U.S. patent application number 11/004361 was filed with the patent office on 2005-07-14 for synthetic fuel with reduced particulate matter emissions and a method of operating a compression ignition engine using said fuel in conjunction with oxidation catalysts.
Invention is credited to Myburgh, Ian Stradling, Schaberg, Paul Werner.
Application Number | 20050154240 11/004361 |
Document ID | / |
Family ID | 34743513 |
Filed Date | 2005-07-14 |
United States Patent
Application |
20050154240 |
Kind Code |
A1 |
Myburgh, Ian Stradling ; et
al. |
July 14, 2005 |
Synthetic fuel with reduced particulate matter emissions and a
method of operating a compression ignition engine using said fuel
in conjunction with oxidation catalysts
Abstract
The invention provides a compression ignition engine fuel
derived from a Fischer-Tropsch process, which fuel has a generally
increasing iso:n paraffins ratio with increasing paraffin carbon
number at least between C.sub.9 to C.sub.18, less than 0.05% m/m
sulphur, and less than 10% by mass aromatics. The fuel may have on
average more than 0.9 alkyl branches per paraffinic molecule as
measured by H.sup.+ NMR analysis. The invention also provides a
method for operating a compression ignition engine to produce low
particulates emissions, which method comprises combusting the fuel
with oxygen or an oxygen containing gas in the engine. Yet further
the invention provides a method of improving the conversion
efficiency of oxidation catalysts used in conjunction with
compression ignition engines, said method including combusting the
fuel in the compression ignition engine in the presence of said
oxidation catalysts and in oxygen or an oxygen containing gas.
Inventors: |
Myburgh, Ian Stradling;
(Vanderbijlpark, ZA) ; Schaberg, Paul Werner;
(Noordhoek, ZA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
34743513 |
Appl. No.: |
11/004361 |
Filed: |
December 3, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11004361 |
Dec 3, 2004 |
|
|
|
PCT/ZA03/00075 |
Jun 6, 2003 |
|
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Current U.S.
Class: |
585/14 |
Current CPC
Class: |
C10L 1/08 20130101 |
Class at
Publication: |
585/014 |
International
Class: |
C10M 171/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 7, 2002 |
ZA |
2002/4572 |
Apr 11, 2003 |
ZA |
2003/2855 |
Claims
What is claimed is:
1. A compression ignition engine fuel derived from a
Fischer-Tropsch process, wherein an iso-paraffin to n-paraffin mass
ratio of the fuel generally increases as paraffin carbon number
increases from C.sub.9 to C.sub.18, wherein the fuel has less than
0.05% m/m sulphur and less than 10% by mass aromatics, and wherein
the fuel has an average of more than 0.9 alkyl branches per
paraffinic molecule as measured by H+ NMR analysis.
2. A compression ignition engine fuel as claimed in claim 1,
wherein the fuel has an average of more than 1 alkyl branch per
paraffinic molecule.
3. A compression ignition engine fuel as claimed in any claim 1,
wherein the iso-paraffin to n-paraffin mass ratio of the fuel
generally increases as paraffin carbon number increases from
C.sub.9 to C.sub.24.
4. A compression ignition engine fuel as claimed in claim 1,
wherein the fuel comprises at least 50 mass % iso-paraffins.
5. A compression ignition engine fuel as claimed in claim 3,
wherein the fuel comprises at least 60 mass % iso-paraffins.
6. A compression ignition engine fuel as claimed in claim 1,
wherein the iso-paraffin to n-paraffin mass ratio is from 1:1 to
4:1.
7. A compression ignition engine fuel as claimed in claim 1,
wherein the fuel predominantly comprises C.sub.8 to C.sub.24
paraffins.
8. A compression ignition engine fuel as claimed in claim 1,
wherein the fuel predominantly comprises C.sub.9 to C.sub.22
paraffins.
9. A compression ignition engine fuel as claimed in claim 1,
wherein the fuel comprises more than 70 mass % of C.sub.12 and
higher paraffins.
10. A compression ignition engine fuel as claimed in claim 9,
wherein the fuel comprises paraffins having an average carbon
number of from 13 to 19.
11. A compression ignition engine fuel as claimed in claim 10,
wherein the fuel comprises paraffins having an average carbon
number of about 15.
12. A compression ignition engine fuel as claimed in claim 1,
wherein the fuel is substantially oxygenate free and comprises less
than 0.1% oxygen.
13. A compression ignition engine fuel as claimed in claim 1,
wherein the fuel has a cetane number of at least 55.
14. A method of improving the conversion efficiency of an oxidation
catalyst used in conjunction with a compression ignition engine,
the method comprising: combusting a compression ignition engine
fuel derived from a Fischer-Tropsch process, wherein an
iso-paraffin to n-paraffin mass ratio of the fuel generally
increases as paraffin carbon number increases from C.sub.9 to
C.sub.18, wherein the fuel has less than 0.05% m/m sulphur and less
than 10% by mass aromatics, and wherein the fuel has an average of
more than 0.9 alkyl branches per paraffinic molecule as measured by
H+ NMR analysis, in a compression ignition engine in the presence
of an oxidation catalyst and an oxygen containing gas, such that a
conversion efficiency of the oxidation catalyst is improved.
