U.S. patent application number 13/609733 was filed with the patent office on 2013-03-21 for open-valve port fuel injection of alcohol in multiple injector engines.
This patent application is currently assigned to ETHANOL BOOSTING SYSTEMS LLC. The applicant listed for this patent is Leslie Bromberg, Daniel R. Cohn. Invention is credited to Leslie Bromberg, Daniel R. Cohn.
Application Number | 20130073183 13/609733 |
Document ID | / |
Family ID | 47881430 |
Filed Date | 2013-03-21 |
United States Patent
Application |
20130073183 |
Kind Code |
A1 |
Cohn; Daniel R. ; et
al. |
March 21, 2013 |
Open-valve Port Fuel Injection Of Alcohol In Multiple Injector
Engines
Abstract
An engine having two or more fuel injectors is disclosed, where
at least one of the injectors is used to port fuel inject fuel into
the cylinder when the air intake valve is open. The open valve port
fuel injector is used to inject a fuel that has alcohol as a
constituent and is the same fuel injected by another fuel injector.
In other embodiments, the open valve fuel injector is used to
inject an anti-knock fuel containing alcohol while a primary fuel,
is introduced by another injector. The operation of the open valve
fuel injector can be optimized to maximize the vaporization
cooling. In other embodiments, the open valve fuel injector may be
used in conjunction with direct injection of the primary fuel or
the anti-knock fuel. Heavy EGR can be optimally used with the
various embodiments.
Inventors: |
Cohn; Daniel R.; (Cambridge,
MA) ; Bromberg; Leslie; (Sharon, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cohn; Daniel R.
Bromberg; Leslie |
Cambridge
Sharon |
MA
MA |
US
US |
|
|
Assignee: |
ETHANOL BOOSTING SYSTEMS
LLC
Cambridge
MA
|
Family ID: |
47881430 |
Appl. No.: |
13/609733 |
Filed: |
September 11, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61535404 |
Sep 16, 2011 |
|
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61603977 |
Feb 28, 2012 |
|
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61663670 |
Jun 25, 2012 |
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61667493 |
Jul 3, 2012 |
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Current U.S.
Class: |
701/104 |
Current CPC
Class: |
F02D 19/081 20130101;
F02D 19/061 20130101; F02D 19/0665 20130101; F02M 35/1085 20130101;
F02D 19/0692 20130101; F02D 19/0694 20130101; Y02T 10/47 20130101;
F02D 19/0655 20130101; F02D 41/005 20130101; F02D 19/0689 20130101;
Y02T 10/30 20130101; Y02T 10/40 20130101; Y02T 10/36 20130101; F02D
41/3094 20130101 |
Class at
Publication: |
701/104 |
International
Class: |
F02D 41/00 20060101
F02D041/00 |
Claims
1. A spark ignition engine, having at least one cylinder and an
intake valve, where a fuel that contains alcohol as a constituent
is introduced into the cylinder by a first port fuel injector and
the same fuel is also introduced into the cylinder by a second port
fuel injector, where the fuel from the second port fuel injector is
introduced in such a way that it vaporizes inside the cylinder and
the vaporization cools the fuel-air mixture in the cylinder;
wherein, for a given amount of fuel injected by a fuel injector,
fuel injected by the second port fuel injector provides more
vaporization cooling than fuel provided by the first port fuel
injector; and wherein the ratio of the amount of fuel from the
second port fuel injector to the amount of fuel from the first port
fuel injector increases with increasing torque.
2. The spark ignition engine of claim 1, where the ratio of the
amount of fuel from the second port fuel to the amount of fuel from
the first port fuel injector is determined by the requirement of
avoiding knock.
3. The spark ignition engine of claim 1, where hot EGR is used at
low loads and the EGR is reduced or eliminated at high loads.
4. The spark ignition engine of claim 1, where at least 30% EGR is
used.
5. The spark ignition engine of claim 1, where the EGR level is
decreased when the alcohol content in the fuel is decreased.
6. The spark ignition engine of claim 1, where the compression
ratio is at least 14.
7. A spark ignition engine, having at least one cylinder and an
intake valve, where a first fuel is introduced by a first fuel
injector and where a second fuel of which alcohol is a constituent
having a higher alcohol concentration than the first fuel and which
has a different composition than the first fuel, is introduced by a
second fuel injector, which is a port fuel injector, where the
second fuel from the second fuel injector is introduced in such a
way that it vaporizes inside the cylinder and the vaporization
cools the fuel-air mixture in the cylinder; wherein the second fuel
from the second fuel injector is introduced while the intake valve
is open; wherein the second fuel injected by the second fuel
injector provides more vaporization cooling than the first fuel
provided by the first fuel injector; and wherein the ratio of the
amount of second fuel introduced from the second fuel injector to
the amount of first fuel introduced from the first fuel injector
increases with increasing torque.
