1
This example demonstrates a reduction in engine
fouling due to the use of a Fischer-Tropsch gas oil in a
petroleum derived diesel fuel composition.
Using the above described injector fouling test,
petroleum derived fuel F1 was compared with the Fischer-
Tropsch derived F2 as well as with blends containing the
two fuels in a range of proportions. The results are shown
in Table 1.
Table 1
Experiment Proportion of fuel F2 (-Sr Mean fouling index
no. w/w) (%)
1.1 0 42.4
(ie, fuel F1 alone)
1.2 10 38.3
1.3 50 33.2
1.4 70 31.5
1.5 100 19.2
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These data establish a clear trend for reduced fouling
with increasing levels of the Fischer-Tropsch gas oil. The
gas oil alone leads to markedly lower engine deposits
compared to the petroleum derived fuel alone. However even
at a level of only 10% w/w, the blending of the Fischer-
Tropsch oil with fuel F1 is associated with a significant
reduction in fouling.
Example 2
This example demonstrates that a Fischer-Tropsch
derived fuel may be used to "clean up" fouled injectors,
ie, to remove deposits which have built up through use of
another fuel.
Following experiment 1.1, in which fuel F1 alone
resulted in a mean fouling index of 42.4%, the same
injectors were subjected to further air flow measurements
to confirm the .nozzle condition (this re-flow yielded a
mean fouling index of 39.6%) and then re-tested using the
Fischer-Tropsch fuel F2 alone.
Surprisingly, the mean fouling index after the re-test
had reduced to 28.5%, indicating not only a reduction in
fouling levels using fuel F2 as opposed to. F1, but also a
significant degree of clean-up of previously accumulated
engine deposits during use of F2.
Example 3
This demonstrates the cumulative benefits of using a
Fischer-Tropsch derived diesel fuel and a detergent
containing additive.
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Example 1 was repeated but with additive A (at twice
its standard treat rate) added to each fuel or blend. The
results are shown in Table 2.
Table 2
Experiment Po. Proportion of fuel F2 Mean fouling index
(% w/w) (%)
3.1 0 25.2
(ie, fuel F1 alone)
3.2 10 23.5
3.3' 50 16.4
3.4 70 10.3
3.5 100 2.3
Comparing these results with those in Table 1, it is
clear that inclusion of the detergent containing additive
results in a further reduction in nozzle fouling for each
fuel or blend tested. Again increasing levels of the
Fischer_Tropsch fuel are associated with decreasing levels
of fouling.
Thus, in-accordance with the invention, a Fischer-
Tropsch derived fuel may be combined with a detergent to
provide yet further improvements in fouling performance in
a diesel engine, either as or as part of a diesel fuel
composition.