15. A method as claimed in claim 14, further comprising: operating
the compression ignition engine at idling or low engine loads.
16. A method as claimed in claim 14, wherein the compression
ignition engine fuel is a gas-to-liquids diesel fuel.
17. A method for operating a compression ignition engine to produce
low particulates emissions, the method comprising: combusting a
compression ignition engine fuel derived from a Fischer-Tropsch
process, wherein an iso-paraffin to n-paraffin mass ratio of the
fuel generally increases as paraffin carbon number increases from
C.sub.9 to C.sub.18, wherein the fuel has less than 0.05% m/m
sulphur and less than 10% by mass aromatics, and wherein the fuel
has an average of more than 0.9 alkyl branches per paraffinic
molecule as measured by H+ NMR analysis, with an oxygen containing
gas in a compression ignition engine, whereby low particulate
emissions are produced.
18. A method as claimed in claim 17, wherein the low particulate
emissions comprise particulates having a maximum number weighted
particle size distribution of less than 1.times.10.sup.8 particles
per cm.sup.3 and an average particle size of from 10 nm to 20
nm.
19. A method as claimed in claim 17, wherein the low particulate
emissions comprise fewer nanoparticles than particulate emissions
produced by a compression ignition engine combusting a diesel fuel
derived from a crude oil.
20. A method as claimed in claim 17, wherein the low particulate
emissions comprise more than 70% fewer particulates of a size less
than or equal to 50 nm when compared to particulate emissions
produced by combusting, under similar combustion conditions, a low
sulphur crude oil-derived diesel fuel.
Description
RELATED APPLICATIONS
[0001] This application is a continuation, under 35 U.S.C. .sctn.
120, of International Patent Application No. PCT/ZA03/00075, filed
on Jun. 6, 2003, under the Patent Cooperation Treaty (PCT), which
was published by the International Bureau in English on Dec. 18,
2003, which designates the United States, and claims the benefit of
South African Patent Application No. 2002/4572, filed on Jun. 7,
2002, and South African Patent Application No. 2003/2855, filed on
Apr. 11, 2003. All above-referenced prior applications are
incorporated by reference herein in their entirety.
FIELD OF THE INVENTION
[0002] This invention relates to a synthetic compression ignition
engine fuel, to a method of making that fuel, and to a method of
operating a compression ignition engine using said fuel, and in
conjunction with oxidation catalysts.
BACKGROUND OF THE INVENTION
[0003] It has been stated that the potential impact of a fuel on
diesel emissions has been recognized by state and federal
regulatory agencies, and fuel specifications have now become a part
of emissions control legislation. Studies both in the U.S. and in
Europe have concluded that particulate emissions are generally a
function of fuel sulfur content, aromatics content and cetane
number. Consequently, the U.S. Environmental Protection Agency has
set a limit on diesel fuel sulfur content of 0.05 wt. % as well as
a minimum cetane number of 40, with even stricter limits on sulphur
content being envisaged in the future. Additionally, the state of
California has set a 10 vol. % maximum on aromatics content. Also,
alternative fuels are beginning to play more of a role for low
emissions vehicles. Thus, the search for efficient, clean burning
fuels, particularly with low particulate emissions remains
ongoing.
[0004] Epidemiological investigations have suggested an association
between health effects and ambient suspended particulate matter.
These studies have associated disease incidence with particulate
matter exposure. Research is continuing in many areas to identify a
biological mechanism whereby this association can be explained, but
as yet there are only hypotheses. Lung responses to particles in
the 50 nm size range have been identified, where there are none
when the same material is introduced as 250 nm particles. This has
lead to the suggestion that adverse health effects are associated
with the ultrafine particle fraction, and has promoted interest in
the potential health effects of the particle itself, rather than
any chemical property of the particle. Thus the number of
nanoparticles emitted is possibly of greater importance than the
composition of the particle.
[0005] Typically, diesel particle emissions have a bimodal size
distribution, when particle number emissions are plotted on a
logarithmic scale. The first mode is associated with particles
formed by accumulation, and has a peak in the size range between
500 and 50 nm. These particles are referred to as ultrafine
particles. The second peak is in the size range between 50 and 5
nm, and is associated with particles formed by nucleation.
Particles in this size range are generally referred to as
nanoparticles. Further distinction is made between fine particles
(or PM2.5, diameter <2,500 nm), and PM10 (diameter <10,000
nm).
[0006] The accumulation mode particles account for most of the mass
of diesel particulate emissions, while the greatest numbers of
particles are found in the nanoparticle size range.
