Note: Descriptions are shown in the official language in which they were submitted.
CA 02564339 2006-10-26
WO 2005/105961 PCT/ZA2005/000060
Crude Oil Derived and Gas-To-Liquids Diesel Fuel Blends
Field of the Invention
The invention relates to crude oil derived and Gas-To-Liquids (GTL) diesel
fuel
blends.
Background of the Invention
Synthetic fuels such as GTL (Gas To Liquids) diesel fuel have seen a
significant rise
in interest in recent years. They are considered to be extremely clean fuels,
with
negligible sulfur and aromatics, and are odor-free and have a cetane number of
> 70.
The GTL diesel fuel used in the examples in this patent specification was
manufactured by means of the Sasol Slurry Phase Distillate (Sasol SPDTM)
process,
which consists of three process steps, as depicted schematically in Fig. 1.
In the first step an auto-thermal reforming process is used to convert the
natural gas
into the synthesis gas, a mixture of CO and H2. In a second step the synthesis
gas is
converted into a so-called syncrude containing predominantly paraffinic
hydrocarbons, by a Fischer-Tropsch process. This syncrude is primarily in the
form of
waxes and distillates, which are further refined in a third, product upgrading
step by
means of mild hydro-processing, in order to produce products that meet
commercial
fuel specifications, such as diesel fuel and kerosene.
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CA 02564339 2010-12-15
Brief Description of the Drawings
Figure 1 is a schematic representation of the GTL production process;
Figure 2 are the results of the chassis dynamometer tests in the
NEDC;
Figure 3 is soot and NOx tradeoff at two operating points: 1600 rev/min
and 3.3 bar bmep, and 2000 rev/min and 5 bar bmep;
Figure 4 is the relative NOx emissions with GTL diesel fuel after
calibration optimization;
Figure 5 is projected soot and NOx tradeoff for all investigated GTL
fuels with DOE computer individual optimized software adaptation; and
Figure 6 is non-linear response in the projected emission reductions
with blends of GTL and sulphur free European diesel fuel.
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Summary of the Invention
The invention provides a diesel fuel composition comprising both crude oil
derived
diesel fuel, which crude oil derived diesel fuel has a density at 15 deg C
below 0.85
kg/I, a sulphur content of less than 10 mg/kg, a polyaromatics content of
below 5
mass%, and a cetane number from 51 to 60, and Gas-to-Liquids (GTL) diesel
fuel,
which GTL diesel has a density at 15 deg C of below 0.78 kg/I, a sulphur
content of
less than 1 mg/kg, polyaromatics below 0.1 mass%, and a cetane number above
65,
in a volumetric ratio range of from 1:99 to 99:1 and with a molar H:C ratio of
between
1.8:1 and 2.1:1.
The diesel fuel composition may have less than 10 mg/kg sulphur.
The diesel fuel composition may have less than 5 mass% polycyclic aromatics.
The crude oil derived diesel fuel may be a fuel meeting the EN590
specification.
The volumetric ratio range may be from 1:9 to 9:1.
The volumetric ratio range may be from 1:5 to 5:1.
The molar H:C ratio may be from 1.85:1 and 2.05:1.
The molar H:C ratio may be from 1.9:1 and 2.00:1.
The diesel fuel composition may have an ASTM D86 10% distillation temperature
of
from 180 C to 220 C.
The ASTM D86 10% distillation temperature may be from 200 C to 215 C.
The diesel fuel composition may have a flash point of between 60 C and 80 C,
typically from 65 C to 78 C.
The diesel fuel composition may have a density at 15 C of from 0.77 kg/I to
0.84 kg/I.
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The diesel fuel composition may have a density at 15 C of from about 0.8 kg/I
to
about 0.82 kg/I.
The diesel fuel composition may have a lower heating value of from 42 500
kJ/kg to
43 800kJ/kg, usually from 43 100 kJ/kg to 43 600 kJ/kg, typically from 43 200
kJ/kg
to 43 500 kJ/kg.
Use of Gas-to-Liquid diesel fuel as a blend component for a diesel fuel
composition,
which, when combusted in an engine, has reduced NOx and soot emissions, which
composition comprises both crude oil derived diesel fuel meeting the European
EN590 specification for sulphur-free diesel fuel (designated EU diesel), and
the Gas-
to-Liquids (GTL) diesel fuel, wherein the crude oil derived diesel fuel to Gas-
to-Liquid
diesel volumetric blend ratio ranges from 1:99 to 99:1 and the composition has
a
molar H:C ratio of between 1.8:1 and 2.1:1.
