U.S. patent application number 13/546220 was filed with the patent office on 2012-11-15 for optimized fuel management system for direct injection ethanol enhancement of gasoline engines.
This patent application is currently assigned to Massachusetts Institute of Technology. Invention is credited to Leslie Bromberg, Daniel R. Cohn, John B. Heywood.
Application Number | 20120285429 13/546220 |
Document ID | / |
Family ID | 46328838 |
Filed Date | 2012-11-15 |
United States Patent
Application |
20120285429 |
Kind Code |
A1 |
Bromberg; Leslie ; et
al. |
November 15, 2012 |
OPTIMIZED FUEL MANAGEMENT SYSTEM FOR DIRECT INJECTION ETHANOL
ENHANCEMENT OF GASOLINE ENGINES
Abstract
Fuel management system for enhanced operation of a spark
ignition gasoline engine. Injectors inject an anti-knock agent such
as ethanol directly into a cylinder. It is preferred that the
direct injection occur after the inlet valve is closed. It is also
preferred that stoichiometric operation with a three way catalyst
be used to minimize emissions. In addition, it is also preferred
that the anti-knock agents have a heat of vaporization per unit of
combustion energy that is at least three times that of
gasoline.
Inventors: |
Bromberg; Leslie; (Sharon,
MA) ; Cohn; Daniel R.; (Cambridge, MA) ;
Heywood; John B.; (Newtonville, MA) |
Assignee: |
Massachusetts Institute of
Technology
Cambridge
MA
|
Family ID: |
46328838 |
Appl. No.: |
13/546220 |
Filed: |
July 11, 2012 |
Related U.S. Patent Documents
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Application
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Filing Date |
Patent Number |
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12701034 |
Feb 5, 2010 |
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13546220 |
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11758157 |
Jun 5, 2007 |
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12701034 |
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11100026 |
Apr 6, 2005 |
7225787 |
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11758157 |
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10991774 |
Nov 18, 2004 |
7314033 |
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11100026 |
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Current U.S.
Class: |
123/575 |
Current CPC
Class: |
F02D 19/0665 20130101;
F02D 35/027 20130101; F02B 51/00 20130101; F02D 19/0655 20130101;
F02D 19/0692 20130101; Y02T 10/12 20130101; F02D 2200/1002
20130101; F02D 19/081 20130101; F02D 19/084 20130101; F02M 37/0088
20130101; F02D 41/0007 20130101; F02M 25/14 20130101; F02D 41/047
20130101; F02D 13/0215 20130101; F02D 19/0636 20130101; F02D 19/12
20130101; F02D 19/08 20130101; F02D 19/0689 20130101; F02D 19/0671
20130101; F02B 17/005 20130101; Y02T 10/30 20130101; F02B 47/04
20130101; F02D 41/3094 20130101; F02D 2200/0406 20130101; F02D
41/0025 20130101 |
Class at
Publication: |
123/575 |
International
Class: |
F02D 19/08 20060101
F02D019/08 |
Claims
1-5. (canceled)
6. A spark ignition engine where two fuels are introduced into the
engine where the first fuel has a greater alcohol concentration
than the second fuel; and where the first fuel is produced by
onboard separation of fuel from a third fuel which is a
gasoline-alcohol mixture; and where the ratio of the first fuel
that is used in the engine to the second fuel that is used in the
engine increases with increasing torque.
7. The spark ignition engine of claim 6 where a membrane is
employed in the onboard separation.
8. The engine system of claim 7 where the membrane is an inorganic
membrane.
9. The engine system of claim 7 where the membrane is an organic
membrane.
10. The engine system of claim 7 where the membrane is a
transfusion membrane.
11. The engine system of claim 7 where the membrane is a porous
membrane.
12. The engine system of claims 6 or 7 where the alcohol in the
gasoline-alcohol mixture is ethanol.
13. The engine system of claims 6 or 7 where the first fuel is
stored in a tank to which additional alcohol can be added.
14. The engine system of claims 6 or 7 where ratio of the first
fuel to the second fuel is varied so as to prevent knock at the
torque is increased.
15. The spark ignition engine of claims 6 or 7 where the engine is
operated with a substantially stoichiometric fuel to air ratio.
16. The spark ignition engine of claims 6 or 7 where a closed loop
control system with a knock detector is used to determine the ratio
of amount of the first fuel to second fuel used in the engine.
17. The spark ignition engine of claims 6 or 7 where an open loop
control system with a look up table is used to determine the ratio
of the first fuel to the second fuel.
18. The spark ignition engine of claims 6 or 7 where a control
system is used to minimize the amount of second fuel that is used
to prevent knock.
19. The spark ignition engine of claims 6 or 7 where the first fuel
is injected so as to increase its vaporization cooling of the
fuel-air mixture in at least one engine cylinder.
20. The spark ignition engine of claim 19 where the first fuel is
directly injected into the engine.
21. The spark ignition engine of claims 6 or 7 where the second
fuel contains gasoline.
22. The spark ignition engine of claim 7 where the second fuel is
produced by onboard separation from the third fuel.
23. A spark ignition engine where two fuels are introduced into the
engine where the first foci has a greater knock resistance than the
second fuel and where the first fuel is introduced into the engine
so as to produce a non-uniform distribution of the first fuel with
a greater concentration in the end gas region; and where the first
and second fuel are produced by on board separation of a third
fuel.
24. The spark ignition engine of claim 23 where a membrane is
employed in the onboard separation.
25. The engine system of claim 23 where the third fuel is a
gasoline-alcohol mixture and the first fuel has a greater alcohol
concentration than the second fuel.
26. The engine system of claim 23 where ratio of the amount of
first fuel used in the engine to the amount of the second fuel used
in the engine is increased so as to prevent knock as the torque is
increased.
27. The spark ignition engine of claim 23 where a closed loop
control system with a knock detector is used to determine the ratio
of amount of the first fuel to second fuel used in the engine.
28. The spark ignition engine of claim 23 where the first fuel is
injected so as to increase its vaporization cooling of the fuel-air
mixture in at least one engine cylinder.
29. The spark ignition engine of claim 23 where the first fuel is
directly injected into the engine.
30. The spark ignition engine of claim 23 where the first fuel is
introduced into the engine so as to have a greater concentration in
the periphery of the engine cylinders.
Description
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/100,026 filed Apr. 6, 2005, which is a
continuation-in-part of U.S. patent application Ser. No. 10/991,774
filed Nov. 18, 2004, the contents of both of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates to an optimized fuel management
system for use with spark ignition gasoline engines in which an
anti-knock agent which is a fuel is directly injected into a
cylinder of the engine.