8. The spark ignition engine of claim 7, where the ratio of the
amount of second fuel from the second port fuel injector to the
amount of first fuel from the first port fuel injector is
determined by the requirement of avoiding knock.
9. The spark ignition engine of claim 7, where hot EGR is used at
low loads and the EGR is reduced or eliminated at high loads.
10. The spark ignition engine of claim 7, where at least 30% EGR is
used.
11. The spark ignition engine of claim 7, where the compression
ratio is at least 14.
12. The spark ignition engine of claim 7, wherein the second port
fuel injector is located closer to the intake valve than the first
port fuel injector.
13. The spark ignition engine of claim 7, wherein the second port
fuel injector produces smaller droplets than the first port fuel
injector.
14. The spark ignition engine of claim 7, wherein the first fuel
injector introduces natural gas or another gaseous fuel into the
engine.
15. A spark ignition engine, having at least one cylinder and an
intake valve, where a first fuel is introduced by a first fuel
injector which is a closed valve port fuel injector and where a
second fuel, which has methanol as a constituent, is introduced by
a second fuel injector which is an open-valve port fuel injector;
and where the second fuel is produced by onboard separation from a
methanol-gasoline mixture, and where the ratio of the amount of
second fuel introduced into the engine from the second fuel
injector to the amount of first fuel introduced into the engine by
the first fuel injector increases with increasing torque.
16. The spark ignition engine of claim 15, where the second fuel
injector is located closer to the intake valve than the first fuel
injector.
17. The spark ignition engine of claim 15, where the second fuel
injector introduces smaller droplets into the engine than the first
fuel injector.
18. The spark ignition engine of claim 15, where hot EGR is used at
low loads and EGR is reduced or eliminated at high loads.
19. The spark ignition engine of claim 15, where the
methanol-gasoline mixture is M15.
20. The spark ignition engine of claim 15, where the amount of
methanol in the methanol-gasoline mixture varies, and where EGR is
used and the EGR level decreases when the amount of methanol in the
methanol-gasoline mixture decreases.
21. The spark ignition engine of claim 15, where the amount of
second fuel that is used in the engine is determined by the
requirement to prevent knock.
22. A spark ignition engine where a first fuel is introduced into
the engine by a first fuel injector and by a second fuel injector,
where the first and second fuel injectors are port fuel injectors,
and the second port fuel injector provides more vaporization
cooling than the first port fuel injector and the ratio of the
amount of fuel provided by the second fuel injector to the amount
provided by the first fuel injector increases with increasing
torque; wherein a second fuel is introduced by third fuel injector,
wherein the third fuel injector is a direct injector; wherein the
ratio of the amount of the second fuel to the amount of first fuel
that is used in the engine increases with increasing torque; and
wherein the engine is operated with a substantially stoichiometric
fuel-air ratio.
23. A spark ignition engine in a vehicle comprising a tank in which
methanol-gasoline mixtures of varying methanol content are stored;
and where a first fuel injector introduces a first fuel and a
second fuel injector introduces a second fuel where the second fuel
is produced from onboard separation from the stored
methanol-gasoline mixture and has a higher methanol content than
both the first fuel and the methanol-gasoline mixture from which it
is produced; where the ratio of the second fuel to the first fuel
increases with increasing torque so as to prevent knock; and where
the operation of the onboard separation system is varied as a
function of the amount of methanol in the methanol-gasoline
mixture.
24. The spark ignition engine of claim 23, where the second fuel
injector introduces a higher fraction of fuel as a liquid into a
least one cylinder in comparison to the first fuel injector.
25. The spark ignition engine of claim 23, where the first fuel
injector is a closed valve port fuel injector.
26. The spark ignition engine of claim 23, where the second fuel
injector is an open-valve port fuel injector.
27. The spark ignition engine of claim 23, where the
methanol-gasoline mixture is M15.
28. The spark ignition engine of claim 23, where, when the methanol
in the methanol-gasoline mixture in the tank is reduced, the
effective compression ratio is reduced.
Description
[0001] This application claims priority of U.S. Provisional Patent
Application Ser. Nos. 61/535,404, filed Sep. 16, 2011; 61/603,977
filed on Feb. 28, 2012; 61/663,670, filed Jun. 25, 2012; and
61/667,493 filed Jul. 3, 2012, the disclosures of which are
incorporated herein by reference in their entireties.
BACKGROUND OF THE INVENTION
[0002] The performance and efficiency of spark ignition engines can
be increased by increasing knock resistance. Direct injection of
alcohol in spark ignition gasoline engines provides strong
vaporization cooling of the fuel-air mixture in the cylinders and
thereby substantially increases knock resistance. The increased
knock resistance allows operation and higher compression ratio
and/or higher levels of turbocharging.