[0007] The concerns regarding the health effects of very small
particles have been compounded by observations that modern diesel
engines, while emitting lower particle mass concentrations than
older engines, may actually emit higher particle number
concentrations than the older engines. Most of the particles
emitted are in the nanoparticle size range, and it has been
suggested that the reason for increased number of these particles
is that the nucleation and growth of nanoparticles is suppressed by
the presence of existing carbon particles which are found in the
accumulation mode size range. Thus, older engines with higher
particulate mass emissions can display lower nanoparticle number
emissions. Since it has been demonstrated that the use of synthetic
diesel fuels results in lower particulate mass emissions than
conventional crude oil-derived diesel fuels, it is possible that
the same mechanism may result in higher particle number
concentrations being emitted with these fuels.
[0008] Surprisingly, after extensive research, the applicant has
now developed a fuel having a composition which results in superior
nanoparticle number emission properties compared to low sulphur
crude oil-derived diesel fuel.
SUMMARY OF THE INVENTION
[0009] In this specification whenever the term diesel fuel is used
it is intended to include any middle distillate cut useful in a
compression ignition engine (CI engine).
[0010] In accordance with this invention there is provided a
compression ignition (CI) engine fuel derived from a
Fischer-Tropsch process, which fuel has a generally increasing
iso:n paraffins ratio with increasing paraffin carbon number at
least between C.sub.9 to C.sub.18, less than 0.05% m/m sulphur, and
less than 10% by mass aromatics.
[0011] Said CI engine, when combusting said fuel, emitting
particulates having a maximum number weighted particle size
distribution of less than 1.times.10.sup.8 particles per cm.sup.3
between 10 nm and 20 nm particle size.
[0012] The iso:n paraffins ratio may generally increase with
increasing paraffins carbon number at least between C.sub.9 to
C.sub.24.
[0013] The particulates which are emitted may have a particle size
distribution in which fewer nanoparticles are produced than that
emitted when a diesel fuel derived from crude oil is combusted in a
compression ignition engine.
[0014] The fuel may contain predominantly branched paraffins, that
is, .gtoreq.50 mass % iso-paraffins, typically >55 mass %, and
more typically .gtoreq.60 mass % iso-paraffins.
[0015] The iso-paraffin to n-paraffin mass ratio may be from 1:1 to
4:1, typically from 3:2 to 3:1, generally 2:1.
[0016] In one embodiment the iso-paraffin to n-paraffin mass ratio
is 21:10.
[0017] The fuel may be predominantly C.sub.8 to C.sub.24
material.
[0018] The fuel may be predominantly C.sub.9-C.sub.22.
[0019] The fuel may include in excess of 70 mass % of C.sub.12 and
heavier.
[0020] The fuel may have an average carbon number of between 13 and
19, typically about 15.
[0021] The fuel may have on average more than 0.9 alkyl branches
per paraffinic molecule as measured by H.sup.+ NMR analysis.
[0022] The fuel may have more than 1 alkyl branch per paraffinic
molecule.
[0023] The fuel may be substantially oxygenate free, typically
having less than 0.1% oxygen. The fuel may have less than 0.01% and
typically less than 0.005% oxygen.
[0024] The fuel may have a cetane number of at least 55, typically
at least 65. The fuel may have a cetane number of 74.
[0025] The invention extends to a diesel fuel which, when combusted
in a compression ignition engine under normal combustion
conditions, results in emissions having a reduction of more than
70% in the number of particles in the .ltoreq.50 nm size range,
when compared to a low sulphur crude oil-derived diesel fuel
combusted under similar conditions.
[0026] The reduction may be greater in the .ltoreq.30 nm range.
[0027] The fuel may have characteristics as set out in Table 1
below:
1TABLE 1 Composition and Characteristics of the Synthetic Diesel
Fuel Property Value Specific Gravity, 60.degree. F. 0.765 Nitrogen
ppm <1 Sulfur ppm <1 Cloud Point .degree. C. -18 Cetane
Number 74.8 Total Aromatics (wt. %) wt. % <1.0 GC-MS Analysis
Paraffins, wt % wt. % 100 Paraffin iso/n ratio Mass 2.1 Olefins, wt
% wt. % 0 Percent of material C12-C24 Mass 80.7 Average Carbon
Number 15.2 Alkyl branches/molecule 1.0 Distillation (D-86, vol. %)
IBP .degree. C. 169 10 .degree. C. 187 50 .degree. C. 251 90
.degree. C. 312 FBP .degree. C. 329
[0028] The branching characteristics of the fuel are summarized in
table 2 below:
2TABLE 2 Branching Characteristic of Low Emission Diesel Fuel
Paraffins iso/n-paraffin n-paraffins % Iso-paraffins % Total Ratio
C9 2.96 0.00 2.96 -- C10 3.59 4.24 7.83 1.18 C11 3.80 4.65 8.45
1.22 C12 3.65 4.77 8.42 1.31 C13 3.41 5.34 8.75 1.57 C14 3.00 5.34
8.34 1.78 C15 2.61 5.56 8.17 2.13 C16 2.33 8.65 10.98 3.71 C17 1.99
5.74 7.72 2.89 C18 1.51 6.11 7.62 4.04 C19 1.60 5.98 7.58 3.73 C20
1.18 5.35 6.53 4.52 C21 0.58 3.82 4.41 6.54 C22 0.22 2.00 2.23
8.94
[0029] According to a further aspect of the invention, there is
provided a method of improving the conversion efficiency of
oxidation catalysts used in conjunction with compression ignition
engines, said method including combusting a compression ignition
engine fuel as described above in the compression ignition engine
in the presence of said oxidation catalysts and oxygen or an oxygen
containing gas.
