Note: Descriptions are shown in the official language in which they were submitted.
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USE OF A VISCOSITY IMPROVER
Field of the Invention
This invention relates to the use of certain types
of additive in diesel fuel formulations for new purposes.
Background to the Invention
It is often desired to improve the performance of
internal combustion engines through the use of modified
fuels. In the past, for example, diesel fuels have been
modified by the addition of relatively high density
components, in order to improve the power-related
performance of engines running on the fuels. In modern
direct injection diesel engines a higher density fuel
will typically lead to an increase in the mass of
combustible material which is delivered into the
combustion chamber through the engine's fixed volume fuel
injectors; this in turn increases the energy made
available through the combustion process.
It is not straightforward to predict how a fuel will
behave in the injection system of an engine, in
particular under the extremely high injection pressures
(often in excess of 2000 bar) to which it will be
subjected in a modern diesel engine. A diesel fuel is a
complex mixture of hydrocarbons of different molecular
weights and not all of these molecules will respond in
the same way to increases in pressure. Moreover the
geometry of the injection system can itself affect the
way in which a fuel's viscosity and other properties will
impact upon engine performance.
It is an aim of the present invention to provide an
alternative way of improving engine performance by
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modifying the properties of diesel fuels, in particular
through the use of fuel-compatible additives.
Statements of the Invention
According to a first aspect of the present invention
there is provided the use of a viscosity-improving
additive, in a diesel fuel formulation, for the purpose
of increasing the compressibility of the formulation.
The present invention is based on the realisation
that it is possible to use additives to modify the
compressibility of a diesel fuel formulation, ie the rate
at which its density changes with increasing pressure. An
increase in the compressibility of a fuel means that as
it is subjected to increasing pressures, such as within a
fuel injection system, its density will increase at a
greater rate. This in turn means that at any given
injection pressure, the fuel will have a higher density.
Thus, at the high pressures experienced in the injection
system of a diesel engine (typically from 1600 to 2500
bar), the fuel will provide a higher energy content in
each injection event. This in turn can increase the power
delivery through the engine, and hence its performance.
It has surprisingly been found that viscosity-
improving additives can, in addition to increasing the
viscosity of a diesel fuel formulation at any given
temperature and pressure, also increase its
compressibility. Moreover, this effect appears to be
particularly marked at the high pressures (for example in
excess of 1500 or even 2000 bar) and high temperatures
(for example in excess of 100 C, often up to 250 C) which
are typically used in modern diesel engines.
Thus, at typical injection pressures and
temperatures, a diesel fuel formulation for use according
to the invention will have a higher density than in the
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absence of the viscosity-improving additive. This can
yield an increase in delivered power from an engine
running on the formulation. In accordance with the
invention, therefore, a viscosity-improving additive may
be used to improve the power-related performance of an
engine running on a diesel fuel formulation, by
increasing the compressibility of the formulation.
Although the additive may not increase the density of the
formulation by a large amount under standard measurement
conditions (for example at atmospheric pressure and
either 15 or 40 C), it can increase the density by a
considerably greater amount under injection conditions.
The invention is expected to have particular
benefits in modern diesel engines, as the rail pressures
used in such engines are continually increasing. A fuel
formulation which is able to respond to increasing
pressure with an increase in energy and power output can
represent a promising candidate for use in high
performance engines and the vehicles which they power.
The viscosity-improving additive used in the present
invention may be any component, or mixture thereof, which
is suitable for use in a diesel fuel formulation and
which, when added to such a formulation, causes an
increase in its viscosity, in particular its kinematic
viscosity. A range of such components are known and
commercially available.
Viscosity improvers have been used in diesel fuels
in the past. WO-A-2005/054411, for example, describes the
use of a viscosity-increasing component in a diesel fuel
composition, for the purpose of improving the vehicle
tractive effort (VTE) and/or acceleration performance of
a diesel engine into which the composition is introduced.
The components used to increase the viscosity of the fuel
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composition include hydrocarbon diesel fuel components
such as in particular Fischer-Tropsch derived diesel
components, and oils, which may be mineral or synthetic
in origin and may also be Fischer-Tropsch derived. US-A-
2009/0241882 discloses the use of a viscosity index (VI)-
improving additive, in an automotive diesel fuel
composition, for the purpose of improving the
acceleration performance of an engine into which the fuel
composition is introduced or of a vehicle powered by such
an engine.
However, such disclosures have failed to establish,
or even to investigate, a link between the viscosity of a
fuel formulation and its compressibility, in particular
at typical fuel injection pressures. Such a link is not
necessarily predictable, due to the relatively complex
constitutions and properties of fuel formulations. Nor
could it have been predicted, from this earlier work,
that viscosity-improving additives would have an effect
on fuel compressibility even at high temperatures and
pressures. Earlier work on the densities and viscosities
of additivated fuels has focused primarily on fuel
properties measured at ambient temperature and pressure,
as in many of the standard (for example ASTM) test
methods, rather than investigating changes in fuel
behaviour under injection conditions.