[0003] The alcohol can be either directly injected from a single
source by itself or along with gasoline or another fuel, or
injected on-demand from a secondary tank into an engine that is
primarily fueled with gasoline. For example, U.S. Pat. No.
7,225,787 and U.S. Pat. No. 7,314,033 describe gasoline engines in
which on-demand use of ethanol or methanol from a secondary tank is
employed to prevent knock at high torque.
[0004] Direct injection, however, has the disadvantage that if it
is to be employed by modifying existing engines that are not direct
injection spark ignition engines, it is necessary to change the
engine head in order to provide the additional penetration for the
direct injector. This can substantially increase the effort that is
required for engine modification. An example is the conversion of a
turbo diesel engine to a spark ignition engine that uses direct
injection.
[0005] On-demand use of alcohol from port fuel injection can be
employed as an alternative to direct injection and is described in
U.S. Pat. No. 7,314,033. However, as discussed in this patent, it
has the disadvantage that, while there is a knock resistance
improvement from the higher chemical octane of the alcohol relative
to gasoline, the vaporization cooling effect inside the cylinder is
lost in conventional port fuel injection. In conventional port fuel
injection, the air intake valve is closed when the fuel is injected
in the manifold and the vaporization cooling takes place outside of
the cylinder.
[0006] Use of open-valve port fuel injection of the alcohol bearing
fuel can provide a way to maintain the advantage of ease of
implementation of port fuel injection while also providing some
vaporization cooling of the injected alcohol bearing fuel. In this
case, some of the liquid fuel from the port fuel injector enters
through the cylinder intake port and provides vaporization cooling
of the fuel-air mixture.
[0007] Employment of two port fuel injectors, where the injectors
inject different fuels and one of the injectors provides alcohol
while the cylinder intake valve is open has been described in U.S.
Pat. No. 7,647,916. However, it does not discuss a set of
approaches that could be particularly effective in increasing the
knock resistance of open-valve port fuel injection and minimizing
the adverse effects of open valve port fuel injection. U.S. Pat.
No. 7,647,916 also did not discuss other uses of open-valve port
fuel injection to enhance the operating characteristics of spark
ignition engines.
[0008] Therefore, improved means to maximize knock resistance and
minimize the adverse effects of open-valve port fuel injection are
needed. The use of open-valve port fuel injection to improve the
capability of spark engines using direct injection and using
different fuels would also be beneficial
SUMMARY OF THE INVENTION
[0009] An engine having two of more fuel injectors is disclosed,
where at least one of the fuel injectors is used to port fuel
inject fuel into the cylinder when the air intake valve is open.
This provides vaporization cooling, thereby increasing the
stability of the gaseous mixture and reducing autoignition. In some
embodiments, the open valve fuel injector is used to inject the
primary fuel, which is typically gasoline. In other embodiments,
the open valve fuel injector is used for separately controlled
injection of an anti-knock fuel that contains alcohol. The position
and operation of the open valve fuel injector can also be modified
to optimize the vaporization cooling provided by the fuel injected
through this injector. In other embodiments, the open valve fuel
injector may be used in connection with direct injection of either
the primary fuel or the anti-knock fuel.
BRIEF DESCRIPTION OF THE FIGURES
[0010] FIG. 1 is a schematic diagram of an engine having two tanks
with two port fuel injectors according to one embodiment.
[0011] FIG. 2 is a schematic diagram of an engine having two tanks
and two port fuel injectors according to another embodiment which
includes a direct fuel injector.
[0012] FIG. 3 is a schematic diagram of an engine having two tanks
and two port fuel injectors according to another embodiment which
includes a direct fuel injector.
[0013] FIG. 4 is a schematic diagram of an engine having a single
fuel tank with two port fuel injectors according to one
embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0014] FIG. 1 shows a schematic diagram of a gasoline engine where
alcohol or some other fluid from a secondary tank 15 is introduced
into the engine cylinder 20 by an open-valve port fuel injector 25
and the gasoline from the primary tank 30 is introduced by a
closed-valve port fuel injector 35. While gasoline and alcohol are
shown in FIG. 1 as being stored in primary tank 30 and secondary
tank 15, respectively, the invention is not limited to this
embodiment. Any primary fuel may be used in the primary tank 30,
including gasoline and gasoline-alcohol mixtures. Similarly, any
fuel which contains alcohol as a constituent can be used in the
secondary tank 15. This includes a fuel which contains only alcohol
or an alcohol-water mixture. In this embodiment, one fuel injector
(the "open-valve port fuel injector") 25 injects fuel when the
intake valve is open or more open than the other fuel injector (the
"closed-valve port fuel injector") 35. For a given amount of fuel
that is introduced into the engine by the fuel injector the
open-valve port fuel injector provides more vaporization cooling
than the closed valve port fuel injector. Additionally, the two
injectors may have different characteristics and/or be positioned
differently.