[0030] The method may include the operation of the compression
ignition engine at idling and low engine loads.
[0031] The compression ignition engine fuel may be a synthetic
Fischer-Tropsch derived fuel which may in turn be a GTL diesel
fuel.
[0032] According to a further aspect of the invention there is
provided a method for operating a compression ignition (CI) engine
to produce low particulate emissions, which method comprises
combusting a CI engine fuel substantially as described above with
oxygen or an oxygen containing gas in a CI engine.
[0033] Said CI engine, when combusting said fuel emitting
particulates having a maximum number weighted particle size
distribution of less than 1.times.10.sup.8 particulates per
cm.sup.3 between 10 nm and 20 nm particle size.
[0034] The particulates which are emitted may have a particle size
distribution in which fewer nanoparticles are produced than that
emitted when a diesel fuel derived from crude oil is combusted in a
compression ignition engine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 schematically depicts a Fischer-Tropsch work-up
process.
[0036] FIG. 2 provides the number weighted particle size
distribution with synthetic diesel fuel and low sulphur diesel
fuel, for the Caterpillar C12 heavy-duty diesel engine.
[0037] FIG. 3 provides the number weighted particle size
distribution with synthetic diesel fuel and low sulphur diesel
fuel, for the VW Tdi passenger car diesel engine.
[0038] FIG. 4 provides the relative integrated particle number
emissions for various size ranges of particles.
[0039] FIG. 5 provides the regulated exhaust emissions with
synthetic diesel fuel, relative to low sulphur diesel fuel.
[0040] FIG. 6 provides modes 2, 5, and 8 of the Tokyo Emission Test
Cycle.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0041] The invention will now be illustrated, by way of
non-limiting examples only, with reference to the accompanying FIG.
1.
[0042] A FT work-up process is outlined in the attached FIG. 1. The
synthesis gas (syngas), a mixture of Hydrogen and Carbon Monoxide,
enters the FT reactor 1 where the synthesis gas is converted to
hydrocarbons by the FT process.
[0043] A lighter FT fraction is recovered in line 7, and may or may
not pass through fractionator 2 and hydrotreater 3. The product 9
(9a) from the hydrotreater may be separated in fractionator 4 or,
alternatively, mixed with hydrocracker 5 products 16 and sent to a
common fractionator 6.
[0044] A waxy FT fraction is recovered in line 13 and sent to
hydrocracker 5. If fractionation 2 is considered then the bottoms
cut 12 are also sent to hydrocracker 5. The products 16, on their
own or mixed with the lighter fraction 9a, are separated in
fractionator 6.
[0045] Depending on the process scheme, a light product fraction,
naphtha 19, is obtained from fractionator 6 or by blending
equivalent fractions 10 and 17. This is a C.sub.5-160.degree. C.
fraction useful as naphtha.
[0046] A somewhat heavier cut i.e. the middle cut, synthetic diesel
20, is obtainable in a similar way from fractionator 6 or by
blending equivalent fractions 11 and 18. This cut is recovered as a
150-370.degree. C. fraction useful as diesel.
[0047] The heavy unconverted material 21 from fractionator 6 is
recycled to extinction to hydrocracker 5. Alternatively, the
residue may be used for production of synthetic lube oil bases. A
small amount of C.sub.1-C.sub.4 gases is also separated in
fractionator 6.
[0048] The described FT work-up process of FIG. 1 may be combined
in a number of configurations. The applicant considers these an
exercise in what is known in the art as Process Synthesis
Optimisation.
EXAMPLES OF USE OF LOW EMISSION DIESEL FUEL
[0049] Tests were conducted using the fuels of the invention:
Example 1
Particle Number Emissions
[0050] For the purposes of comparing particle number emissions and
size distributions, a commercially available, low sulphur diesel
fuel approved by the US Environmental Protection Agency for
on-highway use, was used as the reference fuel. Important
characteristics of the two test fuels are presented in Table 3.
3TABLE 3 Analysis of Test Fuels Low-S Diesel Synthetic Test
Reference Diesel Property Method Fuel Fuel Specific Gravity,
60.degree. F. ASTM D4052 0.8705 0.7647 Kinematic Viscosity., ASTM
D445 3.199 2.007 40.degree. C. (cSt) Flash Point (.degree. C.) ASTM
D93 82 60 Cloud Point (.degree. C.) ASTM D2500 -19 -18 Total
Sulphur (ppm) ASTM D2622 404 <1 Distillation (.degree. C.) ASTM
D86 IBP 196 169 10% 223 187 50% 273 251 90% 330 312 FBP 359 329
Cetane Number ASTM D613 41.5 74.8 Total Aromatics (wt. %) ASTM
D5186 38.4 <1.0 Oxygen as Oxygenates <6 according to GC-MS
analysis, (ppm) Oxygen as primary <6 C12-C24 alcohol (ppm)
Oxygen as primary <6 C7-C12 alcohol (ppm)
[0051] Exhaust particle number emissions and size distributions
were measured using two test engines, a heavy-duty diesel engine,
and a passenger car diesel engine.