Magin et al in Energy & Fuels, vol 26, no 2, pages
1336 to 1343 in a paper entitled 'Bulk Modulus of
Compressibility of Diesel/Biodiesel/HVO' found a
synergistic effect leading to higher values for the bulk
modulus for HVO/Diesel blends which reached a maximum for
a 25% HVO content. The paper speculates that the reason
for this effect is the increase of diversity of
hydrocarbon structures provided by incorporating the HVO
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into the diesel, and that similarly where small amounts
of HVO are utilized in fuel blends, the resultant
decrease in molecular structure diversity yields
significant decreases in the bulk modulus.
In accordance with the invention, the viscosity-
improving additive may be an oligomeric or polymeric, in
particular a polymeric, component. It may be selected
from:
i. olefin-based polymers;
ii. naphthenic, paraffinic, or synthetic base oils;
iii. polymethacrylates; and
iv. mixtures thereof.
It has been found that the olefin-based polymers can
yield a useful increase in compressibility at only a
fraction of the amount of additive than a base oil
additive.
An additive of type (i) is therefore especially
preferred. It is a polymer which comprises one or more
olefinic monomer units. In the context of the present
invention, the term "polymer" includes a copolymer. An
additive of type (i) may be a copolymer, in particular a
block copolymer, which may comprise a mixture of two or
more olefinic monomer units. Olefinic monomer units may
for example be selected from ethylene, propylene,
butylene, butadiene, isoprene and styrene.
An additive of type (i) may be selected from
polyisobutylenes (PIBs), poly-alpha olefins (PA05),
ethylene-propylene copolymers (including both semi-
crystalline and amorphous copolymers), styrene-based
polymers, and mixtures thereof. It may be selected from
ethylene-propylene copolymers, styrene-based polymers,
and mixtures thereof.
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Suitable ethylene-propylene copolymers are available
for example as LZ 706X additives (ex Lubrizol). Suitable
PIBs are commercially available for example as Indopol-H
(ex INEOS). Suitable PAOs are commercially available for
example as Durasyn (ex INEOS) or Synfluid (ex Chevron
Phillips).
In an embodiment, the additive of type (i) comprises
a styrene-based polymer, ie a polymer or copolymer which
comprises one or more styrenic monomer units. It may
comprise a styrene-based copolymer, for example a
copolymer of at least one styrenic monomer with at least
one olefinic monomer. Suitable such polymers are
available for example as KratonTM D or KratonTM G additives
(ex Kraton) or as SVTM additives (ex Infineum, Multisol
and others). They have been used in the past as
viscosity-improving and viscosity index-improving
additives, including in diesel fuel formulations: see for
example US-A-2009/0241882. They have also been used as
additives in lubricants (see WO-A-2008/024111).
The additive of type (i) may in particular be
selected from copolymers of styrenic and olefinic
monomers (in particular copolymers of styrene monomers
with ethylene, propylene, butylene, butadiene and/or
isoprene (2-methyl-1,3-butadiene) monomers), and mixtures
thereof. It may for instance be selected from
polystyrene-polyisoprene copolymers, polystyrene-
polybutadiene copolymers, and mixtures thereof. Such
copolymers may be block copolymers, as for instance SVTM
150 (a linear polystyrene-polyisoprene di-block
copolymer) or the KratonTM additives (styrene-butadiene-
styrene tri-block copolymers or styrene-ethylene-butylene
tri-block copolymers). They may be tapered copolymers,
for instance styrene-butadiene copolymers. They may be
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stellate copolymers, as for instance SVTM 260 and SVm200
(which are polystyrene-polyisoprene star copolymers).
In an embodiment, the additive (i) is selected from
polystyrene-polyisoprene copolymers and mixtures thereof.
In an embodiment, it is selected from SVTM additives and
mixtures thereof, for example from SVm150, SVm200, SVm260
and mixtures thereof. In an embodiment, it is selected
from SVm150, SVm260 and mixtures thereof. In an
embodiment, it comprises SVTM 150.
An additive of type (ii) is most suitably a
lubricant base oil, for example a naphthenic base oil
derived from naphthenic crude oils. It may in particular
be a mineral oil or mixture thereof, for example a
naphthenic mineral base oil. The base oil, or a component
thereof, may be a synthetic product such as a Fischer-
Tropsch-derived component.
A base oil (ii) may for example be a Group III,
Group IV or Group V base oil. In an embodiment, it is an
API (American Petroleum Institute) Group V base oil. The
Group V base oils include non-PAO synthetic components
such as diesters, polyolesters, and alkylated
hydrocarbons such as alkylated naphthenes and alkylated
benzenes.
In a specific embodiment, a base oil (ii) may have a
density at 15 C of from 875 to 885 kg/m3 (DIN 51 757 D;
ISO 12185), for example about 880 kg/m3. It may have a
kinematic viscosity at 40 C (VK 40) of from 7.7 to 8.2
mm2/s (DIN 51 562, T.1; ISO 3104), for example about 7.9
mm2/s; and/or a kinematic viscosity at 100 C (VK 100) of
about 2.1 mm2/s (ISO 3104). It may have a vapour pressure
at 20 C of less than 0.01 kPa; a pour point of -60 C (DIN
ISO 3016); a flash point of 146 C (ISO 2719); and/or a
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polycyclic aromatic compound (PCA) content of about 1%
w/w (IP 346).