[0003] There are a number of important additional approaches for
optimizing direct injection ethanol enhanced knock suppression so
as to maximize the increase in engine efficiency and to minimize
emissions of air pollutants beyond the technology disclosed in
parent application Ser. No. 10/991,774 set out above. There are
also additional approaches to protect the engine and exhaust system
during high load operation by ethanol rich operation; and to
minimize cost, ethanol fuel use and ethanol fuel storage
requirements. This disclosure describes these approaches.
[0004] These approaches are based in part on more refined
calculations of the effects of variable ethanol octane enhancement
using a new computer model that we have developed. The model
determines the effect of direct injection of ethanol on the
occurrence of knock for different times of injection and mixtures
with port fuel injected gasoline. It determines the beneficial
effect of evaporative cooling of the direct ethanol injection upon
knock suppression.
SUMMARY OF THE INVENTION
[0005] In one aspect, the invention is a fuel management system
fear operation of a spark ignition gasoline engine including a
gasoline engine and a source of an anti-knock agent which is a
fuel. The use of the anti-knock agent provides gasoline savings
both by facilitating increased engine efficiency over a drive cycle
and by substitution for gasoline as a fuel. An injector is provided
for direct injection of the anti-knock agent into a cylinder of the
engine and a fuel management control system controls injection of
the anti-knock agent into the cylinder to control knock. The
injection of the antiknock agent can be initiated by a signal from
a knock sensor. It can also be initiated when the engine torque is
above a selected value or fraction of the maximum torque where the
value or fraction of the maximum torque is a function of the engine
speed. In a preferred embodiment, the injector injects the
anti-knock agent after inlet valve/valves are closed. It is
preferred that the anti-knock agent have a heat of vaporization
that is at least twice that of gasoline or a heat of vaporization
per unit of combustion energy that is at least three times that of
gasoline. A preferred anti-knock agent is ethanol. In a preferred
embodiment of this aspect of the invention, part of the fuel is
port injected and the port injected fuel is gasoline. The directly
injected ethanol can be mixed with gasoline or with methanol. It is
also preferred that the engine be capable of operating at a
manifold pressure at least twice that pressure at which knock would
occur if the engine were to be operated with naturally aspirated
gasoline. A suitable maximum ethanol fraction during a drive cycle
when knock suppression is desired is between 30% and 100% by
energy, it is also preferred that the compression ratio be at least
10. With the higher manifold pressure, the engine can be downsized
by a factor of two and the efficiency under driving conditions
increased by 30%.
[0006] It is preferred that the engine is operated at a
substantially stoichiometric air/fuel ratio during part or all of
the time that the anti-knock agent such as ethanol is injected. In
this case, a three-way catalyst can be used to reduce the exhaust
emissions from the engine. The fuel management system may operate
in open or closed loop modes.
[0007] In some embodiments, non-uniform ethanol injection is
employed. Ethanol injection may be delayed relative to bottom dead
center when non-uniform ethanol distribution is desired.
[0008] Many other embodiments of the invention are set forth in
detail in the remainder of this application.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a graph of ethanol fraction (by energy) required
to avoid knock as a function of inlet manifold pressure. The
ethanol fraction is shown for various values of .beta., the ratio
of the change in temperature in the air cylinder charge due to
turbocharging (and aftercooling if used) to the adiabatic
temperature increase of the air due to the turbocharger.
[0010] FIG. 2a is a graph of cylinder pressure as a function of
crank angle for a three bar manifold pressure.
[0011] FIG. 2b is a graph of charge temperature as a function of
crank angle for a three bar manifold pressure.
[0012] FIG. 3 is a schematic diagram of an embodiment of the fuel
management system disclosed herein for maintaining stoichiometric
conditions with metering/control of ethanol, gasoline, and air
flows into an engine.
[0013] FIGS. 4a and 4b are schematic illustrations relating to the
separation of ethanol from ethanol/gasoline blends.
[0014] FIG. 5 is a cross-sectional view of a flexible fuel tank for
a vehicle using ethanol boosting of a gasoline engine.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] Ethanol has a heat of vaporization that is more than twice
that of gasoline, a heat of combustion per kg which is about 60% of
that of gasoline, and a heat of vaporization per unit of combustion
energy that is close to four times that of gasoline. Thus the
evaporative cooling of the cylinder air/fuel charge can be very
large with appropriate direct injection of this antiknock agent.
The computer model referenced below shows that evaporative cooling
can have a very beneficial effect on knock suppression. It
indicates that the beneficial effect can be maximized by injection
of the ethanol after the inlet valve that admits the air and
gasoline into the cylinder is closed. This late injection of the
ethanol enables significantly higher pressure operation without
knock and thus higher efficiency engine operation than would be the
case with early injection. It is thus preferred to the conventional
approach of early injection which is used because it provides good
mixing. The model also provides information that can be used for
open loop (i.e., a control system that uses predetermined
information rather than feedback) fuel management control
algorithms.
[0016] The increase in gasoline engine efficiency that can be
obtained from direct injection of ethanol is maximized by having
the capability for highest possible knock suppression enhancement.
This capability allows the highest possible amount of torque when
needed and thereby facilitates the largest engine downsizing for a
given compression ratio.
[0017] Maximum knock suppression is obtained with 100% or close to
100% use of direct injection of ethanol. A small amount of port
injection of gasoline may be useful in order to obtain combustion
stability by providing a more homogeneous mixture. Port fuel
injection of gasoline also removes the need for a second direct
fuel system or a more complicated system which uses one set of
injectors for both fuels. This can be useful in minimizing
costs.
[0018] The maximum fraction of ethanol used during a drive cycle
will depend upon the engine system design and the desired level of
maximum torque at different engine speeds. A representative range
for the maximum ethanol fraction by energy is between 20% and
100%.
[0019] In order to obtain the highest possible octane enhancement
while still maintaining combustion stability, it may be useful for
100% of the fuel to come from ethanol with a fraction being port
injected, as an alternative to a small fraction of the port-fueled
gasoline.
[0020] The initial determination of the knock suppression by direct
injection of ethanol into a gasoline engine has been refined by the
development of a computer model for the onset of knock under
various conditions. The computer modeling provides more accurate
information for use in fuel management control. It also shows the
potential for larger octane enhancements than our earlier
projections. Larger octane enhancements can increase the efficiency
gain through greater downsizing and higher compression ratio
operation. They can also reduce the amount of ethanol use for a
given efficiency increase.
[0021] The computer model combines physical models of the ethanol
vaporization effects and the effects of piston motion of the
ethanol/gasoline/air mixtures with a state of the art calculational
code for combustion kinetics. The calculational code for combustion
kinetics was the engine module in the CHEMKIN 4.0 code [R. J. Kee,
F. M. Rupley, J. A. Miller, M. E. Coltrin, J. F. Grear, E. Meeks,
H. K. Moffat, A. E. Lutz, G. Dixon-Lewis, M. D. Smooke. J. Warnatz,
G. H. Evans, R. S. Larson, R. E. Mitchell, L. R. Petzold, W. C.
Reynolds, M. Caracotsios, W. E. Stewart, P. Glarborg, C. Wang, O.
