CATEGORY: DIESEL
PATENT
Diesel
Engine Injector Fouling Improvements With A Highly Paraffinic Distillate Fuel
(Sasol Technology (Pty) Ltd)
United States Patent Application 20130125849
Inventors:
Schaberg, Paul Werner (Noord-hoek, ZA)
Velaers, Adrian James (Cape Town, ZA)
Application Number:
13/696026
Publication Date:
05/23/2013
Assignee:
Sasol Technology (Pty) Ltd. (Johannesburg, ZA)
Abstract:
The
invention provides the use of a highly paraffinic distillate fuel in a diesel
fuel composition for reducing the formation of injector nozzle deposits when
combusted in a diesel engine having a high pressure fuel injection system,
wherein the distillate fuel has an aromatics content less than 0.1 wt %, a
sulphur content less than 10 ppm and a paraffinic content of at least 70 wt %,
such that the diesel fuel composition has a relative fouling behaviour of 70%
or less and a density of more than 0.815 g.cm−3 (at 15° C.).
SUMMARY OF THE INVENTION
According to a first aspect
of the invention, there is provided the use of a highly paraffinic distillate
fuel in a diesel fuel composition for reducing the formation of injector nozzle
deposits when combusted in a diesel engine having a high pressure fuel
injection system, wherein the distillate fuel has an aromatics content less
than 0.1 wt %, a sulphur content less than 10 ppm and a paraffinic content of
at least 70 wt %, such that the diesel fuel composition has a relative fouling
behaviour of 70% or less and a density of more than 0.815 g.cm−3 (at
15° C.).
The highly paraffinic distillate fuel may be derived from a Fischer Tropsch
process or may be hydrogenated renewable oil (HRO) or a combination of the two.
According to a second aspect of the invention, there is provided the use of a
highly paraffinic distillate fuel in a diesel fuel composition in a diesel
engine with a high pressure fuel injection system, wherein the distillate fuel
has an aromatics content less than 0.1 wt %, a sulphur content less than 10 ppm
and a paraffinic content of at least 70 wt % and is used for the purpose of
reducing the formation of injector nozzle deposits such that the diesel fuel
composition has a relative fouling behaviour of 60% or less and a density of more
than 0.80 g.cm−3 (at 15° C.).
According to a third aspect of the invention, there is provided the use of a
highly paraffinic distillate fuel in a diesel fuel composition in a diesel
engine with a high pressure fuel injection system, wherein the distillate fuel
has an aromatics content less than 0.1 wt %, a sulphur content less than 10 ppm
and a paraffinic content of at least 70 wt % and is used for the purpose of
reducing the formation of injector nozzle deposits such that the diesel fuel
composition has a relative fouling behaviour of 50% or less and a density of
more than 0.79 g.cm−3 (at 15° C.).
The highly paraffinic distillate fuel may have a cetane number greater than 70.
The diesel fuel composition may further comprise a petroleum-derived distillate
fuel, a bio-derived fuel or a combination of the two.
The diesel fuel composition may have a minimum relative fouling behaviour of
30%.
The diesel engine may be a common rail diesel engine.
The fuel injection system may have one or more injector nozzles.
The one or more injector nozzles may have one or more holes each having a
maximum equivalent diameter of 200 μm.
The one or more holes may each have a maximum equivalent diameter of 150 μm.
FIELD OF THE INVENTION
The present invention relates generally to fuel compositions suitable for
diesel engines with high pressure fuel injection systems; and more specifically
to the use of a highly paraffinic distillate component in these compositions.
BACKGROUND OF THE INVENTION
In recent years, consumer demand and legislation requirements have promoted
diesel engine technology advances resulting in improvements in energy
efficiency and performance; and reductions in emission levels. These advances
have largely been consequent of combustion process improvements achieved
through finely divided atomisation of the fuel prior to combustion. This atomisation
is typically achieved through the use of high pressure fuel injection systems
and highly sophisticated electronic injectors—usually with an increase in the
number; and a reduction in the size of the injector holes over those previously
employed.
Critically, however, in these new injector systems, the negative impact of
injector fouling or coking becomes far more significant. Fouling occurs where
deposits occur in the internal passages or surfaces of the injector or could
even form in other parts of the fuel delivery system. These deposits increase
with degradation of the fuel and typically take the form of carbonaceous
coke-like residues or sticky gum-like residues. This blocking or fouling
results in less efficient fuel delivery and poor mixing with air prior to
combustion. It is further exacerbated in injectors that have very small
holes—where the threshold size for a deposit to have a substantial impact on
performance is much reduced. Furthermore, within the injector body, there can
be very small clearances between moving parts; where the impact of deposit
formation can cause injectors to stick, particularly in the open position. As a
result of these effects, injector fouling is known to lead to multiple problems
such as power loss, increased emission levels and reduced fuel economy.
As previously discussed, high pressure fuel injection systems are also core to
the recent performance improvements associated with this type of engine. In
common rail systems, for example, the fuel is stored at high pressure in the
central accumulator rail prior to being delivered to the injectors. Any unused
heated fuel is then returned to the fuel tank, where it will then be introduced
back into the accumulator rail on demand. Fuel being returned to the fuel tank
via this route has been measured to have a temperature in excess of 100° C.
At the injector nozzle, the fuel pressure is commonly in excess of 1000 bar;
and may be in excess of 2000 bar. Furthermore, as the fuel is circulated
through the injector body itself, it is heated further due to heat conducted
through the injector body from the combustion chamber. The temperature of the
fuel at the tip of the injector can be as high as 250-350° C.
The high pressures inside these fuel delivery systems can also lead to a further
source of stress on the fuel. Cavitation bubbles can form in the fuel because
of the very low static pressure that occurs in high speed nozzle flow near a
sharp inlet corner. The sharper the corner and the higher the velocity, the
more likely cavitation is to occur. The formation of cavitation bubbles in
common rail diesel injectors is well-documented. Typically, this has focused on
the potential for mechanical damage or impact on injector performance; however,
the implosion of cavitation bubbles must also have an impact on the stability
of the fuel due to the extraordinarily high pressures and temperatures
generated during this event.
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