Base oils, in particular mineral base oils, are
widely available, for example from the Shell group of
companies. They have been used in the past to increase
the viscosity and density of racing diesel fuels.
In an embodiment, the additive of type (ii)
comprises the lubricant base oil HNR40D, which is a
naphthenic mineral base oil, available from the Shell
group of companies.
Additives of type (iii) are available for example as
ViscoplexTM 1-300 (ex Evonik), which is used as a pour
point depressant and as a viscosity modifier in
lubricants.
In an embodiment of the invention, the viscosity-
improving additive is selected from olefin-based
polymers; base oils; and mixtures thereof. In an
embodiment, it is selected from styrene-based polymers;
base oils; and mixtures thereof. In an embodiment, it
comprises a styrene-based polymer or mixture thereof.
An additive of the type (i) to (iv) may be used,
according to the invention, in the form of an additive
composition which contains both the active ingredient
(for example an olefin-based polymer) and a suitable
carrier fluid. Carrier fluids (in particular carrier
solvents) include for example mineral oils, aromatic
hydrocarbon solvents such as ShellsolTM A150 (ex Shell),
other hydrocarbons and hydrocarbon mixtures with boiling
points within the normal diesel boiling range, fatty acid
alkyl esters (in particular fatty acid methyl esters),
and mixtures thereof.
Such an additive composition may comprise one or
more additional active substances, for example selected
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from substances which are active as detergents, dehazers,
anti-corrosion additives, antifoam additives, lubricity
improvers, cold flow improvers, cetane improvers, and
mixtures thereof, in particular from substances which are
active as detergents, dehazers, anti-corrosion additives,
antifoam additives, and mixtures thereof.
In an embodiment, the viscosity-improving additive
is a viscosity index-improving additive, ie a component
which, when added to a diesel fuel formulation, causes an
increase in its viscosity index VI. The VI of a fuel
formulation is a measure of the rate of change of the
viscosity of the formulation with temperature. A fuel
formulation with a relatively high VI will exhibit a
smaller reduction in its viscosity than will a fuel
formulation with a relatively low VI, over any given
increase in temperature.
Viscosity index-improving additives (also referred
to as VI improvers) are already known in lubricant
formulations, where they are used to maintain viscosity
as constant as possible over a desired temperature range
by increasing viscosity at higher temperatures. They are
typically based on relatively high molecular weight, long
chain polymeric molecules that can form conglomerates
and/or micelles. These molecular systems expand at higher
temperatures, thus further restricting their movement
relative to one another and in turn increasing the
viscosity of the system.
Known VI improvers include polymethacrylates (PMAs),
polyisobutylenes (PIBs), ethylene-propylene copolymers
and other olefin copolymers (0CPs), and styrene/olefin
copolymers such as those referred to above. Thus, many of
the viscosity-improving additives (i) and (iii) are also
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capable of acting as VI-improving additives in diesel
fuel formulations.
In WO-A-01/48120, certain of these types of additive
are proposed for use in diesel fuel compositions, for the
purpose of improving the ability of an engine to start at
elevated temperatures. They have not however, to our
knowledge, been proposed for use in increasing the
compressibility of a diesel fuel formulation.
In accordance with the invention, the viscosity-
improving additive may be used in the diesel fuel
formulation at an (active matter) concentration of 0.01%
w/w or greater, or of 0.05% w/w or greater, or of 0.1%
w/w or greater. In cases it may be used at an (active
matter) concentration of 0.5 or 1% w/w or greater. It may
be used at an (active matter) concentration of up to 30%
w/w, or of up to 25 or 20 or 15% w/w, or more suitably up
to 10% w/w or up to 7.5 or 5 or 2.5% w/w. In cases it may
be used at an (active matter) concentration of up to 1 or
0.5% w/w, such as from 0.01 to 0.5% w/w or from 0.05 to
0.5% w/w.
In a first specific embodiment, in particular when
the viscosity-improving additive is of type (i) or (iii),
and more particularly when it is an ethylene-propylene
copolymer or styrene-based polymer, most particularly a
styrene-based polymer, its (active matter) concentration
in the diesel fuel formulation may be 0.01% w/w or
greater, or 0.025 or 0.05% w/w or greater, or 0.1% w/w or
greater. In this embodiment the (active matter)
concentration of the additive may be up to 0.5% w/w, or
up to 0.4 or 0.3 or 0.2% w/w, such as from 0.01 to 0.5%
w/w or from 0.04 to 0.2% w/w or from 0.05 to 2% w/w. In
preferred embodiments, an additive of type (i) is used in
the diesel fuel formulation in a concentration in the
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range of from 0.01 to 2% w/w, more preferably from 0.01
to 1% w/w, and especially from 0.01 to 0.5% w/w, for
example from 0.01 to 0.2% w/w, or from 0.04 to 0.2% w/w.
