U.S. patent application number 11/245738 was filed with the patent office on 2006-05-04 for tuning fuel composition for driving cycle conditions in spark ignition engines.
Invention is credited to Kazuhiro Akihama, John T. Farrell, John E. Johnston, Alan M. Schilowitz, Takanori Ueda, Walter Weissman.
Application Number | 20060090727 11/245738 |
Document ID | / |
Family ID | 25224961 |
Filed Date | 2006-05-04 |
United States Patent
Application |
20060090727 |
Kind Code |
A1 |
Weissman; Walter ; et
al. |
May 4, 2006 |
Tuning fuel composition for driving cycle conditions in spark
ignition engines
Abstract
Tuning fuel composition delivered to a spark ignition, internal
combustion engine as a function of driving cycle conditions results
in improvements in one or more of fuel efficiency and combustion
emissions.
Inventors: |
Weissman; Walter; (Basking
Ridge, NJ) ; Farrell; John T.; (High Bridge, NJ)
; Schilowitz; Alan M.; (Highland Park, NJ) ;
Johnston; John E.; (Warren, NJ) ; Ueda; Takanori;
(Shizuoka, JP) ; Akihama; Kazuhiro; (Aichi,
JP) |
Correspondence
Address: |
EXXONMOBIL RESEARCH AND ENGINEERING COMPANY
P.O. BOX 900
1545 ROUTE 22 EAST
ANNANDALE
NJ
08801-0900
US
|
Family ID: |
25224961 |
Appl. No.: |
11/245738 |
Filed: |
October 7, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09818210 |
Mar 27, 2001 |
|
|
|
11245738 |
Oct 7, 2005 |
|
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Current U.S.
Class: |
123/295 ; 123/1A;
123/304; 123/430; 123/577 |
Current CPC
Class: |
Y02T 10/36 20130101;
F02D 19/081 20130101; C10L 1/06 20130101; F02D 19/0649 20130101;
F02D 19/0689 20130101; Y02T 10/30 20130101 |
Class at
Publication: |
123/295 ;
123/304; 123/001.00A; 123/577; 123/430 |
International
Class: |
F02M 43/00 20060101
F02M043/00 |
Claims
1-12. (canceled)
13. A fuel system for spark ignition engines having a CR of 11 or
more, comprising: at least a first fuel and a second fuel; the
first fuel having a RON greater than 100, a burn rate greater than
105% of isooctane and a laminar flame speed greater than 105% of
isooctane; means for injecting the first fuel into the engine for
combustion therein in response to at least a first predetermined
engine operating condition; a second fuel having a RON less than
90, a burn rate greater than 105% of isooctane and a laminar flame
speed greater 105% of isooctane; and means for injecting the second
fuel into the engine for combustion therein in response to at least
a second predetermined engine operating condition.
14. The fuel system of claim 13 including at least a third fuel
having a RON between that of the first and second fuel, further
characterized as having a burn rate and flame speed greater than
105% of isooctane.
15. The fuel system of claim 14 wherein the third fuel is admixed
from the first and second fuel.
16. The fuel system of claim 15 wherein the admixture functions to
allow engine operation at or about MBT.
17. The fuel system of claim 14 wherein the third fuel functions to
allow engine operation at or about MBT.
18. A method for operating spark ignition, internal combustion
engine having a CR of 11 or more comprising: combusting a first
fuel having a RON greater than 100,a burn rate greater than 105% of
isooctane and a laminar flame speed greater than 105% of isooctane
under high load conditions; and combusting a second fuel having a
RON less than 90, a burn rate of greater than 105% isooctane and a
laminar flame speed greater than 105% isooctane under low load
conditions.
19. The method of claim 18 having the additional step of combusting
a third fuel under moderate load conditions wherein said third fuel
has a RON between that of the first and second fuel and further
characterized as having a burn rate and flame speed greater than
105% of isooctane.
20. The method of claim 19 wherein the third fuel is admixed from
the first and second fuel.
21. The method of claim 20 wherein the admixture functions to allow
engine operation at or about MBT.
22. The method of claim 19 wherein the third fuel functions to
allow engine operation at or about MBT.
23. A method for operating a vehicle having a spark ignition engine
to increase the efficiency and reduce the emissions of the engine
under conditions of use comprising: supplying a first fuel to the
engine at about high engine load conditions; and supplying a second
fuel to the engine at about low engine load conditions, the first
fuel having a RON greater than 100, a burn rate greater than 105%
of isooctane and a laminar flame speed greater than 105% of
isooctane; the second fuel having a RON less than 90, a burn rate
greater than 105% of isooctane and a laminar flame speed greater
than 105% of isooctane; and whereby engine efficiency is increased
and emissions are reduced.