Adigun, W. G. Houf, C. P. Chou, S. F. Miller, P. Ho, and D. J.
Young, CHEMKIN Release 4.0, Reaction Design, Inc., San Diego,
Calif. (2004)]. The CHEMKIN code is a software tool for solving
complex chemical kinetics problems. This new model uses chemical
rates information based upon the Primary Reference gasoline Fuel
(PRF) mechanism from Curran et al. [Curran, H. J., Gaffuri, P.,
Pitz, W. J., and Westbrook, C. K. "A Comprehensive Modeling Study
of iso-Octane Oxidation," Combustion and Flame 129:253-280 (2002)
to represent onset of autoignition.
[0022] The compression on the fuel/air mixture end-gas was modeled
using the artifact of an engine compression ratio of 21 to
represent the conditions of the end gas in an engine with an actual
compression ratio of 10. The end gas is defined as the un-combusted
air/fuel mixture remaining after 75% (by mass) of the fuel has
combusted. It is the end gas that is most prone to autoignition
(knock). The larger compression ratio includes the effect of the
increase in pressure in the cylinder due to the energy released in
the combustion of 75% of the fuel that is not in the end gas
region. The effect of direct ethanol vaporization on temperature
was modeled by consideration of the effects of the latent heat of
vaporization on temperature depending upon the time of the
injection.
[0023] The effect of temperature increase due to turbocharging was
also included. The increase in temperature with turbocharging was
calculated using an adiabatic compression model of air. It is
assumed that thermal transfer in the piping or in an intercooler
results in a smaller temperature increase. The effect is modeled by
assuming that the increase in temperature of the air charge into
the cylinder .DELTA.T.sub.charge is
.DELTA.T.sub.charge=.beta..DELTA.T.sub.turbo were
.DELTA.T.sub.turbo is the temperature increase after the compressor
due to boosting and beta is a constant. Values of .beta. of 0.3,
0.4 and 0.6 have been used in the modeling. It is assumed that the
temperature of the charge would be 380 K for a naturally aspirated
engine with port fuel injection gasoline.
[0024] FIG. 1 shows the predictions of the above-referenced
computer model for the minimum ethanol fraction required to prevent
knock as a function of the pressure in the inlet manifold, for
various values of .beta.. In FIG. 1 it is assumed that the direct
injection of the ethanol is late (i.e. after the inlet valve that
admits air and gasoline to the cylinder is closed) and a 87 octane
PRF (Primary Reference Fuel) to represent regular gasoline. The
corresponding calculations for the manifold temperature are shown
in Table 1 for the case of a pressure in the inlet manifold of up
to 3 bar for an engine with a conventional compression ratio of 10.
The temperature of the charge varies with the amount of ethanol
directly injected and is self-consistently calculated in Table 1
and FIG. 1. The engine speed used in these calculations is 1000
rpm.
TABLE-US-00001 TABLE 1 Computer model calculations of temperature
and ethanol fraction required for knock prevention for an inlet
manifold pressure of 3 bar for an engine with a compression ratio
of 10, for various values of .beta. (ratio of change of the
cylinder air charge temperature due to turbocharging to the
adiabatic temperature increase due to turbocharging
.DELTA.T.sub.charge = .beta..DELTA..sub.turbo). The engine speed is
1000 rpm. .beta. 0.3 0.4 0.6 T_charge init K 380 380 380 Delta T
turbo K 180 180 180 Delta T after intercooler K 54 72 108 Delta T
due to DI ethanol and gasoline K -103 -111 -132 T_init equivalent
charge K 331 341 356 Gasoline octane 87 87 87 Ethanol fraction (by
energy) needed to prevent knock 74% 82% 97%
[0025] Direct fuel injection is normally performed early, before
the inlet valve is closed in order to obtain good mixing of the
fuel and air. However, our computer calculations indicate a
substantial benefit from injection after the inlet valve is
closed.
[0026] The amount of air is constant in the case of injection after
the inlet valve has closed. Therefore the temperature change is
calculated using the heat capacity of air at constant volume
(c.sub.v). The case of early injection where the valve that admits
air and fuel to the cylinder is still open is modeled with a
constant-pressure heat capacity (c.sub.p). The constant volume case
results in a larger evaporation induced decrease in charge
temperature than in the case for constant pressure, by
approximately 30%. The better evaporative cooling can allow
operation at higher manifold pressure (corresponding to a greater
octane enhancement) without knock that would be the case of early
injection by a difference of more than 1 bar. The increase in the
evaporative cooling effect at constant volume relative to that at
constant pressure is substantially higher for the case of direct
injection of fuels such as ethanol and methanol than is the case
for direct injection of gasoline.
[0027] Typical results from the calculations are shown in FIG. 2.
The figure shows the pressure (a) and the temperature (b) of the
cylinder charge as a function of crank angle, for a manifold
pressure of 3 bar and a value of .beta.=0.4 Two values of the
ethanol fraction are chosen, one that results in autoignition, and
produces engine knock (0.82 ethanol fraction by fuel energy), and
the other one without autoignition, i.e., no knock (0.83 ethanol
fraction). Autoignition is a threshold phenomenon, and in this case
occurs between ethanol fractions of 0.82 and 0.83. For an ethanol
energy fraction of 0.83, the pressure and temperature rise at
360.degree. (top dead center) is due largely to the compression of
the air fuel mixture by the piston. When the ethanol energy
fraction is reduced to 0.82, the temperature and pressure spikes as
a result of autoignition. Although the autoignition in FIG. 2
occurs substantially after 360 degrees, the autoignition timing is
very sensitive to the autoignition temperature (5 crank angle
degrees change in autoignition timing for a change in the initial
temperature of 1 K, or a change in the ethanol energy fraction of
1%).
[0028] The effect of evaporative cooling from the antiknock agent
(in this case, ethanol) is shown in Table 2, where three cases are
compared. The first one is with port fuel injection of ethanol, in
this case the vaporization of the ethanol on the walls of the
manifold has a negligible impact on the temperature of the charge
to the cylinder because the walls of the manifold are cooled rather
than the air charge. The second case assumes direct injection, but
with the inlet valve open, with evaporation at constant pressure,
where the cooling of the charge admits additional air to the
cylinder. The third case assumes, as in the previous discussions,
late injection after the inlet valve has closed. It is assumed
stoichiometric operation, that the baseline temperature is 380 K,
and that there is cooling in the manifold after the turbocharger
with .beta.=0.4.