It is a significant advantage that the increase in
compressibility can be provided by such viscosity-
improving additives at such low concentrations as are
typically associated with fuel additives. This is, for
example, preferred in order to minimise the impact of the
invention on fuel preparation and handling processes.
In a second specific embodiment, in particular when
the viscosity-improving additive is of type (ii), its
concentration in the diesel fuel formulation may be 1%
w/w or greater, or 2% w/w or greater, or in cases 5 or
10% w/w or greater. In this embodiment the concentration
of the additive may be up to 30% w/w, or up to 25 or 20
or 15% w/w, suitably up to 10% w/w or up to 7.5 or 5%
w/w, such as from 1 to 10% w/w or from 1 to 5% w/w. Such
viscosity-improving additives may thus be included in
fuel formulations at concentrations typically associated
with fuel components. Ideally, in such a case, the
additive will not be detrimental to the properties of the
overall formulation, ie the overall formulation will
still comply with relevant applicable standards such as
EN 590 or ASTM D975, even though it has a higher density
and compressibility under injection temperatures and
pressures.
A diesel fuel formulation used according to the
invention (ie a diesel fuel formulation in which a
viscosity-improving additive is or has been used in
accordance with the invention) may comprise, in addition
to the viscosity-improving additive, one or more diesel
fuel components and/or additives, as are known in the
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art. It may for example comprise a diesel base fuel or
mixture thereof.
A diesel base fuel may be any fuel component, or
mixture thereof, which is suitable and/or adapted for use
in a diesel fuel formulation and therefore for combustion
within a compression ignition (diesel) engine. It will
typically be a liquid hydrocarbon middle distillate fuel,
more typically a gas oil. It may be petroleum-derived. It
may be or contain a kerosene fuel component.
Alternatively it may be synthetic: for instance it may be
the product of a Fischer-Tropsch condensation. It may be
derived, either directly or indirectly, from a biological
source such as plant biomass. It may be or include an
oxygenate such as a fatty acid alkyl ester, in particular
a fatty acid methyl ester (FAME) such as rapeseed methyl
ester or palm oil methyl ester.
A diesel base fuel will typically boil in the range
from 150 or 180 to 370 C (ASTM D86 or EN ISO 3405). It
will suitably have a measured cetane number (ASTM D613)
of from 40 to 70 or from 40 to 65 or from 51 to 65 or 70.
It will suitably have a density of from 750 to 900 kg/m3,
or from 800 to 860 kg/m3, or more suitably from 820 to
845 kg/m3, at 15 C (ASTM D4052 or EN ISO 3675), and/or a
VK 40 of from 1.5 to 6.0 mm2/s or from 2.0 to 4.5 mm2/s
(ASTM D445 or EN ISO 3104).
Where a fuel formulation used according to the
invention comprises a diesel base fuel, the concentration
of the base fuel in the formulation may be 60% v/v or
greater, or 65 or 70 or 75 or 80 or 85 or 90% v/v or
greater, or in cases 95% v/v or greater. Its
concentration may be up to 99.99% v/v, or up to 99.95 or
99.9% v/v, or up to 99.8 or 99.5% v/v, or up to 99 or 98
or 95% v/v. The base fuel may represent the major part of
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the fuel formulation: after inclusion of the viscosity-
improving additive, and any further (optional) fuel
components and additives, the diesel base fuel may
therefore represent the balance to 100%.
A diesel fuel formulation used according to the
invention will suitably comply with applicable current
standard diesel fuel specification(s) such as for example
EN 590 (for Europe) or ASTM D975 (for the USA). By way of
example, the overall formulation may have a density from
820 to 845 kg/m3 at 15 C; a 195 boiling point (ASTM D86
or EN ISO 3405) of 360 C or less; a measured cetane
number of 40 or greater, ideally of 51 or greater; a VK40
from 2 to 4.5 mm2/s; a flash point (ASTM D93 or EN ISO
2719) of 55 C or greater; a sulphur content (ASTM D2622
or EN ISO 20846) of 50 mg/kg or less; a cloud point (IP
219) of less than -10 C; and/or a polycyclic aromatic
hydrocarbons (PAH) content (EN 12916) of less than 11%
w/w. It may have a lubricity, measured using a high
frequency reciprocating rig for example according to ISO
12156 and expressed as a "HFRR wear scar", of 460 pm or
less. Relevant specifications may however differ from
country to country, from season to season and from year
to year, and may depend on the intended use of the
formulation. Moreover a formulation used according to the
invention may contain individual fuel components with
properties outside of these ranges, since the properties
of an overall blend may differ, often significantly, from
those of its individual constituents.
A fuel formulation used according to the invention
may comprise one or more fuel or refinery additives, in
particular additives which are suitable for use in
automotive diesel fuels. Many such additives are known
and commercially available. The formulation may for
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example comprise one or more additives selected from
detergents, dehazers, anti-corrosion additives, antifoam
additives, cetane improvers such as 2-ethylhexyl nitrate
(2-EHN), antistatic additives, lubricity additives,
conductivity additives, cold flow additives, and
combinations thereof. It may comprise one or more
additives selected from detergents, dehazers, anti-
corrosion additives, antifoam additives, and mixtures
thereof. Such additives may each be included at an
(active matter) concentration of up to 300 ppmw (parts
per million by weight), for example of from 50 to 300
ppmw.