24. The method of claim 23 wherein said engine is a direct
injection, stratified charge engine.
25. The method of claim 23 wherein said engine is a port fuel
injected, stratified charge engine.
26. The method of claim 23 having an additional step of supplying a
third fuel to the engine at about moderate load levels, said third
fuel having a RON less than about 100 and greater than about
90.
27. The method of claim 26 wherein the third fuel is admixed from
the first and second fuel.
28. The method of claim 27 wherein the admixture functions to allow
engine operation at or about MBT.
29. The method of claim 26 wherein the third fuel functions to
allow engine operation at or about MBT.
30. A fuel system for spark ignited engines that operate under high
exhaust gas recycle during low to moderate engine load conditions
the system comprising: means for supplying to the engine a first
fuel during high load conditions; and means for supplying to the
engine a second fuel during low load conditions; the first fuel
having a RON greater than 100, a burn rate greater than 105% of
isooctane and a laminar flame speed greater than 105% of isooctane;
the second fuel having a RON less than 90, a burn rate greater than
105% of isooctane and a laminar flame speed greater than 105% of
isooctane; and whereby engine efficiency is increased and emissions
are reduced.
31. The method of claim 30 further including means for supplying to
the engine a third fuel during moderate load conditions, said fuel
having a RON greater than about 90 and less than about 100, a burn
rate and flame speed greater than about 105% of isooctane.
32. The method of claim 31 wherein the third fuel is admixed from
the first and second fuel.
33. The method of claim 32 wherein the admixture functions to allow
engine operation at or about MBT.
34. The method of claim 31 wherein the third fuel functions to
allow engine operation at or about MBT.
35. In a vehicle having spark ignition engine, the improvement
wherein the engine has a CR of 11 or more; wherein at least a first
fuel and a second fuel are available on the vehicle for combustion
by the engine, the first fuel having a RON greater than 100, and
under high load conditions a burn rate greater than 105% of
isooctane and a laminar flame speed greater than 105% of isooctane,
and the second fuel having a RON less than 90, and under low load
conditions a burn rate greater than 105% of isooctane and a laminar
flame speed greater than 105% of isooctane; and wherein the first
fuel is supplied to the engine when operating under high load
conditions and the second fuel is supplied to the engine when
operating under low load conditions.
36. The vehicle of claim 35 wherein a third fuel is available on
the vehicle and is supplied to the engine thereof, said fuel having
a RON greater than about 90 and less than about 100, and a burn
rate and flame speed greater than about 105% of isooctane.
37. The vehicle of claim 36 wherein the third fuel is admixed from
the first and second fuel.
38. The vehicle of claim 37 wherein the admixture functions to
allow engine operation at or about MBT.
39. The vehicle of claim 36 wherein the third fuel functions to
allow engine operation at or about MBT.
40. A method of operating an internal combustion engine having a CR
of 11 or more, the method comprising: providing a plurality of
fuels of different and predetermined combustion properties, each
fuel selected to improve engine performance under preselected
operating conditions; and supplying the selected fuel to the engine
when operating at the preselected condition.
41. A method of reducing emissions and increasing efficiency of a
spark ignition internal combustion engine having a CR of 11 or
more, the method comprising: providing a plurality of fuels of
different and predetermined combustion properties, each fuel
selected to improve engine performance under preselected operating
conditions; and supplying the selected fuel to the engine when
operating at the preselected condition.
42. A fuel system for spark ignition engines having a CR of 11 or
more, comprising: at least a first fuel and a second fuel; the
first fuel having a RON set at the minimum required to allow
operating the engine at MBT when at wide open throttle at the rpm
setting for maximum power, a burn rate greater than 105% of
isooctane and a laminar flame speed greater than 105% of isooctane;
means for injecting the first fuel into the port or engine for
combustion therein in response to at least a first predetermined
engine operating condition; a second fuel having a RON less than
90, a burn rate greater than 105% of isooctane and a laminar flame
speed greater than 105% of isooctane; and means for injecting the
second fuel into the port or engine for combustion therein in
response to at least a second predetermined engine operating
condition.
43. The fuel system of claim 42 further comprising a third fuel
having a RON greater than about 90 and less than about 100, and a
burn rate and flame speed greater than about 105% of isooctane.
44. The fuel system of claim 43 wherein the third fuel is admixed
from the first and second fuel.
45. The fuel system of claim 44 wherein the admixture functions to
allow engine operation at or about MBT.
46. The fuel system of claim 43 wherein the third fuel functions to
allow engine operation at or about MBT.
Description
FIELD OF INVENTION
[0001] This is a divisional application that claims priority to,
and incorporates by reference, U.S. Ser. No. 09/818,210 filed Mar.