[0015] The ratio of fuel from the secondary tank 15 to fuel from
the first tank 30 is controlled by the ECU 40, which also
determines the timing of the injection. This ratio increases with
increasing torque so as to prevent knock. In the preferred
embodiment, in addition to timing relative to valve opening, the
open-valve port fuel injector 25 is located so as to maximize
vaporization cooling.
[0016] Maximization of vaporization cooling may be achieved through
various means, including, but not limited to, spatial positioning
of the open-valve injector 25 that is different from that of the
closed-valve injector 35, such as being closer to the intake valve,
so as to maximize the amount of liquid fuel that enters the engine
cylinder 20; operation of the open-valve injector 25 with a
different spray pattern than the closed-valve injector 35; and
operation of the open-valve injector 25 with a higher pressure or
with an air assist injector so as to optimize droplet size
distribution. Droplet size optimization means decreasing the size
of the droplets in order to allow the droplets to closely follow
the air flows, for increased transmission of the droplets into the
cylinder and decreased wall wetting, once inside the cylinder.
Droplet size distribution is not important for conventional
(closed-valve) port fuel injectors. For the "open-valve fuel
injectors" 25, spray pattern as well as droplet size distribution
is important.
[0017] The "open-valve port fuel injector" 25 shown in FIG. 1 may
be located at a different position within the cylinder 20 than the
port fuel closed valve injector 35 and could provide a different
spray characteristics (pattern and/or droplet size
distribution).
[0018] Also, as shown in FIG. 1, the alcohol to gasoline ratio can
be determined by closed loop control using a knock detector 45. In
other embodiments, the ratio can be controlled by open loop control
using a look up table. It is preferred that the engine 20 be
operated with a substantially stoichiometric fuel-air ratio, which
determines the total amount of fuel injected into the cylinder,
while the ratio of the two fuels is determined, as least in part,
by knock.
[0019] The alcohols that are provided by the second tank include
ethanol, methanol, a mixture of ethanol and methanol, and alcohol
mixtures with water. The alcohols could also include
ethanol-gasoline mixtures including, but not limited to, E85 and
methanol-gasoline mixtures including, but not limited to M85. For a
given amount of fuel energy from the alcohol, methanol would
provide significantly more knock resistance than ethanol.
[0020] In another embodiment, only one fuel tank may be needed.
This embodiment uses two port fuel injectors, where one is an open
valve port fuel injector that injects a different fuel from the
other injector. These two different fuels are obtained by onboard
separation from an alcohol-gasoline mixture that is stored in the
tank on the vehicle.
[0021] In this embodiment, the alcohol-gasoline mixture from the
tank is sent to an onboard fuel separator that produces two fuel
streams. One of the fuel streams has a higher alcohol content than
the stored gasoline-alcohol mixture, while the other fuel stream
has a lower alcohol content than either the other fuel stream from
the onboard fuel separator or the stored gasoline-alcohol fuel
mixture. The higher alcohol content fuel stream from the onboard
fuel separator is sent to the open valve port fuel injector. The
fuel separation can be obtained by using a membrane as described in
U.S. Pat. No. 7,225,787 where an onboard fuel separator separates
ethanol from a gasoline-ethanol mixture using a membrane.
[0022] For example, ethanol could be obtained from onboard
separation from a low concentration ethanol-gasoline mixture such
as E10, which is generally available at service stations in the
United States. The higher ethanol concentration stream is sent to
the open valve port fuel injector and the lower ethanol
concentration stream is sent to the closed valve port fuel
injector. The ratio of the higher ethanol concentration fuel stream
to the lower ethanol concentration fuel stream increases with
increasing torque. The ratio can be controlled so as to prevent
knock using closed loop control with a knock detector or open loop
control using a lookup table.
[0023] Onboard separation could also be used to separate methanol
from M15 or another methanol-gasoline mixture stored on the
vehicle. M15 use is rapidly growing in China. The high
concentration methanol stream could be introduced into the engine
by an open valve port fuel injector in the same way as described
above for ethanol and controlled by closed or open loop
control.
[0024] In another embodiment, the onboard separation described
above can be used with a two tank system, such as that shown in
FIG. 1, where the secondary tank stores an alcohol-based mixture,
which is used for open valve fuel injection. In this case the
alcohol-gasoline mixture in the primary tank is sent to the onboard
fuel separator which then provides an alcohol based fuel to either
the secondary tank or directly to the open valve port fuel
injector. The open valve port fuel injector can then inject fuel
that is provided by the onboard fuel separator, an external source
that provides fuel to the secondary tank or a combination of fuel
that is provided externally to the secondary tank and fuel that is
provided by onboard separation of fuel from the primary tank.