[0052] The heavy-duty diesel engine was a Caterpillar.TM. model C12
modified to be compliant with 1998 US emission levels. This engine
is a 6 cylinder, 12 liter, turbocharged, after-cooled diesel engine
rated at 312 kW at 2100 rev/min, with a peak torque of 2237 Nm at
1200 rev/min. A 5W-40 synthetic lubricating oil, which had been
aged for 40 hours, was used in the engine during the tests.
[0053] The passenger car engine was a 1999 Volkswagen.TM. TDI
diesel engine. This engine is a 4 cylinder, 1.9 liter,
turbocharged, charge-air cooled diesel engine, rated at 66 kW. The
standard exhaust aftertreatment equipment, in the form of an
oxidation catalyst, was fitted for the tests. A 5W-40 synthetic
lubricating oil, which had approximately 125 hours of running time
in the engine at the onset of testing, was used in the engine
during the tests.
[0054] The test engines were fully warmed up and operated under
steady-state conditions while the measurements were conducted. The
heavy-duty engine was tested at four different speed and load
settings, while the passenger car engine was tested at five
different speed and load settings. The speed and load settings used
for the two engines are presented in Table 4. For each fuel, one
set of measurements was made per day for three consecutive days,
and the results averaged to obtain the final size distribution for
each test made. For the purposes of illustration, a single
composite size distribution was then obtained for each engine and
fuel, by averaging the size distributions from each test mode.
4TABLE 4 Engine Test Modes Heavy-duty Passenger Car Engine Test
Modes Engine Test Modes Mode Speed Load Speed Load Number (rev/min)
(Nm) (rev/min) (Nm) 1 1,700 569 2,620 72 2 1,400 366 2,500 152 3
1,200 814 1,900 101 4 800 idle 1,400 40 5 -- -- 1,200 idle
[0055] Particle size distributions in the exhaust were measured by
means of a micro-dilution device, a Scanning Mobility Particle
Sizer (SMPS), and a Condensation Particle Counter (CPC). The SMPS
measures particle electric mobility diameter and the CPC measures
particle number concentrations in the diameter range of 7 to 300 nm
in a 4-minute (2 minutes up, 2 minutes down) scan time. This
particle measurement system consists of a neutralizer, a mobility
section, a TSI model 3010 CPC, and a computerized control and data
acquisition system. The dilution system is described in more detail
in SAE Paper 1999-01-1142, 1999 by Abdhul-Khalek, I. S., Kittelson,
D. B., and Brear, F., "The Influence of Dilution Conditions on
Diesel Exhaust Particle Size Distribution Measurements", and SAE
Paper 1999-01-1142, 1999 by Abdhul-Khalek, I. S., Kittelson, D. B.,
and Brear, F., "The Influence of Dilution Conditions on Diesel
Exhaust Particle Size Distribution Measurements".
[0056] The micro-dilution tunnel pre-conditions the exhaust sample
before the sample enters the SMPS. In the configuration used in
these tests, the first-stage dilution temperature was held constant
at approximately 40.degree. C. for the heavy duty engine tests, and
30.degree. C. for the passenger car engine tests.
[0057] The two-stage air ejector exhaust dilution system is
designed to allow variation of the residence time in the primary
dilution stage, before secondary dilution. For these tests, a
relatively short residence time (0.8 seconds) in the micro-dilution
tunnel was maintained. The exhaust enters a sampling probe that is
immersed in the exhaust flow and then passes through a short
section of stainless steel tube that is insulated and heated to
keep the sample temperature and the exhaust temperature equal.
Downstream of the sample line, an ejector pump with a flow orifice
provides the first stage (primary) dilution. The ejector pump
consists of a compressed air inlet, sample inlet (orifice
location), and one outlet. Filtered and compressed air at 276 kPa
(40 psi) is used to drive the ejector pump, which in turn draws an
exhaust sample flow through the orifice. This air then mixes with
the exhaust sample providing primary dilution. The primary dilution
ratio varied between 9:1 and 12:1.
[0058] The secondary dilution stage is designed to halt additional
particle growth and to provide a final particle number
concentration in the dilute exhaust sample within the measurement
range of the CPC. Filtered, compressed air at 207 kPa (30 psi) is
used to drive the ejector pump, which draws an exhaust sample flow
through an orifice, from the micro-dilution tunnel. The secondary
dilution ratio varied between 19:1 and 22:1.
[0059] The composite, number weighted, particle size distributions
for the synthetic diesel fuel and the reference fuel, are shown in
FIGS. 2 and 3, for the heavy-duty engine and the passenger car
engine, respectively. As the ranges of the measured particle number
emissions and sizes are large, the graphs are plotted with
logarithmic axes.