27, 2001. The present invention relates generally to engine fuel
compositions and their use in port or direct fuel injection spark
ignition, internal combustion engines especially those having a
compression ratio (CR) of 11 or more.
BACKGROUND OF INVENTION
[0002] Both petroleum refineries and engine manufacturers are
constantly faced with the challenge of continually improving their
products to meet increasingly severe governmental efficiency and
emission requirements, and consumers' desires for enhanced
performance. For example, in producing a fuel suitable for use in
an internal combustion engine, petroleum producers blend a
plurality of hydrocarbon containing streams to produce a product
that will meet governmental combustion emission regulations and the
engine manufacturers performance fuel criteria, such as research
octane number (RON). Similarly, engine manufacturers conventionally
design spark ignition type internal combustion engines around the
properties of the fuel. For example, engine manufacturers endeavor
to inhibit to the maximum extent possible the phenomenon of
auto-ignition which typically results in knocking and, potentially
engine damage, when a fuel with insufficient knock-resistance is
combusted in the engine.
[0003] Under typical driving situations, engines operate under a
wide range of conditions depending on many factors including
ambient conditions (air temperature, humidity, etc.), vehicle load,
speed, rate of acceleration, and the like. Engine manufacturers and
fuel blenders have to design products which perform well under such
diverse conditions. This naturally requires compromise, as often
times fuel properties or engine parameters that are desirable under
certain speed/load conditions prove detrimental to overall
performance at other speed/load conditions.
[0004] One object of this invention to provide an engine with fuels
specifically designed to enhance engine performance at low and high
load engine conditions.
[0005] Another object of the invention is to provide an engine with
fuels specifically designed to enhance engine performance across
the driving cycle.
[0006] Also, spark ignition engines are generally designed to
operate at a compression ratio (CR) of 10:1 or lower to prevent
knocking at high load. As is known, higher CRs, up to about 18:1,
are optimum from the standpoint of maximizing the engine thermal
efficiency across the load range. Compression Ratio (CR) is defined
as the volume of the cylinder and combustion chamber when the
piston is at Bottom Dead Center (BDC) divided by the volume when
the piston is at Top Dead Center (TDC). A higher CR leads to
greater thermal efficiency by maximizing the work obtainable from
the theoretical Otto (engine compression/expansion) cycle. Higher
CRs also lead to increased burn rates, giving a further improvement
in thermal efficiency by creating a closer approach to this ideal
Otto cycle. The use of high compression ratio spark ignition
engines, however, is limited by insufficiently high fuel octane, as
in practice it is difficult to supply a single fuel with
sufficiently high octane overall to allow for a significant
increase in compression ratio without having engine knocking at
high loads.
[0007] Therefore, another objective of this invention is to
facilitate the design of high compression ratio engines that
realize greater thermal efficiency across the entire driving cycle
without the problem of knocking at high load.
[0008] In theory, higher efficiency engine operation at certain
moderate to high loads can be achieved by adjusting the spark
ignition timing closer to the value that provides MBT spark timing.
MBT is defined as minimum spark advance for best torque. Experience
has shown, however, that adjusting the ignition timing to allow MBT
to be reached is not practical since knocking typically occurs
under conditions of moderate to high load at timings earlier than
MBT with commercially available gasolines. In principle, operating
with a very high octane fuel would allow running the engine at MBT
across the drive cycle. We will show below that a more preferred
approach is to supply the engine with a fuel that has sufficient
octane to approach or operate at MBT without knocking, together
with other combustion properties tailored to optimize
performance.
[0009] Yet another object of the invention is to provide fuel
compositions that allow adjusting the spark ignition timing closer
to that which provides MBT.
[0010] Presently spark ignition engines are capable of operating
with known fuels at a normalized fuel to air ratio (".phi.") below
1.0 under low to moderate load conditions. The normalized fuel to
air ratio is the actual fuel to air ratio divided by the
stoichiometric fuel to air ratio. In addition, these engines can be
operated with exhaust gas recycle (EGR) as the "leaning out"
diluent, at a .phi. of 1.0 or lower. EGR is understood to include
both recycled exhaust gases as well as residual combustion gases.
One challenge associated with operating the engine lean is the
difficulty of establishing a rapid and complete burn of the
fuel.
[0011] Another object of this invention therefore is to provide
high burn rate fuel for use under lean conditions to shorten the
burn duration and thereby improve the thermodynamic efficiency. A
faster burn rate also serves to maximize conversion of the fuel,
thereby increasing the overall fuel economy and reducing emissions.
As known in the art, autoignition of the fuel at sufficiently high
loads can pose a threat of mechanical damage to the engine, i.e.,
knocking. However, at certain low load conditions, for example lean
stratified operation, autoignition of the fuel can be beneficial to
overall engine operation by optimizing burn characteristics that
result in reduced engine emissions and higher efficiency. An
additional object of this invention, therefore is to provide a high
autoignition tendency, low octane fuel. A further object is to
provide a high laminar flame speed fuel.