A fuel formulation used according to the invention
should be suitable and/or adapted for use in a
compression ignition (diesel) internal combustion engine.
It may in particular be an automotive fuel formulation.
In an embodiment, it is suitable and/or adapted for use
in a diesel engine which operates using high fuel
injection pressures, for example pressures greater than
about 1800 bar or of about 2000 bar or greater. Such an
engine may for example be of the common rail or unit
injector type, and/or of the type referred to as "Euro
5".
In embodiments, the present invention may be used to
prepare at least 1,000 litres of the additive-containing
diesel fuel formulation, or at least 5,000 or 10,000 or
20,000 or 50,000 litres.
In accordance with the invention, the viscosity-
improving additive is used for the purpose of increasing
the compressibility of a diesel fuel formulation. It may
in particular be used to increase the compressibility of
the formulation at a pressure of 1000 bar or greater, or
of 1500 bar or greater, or of 2000 bar or greater, for
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example from 1000 to 2500 bar or from 1500 to 2500 bar or
from 2000 to 2500 bar. It may be used to increase the
compressibility of the formulation at a temperature of
100 C or greater, or of 150 C or greater, or of from 100
to 250 C or from 100 to 200 C or from 100 to 175 C or
from 100 to 150 C. In an embodiment, the viscosity-
improving additive is used to produce a diesel fuel
formulation which has an increased compressibility at a
pressure of from 2000 to 2500 bar and a temperature of
from 100 to 150 C, in particular at a pressure of 2000
bar and a temperature of 150 C.
In the present context, "compressibility" is
suitably isothermal compressibility, ie the rate of
change of density with pressure at a constant
temperature.
The isothermal compressibility of a fuel formulation
may be assessed using any suitable method, for instance
as described in the examples below. Its reciprocal,
referred to as the bulk modulus, is typically defined as
the ratio of the change in pressure to the relative
change in density at constant temperature. Isothermal
compressibility and bulk modulus may thus be assessed by
measuring the density of the fuel formulation at a range
of pressures and observing the way in which the density
changes with pressure. The results may for example be
plotted on a graph of density against pressure. The
density measurements should be taken at a constant
temperature, for example a temperature to which the fuel
formulation might typically be subjected in the injection
system of a diesel engine. In particular, the density
measurements may be taken at a constant temperature which
is in the range from 40 to 200 C, or in the range from 40
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to 150 C, or in the range from 100 to 150 C, such as at
about 150 C.
The density of a fuel formulation may be measured
using a standard test method such as ASTM D4052 or an
analogous method.
The invention may be used to achieve any degree of
increase in the compressibility of the fuel formulation,
and/or to achieve a desired target compressibility, for
example a target set by an applicable regulatory
standard, or a target set by a user (which includes a
handler, keeper or distributor) or potential user of the
formulation. The increase in compressibility will
typically be as compared to the compressibility of the
formulation prior to adding the viscosity-improving
additive to it.
The invention may be used to achieve a desired
increase in compressibility at a specific temperature, or
within a specific range of temperatures. It may be used
to achieve a desired increase in compressibility at a
specific pressure, or within a specific range of
pressures.
"Achieving" a desired target property also embraces
- and in an embodiment involves - improving on the
relevant target. Thus, for example, the viscosity-
improving additive may be used to produce a diesel fuel
formulation which has a compressibility higher than a
desired target value.
The increase in compressibility of the diesel fuel
formulation may be as compared to the compressibility of
the formulation, and/or of an otherwise analogous fuel
formulation intended (eg marketed) for use in an
analogous context, prior to the realisation that the
viscosity-improving additive could be used in the way
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provided by the present invention, or prior to adding the
viscosity-improving additive to the formulation in
accordance with the invention. Thus, the increase may be
as compared to the compressibility of the diesel fuel
formulation without the viscosity-improving additive. At
a given pressure and temperature, the increase in
compressibility may for example be 0.5% or more, or 0.75
or 1% or more, or in cases 2.5 or 3 or 4 or 5% or more,
of the compressibility which it is desired to improve
upon. At a given pressure and temperature, the increase
in compressibility may for example be up to 20%, or up to
or 10%, or up to 7.5 or 5%, of the compressibility
which it is desired to improve upon.
The invention may additionally or alternatively be
15 used to adjust any property of the diesel fuel
formulation which is equivalent to or associated with its
compressibility, for instance to effect an increase in a
desired property or behaviour and/or a reduction in an
undesired property or behaviour. In particular, an
increase in compressibility may be manifested by an
improvement in the performance of a fuel-consuming system
(in particular a diesel engine) running on the fuel
formulation. Such an improvement may for example comprise
a higher delivered torque under steady state conditions
(ie at constant engine speed and load), shorter
acceleration times, and/or a higher power output
(manifested for example by a higher brake mean effective
pressure). It may thus be manifested by an improvement in
one or more power-related aspects of the performance of
the fuel-consuming system. In accordance with the
invention, the viscosity-improving additive may be used
in a diesel fuel formulation for the purpose of achieving
one or more of these effects, in particular to improve
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the power-related performance of an engine in which the
fuel formulation is, or is intended to be, used. It may
be used to increase the combustion energy generated with
each injection of the fuel formulation into a combustion
chamber of an engine running on the formulation.