TABLE-US-00002 TABLE 2 Knock-free operation of ethanol port fuel
injection (assuming no charge cooling), and of direct injection
before and after the inlet valve is closed. Compression ratio of
10, baseline charge temperature of 380K, intercooler/cooling post
turbo with .beta. = -0.4, stoichiometric operation, gasoline with
87 RON. Engine speed is 1000 rpm. No Evaporative cooling
Evaporative Before After Cooling Valve Closing Valve Closing
Ethanol fraction 0.95 0.95 0.95 (by energy) Max manifold pressure
(bar) 1.05 2.4 4.0 Cylinder pressure after 1.05 2.4 3.0 cooling
(bar) Cylinder charge temperature 383 360 355 after cooling (K)
[0029] The results indicate the strong effect of the cooling. The
maximum manifold pressure that prevents knock (without spark
retard), with 0.95 ethanol fraction by energy in the case of port
fuel injection is 1.05 bar. With direct injection of the ethanol,
the maximum knock-free manifold and cylinder pressures are 2.4 bar,
with a temperature decrease of the charge of .about.75K. The final
case, with injection after inlet valve closing, allows a manifold
pressure of 4 bar, a cylinder pressure (after cooling) of 3 bar,
and a charge temperature decrease of .about.120 K. It should be
noted that the torque of the late injection case after the valve
has closed is actually higher than that of the early injection
case, even though the early injection case allows for additional
air (at constant pressure). For comparison, the model is also used
to calculate the manifold pressure at which knock would occur for
port fuel injection of 87 octane gasoline alone. This pressure is
.about.0.8 bar assuming spark timing at MBT (Maximum Brake Torque).
Conventional gasoline engines operate at 1 bar by retarding the
timing at high torque regions where knock would otherwise occur.
Thus the model indicates that evaporative cooling effect of direct
injection of ethanol after the inlet has closed can be
significantly greater than that the higher octane number rating of
ethanol relative to gasoline.
[0030] A manifold pressure of 4 bar is very aggressive. Table 2 is
indicative of the dramatically improved performance of the system
with direct injection after the inlet valve has closed. The
improved performance in this case can be traded for increased
compression ratio or reduced use of the anti-knock agent.
[0031] It should be noted that, as mentioned above, the
calculations of autoignition (knock) are conservative, as
autoignition for the case shown in FIG. 2 occurs relatively late in
the cycle, and it is possible that the fuel has been combusted
before it autoignites. Also it should be noted that the
calculations in FIG. 2 break down after autoignition, as the
pressure trace would be different from that assumed. Figures
similar to FIG. 2 are used to determine conditions where
autoignition would not occur, and those conditions are then used to
provide the information for FIG. 1. The initial temperatures of the
cases shown in FIG. 2 are 341 K for 0.82 ethanol fraction, and 340
K for 0.83 ethanol fraction, a difference of 1 K (the difference
due to the cooling effect of the ethanol).
[0032] Because of the large heat of vaporization, there could be
enough charge cooling with early injection so that the rate of
vaporization of ethanol is substantially decreased. By instead
injecting into the hot gases, which is the case with injection
after the inlet valve has closed, the temperature at the end of
full vaporization of the ethanol is substantially increased with
respect to early injection, increasing the evaporation rate and
minimizing wall wetting.
[0033] The optimum timing of the injection for best mixing and a
near homogeneous charge is soon after the inlet valve closes,
provided that the charge is sufficiently warm for antiknock agent
vaporization. If, on the other hand, a non-uniform mixture is
desired in order to minimize ethanol requirements and improve
ignition stability, then the injection should occur later than in
the case where the best achievable mixing is the goal.
[0034] Late injection of the ethanol after the inlet valve has
closed can be optimized through the use of diesel-like injection
schemes, such as injectors with multiple sprays. It is important to
inject the fuel relatively quickly, and at velocities which
minimize any cylinder wall wetting, which as described below could
result in the removal of the lubrication oils from the cylinder
liner. Multiple sprays from a nozzle that has multiple holes
results in a distributed pattern of sprays, with relatively low
injection velocities. This is particularly important thr ethanol,
because of the higher volume throughputs (as compared with
gasoline) of ethanol for equal energy content.
[0035] Injection after the valve has closed may require that a
modest fraction of the fuel 25%) be port injected in order to
achieve the desired combustion stability. A tumble-like or swirl
motion can be introduced to achieve the desired combustion
stability. The port injected fuel can be either gasoline or
ethanol.
[0036] Use of the computer model for operation with gasoline alone
gives results that are consistent with the observed occurrence of
knock in gasoline engine vehicles, thereby buttressing the
credibility of the projections for ethanol. The computer model
indicates that for knock-free gasoline operation alone with a
compression ratio of 10, knock imposes a severe constraint upon the
allowed manifold pressure for a naturally aspirated gasoline engine
and very limited (i.e., less than 1.2 bar) manifold pressure can be
achieved even with direct injection of gasoline unless spark retard
and/or rich operation is used. These changes, however, can reduce
efficiency and increase emissions.
[0037] FIG. 1 shows that knock can be prevented at manifold
pressures greater than 2 bar with direct injection of an ethanol
fraction of between 40 and 80% in an engine with a compression
ratio of 10. The manifold pressure can be at least 2.5 bar without
engine knock. A pressure of 3 bar would allow the engine to be
downsized to .about.1/3 of the naturally aspirated gasoline engine,
while still producing the same maximum torque and power. The large
boosting indicated by the calculations above may require a
multiple-stage turbocharger. In addition to a multiple stage
turbocharger, the turbocharger may be of the twin-scroll turbo type
to optimize the turbocharging and decrease the pressure
fluctuations in the inlet manifold generated by a small number of
cylinders.
[0038] With an increase in allowed manifold pressure in an engine
by more than a factor of the engine could be downsized by a factor
of 2 (that is, the cylinder volume is decreased by a factor of 2 or
more) and the compression ratio could be held constant or raised.
For example, the performance of an eight cylinder engine is
achieved by a four cylinder engine.
[0039] The occurrence of knock at a given value of torque depends
upon engine speed. In addition to providing substantially more
maximum torque and power, direct injection of ethanol can be used
to provide a significant improvement in torque at low engine speeds
(less than 1500 rpm) by decreasing or eliminating the spark retard.
Spark retard is generally used with gasoline engines to prevent
knock at low engine speeds where autoignition occurs at lower
values of torque than is the case at high engine speeds.
[0040] FIG. 1 can also be used to determine the ethanol fraction
required to prevent knock at different levels of torque and
horsepower, which scale with manifold pressure in a given size
engine. This information can be used in an open loop control
system.
[0041] The efficiency of a gasoline engine under driving conditions
using direct ethanol injection enhancement can be at least 20% and
preferably at least 30% greater than that of a naturally aspirated
gasoline engine with a compression ratio of 10. This increase
results from the substantial engine boosting and downsizing to give
the same power, and also the high compression ratio operation
(compression ratio of 11 or greater) that is enabled by a large
octane enhancement. With more aggressive downsizing of more than
50% (where the same engine performance is obtained with less than
one-half the displacement), the increase in efficiency could exceed
30%.