[0012] Other objects of the invention and their attendant
advantages will be apparent from the reading of this
specification.
SUMMARY OF INVENTION
[0013] One aspect of the invention is the provision of a plurality
of unleaded fuel compositions for use in operating a spark
ignition, internal combustion engine, especially an engine having a
CR of 11 or more, each of which compositions have different
predetermined combustion properties suitable for use under
preselected engine operating conditions to improve one or more of
fuel efficiency and combustion emissions.
[0014] In one embodiment at least a first and second fuel
composition is provided, the first fuel having combustion
properties sufficient to improve combustion thereof under high
engine load conditions and the second fuel having combustion
properties sufficient to improve combustion thereof under low
engine load conditions.
[0015] Especially preferred fuels for use under low load conditions
are those unleaded fuels boiling in the gasoline boiling range that
have a RON less than 90 and an average burn rate in the engine,
defined as 1/ crank angles for 90% burn completion, >105% % of
isooctane at this time in the engine operating cycle and a laminar
flame speed >105% % of isooctane measured at a temperature and
pressure representative of conditions in the engine at or about
this time in the engine operating cycle.
[0016] Especially preferred fuels for use under low load conditions
are those unleaded fuels boiling in the gasoline boiling range that
have a RON less than 90 and an average burn rate in the engine
defined as 1/ crank angles for 90% burn completion, >105% % of
isooctane at this time in the cycle and a laminar flame speed
>105% % of isooctane measured at a temperature and pressure
representative of conditions in the engine at the low end of the
load scale.
[0017] In view of the foregoing it will be readily appreciated that
a wide range of modifications and variations of the invention are
within the broad aspects set forth above and the unique scope of
the invention will become even more apparent upon a reading or the
detailed description which follows.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 demonstrates the effect of fuel composition and
compression ratio on output torque for a fuel of the invention
compared to isooctane.
[0019] FIG. 2 compares relative engine brake efficiency vs. spark
advance for isooctane and one fuel of the invention.
[0020] FIG. 3 are graphs of Burn Rate and Heat Release Rate that
compare burn curves for isooctane and one fuel of the
invention.
[0021] FIG. 4 demonstrates the effect on output torque of fuel
composition and compression ratio at various injection timings for
a fuel of the invention compared to reference fuel LFG-2B
[0022] FIG. 5 demonstrates emission benefits obtained by the
invention.
[0023] FIG. 6 demonstrates the effect of higher compression ratio
and fuel composition on output torque for a fuel of the invention
compared to reference fuel LFG-2B.
[0024] FIG. 7 compares burn curves for reference fuel LFG-2B and
one fuel of the invention.
[0025] FIG. 8 demonstrates emission benefits obtained by the
invention.
[0026] FIG. 9 compares engine brake efficiency at constant NOx
emissions for reference fuel LFG-2B and one fuel of the
invention.
[0027] FIG. 10 compares emissions data for one fuel of this
invention reference fuels LFG-2B and RON91 at a medium load
condition.
[0028] FIG. 11 demonstrates the effect of fuel composition and
compression ratio on relative output torque for a fuel of the
invention compared to reference fuels LFG-2B and RON91
[0029] FIG. 12 demonstrates relative fuel efficiency improvements
obtained by the invention.
[0030] FIG. 13 demonstrates fuel efficiency and emission
improvements obtained by the invention.
[0031] [FIG. 4 compares heat release curves for reference fuel
isooctane and several low octane test fuels.
DETAILED DESCRIPTION OF INVENTION
[0032] As is well known in the art, gasoline fuels generally are
composed of a mixture of hydrocarbons boiling at atmospheric
pressure in the range of about 77.degree. F. (25.degree. C.) to
about 437.degree. F. (225.degree. C.). Typically gasoline fuels
comprise a major amount of a mixture of paraffins, cycloparaffins,
olefins and aromatics, and lesser, or minor amounts of additives
including oxygenates, detergents, dyes, corrosion inhibitors and
the like. Typically also, gasoline fuels are formulated to have a
RON of about 98 for premium grade and about 92 for regular grade
and are used alone in a vehicle engine the grade used normally
depending upon the vehicle manufacturer's recommendation.
[0033] The present invention departs form the practice of
formulating a single fuel for a specific vehicle engine. Indeed,
the present invention is based on the discovery that significant
benefits can be achieved by providing a range of fuel compositions
having combustion properties tailored to the engine's specific
operating condition.
[0034] The fuel compositions of the invention are unleaded fuels
boiling in the gasoline range and capable of being used in spark
ignition, internal combustion engines especially those having a CR
of 11 or higher.