An improvement in the power-related performance of a
fuel-consuming system may also embrace mitigation, to at
least a degree, of a decrease in acceleration performance
due to another cause, in particular due to another fuel
component or additive included in the fuel formulation on
which the system is running. By way of example, a fuel
formulation may contain one or more components intended
to reduce its overall density so as to reduce the level
of emissions which it generates on combustion; a
reduction in density can result in loss of engine power,
but this effect may be overcome or at least mitigated by
the use of a viscosity-improving additive in accordance
with the present invention.
An improvement in power-related performance may also
embrace restoration, at least partially, of performance
which has been reduced for another reason such as the use
of a fuel containing an oxygenated component (for example
a so-called "biofuel"), or the build-up of combustion-
related deposits in the engine (typically in the fuel
injectors).
In the context of the present invention, "use" of a
viscosity-improving additive in a diesel fuel formulation
means incorporating the additive into the formulation,
typically as a blend (ie a physical mixture) with one or
more other diesel fuel components, for example a diesel
base fuel and optionally one or more other diesel fuel
additives. The viscosity-improving additive will
conveniently be incorporated before the formulation is
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introduced into an engine or other system which is to be
run on the formulation. Instead or in addition, the use
of a viscosity-improving additive may involve running a
fuel-consuming system, typically an internal combustion
engine, on a diesel fuel formulation containing the
additive, typically by introducing the formulation into a
combustion chamber of an engine. It may involve running a
vehicle which is driven by a fuel-consuming system, on a
diesel fuel formulation containing the additive. In such
cases the fuel-consuming system is suitably a compression
ignition (diesel) engine.
"Use" of a viscosity-improving additive in the ways
described above may also embrace supplying the additive
together with instructions for its use in a diesel fuel
formulation in order to increase the compressibility of
the formulation. The additive may itself be supplied as
part of a composition which is suitable and/or adapted
and/or intended for use as a fuel additive, in which case
the viscosity-improving additive may be included in such
a composition for the purpose of influencing its effects
on the compressibility of a diesel fuel formulation.
In general, references to "adding" a component to,
or "incorporating" a component in, a fuel formulation may
be taken to embrace addition or incorporation at any
point during the production of the formulation or at any
time prior to its use. Thus, for example, the viscosity-
improving additive may be incorporated into a diesel base
fuel at the refinery, or more suitably it may be added to
a diesel fuel formulation at the depot, downstream of the
refinery.
A diesel fuel formulation used according to the
invention may be marketed with an indication that it
benefits from an improvement due to the inclusion of the
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viscosity-improving additive, in particular a higher
compressibility and/or an improvement in the power-
related performance of an engine which is running on the
fuel formulation. The marketing of such a formulation may
comprise an activity selected from (a) providing the
formulation in a container that comprises the relevant
indication; (b) supplying the formulation with product
literature that comprises the indication; (c) providing
the indication in a publication or sign (for example at
the point of sale) that describes the formulation; and
(d) providing the indication in a commercial which is
aired for instance on the radio, television or internet.
The improvement may be attributed, in such an indication,
at least partly to the presence of the viscosity-
improving additive. The invention may involve assessing
the relevant property (in particular the compressibility)
of the formulation during or after its preparation. It
may involve assessing the relevant property both before
and after incorporation of the viscosity-improving
additive, for example so as to confirm that the additive
contributes to the relevant improvement in the
formulation.
Similarly, a diesel fuel additive composition
containing a viscosity-improving additive may, in
accordance with the invention, be marketed with an
indication that it benefits from an improvement due to
the inclusion of the viscosity-improving additive, the
improvement being the ability of the composition to
increase the compressibility of a diesel fuel formulation
in which it is used, and/or to improve the power-related
performance of an engine which is running on such a
diesel fuel formulation.
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Throughout the description and claims of this
specification, the words "comprise" and "contain" and
variations of the words, for example "comprising" and
"comprises", mean "including but not limited to", and do
not exclude other moieties, additives, components,
integers or steps.
Preferred features of each aspect of the invention
may be as described in connection with any of the other
aspects. Other features of the invention will become
apparent from the following examples. Generally speaking
the invention extends to any novel one, or any novel
combination, of the features disclosed in this
specification (including any accompanying claims and
drawings). Thus features, integers, characteristics,
compounds, chemical moieties or groups described in
conjunction with a particular aspect, embodiment or
example of the invention are to be understood to be
applicable to any other aspect, embodiment or example
described herein unless incompatible therewith.
Where upper and lower limits are quoted for a
property, for example for the concentration of a fuel
component, then a range of values defined by a
combination of any of the upper limits with any of the
lower limits may also be implied.
In this specification, references to fuel and fuel
component properties are - unless stated otherwise - to
properties measured under ambient conditions, ie at
atmospheric pressure and at a temperature of from 16 to
22 or 25 C, or from 18 to 22 or 25 C, for example about
20 C.
The present invention will now be further described
with reference to the following non-limiting examples.