[0025] Alcohol (either ethanol or methanol) from onboard separation
of alcohol from an alcohol-gasoline mixture stored in a tank
onboard the vehicle can be employed in flexible fuel vehicles,
where the alcohol content in the alcohol-gasoline mixture varies
from 100% alcohol to 0% alcohol. Therefore, the terms
"alcohol-gasoline mixture", "ethanol-gasoline mixture" and
"methanol-gasoline mixtures" all include mixtures in which no
alcohol is present. The operation of the onboard separation system,
including its use or non-use, can be adjusted as a function of the
amount of alcohol in the alcohol-gasoline mixture.
[0026] When the stored fuel does not include alcohol, increased
spark retard and/or reduced turbocharger pressure (if a
turbocharger is used) can be used to prevent knock that would
otherwise occur. Reduction of the effective compression ratio by
variable valve timing can also be used to prevent knock that would
otherwise occur. In these cases, the vehicle can be operated,
albeit with reduced efficiency and/or performance.
[0027] The onboard separation embodiment and other embodiments
disclosed here can be more generally used with the use of two
injectors where one injector introduces a higher fraction of the
fuel in the form of a liquid into the cylinder and this injector
provides the fuel with higher alcohol content.
[0028] Open valve port fuel introduction of methanol, which is
produced by onboard separation of a methanol-gasoline mixture, into
a spark ignition engine, which is a modified diesel engine,
provides the strength for high compression ratio, high turbo
pressure operation, and could provide a gasoline engine with
diesel-like efficiency and torque. Another engine that would be
relatively straightforwardly modified for this application would be
a spark ignition engine that is used for natural gas operation in
heavy duty vehicles.
[0029] Alcohol that is open-valve port fuel injected from a second
source can also be used to increase the knock resistance of engines
that are primarily fueled with natural gas or another gaseous fuel
such as propane or hydrogen-rich gas provided by reforming. The
ratio of the amount of alcohol to the amount of natural gas would
be increased with increasing torque and controlled so as to prevent
knock using closed loop control with a knock detector and/or using
open loop control.
[0030] Another embodiment of open-valve port fuel injection in a
spark ignition engine fueled with natural gas is use in a vehicle
that is externally supplied with natural gas which is placed in a
first tank and with a gasoline-alcohol mixture which is placed in a
second tank. Onboard separation is employed to separate the alcohol
from the alcohol-gasoline mixture and produce a fuel that has a
higher alcohol concentration than the alcohol-gasoline mixture in
the second tank. This embodiment can allow an engine that is
designed to make use of the high knock resistance of natural gas to
also be operated on an externally supplied gasoline-alcohol mixture
that provides a separated fuel which provides the same or higher
knock resistance as natural gas. Using onboard separation of
alcohol from a low concentration alcohol-gasoline mixture, such as
E10, the engine could provide the same or greater efficiency on an
energy basis than it provides when operated with natural gas
alone.
[0031] In this embodiment, natural gas or another gaseous fuel such
as hydrogen or propane, would be introduced into the engine by a
first means. Onboard separated gasoline with reduced alcohol
content relative to the externally supplied gasoline mixture would
be introduced by a second means which is a port fuel injector; and
alcohol or onboard separated gasoline with a higher alcohol content
would be introduced by a third means which is a open-valve port
fuel injector. When there is no natural gas available to fuel the
engine, it can be run on fuel provided by the second and third
means of fuel introduction, where the ratio of the fuel introduced
from the third fuel introduction means to fuel provided by the
second fuel introduction means increases with increasing torque.
Direct injection could be used as an alternative to open-valve port
fuel injection for the third fuel introduction means.
[0032] Knock suppression can be increased by using controlled valve
lift to assist in conditioning the liquid aerosols. Small inlet
valve opening during the time of injection, with high air speeds,
aids the formation of small aerosols, through the breakup of larger
aerosols. The injectors can be positioned such that, when
operating, they are providing fuel flow in the general direction of
the opening generated by the valve opening. Late injection, i.e.
when the cylinder is closer to bottom dead center (BDC), also
offers advantages. The amount of alcohol that is injected is
greatest at high torque, operation at wide open throttle (WOT) or
operation at high pressure (with turbocharging or supercharging).
Therefore, use of conditions near the valve which create small
droplets (i.e., high air speed near the valves) must be balanced
with the need of accepting the largest amount of air possible,
which requires large opening of the valves. At higher speeds, when
injection time crank-angle degrees become a substantial fraction of
the inlet valve open time, it is necessary to start injecting the
alcohol earlier. However, the calculations discussed in U.S. Pat.
No. 7,225,787 show that the alcohol requirement decreases at the
higher speed, as the tendency of the engine to knock decreases with
engine speed.
[0033] There are advantages of combining the approach with VVT
(variable valve timing), and with variable valve lift, to minimize
the alcohol required by optimizing the injection. Optimization of
the injection refers to avoiding wall-wetting, increasing the
evaporative cooling effect of the injected liquid fuels, achieving
appropriate droplet size distribution.