[0035] In one embodiment the fuel compositions will comprise at
least one first fuel and a second fuel. The first fuel will have a
RON greater than 100, and a burn rate greater than 105% of
isooctane at the high load end of the cycle and a laminar flame
speed of greater than 105% of isooctane measured at a temperature
and pressure representative of conditions in the engine at the high
end of the load scale. The second fuel will have a RON less than
90, a burn rate greater than 105% of isooctane at the low end of
the cycle and a laminar flame speed greater than 105% of isooctane
measured at a temperature and pressure representative of conditions
in the engine at the low end of the load scale.
[0036] The laminar flame speed of the fuel compositions is measured
by combustion-bomb techniques that are well known in the art. See,
for example, M. Metghalchi and J. C. Keck, Combustion and Flame,
38:143-154 (1980).
[0037] A particularly useful unleaded fuel for operating the engine
in the high load portion of the drive cycle comprises a mixture of
hydrocarbons boiling in the gasoline range with an RON>100 and
containing greater than about 45 vol % aromatics and preferably
greater than about 55 vol %.
[0038] A particularly useful unleaded second fuel for operating the
engine in the low load portion of the drive cycle comprises a
mixture of hydrocarbons boiling in the gasoline range having an
RON<90 and containing less aromatics than the first fuel, for
example, less than about 45 vol % aromatics and preferably less
than 20 vol %.
[0039] Fuels meeting the foregoing characteristics provide
efficiency benefits for various types of spark ignited internal
combustion engines when operating under high load conditions. High
load conditions are defined as being those regions of the engine
operating map where at MBT spark timing knocking occurs with a
gasoline of RON 98. Knocking is defined as autoignition under
sufficiently severe in-cylinder conditions that it results in a
detonation that poses a risk of mechanical damage to the
engine.
[0040] In the case of port fuel injection engines, use of fuels
having the properties of the first fuel above permits the engine to
be designed to operate at a CR of 11 or more and permits advance
spark timing closer to that for MBT. These design features enhance
overall cycle efficiency, i.e., provide improved fuel economy.
[0041] More particularly these benefits are achieved with direct
fuel injection engines and especially direct injection, lean burn
engine systems, such as stratified charge direct injection systems.
Stratified charge is an in-cylinder condition wherein there is an
inhomogeneous air:fuel ratio distribution. As is known, "lean burn"
engines operate at normalized fuel to air ratios (".phi.") of below
1.0 and/or with exhaust gas recycle as the "leaning out" diluent,
at a .phi. of 1.0 or lower.
[0042] Fuels having the combustion properties of the second fuel
above are suitable for use especially in the operation of spark
ignition engines, included stratified fuel systems, operating under
low load conditions with exhaust gas recycle. Low engine load
conditions are those regions of the engine operating map at or
below which the engine can be operated at MBT timing with a fuel
having a RON of approximately 90 without the condition of knocking
as defined above.
[0043] Fuels having a range of combustion properties between the
first and second fuel offer even more complete tuning of the fuel
compositions to engine operating conditions. Indeed, a third fuel
composition can be provided having a RON between those of the first
and second fuel, and most desirably a burn rate greater than 105%
of isooctane at the medium load end of the cycle and most desirably
a laminar flame speed of greater than 105% of isooctane measured at
a temperature and pressure representative of conditions in the
engine at the medium end of the load scale. Such a fuel can be used
under moderate engine load conditions, i.e., conditions wherein the
octane required for MBT is less than 98 RON and more than 90
RON.
[0044] One way to achieve the benefits of the invention is by
supplying the high octane fuel to an engine at the high end of the
engine load scale, for example, and the low octane fuel at the low
end of the engine load scale. There are many ways in which this can
be accomplished. For example, two fuel tanks, one containing the
first and the other containing the second fuel can be provided with
the fuel supplied to the engine being based on a predetermined
engine condition. The electronic control unit map will be the basis
for this decision. Optionally, the first and second fuels can be
blended in appropriate proportions to provide a third fuel to be
supplied to the engine under moderate load conditions.
[0045] In yet another embodiment of the invention a single fuel,
i.e., a regular grade gasoline of about 92 RON is stored in a
vehicle primary fuel tank. Under moderate engine load conditions
fuel is supplied directly to the engine. A portion of the fuel from
the primary tank is also separated into two streams. Under high
load conditions a first fuel stream having a RON greater than 100
and greater than 45 vol. % aromatics which is stored for use at
high load conditions, is delivered to the engine. Under low load
conditions, a second fuel stream of RON less than 90 and less
aromatics than the first fuel which is stored in a secondary tank
is supplied to the engine. Separation of the fuel into the two
streams is achieved preferably by pervaporation membranes
separation techniques (See for example patent EP466469 which
teaches use of a polyethylene terephtalate membrane for separation
of gasoline boiling range aromatics and nonaromatics under
pervaporation conditions, which is incorporated herein by
reference.)