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Example 1
Diesel fuel formulations were prepared, in
accordance with the invention, by blending a diesel base
fuel with four viscosity-improving test additives. The
additives were:
a. SVTM 150, a fuel additive containing a polystyrene-
polyisoprene block copolymer, ex-Infineum.
b. SVTM 200, a fuel additive containing a polystyrene-
polyisoprene star copolymer, ex-Infineum.
c. SVTM 260, a fuel additive containing a styrene-
polyisoprene star copolymer, ex-Infineum.
d. HNR40D, a lubricant base oil, ex Shell.
The base fuel was a zero sulphur diesel fuel (ex
Shell), which conformed to the European diesel fuel
specification EN 590. It contained 7% v/v of rapeseed
methyl ester (RME), together with standard refinery
additives. It had a VK 40 of 2.86 mm2/s (DIN EN ISO
3104), and a density at 40 C of 817.28 kg/m3 (DIN EN ISO
12185).
HNR4OD is a highly refined API Group V mineral oil,
ex Shell. It is manufactured from naphthenic crude oils
via a process involving vacuum distillation and
hydrotreatment. It has a density at 15 C of 880 kg/m3
(ISO 12185); a VK 40 of 7.9 mm2/s (ISO 3104); a VK 100 of
2.1 mm2/s (ISO 3104); a flash point of 146 C (ISO 2719);
a polycyclic aromatic compound (PCA) content (IP 346) of
1% w/w; and a colour index (ASTM 1500) of less than 0.5.
The test additives were incorporated into the base
fuel at a treat rate of 0.04% w/w and 0.2% w/w for the
SVTM 150; 0.2% w/w for the SVTM 200; 0.15% w/w for the SVTM
260 and 26% w/w for the HNR40D.
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The densities of the resultant formulations, and of
the unadditivated base fuel, were measured at 100 C using
a density sensor, at a series of pressures from 0 to 2500
bar (relative to atmospheric) in steps of 250 bar. The
experiment was then repeated at 150 C.
The results are shown in Tables 1 and 2 below, for
the measurements taken at 100 C and 150 C respectively.
The figures in the tables are the base fuel and fuel
formulation densities, in kg/m3. A pressure designated
"0" corresponds to ambient pressure (1 bar).
Table 1 - Densities at 100 C
Pressure Base Base Base Base Base Base
(bar) fuel fuel + fuel + fuel + fuel + fuel +
alone SVul SVul SVul SVD, IINR4OD
150 150 200 260
(2696
(0.0496 (0.296 (0.296 (0.1596 w/w)
w/w) w/w) w/w) w/w)
0
776.13 777.08 777.09 777.46 777.55 789.18
250 797.70 798.61
798.67 798.83 799.16 810.39
500 816.13 817.24
817.41 817.27 817.85 828.99
750 832.32 833.75
834.07 833.58 834.43 845.66
1000 846.83 848.67 849.13 848.29 849.39 860.83
1250 860.03 862.31 862.93 861.72 863.07 874.79
1500 872.16 874.91 875.7 874.11 875.71 887.77
1750 883.42 886.66 887.61 885.65 887.49 899.90
2000 893.95 897.68 898.79 896.47 898.53 911.33
2250 903.85 908.07 909.34 906.66 908.95 922.15
2500 913.20 917.92 919.36 916.31 918.83 932.43
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Table 2 - Densities at 150 C
Pressure Base Base Base Base Base Base
(bar) fuel fuel + fuel + fuel + fuel + fuel +
alone SVul SVD, SVD, SVD, IINR4OD
150 150 200 260
(2696
(0.0496 (0.296 (0.296 (0.1596 w/w)
w/w) w/w) w/w) w/w)
0
741.85 743.15 742.51 743.14 743.44 755.88
250 769.10 771.51
770.72 770.86 771.95 783.29
500 791.41 794.95
794.14 793.73 795.49 806.41
750 810.49 815.12
814.38 813.41 815.75 826.60
1000 827.27 832.97 832.33 830.79 833.66 844.64
1250 842.33 849.05 848.54 846.43 849.80 861.02
1500 856.04 863.74 863.37 860.72 864.54 876.07
1750 868.66 877.31 877.08 873.9 878.16 890.05
2000 880.38 889.95 889.87 886.17 890.84 903.13
2250 891.34 901.80 901.88 897.68 902.73 915.44
2500 901.66 912.99 913.22 908.52 913.95 927.09
The measured densities were used to calculate the
isothermal compressibilities of the base fuel and the
test formulations, at each pressure and temperature.
Isothermal compressibility at temperature T (KT) is
defined as a fractional volume reduction divided by the
associated change in pressure, according to the following
formula:
KT = - 1 . (3v)
vo (3p)
where V is the volume of the relevant fuel sample at
temperature T and pressure P. and VO is the volume of the
same sample at temperature T and ambient pressure (1
atmosphere).
For the present purposes, it can be defined
according to the formula:
A13-1
19*Ap
KT
where p is the density of the fuel sample at temperature
T and pressure P.