[0042] Greater downsizing and higher efficiency may also be
obtained by decreasing the octane requirement of the engine by
using variable valve timing (VVT). Thus, at conditions of high
torque, variable valve timing can be used to decrease the
compression ratio by appropriately changing the opening/closing of
the inlet and exhaust valves. The loss in efficiency at high torque
has a small impact on the overall fuel economy because the engine
seldom operates in these conditions.
[0043] VVT can also be used to better scavenge the exhaust gases
[B. Lecointe and G. Monnier, "Downsizing a Gasoline Engine Using
Turbocharging with Direct Injection" SAE paper 2003-01-0542].
Decreasing the exhaust gas decreases the air/fuel temperature.
Keeping both the inlet and exhaust valves open, while the pressure
in the inlet manifold is higher than in the exhaust, can be used to
remove the exhaust gases from the combustion chamber. This effect,
coupled with slightly rich operation in-cylinder, can result in
increased knock avoidance while the exhaust is still
stoichiometric. Cooled EGR and spark timing adjustment can also be
used to increase knock avoidance.
[0044] Any delay in delivering high engine torque at low engine
speeds can decrease drivability of the vehicle. Under these
conditions, because of the substantial engine downsizing, the
vehicle would have insufficient acceleration at low engine speeds
until the turbo produces high pressures. This delay can be removed
through the use of direct injection of ethanol by reduction of the
spark retard or ethanol/gasoline with rich operation and also with
the use of variable valve timing.
[0045] Another approach would be to use an electrically assisted
turbo charger. Units that can generate the required boosting for
short periods of time are available. The devices offer very fast
response time, although they have substantial power
requirements.
[0046] A multiple scroll turbocharger can be used to decrease the
pressure fluctuations in the manifold that could result from the
decreased number of cylinders in a downsized engine.
[0047] The temperature of the air downstream from the turbocharger
is increased by the compression process. Use of an intercooler can
prevent this temperature increase from increasing the engine's
octane requirement. In addition, in order to maximize the power
available from the engine for a given turbocharging, cooling of the
air charge results in increased mass of air into the cylinder, and
thus higher power.
[0048] In order to minimize emissions, the engine should be
operated substantially all of the time, or most of the time, with a
stoichiometric air/fuel ratio in order that a 3-way exhaust
catalyst treatment can be used, FIG. 3 shows a 3-way exhaust
treatment catalyst 10 and air, gasoline and ethanol control needed
to maintain the substantially stoichiometric ratio of fuel to air
that is needed for its effective operation. The system uses an
oxygen sensor 12 as an input to an electronic control unit (ECU)
14. The ECU 14 controls the amount of air into a turbocharger 16,
the amount of gasoline and the amount of ethanol so as to insure
stoichiometric operation. During transients, open-loop algorithms
from a stored engine map (not shown) are used to determine air,
gasoline and ethanol flows for keeping substantially stoichiometric
combustion in a cylinder of the engine 18.
[0049] Thus when variable ethanol octane enhancement is employed,
the fuel management system needs to adjust the amounts of air,
gasoline and ethanol such that the fuel/air ratio is substantially
equal to 1. The additional control is needed because, if the air;
gasoline ratio determined by the fuel management were not be
corrected during the injection of ethanol, the mixture would no
longer be stoichiometric. In contrast to the lean boost approach of
Stokes et al. [J. Stokes, T. H. Lake and R. J. Osborne, "A Gasoline
Engine Concept for Improved Fuel Economy--The Lean Boost System,"
SAE paper 2000-01-2902] stoichiometric operation with a 3-way
catalyst results in very low tailpipe emissions.
[0050] There are certain regions in the engine operating map where
the ECU 14 may operate open loop, that is, the control is
determined by comparison to an engine map lookup table rather than
by feedback from a sensed parameter which in this case is engine
knock (closed loop). As mentioned previously, open loop operation
during transients may be advantageous.
[0051] Another situation where open loop control can be
advantageous would be under high load, where fuel rich conditions
(where the fuel/air ratio is greater than stoichiometric) may be
required to decrease the temperature of the combustion and thus
protect the engine and the exhaust system (especially during
prolonged operation). The conventional approach in gasoline engine
vehicles is to use increased fuel/air ratio, that is, operating at
rich conditions. The presence of ethanol on-board allows for two
alternatives. The first is the use of ethanol fuel fractions beyond
what is required to control knock, thus reducing the combustion
temperature by a greater amount than could be obtained by gasoline
alone due to the higher cooling effect of evaporation in direct
ethanol injection, even while at stoichiometric conditions. The
second one is, as in conventional applications, the use of
increased fueling in rich operation (which could result in relative
air/fuel mass ratios as low as 0.75 where a stoichiometric mixture
has a relative air/fuel ratio of 1). The control system can choose
between two fuels, ethanol and gasoline. Increased use of ethanol
may be better than use of gasoline, with emissions that are less
damaging to the environment than gasoline and decreased amount of
rich operation to achieve the temperature control needed. Open loop
operation with both gasoline and ethanol may require substantial
modification of the engine's "lookup table."
[0052] Thus, a method of operating an engine is, under conditions
of partial load, to operate closed loop with the use of only
gasoline. As the engine load increases, the engine control system
may change to open loop operation, using a lookup table.
[0053] The closed loop control of the engine can be such that a
knock sensor (not shown) determines the fraction required of
ethanol, while the oxygen sensor 12 determines the total amount of
fuel. A variation of this scheme is to operate the knock control
open loop, using a lookup table to determine the ethanol to
gasoline ratio, but a closed loop to determine the total amount of
fuel.
[0054] In order to evaporative emission of the ethanol (which has a
relatively low boiling point), solvents can be added to the ethanol
to minimize the effect. An alternative means is to place an
absorptive canister between the ethanol tank and the atmosphere
that captures the ethanol and releases it when the engine is
operational.
[0055] Because of the large cooling effect from ethanol, it has
been known for some time that startup of a cold engine is difficult
(for example, during the first 30 seconds). With the multiple
fuels, it is possible to start up the engine without ethanol
addition. Gasoline vaporizes easier than ethanol, and conventional
operation with port-fuel or direct injected gasoline would result
in easier engine start up. A greater fraction of gasoline than
would be ordinarily used can be used to facilitate start-up
operation at times during the first 30 seconds of engine
operation.
[0056] Increased efficiency due to engine downsizing made possible
through the use of 100% or close to 100% ethanol at the highest
values of torque has the undesirable effect of requiring higher
ethanol fractions. Hence the use of non-uniform ethanol
distribution to minimize the use of ethanol at these values of
torque becomes more attractive when achievement of the maximum
efficiency gain is desired.