[0034] By adjusting the closing of the inlet valves, it is also
possible to dynamically adjust the effective compression ratio.
Decreasing the effective compression ratio is a practical way of
maintaining the performance of the engine when the alcohol-based
fuel has been depleted or when the concentration of alcohol in the
secondary fuel (and thus the evaporative cooling effect) is lower.
In this manner, although the efficiency of the engine is lowered,
the performance of the engine can be maintained. Decreasing the
effective compression ratio can also be used in embodiments where
there is only one fuel tank containing an alcohol-gasoline mixture
and the alcohol content in the mixture is decreased.
[0035] However, for some low-end applications, avoiding VVT and
variable lift may be preferable, thereby avoiding costly
components, but requiring higher alcohol fractions.
[0036] An illustrative ratio of the amount of methanol-based fuel
to the amount of gasoline in a dual fuel engine with on-demand
alcohol injection is 0.3. For stoichiometric conditions, the
air/methanol ratio is about 6.5, and the air/gasoline ratio is
about 14. Therefore, in this case, the air/methanol fuel ratio is
about 50:1. Assuming that the maximum mass of the atomized liquid
to the air is about 20%, then the fuel needs to be injected during
at least 10% of the air induction. A faster rate of fuel delivery
of the alcohol fuel can be used, such as delivering the fuel during
the time when the air inducted into the cylinder has the highest
speed. The fastest air induction occurs approximately when the
cylinder is halfway between Top Dead Center (TDC) and BDC,
especially during conditions of high load. The rate of fuel
delivery is substantially higher than that of conventional port
fuel injection (PFI), where fuel is sprayed onto the valve over a
substantial fraction of the engine revolution.
[0037] The use of fast delivery can be used to generate a fine
spray with droplets smaller than conventional PFI. In some
embodiments, the droplets may be about 120-150 micron in diameter.
Injectors operating at slightly higher pressures than conventional
PFI systems can be used to assist in generating a fine spray. In
addition, the open-valve port fuel injector can be located close to
the valve, in order that the high velocity of the air inducted into
the engine aids in the droplet breakup. The open valve port fuel
injector can be located closer to valve than the closed valve port
fuel injector. It can also be located and aimed so that the fuel is
sent in the general direction of the intake valve opening.
[0038] In the case of multiple inlet valves, it is possible to
direct the alcohol-based injector toward any one of the valves or
toward all valves. The use of a single valve could provide a degree
of stratification of the air/fuel mixture. It is possible to have
different valve-lift in each valve or a multiple valve system, to
best accommodate the injection of the alcohol-based fuel.
[0039] The fuel from the open-valve port fuel injector can be
injected in the cylinder without the formation of the usual film
that is present in conventional port fuel injection. If the alcohol
based fuel is sprayed directly onto a dry section (that is, a
region of the inlet valve devoid of film associated the first fuel)
of the inlet valve where the air inducted into the engine flows, it
has been shown that the liquid droplets from the injector (120-150
microns) impinge on the surface but are bounced back into the air
flow as smaller droplets (.about.40 micron droplets). [C. Brehm and
J. H. Whitelaw, L. Sassi, C. Vafidis, Air and Fuel Characteristics
in the Intake Port of a SI Engine, SAE paper 1999-01-1491]. The
process can allow for finer sprays, with the smaller aerosols being
able to follow the air through the opening around the inlet valve,
and avoid/minimize wall wetting once in the cylinder, and allow for
faster vaporization.
[0040] The use of two injectors allows increased operational
flexibility of the engine. The additional flexibility is useful
during transients, as a non-limiting example. For example, the
delaying effect due to build-up of films in the inlet valves in
gasoline engines can be eliminated by the injection of the alcohol
based fuel, which allows for fast (cycle-to-cycle) variation in the
amount of fuel injected into the cylinder.
[0041] An alternative to using two separate port fuel injectors is
to use a single port fuel injector where the fuel from the
secondary tank and fuel from the primary tank are mixed in varying
ratios as the torque is increased as described in U.S. Pat. No.
7,314,033. The timing of the fuel injection can be varied so that
it increases with increasing torque so as to prevent knock. A
disadvantage of this approach is that it may be difficult to
spatially and operationally optimize one fuel injector for both
good mixing and vaporization cooling. In addition, there is a need
for means to rapidly vary the ratio of the two fuels as the torque
changes. This requirement can be met by using a single injector
with two valves. The injector can have either one nozzle or set of
nozzles per valve, or two nozzles or sets of nozzles, one for each
valve. Each valve would separately inject either the gasoline or
the alcohol.
[0042] The use of an open-valve port fuel injector in conjunction
with closed valve port fuel injector can also be used together with
direct injection to reduce alcohol-based fuel consumption in a dual
fuel gasoline engine 120 with on-demand direct injection of
alcohol. This embodiment is shown in FIG. 2. In this embodiment,
the two port fuel injectors 125, 135 would be employed to obtain
increased maximum torque using only fuel from the primary tank 130.