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The results are shown in Tables 3 and 4 below, for
the experiments conducted at 100 C and 150 C
respectively. The figures in the table are KT values
times 1E-6, per bar. Again, a pressure designated as "0"
corresponds to ambient pressure (1 bar).
Table 3 - Isothermal Compressibilities at 100 C
Pressure Base Base Base Base Base Base
(bar) fuel fuel fuel fuel
fuel fuel +
IINR4OD
SVIK SVIK SVIK SVIK (2696
150 150 200 260 w/w)
(0.0496 (0.296 (0.296 (0.1596
w/w) w/w) w/w) w/w)
0
121.62 120.27 120.39 119.56 120.72 115.69
250 96.61 97.03 97.46 96.16 97.32 95.03
500 80.14 81.31 81.86 80.43 81.51 80.62
750 68.46 69.97 70.57 69.12 70.13 70.01
1000 59.76 61.41 62.02 60.59 61.53 61.87
1250 53.01 54.72 55.31 53.94 54.81 55.42
1500 47.64 49.34 49.91 48.61 49.42 50.19
1750 43.25 44.92 45.48 44.23 44.99 45.87
2000 39.61 41.23 41.76 40.58 41.29 42.22
2250 36.53 38.10 38.61 37.49 38.15 39.12
2500 33.89 35.42 35.9 34.83 35.46 36.44
Table 4 - Isothermal Compressibilities at 150 C
Pressure Base Base Base Base Base Base
(bar) fuel fuel fuel fuel
fuel fuel +
IINR4OD
SVIK SVIK SVIK SVIK (2696
150 150 200 260 w/w)
(0.0496 (0.296 (0.296 (0.1596
w/w) w/w) w/w) w/w)
0
165.46 170.83 169.48 167.09 171.77 160.09
250 122.37 127.45
127.31 124.69 127.98 123.05
500 97.09 101.64 101.94 99.46
101.98 99.93
750 80.46 84.53 85.00 82.72 84.76 84.13
1000 68.70 72.35 72.89 70.8 72.52 72.64
1250 59.94 63.23 63.80 61.89 63.36 63.91
1500 53.16 56.16 56.73 54.96 56.26 57.06
1750 47.75 50.51 51.06 49.44 50.59 51.53
2000 43.35 45.89 46.43 44.92 45.96 46.98
2250 39.69 42.05 42.57 41.16 42.11 43.17
2500 36.60 38.80 39.30 37.98 38.85 39.93
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Tables 1 and 2 show that the viscosity-improving
additives increase the density of the base fuel, in
particular at higher pressures. Moreover, the difference
between the density of the additivated base fuel and that
of the base fuel alone increases with increasing
pressure, indicating an increase in the compressibility
of the base fuel when combined with the relevant
additive. This increase in compressibility, compared to
that of the base fuel alone, is clearly seen in the Table
3 and 4 data. It is apparent at both measurement
temperatures, in particular at 150 C, which confirms the
likely utility of the present invention under typical
fuel injection conditions.
When the Table 1 results are plotted on a graph of
density against pressure, the curves for the additivated
fuel formulations can be seen to diverge from the curve
for the base fuel alone, in particular at higher
pressures above about 1000 bar. The rate of change of
density with pressure (ie the compressibility) is, at
such higher pressures, significantly greater for the five
additivated formulations than for the unadditivated base
fuel. The increase in compressibility, at any given
pressure, is greater with the SVTM 150 and SVTM 260 than
with the SVTM 200. Indeed the SVTM 150 has an effect even
at a treat rate as low as 0.04% w/w. Similar comments
apply to the Table 2 results, where the divergence of the
curves is enhanced compared to that seen at 100 C.
The base fuel/HNR4OD blend has a much higher initial
density than the base fuel alone. Its density remains
greater than that of the base fuel at all pressures, but
again its rate of change of density with increasing
pressure has been shown to be higher than that of the
base fuel alone, at both 100 and 150 C. However the use
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of base oil HNR4OD to improve isothermal compressibility
requires a far greater amount of the additive (in these
examples 26% w/w), whereas for each of the olefin-based
polymer additives a benefit in compressibility is
provided when using a significantly lower amount - 0.2%
w/w or lower.
Overall, these results confirm the known
relationship between isothermal compressibility and
pressure, ie that the compressibility decreases with
increasing pressure. What they also show, however, which
was not previously appreciated, is that a small amount of
a suitable viscosity-improving additive can influence the
way in which the compressibility of a diesel fuel
formulation changes over the range of typical fuel
injection pressures, resulting in higher fuel densities
under injection conditions.
Thus, the present invention can provide a way of
increasing the compressibility of a diesel fuel
formulation, in many cases through the use of relatively
small quantities of diesel fuel-compatible additives. An
increase in compressibility means that, at the higher
pressures to which it is subjected in the fuel injection
system of an engine, the fuel formulation will have a
greater density and will thus deliver, through the
volumetrically-calibrated injection system, a greater
combustion energy. In this way, the additivated fuel can
be used to improve the power-related performance of a
diesel engine.