[0060] It can be seen that with both engines, the particle size
distributions with the reference fuel have distinctive bimodal size
distributions, with both the nucleation mode and the accumulation
mode being present. It can also be seen that, with both engines,
the numbers of particles in the size range below approximately 30
nm are significantly lower with the synthetic diesel fuel, than
with the low sulphur reference diesel fuel. Because most of the
particle number emissions are concentrated in this size range, this
has the consequence that the total particle number emissions are
also significantly lower with the synthetic diesel fuel, than with
the low sulphur diesel fuel. These findings are summarised in FIG.
4, which shows a comparison of the integrated particle numbers in
the size ranges below 30 nm, below 50 nm, and below 300 nm. It can
be seen that for both engines, there are reductions in the number
of particles emitted in these different size classifications, of
greater than 65%.
[0061] Regulated Exhaust Emissions
[0062] For the purposes of comparing regulated exhaust emissions, a
fuel meeting the US Environmental Protection Agency requirements
for low sulphur diesel fuel for on-highway use, was used as the
reference fuel in the tests. Important characteristics of the
reference fuel and the synthetic diesel fuel are shown in Table
5.
5TABLE 5 Properties of Test Fuels Low Sulphur Diesel Synthetic Test
Reference Diesel Property Method Fuel Fuel Density at 15.degree. C.
ASTM D4052 0.8457 0.7769 (kg/l) Distillation (.degree. C.) ASTM D86
IBP 184 189 10% 214 209 50% 259 256 90% 312 331 FBP 342 356
Viscosity at 40.degree. C. ASTM D445 2.35 2.43 (cSt) Cetane Number
ASTM D613 40.3 >73.7 Total Sulphur (mass %) ASTM D4294 0.022
0.001 Total Aromatics (mass %) HPLC 42.78 0.47 Polynuclear
Aromatics 9.39 0.03 (mass %) Cloud Point (.degree. C.) ASTM D2500
-18 -29 CFPP (.degree. C.) IP 309 -21 -37
[0063] Regulated exhaust emissions were measured using the diesel
engine described in Table 6. This unit was modified and calibrated
to meet the 1991 US emission standards. Hot-start transient
emission tests were conducted in accordance with the EPA Federal
Test Procedure (FTP) as specified in the Code of Federal
Regulations (CFR), Title 40, Part 86, Subpart N. Testing procedures
incorporated instrumentation and sample system calibrations, engine
performance checks, gaseous and particulate emissions sampling and
measurement, and transient test performance evaluations. The
emissions measured included unburned hydrocarbons (HC), carbon
monoxide (CO), nitrogen oxides (NOx), and particulate matter
(PM).
[0064] Three hot-start tests were performed with each fuel, and the
results presented represent the averaged values from the three
tests. The transient torque map that was used during the tests was
generated using the synthetic fuel, thereby ensuring that peak
engine loads attained during test runs would be similar for both
fuels.
6TABLE 6 Characteristics of 1988 DDC Series 60 Engine Engine
configuration In-line 6 cylinder, Displacement 12.7 liter (130 mm
bore, 160 mm stroke) Aspiration Turbocharged, intercooled Rated
Power 261 kW at 1800 rev/min Rated Torque 1830 Nm at 1200 rev/min
Fuel Injection Direct injection, electronically controlled unit
injectors Restrictions for Transient Inlet: 4.0 kPa Cycle Exhaust:
9.5 kPa Low idle speed 600 rev/min
[0065] The results of the emission tests are presented numerically
in Table 7, and are compared between the two test fuels graphically
in FIG. 5.
7TABLE 7 Results of Transient Hot-Start Emission Tests Hot Start
Transient Emissions (g/kWh) Low Sulphur Synthetic Emission Diesel
Fuel Diesel Fuel HC Mean value 0.215 0.094 Std. Deviation 0.011
0.006 Coeff. of Var., % 5.1 6.4 CO Mean value 3.829 2.571 Std.
Deviation 0.100 0.042 Coeff. of Var., % 2.6 1.6 NOx Mean value
7.050 5.081 Std. Deviation 0.033 0.049 Coeff. of Var., % 0.5 1.0 PM
Mean value 0.277 0.217 Std. Deviation 0.006 0.003 Coeff. of Var., %
2.2 1.4
[0066] It can be seen that with the synthetic diesel fuel produced
significantly lower emissions relative to the low sulphur diesel
fuel.
Example 2
Oxidation Catalyst Performance Tests
[0067] Various exhaust emission tests were carried out to compare a
Japanese low sulphur diesel fuel derived from crude oil and GTL
diesel fuel, a synthetic compression ignition fuel of the present
invention. The tests focused on regulated emissions of hydrocarbons
(HC), carbon monoxide (CO), nitrogen oxides (NOx) and particulate
matter (PM), as well as carbon dioxide (CO.sub.2). The emission
tests were performed on a Japanese heavy-duty vehicle, and tests
were conducted both with and without an oxidation catalyst fitted
in the vehicle exhaust.
[0068] The types of emission tests performed were a Japanese 13
mode steady-state test cycle for heavy-duty engines, and modes 2,
5, and 8 of the Tokyo test cycle, a special test cycle
representative of congested traffic patterns encountered in the
Tokyo inner city environment.