[0057] Below a certain value of torque or boost pressure it can be
advantageous to use a non-uniform ethanol distribution in order to
reduce the amount of ethanol that is used. Above certain torque or
turbocharger or supercharger boost pressures, non-uniform charge
would not be used since the engine is operating mostly on ethanol
and ethanol non-uniformity cannot be used for minimizing ethanol
consumption. This is especially important if the desired fraction
is higher than 50%.
[0058] The capability to minimize the use of ethanol by non-uniform
ethanol distribution in the cylinder can be realized by certain
ethanol injection geometries. Ethanol can be injected in the
periphery of a swirling charge. In order to minimize wall wetting
by the ethanol, it would be convenient to achieve the injection in
a manner such that the ethanol injection matches the swirling
motion of the charge. The injection direction is thus positioned at
an angle with respect to the main axis of the cylinder, injecting
the ethanol with an angular direction component. Charge
stratification in the case of swirl can be maintained by
temperature stratification, with the cooler (and denser) regions in
the periphery, which correspond to the end-gas zone.
[0059] An alternative or additional method to provide ethanol
non-uniform distribution in the cylinder is to inject the ethanol
relatively late with respect to bottom dead center. Thus the time
for transport and diffusion of the ethanol is minimized. However,
sufficient time should be allowed for full vaporization of the
ethanol. As the temperatures are higher after Bottom-Dead-Center
(BDC), the vaporization time is reduced, and it is less likely that
the ethanol would wet the cylinder walls, improved vaporization of
the ethanol can also be achieved by using injectors that produce
small droplets. The injector could be a single spray pattern
injector with a relatively narrow directed jet. This type of jet
would optimize the deposition of the ethanol in the desired
region.
[0060] Creating a non-uniform ethanol distribution in the cylinder
(in the outer regions of the cylinder) has two advantages. The
first one is the increased cooling effect of the region that has
the propensity to autoignite (knock), the end gas region. The
second is that the central region is not cooled, improving ignition
and initial flame propagation. It is preferable to keep the central
region hot, as having a fast flame speed early in the flame
propagation has antiknock advantages, by reducing the burn time and
the time for precombustion chemistry of the end gas. Minimizing the
burn time decreases the propensity to knock, as there is no knock
if the end gas is burned before it can autoignite. Thus it is
possible to have good ignition properties of the air/fuel mixture,
even under conditions where the gasoline is evenly spread
throughout the cylinder.
[0061] Stratified operation can result in locally increased charge
cooling. This is because the injected ethanol cools only a small
fraction of the charge, and thus, for a given amount of ethanol,
the local decrease in temperature is larger with stratified
operation than the average decrease of temperature with uniform
ethanol distribution. Late injection can aid in the formation of a
non-uniform air/ethanol mixture as mixing time is limited. Since a
fraction of the gasoline is port-fuel injected, it can be assumed
that this fuel is homogeneously distributed in the cylinder, but
ethanol is preferentially in the cooler edges (the end-gas). Thus,
although overall the air/fuel charge is stoichiometric, locally
near the spark it is lean while in the region of the end gas it is
rich. Both of these conditions are advantageous, since the ignition
occurs in a region with higher temperature (although slightly
lean), while the outside is rich and cool, both of which are
knock-suppressors.
[0062] In the case of swirl or tumble stratified air fuel charges
with hot air/gasoline in the center and colder air/ethanol or
air/ethanol/gasoline mixtures in the end gas, it is advantageous to
place the spark in the region of the hot air/gasoline mixture
(substantially near the center of the combustion chamber).
[0063] Ethanol consumption can be minimized if the gasoline is also
directly injected. In this case, the heat of vaporization of
gasoline is also useful in decreasing the temperature of the charge
in the cylinder. The gasoline can be injected using a separate set
of injectors. This would provide the most flexibility. However, it
may be difficult to fit two sets of injectors per cylinder in the
limited space in the cylinder head. An alternative means is to
provide a single set of injectors for injection of both the ethanol
and the gasoline. Two options are possible, one in which there is a
single nozzle and valve (and the gasoline and ethanol are
co-injected), and one in which each fuel has a separate nozzle and
valve.
[0064] Using direct injection of both the gasoline and the ethanol
has the disadvantage of increased cost. In addition to a
sophisticated injector or injectors, a second high pressure fuel
pump is also needed. The ethanol and the gasoline also need to have
parallel common plenums.
[0065] When a single nozzle is used, the ethanol and the gasoline
are distributed in the same manner in the cylinder. In the case
with a single nozzle and single valve, the fuels need to be mixed
prior to the valve/nozzle part of the injector. This could be done
either outside of the injector or in the injector body. The volume
between the mixing point and the nozzle should be minimized to
allow for fast response of the fuel mixture.
[0066] A slight modification of the above embodiment involves an
injector that has two valves but a single nozzle. This minimizes
the need for a second valve outside the injector for controlling
the gasoline/ethanol mixture, in addition to minimizing the volume
between the mixing point and the valves.
[0067] It is possible to use a separate nozzle/valve for each fuel
in a single injector. In this case, the gasoline and the ethanol
can be deposited in different regions of the cylinder. An
additional advantage would be to provide different spray patterns
for the ethanol and for the gasoline. This would provide the most
flexible system (comparable to two independent injectors), with
possibilities of simultaneous or asynchronous injection of varying
fractions of ethanol/gasoline, as well as being able to deposit the
ethanol and the gasoline in the desired location of the charge, for
optimal non-uniform distribution of ethanol in the cylinder.
Optimal distribution means knock avoidance with minimal consumption
of ethanol, while maintaining engine drivability. Optimal
non-uniform ethanol distribution can be obtained by centrally
depositing the gasoline and by preferentially depositing the
ethanol in the periphery of the cylinder, where the end gas will
be. This can be accomplished more easily with direct injection as
opposed to achieving non-uniform distribution of the gasoline
through non-uniform spraying in the inlet manifold. Because the
heat of vaporization of the gasoline is substantially lower than
for ethanol (a factor of 4 smaller on an energy basis), the cooling
effect in the region near the spark is smaller, affecting less the
initial flame propagation. In addition, it may be beneficial to
retard the injection of the ethanol with respect to the
gasoline.
[0068] When the ethanol has been exhausted, the engine can operate
in a `lower performance gasoline only` mode with turbocharger boost
decrease (e.g. by a wastegate) and elimination or avoidance of
operation at maximum torque levels. These conditions could be
limiting, and in some cases a means of operating the vehicle at
higher loads would be desired. This could be accomplished by using
gasoline in the ethanol system with gasoline direct injection
(GDI), while at the same time port-fuel injecting a fraction of the
gasoline. Under these conditions the engine will operate at higher
loads and higher torques, but still far below what ethanol could
achieve. Only the cooling effect of the direct injection fuel is
obtained, since the directly injected fuel has the same octane
number as the port-injection fuel (gasoline in both cases).