As described above, the primary tank, though labeled gasoline tank
130, may contain any primary fuel, including gasoline or
gasoline-alcohol mixtures. The fuel from the secondary tank 115
would be directly injected through direct injector 150. Again, the
secondary tank 115 may contain any fuel that has alcohol as a
constituent. This approach would minimize the amount of
alcohol-based-fuel from the secondary tank 115 that is used over a
drive cycle. The timing of the open valve and closed valve port
injectors 125, 135 may be controlled by ECU 140 using knock sensor
145, as described above.
[0043] A variation of this embodiment would be to use a single port
fuel injector for the fuel that is provided by the primary tank,
such as gasoline or gasoline with a low concentration of alcohol,
and vary the injection timing so as to transition from closed valve
injection to open valve injection as the torque is increased.
During the increased torque, faster response of the system to
fueling requirements can be achieved by the changing first the open
valve injection rate, which can in principle be adjusted from cycle
to cycle, and then adjust the ratio on a longer time scale. The
same can be done when the engine is decreasing torque.
[0044] Another use of two port fuel injectors and one direct fuel
injector is to use a closed-valve port fuel injector 235 and a
direct injector 250 for providing fuel from the primary fuel tank
230 and an open-valve port fuel injector 225 for providing fuel
from the secondary tank 215, as shown in FIG. 3. The use of port
fuel injection of the fuel from the secondary tank 215 could be the
easiest alcohol boosted technology to implement on existing
gasoline direct injection engines and open-valve port fuel
injection provides the highest knock resistance. The use of a
closed-valve port fuel injector 235 for introduction of the primary
fuel at low loads provides improved mixing and combustion stability
at low loads. The timing of the open valve and closed valve port
injectors 225, 235 may be controlled by ECU 240 using knock sensor
245, as described above. As described above, the primary tank,
though labeled gasoline tank 230, may contain any primary fuel,
including gasoline or gasoline-alcohol mixtures. Again, the
secondary tank 215 may contain any fuel that has alcohol as a
constituent.
[0045] The use of both a closed-valve port fuel injector and an
open-valve port fuel injector can also be employed where there is
no secondary tank or onboard separation and both injectors provide
the same fuel to the engine cylinders. This is shown in FIG. 4. In
this embodiment, one fuel injector (the "open-valve port fuel
injector") 325 injects fuel when the intake valve is open or more
open than is the case for the other fuel injector (the
"closed-valve port fuel injector") 335. Additionally, the two
injectors 325, 335 may have different characteristics and/or be
positioned differently. The closed-valve port fuel injector 335
provides the advantage of better combustion stability and better
fuel air mixing while the open valve port fuel injector 325
provides the higher knock resistance, which allows higher
compression ratio operation and/or higher levels of turbocharging
than would be possible with closed-valve port fuel injection. As
described above, the primary tank, though labeled gasoline tank
330, may contain any primary fuel, including gasoline or
gasoline-alcohol mixtures.
[0046] By using closed-valve port fuel injection at low loads and
open-valve port fuel injection at high loads with the same fuel
introduced by both injectors, greater combustion stability and thus
operation at higher EGR can be obtained while, at the same time,
knock resistance is stronger at higher loads where knock would
otherwise occur. The ratio of the amount of fuel provided by the
open-valve port fuel injection to fuel provided by closed-valve
port fuel injection may increase with torque. This ratio could be
controlled with an ECU 340 using closed loop control with a knock
detector 345 or by open-loop control using a look up table. For a
given level of knock-free torque, the control system 340 minimizes
the amount of fuel that is introduced into the engine 320 with
open-valve port fuel injection and thus maximizes mixing and
combustion stability and minimizing particulate emissions. In FIG.
4, the open-valve port fuel injector 325 can be positioned
differently than the closed-valve port fuel injector 335 in order
to maximize knock resistance.
[0047] This embodiment could be particularly important for fuels
that contain alcohol as a constituent, such as gasoline-ethanol or
gasoline-methanol mixtures, ethanol or methanol where a substantial
increase in knock resistance can be obtained by using open-valve
port fuel injection instead of closed-valve port fuel
injection.
[0048] An alternative for the use of two separate port fuel
injectors for injecting fuel from a single tank is to use one port
fuel injector where the timing of the port fuel injection is such
that the amount of fuel that is introduced when the intake valve is
open increases with increasing torque.
[0049] Heavy EGR can be employed to increase the efficiency gain
provided by any of the above open-valve port fuel injector
embodiments. It is preferred to use EGR levels of at least 30% and
in more preferably at least 40%. It is also preferred to operate
with a compression ratio of at least 14 and more preferably at
least 15.
[0050] The use of heavy EGR to increase alcohol fueled spark
ignition engine efficiency has been shown by M. J. Brusstar and C.