[0069] The properties of the synthetic diesel fuel used for the
tests were typical of diesel produced by low temperature
Fischer-Tropsch processes, with a very high cetane number (>70),
very low sulphur (<1 ppm), and a very low aromatics content
(<1%). In addition, the GTL diesel used in this study also has
good natural cold flow properties (CFPP <-20.degree. C.). The
reference diesel fuel used had a sulphur content of 29 ppm, an
aromatics content of 21%, and a cetane number of 57.5. The
properties of the test fuels are shown in Table 8.
8TABLE 8 Physical Properties of the Test Fuels Japanese Low Sulphur
Diesel Test (50 ppm sulphur Property Method GTL Diesel
specification) Feedstock -- Natural gas Crude oil Sulphur ppm
(mass) JIS K <1 29 2541 Density at 15.degree. C. kg/l JIS K
0.7680 0.8185 2249 Viscosity at 30.degree. C. mm.sup.2/s JIS K
2.335 2.770 2283 Cloud Point .degree. C. JIS K -20 -11 2269 Cold
Filter Plugging .degree. C. JIS K -30 -22.5 Point 2288 Lower Heat
of MJ/kg JIS K 43.72 43.26 Combustion 2279 MJ/l @ 15.degree. C.
calculated 33.58 35.41 Cetane Number JIS K 74.1 57.5 2280 Cetane
Index JIS K 79.8 57.4 2280 Distillation IBP .degree. C. JIS K 159.5
179.5 10% .degree. C. 2254 183.5 204.0 30% .degree. C. 214.0 233.0
50% .degree. C. 248.5 259.0 70% .degree. C. 282.0 283.5 90%
.degree. C. 314.0 317.5 95% .degree. C. 324.0 330.0 FBP .degree. C.
334.0 344.5 HPLC Saturates % (mass) JPI 99.9 78.7 Olefins % (mass)
5S-49-97 0.0 0.1 Total aromatics % (mass) 0.1 21.2 1-aromatics %
(mass) 0.1 18.7 2-aromatics % (mass) 0.0 2.3 +3-aromatics % (mass)
0.0 0.1 CHN C % (mass) ASTM 85.0 86.1 Content H % (mass) D 5291
14.9 13.8 N ppm (mass) <3 5
[0070] Details of the test vehicle are given in Table 9, and
details of the emission test cycles are given in Table 10 for the
13 mode test, and FIG. 6 for modes 2, 5, and 8 of the Tokyo test
cycle.
9TABLE 9 Heavy-Duty Test Vehicle Vehicle Type Truck Model Year 1998
Vehicle Weight kg 2 808 Equivalent Inertia Weight kg 6 025 Engine
In-line 5 cylinder Displacement l 6.634 Compression Ratio 19.2:1
Fuel Injection DI, In-line injection pump Aspiration Natural Peak
Power kW @ r/min 125 @ 2,900 Peak Torque Nm @ r/min 450@ 1,600
Equipment for EGR low emissions Oxidation catalyst
[0071]
10TABLE 10 Japanese 13-Mode Steady-State Emission Test Cycle for
Heavy-Duty Engines Speed Load Weighting Mode (% of rated) (% of
rated) Factor 1 idle -- 0.205 2 40 20 0.037 3 40 40 0.027 4 idle --
0.205 5 60 20 0.029 6 60 40 0.064 7 80 40 0.041 8 80 60 0.032 9 60
60 0.077 10 60 80 0.055 11 60 95 0.049 12 80 80 0.037 13 60 5
0.142
[0072] During testing, the exhaust gas was diluted with purified
air, supplied at a temperature of 25.degree. C. and a relative
humidity of 50%, in a dilution tunnel. The exhaust gas measurement
system (Horiba VETS-9000) included an exhaust gas analyser (Horiba
MEXA-9400F), a constant volume sampler (CVS-120T) and a low-volume
sampler (LVS). A glass fibre filter (Pallflex TX40HI20--WW) of 70
mm diameter was used for sampling PM in the LVS.
[0073] The results of each of the emission tests are presented in
Tables 11, 12, 13, and 14. It can be seen that, in general, all of
the regulated emissions (HC, CO, NOx, and PM) are lower with the
GTL diesel fuel, when compared to the Japanese low sulphur diesel
fuel. Also shown in each table, is the apparent conversion
efficiency of the oxidation catalyst fitted in the vehicle exhaust.
This is defined as the difference in emission level measured with
and without the catalyst fitted, expressed as a percentage of the
emission level without the catalyst fitted. The oxidation catalyst
is fitted to primarily to reduce HC, CO, and PM emissions, and the
conversion efficiencies for NOx are therefore not indicated.
[0074] It can be seen that the conversion efficiencies measured
with the GTL diesel fuel for HC and CO are always higher than those
measured with the low sulphur diesel. The conversion efficiency for
PM was lower with the GTL fuel for Mode 8 of the Tokyo test cycle,
but higher for all other tests. The averaged conversion
efficiencies for all of the tests are shown in Table 15, where it
can be seen that the conversion efficiency with the GTL diesel fuel
was higher than that of the Japanese low sulphur diesel by 29, 27,
and 3 percentage points, for HC, CO, and PM, respectively.