[0046] In another embodiment the invention is applicable to engines
that operate under high exhaust gas recycle, i.e., 20% or greater,
during the low to moderate engine load.
EXAMPLES
Example 1
[0047] The effects of a high octane, high knock-resistant, high
burn rate fuel on combustion efficiency and performance were
investigated in an in-line 4-cylinder (2.0 L displacement) DOHC 4
valve/cylinder direct injection spark ignition engine with a
shell-shaped piston cavity, a straight intake air port, and a
fan-shaped fuel spray. The engine was operated at high load/wide
open throttle (WOT) at a compression ratio of 13.0. The base fuel
was pure iso-octane with RON=100. The test fuel, called "DF-2" was
comprised of 60% toluene, 33% iso-octane, and 7% n-heptane
(measured RON=103). The fuel properties are listed in Table 1. Both
fuels were combusted under the following conditions: engine
speed=4000 rpm, fuel/air ratio (.phi.)=1.15, spark advance
timing=11-24 degrees before top dead center (BTDC). In this example
and the others that follow, the injection quantities of the fuel
are adjusted so as to maintain equivalent total heating values
TABLE-US-00001 TABLE 1 FUEL PROPERTIES FOR WOT TESTS Test Fuel DF-2
Isooctane Density g/cm.sup.3 @ 15.degree. C. 0.7945 0.694 RON --
103.1 100 MON -- 93.2 100 LHV KJ/g 44.4 H/C mol/mol 1.553 2.25
Aromatics vol % 60 0 A/F stoich 15.1 Viscosity mm.sup.2/s @
30.degree. C. 0.569 Distillation IBP .degree. C. 98.5 99 T5
.degree. C. 102.0 99 T10 .degree. C. 102.0 99 T20 .degree. C. 102.5
99 T30 .degree. C. 103.0 99 T40 .degree. C. 103.0 99 T50 .degree.
C. 103.5 99 T60 .degree. C. 104.0 99 T70 .degree. C. 104.5 99 T80
.degree. C. 105.0 99 T90 .degree. C. 106.5 99 T95 .degree. C. 107.5
99 EP .degree. C. 109.5 99
[0048] The effect of higher compression ratio on output torque is
shown in FIG. 1. Comparison of the "base" and iso-octane data shows
that the peak engine torque is 8% higher at a compression ratio of
13.0 vs. 9.8. The engine operation for iso-octane is limited to a
spark advance of .about.18 degrees BTDC due to a knock limitation.
Comparison of the DF-2 data to the iso-octane data shows that not
only can the spark advance be set early enough to reach a plateau
in the engine torque output i.e., operate at MBT but at the same
spark advance, there is a significant torque benefit for fuel DF-2
vs. iso-octane. The combination of higher compression ratio and
fuel-derived benefits leads to significant improvement in overall
torque of 11.8%.
[0049] FIG. 2 shows the engine brake efficiency vs. spark advance
for iso-octane and fuel DF-2. Comparison of the base and iso-octane
data shows that the increase in compression ratio from 9.8 to 13.0
enabled by operating on isooctane raises the relative efficiency by
.about.11.6% . The high octane DF-2 allows the engine to be
operated at a sufficiently early spark advance to reach MBT at 13
CR giving an added benefit over that for isooctane. The overall
benefit associated with using the high octane fuel DF-2 is an
increase in relative brake efficiency of .about.14.6%.
[0050] FIG. 3 shows burn curves for both iso-octane and fuel DF-2,
from which it can be seen that fuel DF-2 exhibits a faster heat
release rate (right figure). This is corroborated by the data in
the table at the bottom of the figure, which shows that fuel DF-2
takes fewer engine crank angles to reach both 50% and 90% burn.
This faster burn releases more energy near top dead center,
resulting in higher efficiency.