L. Gray, Jr, (High Efficiency with Future Alcohol Fuels in a
Stoichiometric Medium Duty Spark Ignition Engine, SAE paper
2007-01-3993). They used cooled EGR in a turbocharged engine that
was port injected with M85 or E85, and operated at a very high
compression ratio (16). The engine used one port fuel injector per
cylinder.
[0051] In contrast to Brusstar and Gray, the preferred use of heavy
EGR in the open valve port fuel injector embodiments described here
is to use hot EGR (that is, EGR that is not cooled by a heat
exchanger as is the case with cooled EGR). An additional difference
is that, while EGR is used at low loads to increase efficiency, it
is reduced or eliminated at high loads so as to remove the adverse
effect of hot EGR on knock. This use of hot EGR removes the expense
and complexity of cooling and has a less adverse effect on
combustion stability than cooled EGR.
[0052] Heavy EGR allows the engine to operate nearer to wide-open
throttle conditions at partial load, to decrease the engine
friction losses, and would be decreased at higher loads. The amount
of heavy hot EGR that would be used at low and intermediate loads
would be greater than that which is employed in present production
gasoline engine vehicles,
[0053] The amount of EGR that can be employed is limited by
combustion stability. Combustion stability is improved by use of
high compression ratio. It is also improved by the amount of
alcohol in an alcohol-gasoline mixture since alcohol has a higher
flame speed. For flexible fuel engines with a wide range of
alcohol-gasoline mixtures, it can be advantageous to vary the EGR
level as the alcohol-gasoline ratio is varied. The EGR level can be
decreased when the alcohol concentration in the fuel decreases. The
EGR level can be controlled by closed loop control using a misfire
detector or by open loop control using a look up table.
[0054] Combustion stability is also better with closed valve port
fuel injection rather than open valve port fuel injection.
Consequently, the use of closed valve port fuel injection at low
load and open valve port fuel injection at high load can maximize
the amount of EGR at low loads and also the amount of knock
suppression at high loads.
[0055] An additional means to increase the efficiency is to use
engine cylinders of sufficiently large volume so as maximize the
efficiency impact of high compression ratio operation by minimizing
the surface to volume ratio and resulting heat losses. The
preferred engine cylinder size is at least 0.5 liters and more
preferably greater than 0.6 liters. The engine size can be kept
small by decreasing the number of cylinders.
[0056] Because the engine is operated at a high compression ratio,
it is important not to run out of alcohol when the alcohol is
provided by a second tank. Otherwise, the engine performance might
have to be substantially degraded in order to prevent knock. As
discussed in U.S. Pat. Nos. 7,225,787 and 7,314,033, the alcohol
consumption could be reduced in a gradual way by increasing spark
retard as a function of the remaining fluid in the alcohol tank. In
addition, various warning lights could activate at various times to
alert the driver of a low supply.
[0057] Very high compression ratio operation and use of heavy hot
EGR at low loads could also be used in engines that employ direct
injection instead of open valve port fuel injection. In this case,
in addition to very high compression ratio operation, the engines
could operate at very high turbocharger boost pressures without
knock.
[0058] Another embodiment of this invention is the use of a
constant level of hot EGR throughout the torque range so as
minimize the cost of EGR control.
[0059] In order to minimize poor performance with charge cooling,
it is advantageous to use a combustion process that is fast. The
addition of EGR, coupled to or independent of the large evaporative
cooling, has a detrimental impact on the combustion initiation
(defined as time to combust 10% of the fuel) as well as combustion
duration (defined as time to combust of 10% to 90% of the fuel).
Combustion initiation has an impact on misfire (cycle-to-cycle
variation of combustion), while combustion duration has an impact
on the efficiency. In order to minimize the use of the alcohol from
the second tank, the use of a fast combustion engines (short
combustion duration) is good. The use of a high performance
ignition system, and a chamber optimized for fast combustion (both
through in-cylinder charge motion/turbulence as well as appropriate
location of the spark) and design of the cylinder and piston
(having a condition that is closer to a sphere rather than a disk,
with the spark near the center), decreases the tendency of knock by
combusting the fuel before it has time to autoignite. The use of a
high performance ignition system can be used to extend the
misfire-free engine operating region, which could occur at high
loads when there is large amount of EGR or large amounts of water
in the anti-knock additive.
[0060] Heavy EGR use at low loads can be used in all of the open
valve port fuel injection embodiments described previously. High
compression ratio operation can also be used. Use of heavy EGR in
the all of embodiments described previously could also be used in
an engine where direct injection is used instead of open valve port
fuel injection.
[0061] The increased combustion stability provided by the
combination of closed valve port fuel injection, high compression
ratio and the use of alcohol as a fuel constituent can also be
employed with the open-valve embodiments described previously to
enable a higher air/fuel ratio and extend the lean limit of engine
operation.
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