11TABLE 11 Results for 13-Mode Heavy-Duty Test Cycle Conversion
Without With Efficiency Oxidation Catalyst GTL GTL GTL Fuel LSD
diesel LSD diesel LSD diesel Emissions THC g/kWh 0.84 0.91 0.26
0.20 69% 78% CO g/kWh 2.55 2.00 0.78 0.31 69% 85% NOx g/kWh 4.93
4.21 4.64 4.07 -- -- PM g/kWh 0.17 0.14 0.14 0.11 18% 21%
[0075]
12TABLE 12 Results for Mode 2 of the Tokyo Test Cycle Conversion
Without With Efficiency Oxidation Catalyst GTL GTL GTL Fuel LSD
diesel LSD diesel LSD diesel Emissions THC g/kWh 0.59 0.37 0.24
0.08 59% 78% CO g/kWh 1.73 1.09 1.35 0.41 22% 62% NOx g/kWh 3.76
3.23 3.56 3.08 -- -- PM g/kWh 0.09 0.06 0.06 0.04 33% 33%
[0076]
13TABLE 13 Results for Mode 5 of the Tokyo Test Cycle Conversion
Without With Efficiency Oxidation Catalyst GTL GTL GTL Fuel LSD
diesel LSD diesel LSD diesel Emissions THC g/kWh 1.21 0.82 0.73
0.07 40% 91% CO g/kWh 0.40 0.29 0.18 0.05 55% 83% NOx g/kWh 2.61
2.22 2.45 2.12 -- -- PM g/kWh 0.07 0.05 0.05 0.03 29% 40%
[0077]
14TABLE 14 Results for Mode 8 of the Tokyo Test Cycle Conversion
Without With Efficiency Oxidation Catalyst GTL GTL GTL Fuel LSD
diesel LSD diesel LSD diesel Emissions THC g/kWh 1.21 0.82 0.73
0.07 31% 67% CO g/kWh 0.4 0.29 0.18 0.05 64% 91% NOx g/kWh 2.61
2.22 2.45 2.12 -- -- PM g/kWh 0.07 0.05 0.05 0.03 25% 20%
[0078]
15TABLE 15 Averaged Oxidation Catalyst Conversion Efficiencies for
CO, HC, and PM GTL Fuel LSD diesel Emissions THC g/kWh 50% 79% CO
g/kWh 53% 80% PM g/kWh 26% 29%
[0079] The following acronyms and abbreviations are used in the
above example: CHN--Carbon, hydrogen and nitrogen; CO--Carbon
monoxide; CO.sub.2--Carbon dioxide; CVS--Constant volume sampler;
DI--Direct injection; DPF--Diesel particulate filter; EGR--Exhaust
gas recirculation; FBP--Final boiling point; GTL--Gas-to-liquids;
HC--Unburned hydrocarbons; H/C Hydrogen/carbon ratio; HPLC--High
pressure liquid chromatography; IBP--Initial boiling point;
IC--Intercooled; LVS--Low volume sampler; NOC--Nippon Oil
Corporation; NOX--Oxides of nitrogen; PM--Particulate matter;
ppm--Parts per million; SOF--Soluble organic fraction; SPD--Slurry
Phase Distillate; TC--Turbocharging; THC--Total Unburned
Hydrocarbons.
[0080] Without admitting them as prior art, the following articles
are incorporated herein by reference, as if specifically reproduced
here in their totality, in order to improve in understanding the
invention and the examples: Abdul-Khalek, I., et al, "Diesel
Exhaust Particle Size: Measurement Issues and Trends", SAE Paper
980525, Society of Automotive Engineers, 1998; Schaberg, P. W., et
al, "Diesel Exhaust Emissions Using Sasol Slurry Phase Distillate
Process Fuels", SAE Paper 972898, Society of Automotive Engineers,
1997; Khalek, I., Kittelson, D. B., and Brear, F., "Nanoparticle
Growth during Dilution and Cooling of Diesel Exhaust: Experimental
Investigation and Theoretical Assessment", SAE Paper 2000-01-0515,
2000; Abdhul-Khalek, I. S., Kittelson, D. B., and Brear, F., "The
Influence of Dilution Conditions on Diesel Exhaust Particle Size
Distribution Measurements", SAE Paper 1999-01-1142, 1999;
Abdhul-Khalek, I. S., Kittelson, D. B., and Brear, F., "The
Influence of Dilution Conditions on Diesel Exhaust Particle Size
Distribution Measurements", SAE Paper 1999-01-1142, 1999; and
Schaberg, P. W., Myburgh, I. S., Botha, J. J., Roets, P. N. J.,
Voljoen, C. L., Dancuart, L. P., and Starr, M. E., "Diesel Exhaust
Emissions Using Sasol Slurry Phase Distillate Process Fuels", SAE
Paper 972898, 1997.
* * * * *