[0051] The benefits of the high octane fuel DF-2 are identified in
the following table. TABLE-US-00002 TABLE 2 % Credit % Credit Fuel
in Torque in Efficiency Regular Gas -- -- Iso-octane 7.8 11.6 DF-2
11.8 14.6
Example 2
[0052] The effects of a low octane, low autoignition-resistant,
high burn rate fuel on combustion efficiency and performance were
investigated the same in-line 4-cylinder (2.0 L displacement) DOHC
4 valve direct injection spark ignition engine described in Example
1. The engine was operated at various low and moderate load
conditions at a compression ratio of 9.8 and 13.0. The base fuel
was a commercial Japanese regular gasoline, named LFG-2B, with a
RON value of 91.7. The low octane test fuel, named DF-1, was
comprised of 68% iso-octane, 22% n-heptane, and 10% toluene
(measured RON=83.8). The fuel properties are shown in Table 3:
TABLE-US-00003 TABLE 3 Fuel Properties DF-1 Cal- Test Fuel Measured
culated RON91 LFG-2B Density g/cm3 @ 0.7091 0.7094 0.6931 0.7356 15
C. RON -- 83.8 80? 91 91.7 MON -- 82.2 ? 91 82.7 LHV kj/g 43.91
44.5 43.0 H/C mol/mol 2.164 2.112 2.25 1.87 A/F stolch 14.900 15.1
14.7 Viscosity mm2/s @ 0.603 30 C. Distillation IBP deg C. 95.0
Approx. 31.5 99 T5 deg C. 98.0 42.5 T10 deg C. 98.0 50.5 T20 deg C.
98.5 62.0 T30 deg C. 98.5 72.5 T40 deg C. 98.5 85.5 T50 deg C. 98.5
101.0 T60 deg C. 98.5 114.5 T70 deg C. 98.5 127.5 T80 deg C. 98.5
144.5 T90 deg C. 98.5 157.0 T95 deg C. 98.5 164.5 EP deg C. 120.0
Approx. 175.5 99 Aromatics vol % 10 0 28.7
[0053] A comparison of torque output vs. injection timing is shown
in FIG. 4 for fuel DF-1 and the base fuel LFG-2B at engine
conditions of 1200 rpm and fixed spark timing=23 degrees BTDC.
Significantly higher torque values (left figure) and generally
lower torque fluctuations (right figure) are realized with fuel
DF-1. The DF-1 fuel also generates significantly lower NO.sub.x,
HC, and smoke emissions (see FIG. 5). The effect of compression
ratio on efficiency is shown in FIG. 6, which shows brake
efficiency vs. injection timing for LFG-2B at CR=9.8 (base) and
13.0. The overall boost in relative efficiency realized by higher
CR operation is .about.1.5%. The effect of fuel composition on
overall relative efficiency even larger than this, as is shown in
FIG. 6. The relative efficiency increase associated with combusting
DF-1 vs. LFG-2B is .about.5.5%, for an overall relative efficiency
gain of 7%. The relative efficiency benefits are summarized in
Table 4. TABLE-US-00004 TABLE 4 % Credit in Relative Fuel
Efficiency LFG-2B (CR = 9.8) -- LFG-2B (CR = 13) 1.5 DF-1(CR = 13)
5.5 Total 7.0
[0054] FIG. 7 shows the burn curves for DF-1 and LFG-2B at
identical injection and spark advance timings of Spark Timing: 23
degrees BTDC, Injection Timing: 54 degrees BTDE. As can be seen,
the burn curve for Fuel DF-1 shows two stages of heat release. This
heat release behavior is indicative of multipoint autoignition that
occurs with the lower octane fuels. Even though the overall average
burn rate for these fuels is comparable, both fuels being
relatively high in burn rate, the data showing higher efficiency
and lower emissions demonstrate the importance of maintaining low
RON to get the benefits of autoignition.
Example 3
[0055] The effects of a low octane, low autoignition-resistant,
high burn rate fuel on combustion efficiency and performance have
been investigated at a different region of the driving cycle in the
same in-line 4-cylinder (2.0 L displacement) DOHC 4 valve direct
injection spark ignition engine described in Examples 1 and 2. The
engine was operated at an engine speed of 3000 rpm and fuel/air
ratio of .phi.=0.56, which is located on a different part of the
speed/load map than the engine conditions described in Example 2.
The engine was operated at a compression ratio of 9.8 and 13.0. The
base fuel was a commercial Japanese regular gasoline, named LFG-2B,
with a RON value of 91.7. The low octane test fuel, named DF-1, is
the same fuel described in Example 2, and is comprised of 68%
iso-octane, 22% n-heptane, and 10% toluene (measured RON=83.8). The
fuel properties are shown in Table 3: As was observed under the
engine operating conditions of Example 2, significantly lower
NO.sub.x and smoke emissions are observed with Fuel DF-1 than with
the base fuel LFG-2B (see FIG. 8).
[0056] The effect of compression ratio on relative efficiency is
shown in FIG. 9, which shows relative brake efficiency vs.
injection timing for LFG-2B at CR=9.8 (base) and 13.0. The overall
boost in relative efficiency realized by higher CR operation is
.about.3%. The effect of fuel composition on overall relative
efficiency is even larger than this, as is shown in FIG. 8. The
relative efficiency increase associated with combusting DF-1 vs.
LFG-2B is .about.5%, for an overall relative efficiency gain of 8%.
The relative efficiency benefits are summarized in Table 5.