Reductions in both NOx and soot emissions may be obtained which are greater
than
indicated by the blending ratio of the GTL diesel in the crude oil derived
diesel fuel.
Thus, more than 70% of the reduction in both NOx and soot emissions which may
be
be obtained with neat GTL diesel fuel, may be obtained with a 1:1 GTL:Crude
derived diesel ratio.
More than 40% of the reduction in both NOx and soot emissions which may be
obtained with neat GTL diesel, may be obtained with a 1:4 GTL:Crude derived
diesel
ratio.
However, in some embodiments the reduction in NOx emissions may be less than
the reduction in soot emissions, and vice versa.
In some embodiments, the reduction in NOx may be minimal, however, the NOx
will
be reduced by the use of GTL diesel in accordance with the invention.
The properties of the composition and the blending ratios of the components
are as
described above for the composition.
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Examples Involving the Invention
The effect of GTL diesel fuel blends on exhaust emissions and engine
performance
has been studied. EU diesel fuel was used as a reference fuel, in addition to
being
the base stock for the blends. The properties of test fuels used in the
investigation
are shown in Table 1.
Table 1 Properties of the fuels investigated in this study.
GTL EU50 EU80 EU
2005
Property Units 100% 100/o GTL 50:50 Blend 80:20 Blend European
diesel fuel EU:GTL EU:GTL sulphur-free
diesel fuel
Density 15 C k /I 0.768 0.802 0.821 0.836
Density 20 C k /I 0.765 0.798 0.817 0.832
Cetane Number 71 62 58 54
Total Sulphur mg/kg < 1 4 6 7
D86 Distillation IBP C 169 157 174 193
5% C 180 193 204 214
10% C 187 201 212 221
20% C 200 215 225 233
30% C 219 231 240 248
40% C 235 248 256 264
50% C 251 264 270 277
60% C 267 277 282 287
70% C 283 291 294 299
80% C 297 305 307 313
90% C 312 322 324 332
95% C 321 337 339 354
FBP C 329 346 350 360
Flash Point C 59 66 76 82
Kinematic Viscosity 40 C mm /s 1.97 2.54 2.79 2.95
CFPP C -19 -18 -17 -17
Cloud Point C -18 -17 -15 -14
Total Aromatics* % m/m 0.1 13.5 21.5 26.8
Bi- and Pol c clic aromatics* % m/m 0.0 2.3 3.7 4.6
Hydrogen Content* % m/m 15.0 14.3 13.8 13.5
H/C ratio (molar)* - 2.10 1.98 1.91 1.86
Lower Heating Value* MJ/kg 43.8 43.5 43.2 43.1
HFRR Wear Scar Diameter ,um 370 < 400 < 400 394
* Values for blends calculated according to blending ratio
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Dynamometer tests were conducted with a Mercedes BenzTM E220 CDI vehicle,
using the New European Driving Cycle (NEDC) emission test, and without any
changes to the basic EU3 emission level engine calibration or engine hardware.
The
vehicle was tested with its standard calibration without any adaptation, with
EU
diesel, the 1:1 blend and for the neat GTL fuel. The relevant test vehicle
data are
shown in Table 2.
Table 2 Test vehicle and engine data
Vehicle designation Mercedes E 220 CDI Limousine
Model year 2003
Transmission 6-speed manual gearbox
Gross vehicle mass 2 145 kg
Engine designation MB OM646, EU3 emission level
Displacement, configuration 2,2 L, in-line 4 cylinder, 4 valves per
cylinder
Compression ratio 18: 1
Fuel management Common rail fuel injection (peak pressure
1 600 bar)
Air management Turbocharged (VNT), intercooled
Emission control Cooled EGR, inlet swirl control, close
coupled and underfloor oxidation catalysts
Rated torque 340 Nm at 2 000 rev/min
Rated power 110 kW at 4 200 rev/min
The results of the unadapted vehicle emission tests are depicted in Fig. 2 for
the EU
diesel, EU50, and GTL diesel fuel. The averaged results for the test runs are
presented as the percentages relative to the EU diesel reference fuel. FC
indicates
the volumetric fuel consumption.