[0069] If the ratio of ethanol in the ethanol fuel tank to gasoline
in the gasoline fuel tank is lower than a predetermined value
(because of the lack or availability of ethanol or for some other
reason), it is possible to change the engine operation condition
such that the ethanol/gasoline consumption ratio over a drive cycle
is decreased. This is done for reducing the maximum ethanol
fraction at a given engine speed that can be used in the engine.
The allowed level of turbocharging and the maximum pressure, torque
and horsepower would be correspondingly reduced to prevent knock,
in this way, a continuous tradeoff between the ethanol/gasoline
consumption ratio and the maximum torque and horsepower can be
accomplished.
[0070] By proper expert system evaluation of the recent
ethanol/gasoline usage and amounts of gasoline and ethanol it is
possible to provide means to minimize the need of the `low
performance, gasoline only` mode. The usage of the antiknock agent
can be restricted when the amount left in the tank is below a
predetermined level, such that the main fuel will be exhausted
prior to or simultaneously with the ethanol. It would be desirable
to place a switch so that the operator could override the
limitations, in those conditions where the desired vehicle
operation will not be limited by the exhaustion of the antiknock
agent.
[0071] Over a drive cycle, the amount of ethanol (by energy)
required to enhance the octane number sufficiently to increase
efficiency by at least 25% would be less than 15% of the fuel
(ethanol+gasoline energy) without ethanol stratification and less
than 5% with ethanol stratification.
[0072] Onboard separation of ethanol from diesel by fractional
distillation has been demonstrated for use in ethanol exhaust
aftertreatment catalysts ["Fuel-Borne Reductants for NOx
Aftertreatment: Preliminary EtOH SCR Study", John Thomas, Mike
Kass, Sam Lewis, John Storey, Ron Graves, Bruce Bunting, Alexander
Panov, Paul Park, presented at the 2003 DEER (Diesel Engine
Emissions Reduction] Workshop, Newport R.I. August 2003]. This
approach could be employed for onboard separation of ethanol from a
gasoline mixture. However, use of membrane separation can be
simpler and less expensive. Although there is information about the
use of membranes for the separation of ethanol from water, to our
knowledge there is no available information on the membrane
separation of ethanol from gasoline. Because the ethanol molecule
is on the order of 4 Angstroms and the typical hydrocarbon fuel
molecules are much lamer, it is possible to use membranes bar the
separation. Both organic and inorganic membranes could be used.
Since it is not necessary to obtain high purity ethanol, the
process is relatively simple and requires low pressure.
[0073] Both porous and transfusion membranes can be used because
ethanol with two carbon atoms has significantly different
properties than most other gasoline compounds which have five to
ten carbon atoms. The other antiknock agents contemplated for use
in this invention also have a small number of carbons relative to
gasoline. For example, methanol has one carbon. The membrane
approach can be significantly simpler than the distillation or
absorption/desorption approaches (see Ilyama et al, U.S. Pat. No.
6,332,448) that have been suggested for separation of various
gasoline/diesel fuels where there is much less of a difference in
the number of carbon atoms.
[0074] The location of the membrane could be in the region of high
pressure in the fuel line (downstream horn the pump), or upstream
from it. If it is located downstream, the separation occurs only
when the engine is operational and the pump is on, while it is
upstream the separation is continuous. The pressure of the fuel
downstream from the pump is a few bars (characteristic of port fuel
injection). This is to be differentiated from the pressure of the
ethanol system, which is directly injected and thus requires much
higher pressures.
[0075] The separated ethanol is transported to a separate tank
where it is stored. If there is too much ethanol, three options are
available: 1) additional separation is stopped; 2) some ethanol is
used in the engine, even if not required 3) ethanol is returned to
the main gasoline tank.
[0076] The tank should be reachable, in order to be able to
introduce additional ethanol when required, as when towing, in high
temperatures, or when doing extensive climbing, conditions that
require operation at high torque and which if for extended periods
of time would consume ethanol at a rate higher than what can be
extracted from the fuel.
[0077] Extraction of ethanol from the gasoline can have the
unintended effect of reducing the octane of the rest of the fuel.
Thus, it is likely that somewhat increased use of injected ethanol
would be required to prevent knock. Even in the case without
non-uniform distribution of the ethanol, under normal driving
conditions the system can be designed so that the amount of ethanol
extracted from the fuel matches the required ethanol.
[0078] It may also be advantageous to separate the ethanol from a
gasoline/ethanol mixture at the fueling station. As with onboard
separation, this approach also allows use of the present fuel
transportation infrastructure. The potential advantages could be
greater flexibility in choice of a fuel separation system and lower
cost relative to onboard separation. It may be of particular
interest during the introductory phase of ethanol boosted engine
vehicles.
[0079] It can be useful to have the capability to adjust the volume
of the ethanol tank, thus varying the maximum amount of ethanol in
the ethanol tank. This capability would make it possible to drive
longer distances between ethanol refueling and to operate on
different gasoline/ethanol ratios over a drive cycle, depending on
the availability and cost of ethanol and gasoline. In some cases,
it may be advantageous to use more ethanol than is needed to
provide the desired octane enhancement (e.g., to meet alternative
fuel or CO.sub.2 reduction goals). It is desirable to have this
capability without increasing the overall fuel tank size. A single
fuel tank with a membrane or plate separating variable amounts of
gasoline and ethanol can be used to accomplish this goal.
[0080] The tank can be configured to have a horizontal or vertical
moveable/deformable walls that are substantially impervious and
separate the regions that are filled with gasoline and ethanol.
Separate filling ports and fuel lines are incorporated for each
region as shown in FIGS. 4a and b. The separation between the
gasoline and ethanol (or other anti-knock agent) does not have to
be perfect since a small amount of leakage of one fuel into the
other will not adversely affect operation of the vehicle. The wall
can be moved in response to the amount of either fuel in the tank.
This process is automatic in the case of a separating membrane, and
the latter can be more impervious to leaks from one fuel to the
other.
[0081] Ethanol is denser than gasoline. The movable/deformable wall
can be placed such that the ethanol is located either on top of the
gasoline or below the gasoline. However, since it is expected that
less ethanol is required than gasoline, the preferred embodiment
has the ethanol above the gasoline, as shown in FIG. 5.
[0082] If the ethanol is stored so that it is separate from the
gasoline, it can be mixed with various additives to insure the
desired operation of the ethanol injection system. In addition, it
is possible to use gasoline-ethanol mixtures, such as E85 (which
contains 15% by volume of gasoline). The lubricity additives
include fatty acids, organic amine salts (amine salts of acid
phosphates and polyethyleneoxy acid phosphates), alkyl and aryl
acid phosphates and dialkyl alkyl phosphonates.