TABLE-US-00005 TABLE 5 % Credit in Relative Fuel Efficiency LFG-2B
(CR = 9.8) -- LFG-2B (CR = 13) 3 DF-1(CR = 13) 5 Total 8
Example 4
[0057] The effects of fuel octane and autoignition-resistance on
combustion efficiency and performance have been investigated at
medium load in the same in-line 4-cylinder (2.0 L displacement)
DOHC 4 valve direct injection spark ignition engine described in
Examples 1-3. The engine was operated at an engine speed of 2400
rpm and fuel/air ratio of .phi.=0.63, which is located on a
different part of the speed/load map than the engine conditions
described in Example 2 and 3. The engine was operated at a
compression ratio of 9.8 and 13.0. Two base fuels were used in this
study; the first was a commercial Japanese regular gasoline, named
LFG-2B, with a RON value of 91.7. The second was a blend of 91%
iso-octane and 9% n-heptane, named RON91, with a RON value of 91.
The low octane test fuel, named DF-1, is the same fuel described in
Example 2 and 3, and is comprised of 68% iso-octane, 22% n-heptane,
and 10% toluene (measured RON=83.8). The fuel properties are shown
in Table 3. As was observed under the engine operating conditions
of Example 2 and 3, significantly lower NOx and smoke emissions are
observed with Fuel DF-1 than with the base fuel LFG-2B (see FIG.
10).
[0058] The effect of compression ratio on torque output is shown in
FIG. 11, which shows relative torque output vs injection timing for
LFG-2B at CR=9.8 and 13.0. Also shown are data for RON91 and DF-1.
Unlike the two previous examples, the low octane fuel DF-1 has
lower relative torque output than the higher octane fuels.
Similarly, the engine relative efficiency is lower with the low
octane fuel DF-1 than with RON91 and LFG-2B (see FIG. 12). The
reason for the diminished performance is that the engine cannot
operate with the low octane fuel DF-1 with spark advance timings
that approach MBT due to knock limitations. These data demonstrate
that at intermediate loads, fuel properties (octane levels and
composition) more commensurate with conventional gasoline are more
suitable than the low octane fuels (such as fuel DF-1).
Example 5
[0059] The effects of a low octane, low autoignition-resistant,
high burn rate fuel on combustion efficiency and performance have
been investigated in an in-line 4-cylinder (2.0 L displacement)
DOHC 4 valve direct injection spark ignition engine similar to the
engine described in Examples 1-4. Then engine had a swirl injector
rather than the fan spray injector described in Examples 1-4 and
was operated at a lower compression ratio of 10.3. The engine was
operated at an engine speed of 1200 rpm and fuel/air ratio of
.phi.=0.5. The base fuel was 100% iso-octane (RON=100) and several
low octane test fuels were studied, i.e., n-hexane (RON=25),
2-methylpentane (RON=69), and cyclohexane (RON=84).
[0060] Burn curves for these fuels are shown in FIG. 13. Several
observations are noteworthy. First, the burn curve for n-hexane is
the most rapid and reaches 80% burn completion much quicker than
the other fuels. By virtue of this, the overall efficiency is 8%
higher than iso-octane. Second, the NO.sub.x levels for n-hexane
are much lower than iso-octane. This reflects the very fast heat
release, and the tendency to form less NO.sub.x when the
combination of high temperature and time is minimized. Third,
relative efficiency benefits similar to those identified for
n-hexane are observed with the other two low octane fuels, i.e.,
2-methylpentane and cyclohexane, where credits of 2% and 6% are
observed, respectively. The high relative efficiency of these low
octane fuels reflects the fast burn rates of the low octane fuels.
This high burn rate has two primary contributing factors, i) high
laminar flame speed, and ii) controlled autoignition. High laminar
flame speed is the primary factor responsible for the high relative
efficiency of cyclohexane, while autoignition is likely to be the
main factor responsible for the increased relative efficiency of
n-hexane and 2-methylpentane. This is evident in FIG. 14, which
shows heat release curves for these fuels. The very rapid heat
release for n-hexane is postulated to originate from multipoint
autoignition initiated by end gas compression from the flame front
and piston movement. It is worth noting that under these
conditions, autoignition does not generate the heat release levels
typically encountered under knocking conditions at higher load, and
thus no deleterious effects associated with autoignition are
observed.
[0061] It is important to note that while these data were obtained
in an engine with a compression ratio of 10:1, the benefits of low
octane are expected to be realized at higher CR as well. This was
demonstrated in Examples 2 and 3, where increasing the CR from 9.8
to 13 led to higher efficiency at all loads and speeds. The further
efficiency and emission benefits observed for these examples with
the low octane fuel are also expected to realized with these fuels
in a higher CR engine under similar operating conditions.
* * * * *