For neat GTL diesel fuel, an unexpectedly high reduction of >90% for HC and CO
emissions was observed. The CO and HC reductions for the 50% blend scale
roughly with the blending ratio. The NOx emissions were reduced marginally,
with
the 50% blend again showing about half the reduction of the neat GTL diesel
fuel.
The same applies for the HC+NOx data.
PM emissions were reduced by up to 30% with the GTL diesel. Surprisingly, a
strong
non-linear characteristic was evident with the 50% blend (EU50), which showed
a
reduction of approximately 22%.
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The potential for further emission reductions with the test fuels, and
including the
optimisation of a limited number of software parameters in the Engine Control
Unit
(ECU) of the engine was then investigated. For this purpose, an engine mounted
on
a test bench was used. Steady state test runs were carried out at five
operating
points characteristic for NEDC emission test cycle. The software parameters
investigated were the Exhaust Gas Recirculation (EGR) rate, the start of pilot
injection (SOPI) and the start of main injection (SOMI). The five operating
points are
shown in Table 3
Table 3 Steady state engine test points chosen to reflect NEDC
characteristics.
Engine Test Engine Speed bmep Power Description
Point rev/min (bar) kW
1 1 000 0 0 Pseudo Idle
2 1 600 3.3 9 Characteristic operating
3 2 000 2 7 points for the NEDC
4 2 000 5 18 emission test
5 2 800 4 20
Fig. 3 shows two examples of results obtained from the steady state test bench
work.
The figure depicts representative data for the effect of GTL diesel fuel and
its blends
on the soot - NOx trade-off characterisitc at two operating points, namely 1
600
rev/min and 3,3 bar bmep (brake mean effective pressure), and 2 000 rev/min
and 5
bar bmep. In this case, the EGR rate was varied, while the SOPI and SOMI were
kept constant and equal to the reference values. Soot emission levels were
calculated from exhaust smoke levels determined by FSN (Filter Smoke Number)
measurements.
It is evident that GTL diesel offers a significant reduction in terms of both
soot
emissions and NOx for all the EGR rates tested. The soot emission increase for
decreasing NOx values follows the expected pattern, and enables a wide range
of
possible alternative software calibrations. Surprisingly, the strong non-
linear
behavior of the EU50 blend is again evident - this fuel exhibits almost the
same
benefits as neat GTL diesel fuel.
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A design of experiments (DOE) method was used to numerically optimize the
three
software parameters simultaneously. The DOE predictions were verified by
actual
experiments, and an example of the results of the simultaneous optimisation of
all
three calibration parameters at each of the engine operating points is shown
in Fig. 4.
In this case the optimisation has been performed to minimise NOx emissions
with the
GTL diesel fuel. Reductions of between 30% and 75% were obtained, without
compromising the other emissions, when compared to the EU diesel.
The measured data at the five steady-state test points was used to predict the
emissions over the NEDC test cycle. Empirical factors were used to account for
the
differences between the steady-state and transient engine operation. All
results from
the selected operating points have been normalized and combined into one
universal
plot, shown in Fig. 5, to mimic the behavior in a NEDC test with an optimized
calibration for each fuel. A surprisingly large reduction in soot and NOx
appears to
be possible for the GTL diesel fuel and the EU50 and EU80 blends. These
reductions are possible without hardware changes to the engine.
The neat GTL would allow for a simultaneous soot and NOx reduction of at least
35%
compared to the EU diesel calibration. For constant engine-out soot emission,
a
NOx reduction of 45% seems possible. Due to the non-linear response with the
GTL
blends, reductions in soot and NOx that are greater than expected when
considering
the blending ratio, could be obtained with the EU80 and EU50 fuels. This non-
linear
response is depicted graphically in Fig. 6.
A 50% GTL blend would recover approximately 85% of the soot/NOx benefits of
neat
GTL, while a 20% GTL blend would recover approximately 48% of the benefit. It
should be noted that the results shown so far have been facilitated by a
simple and
cost-efficient software adaptation only. It is to be expected that further
improvements
will.be possible if additionally hardware changes, e.g. in the injection
system and/or
the combustion chamber design are taken into account.
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