[0083] The modeling calculations show that for direct injection of
alcohols, the larger impact of knock suppression is not the
intrinsic knock-resistance of the fuel antiknock agent but rather
its high heat of vaporization. In order to evaluate alternatives to
ethanol, Table 3 shows the properties of proposed fuel
antiknock/alternative fuels. Although some of these additives have
higher octane numbers than gasoline, some of them have a much
larger effect on the cylinder charge temperature (Table 3 assumes
injection after the inlet valve has closed). Some of these
additives (mostly the ethers) have a comparable charge temperature
effect to that of gasoline direct injection, and thus are of less
interest. The alcohols have optimal properties for the application,
with temperature changes that are a factor of 3 or more larger than
the temperature change due to gasoline direct injection (for 100%
or near 100% operation with the additive). For ethanol, the change
in temperature is a factor of more than 4 larger than that of
gasoline, and for methanol the change is about 9 times larger. The
temperature decrease of the air increases with the amount of oxygen
in the fuel (in terms of the O/C ratio). Thus, it is highest for
methanol, with an O/C ratio of 1, second for ethanol (O/C=2), and
so on.
TABLE-US-00003 TABLE 3 Antiknock properties of various fuels
(calculated from data obtained in SAE standard J 1297 Alternative
Automotive Fuels, September 2002) Equiv. Latent Vapori- Latent Net
heat of zation heat of heat of vapori- energy/ Stoic vapori- (R +
Combustion zation heat of air/fuel zation .DELTA.T air Fuel type
Chemical formula RON MON M)/2 MJ/kg MJ/kg combustion ratio MJ/kg
air X Gasoline 42.8 0.30 0.007 14.6 0.020 -28 Ethyl t-Butyl Ether
CH3CH2--O--C(CH3)3 118 102 110 36.3 0.31 0.009 12.1 0.026 -35
t-Amyl Methyl Ether C2H5 C (CH3)2--O--CH3 111 98 105 36.3 0.32
0.009 12.1 0.027 -36 Toluene C7H8 111 95 103 40.5 0.36 0.009 13.5
0.027 -37 Methyl t-Butil Ether CH3--O--C(CH3)3 116 103 110 35.2
0.32 0.009 11.7 0.028 -37 Diisopropyl Ether (CH3)2CH--O--CH(CH3)2
110 97 103 38.2 0.34 0.009 12.1 0.028 -39 t-Butyl Alcohol (CH3)3
C--OH 103 91 97 32.9 0.60 0.018 11.1 0.054 -74 Isopropanol
(CH3)2CHOH 118 98 108 30.4 0.74 0.024 10.4 0.071 -97 Methanol with
50% methanol/TBA 114 96 105 26.5 0.88 0.033 8.8 0.100 -137
cosolvent Ethanol CH3CH2OH 129 102 115 26.7 0.91 0.034 9 0.102 -138
Methanol CH3OH 133 105 119 20.0 1.16 0.058 5.4 0.181 -246
[0084] Also shown in Table 3 are the ratios of the heat of
vaporization to the heat of combustion, a measure of the potential
effects when used as antiknock agents. This parameter gives a
measure of the amount of evaporative cooling for a given level of
torque. The last entry, .DELTA.T.sub.air, measures the decrease in
air temperature for a stoichiometric mixture with injection after
the inlet valve closes. Although the effect clearly is maximized by
the use of methanol, other considerations may make ethanol the
preferred choice. Methanol is toxic and corrosive.
[0085] Hydrous ethanol (with a small amount of water) has the
advantage of lower cost than pure (neat) ethanol. Removing the last
10% to 15% water from ethanol has significant expense and consumes
considerable energy. Manufacturing facilities typically produce
ethanol with about 10% water by volume unless there is a need for
essentially pure (anhydrous) ethanol. It could be advantageous to
use ethanol with a water concentration of 5% to 15% by volume.
[0086] By using a closed loop approach to identify engine knock,
flexible gasoline grades (with different octane ratings) and
flexible knock-prevention fuel grades can be used. An open loop
system would require measurement of the quality of the antiknock
additive. Similarly, an open loop system would require determining
the quality of the fuel (octane number). Closed loop operation
allows the use of less expensive gasoline, when available, thus
partially compensating for the more expensive anti-knock agent. It
is also possible to use different antiknock feel according to its
availability, such as ethanol in the regions that produce and
process corn, and methanol in those that have methanol production
capabilities. Thus, the least expensive grade of gasoline available
and the least expensive antiknock fuel can be used, allowing a
decrease of the cost of operating the vehicle as well as increasing
the availability of the antiknock fuel.
[0087] Although the above discussion has featured ethanol as an
exemplary anti-knock agent, the same approach can be applied to
other high octane fuel and fuel additives with high vaporization
energies such as methanol (with higher vaporization energy per unit
fuel), and other anti-knock agents such as isopropanol, tertiary
butyl alcohol, or ethers such as methyl tertiary butyl ether
(MTBE), ethyl tertiary butyl ether (ETBE), or tertiary amyl methyl
ether (TAME). It may be advantageous to use various mixtures of
these fuels and additives with each other and with ethanol.
[0088] Particularly during the introduction phase of the present
invention, the ethanol fueling could be performed by the use of
containers, such as one-gallon containers. To facilitate ease of
fueling an expandable pipe and funnel can be built into the ethanol
fuel tank of the vehicle.
[0089] The ethanol in these containers would be denatured so as to
prevent human consumption as an alcoholic beverage and could
contain the additives described above. Ethanol sold for fuel, such
as in Brazil, is denatured by a small fraction of gasoline (2%)
among other denaturing agents (methanol, isopropanol and
others).
[0090] Recycling of the container could take place at certain
specific locations such as gasoline stations
[0091] Using a signal from a knock sensor to determine when and how
much ethanol or other anti-knock agent must be used at various
times in a drive cycle to prevent knock, the heel management system
can be employed to minimize the amount of ethanol or other
anti-knock agent that is consumed over the drive cycle. If
sufficient ethanol or other anti-knock agent is available, the fuel
management system can also be used to employ more ethanol than
would be needed to prevent knock. This would allow greater gasoline
savings (the gasoline savings component from substitution of
ethanol for gasoline would increase) and carbon dioxide reduction.
In this case it may be desirable to operate at an anti-knock agent
fraction which is either varied or constant during the drive
cycle.
[0092] The contents of all of the references cited in this
specification are incorporated by reference herein in their
entirety.
[0093] It is recognized that modifications and variations of the
inventions disclosed herein will be apparent to those of ordinary
skill in the art and all such modifications and variations are
included within the scope of the appended claims.
* * * * *