Note: Descriptions are shown in the official language in which they were submitted.
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BAROMETRIC PRESSURE DIESEL TIMING CONTROLLER
CROSS REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED
RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates generally to diesel engines and, more particularly, to
medium
speed diesel engines for operation at high altitudes.
BACKGROUND ART
Power is generated in a diesel engine by diffusing and combusting diesel fuel
in a
plurality of engine cylinders. Liquid fuel is injected into the engine
cylinders, which
are full of compressed air at high temperature. The fuel is broken up into
droplets,
which evaporate and mix with the air in the cylinders to form a flammable
mixture.
Complete and efficient combustion in the cylinders requires full oxidation of
fuel
through evaporation, species diffusion, and mixing with air, and timely heat
release
during the combustion process. Thus, the amount of air charged into the
cylinder, or
the air to fuel ratio of the mixture, plays an important role in diesel engine
fuel-air
mixing and combustion, which, in turn affects fuel efficiency and exhaust
emissions.
This is particularly true for quiescent chamber type medium speed heavy-duty
diesel
engines where the cylinder air intake swirling is slight, such as locomotive
or marine
engines having cylinders with relatively large displacement volumes. The fuel
injection timing of medium speed diesel engines operating at full load is
typically set
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so that the actual peak firing pressure in the cylinders is at or below a
maximum
cylinder firing pressure under normal altitude operation, i.e., at about sea
level.
Engine exhaust emissions, including carbon monoxide (CO), particulate matter
(PM),
and smoke, are generated when the air-fuel mixture is incompletely combusted.
When engines are operated at higher altitudes, i.e., at a low barometric
pressure, lesser
amounts of air are introduced into the cylinders, causing the air-fuel mixing
process to
be deteriorated relative to lower altitude, higher ambient pressure
environments. This
combination of factors increases late and incomplete combustion in the engine
cylinders, which lowers fuel efficiency and increases exhaust emissions of CO,
PM,
and smoke. The reduced amount of air for the fuel-air mixture combustion,
together
with the increased amount of late and incomplete combustion, typically leads
to
reduced peak cylinder firing pressure and increased cylinder exhaust gas
temperatures. For engines including a turbocharger, the decreased barometric
pressure and the increased exhaust temperature cause an increase in
turbocharger
speed. This usually requires power deration to prevent turbocharger damage
from
overheating and excessive speed.
Accordingly, it would be desirable to operate a diesel engine at higher
altitudes that
avoids the resultant increase in exhaust emissions. Additionally, it would be
desirable
to operate a diesel engine at higher altitudes with minimal deterioration of
engine
efficiency, pawer capacity, and engine performance relative to normal altitude
operation.
BRIEF SUMMARY OF THE INVENTION
In an exemplary embodiment of the invention, a fuel injection system for a
diesel
engine having at least one fuel injection pump and at least one fuel injector
connected
to at least one engine cylinder includes a fuel injection controller, a
throttle position
sensor and a sensor which senses the value of a parameter relative to the
engine intake
air. In the present invention, that is, the value of a parameter relative to
the engine
intake air is sensed, rather than sensing the barometric pressure itself.
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This engine intake air parameter could be the air pressure in the engine
intake
manifold or the turbocharger speed, for example. The intake air pressure type
sensor
can be in fluid communication with the engine intake manifold to sense the
pressure
therein. The turbocharger speed type sensor can be a tachometer output on the
turbocharger, for example. In either case, the output of the engine intake air
parameter sensor is connected to a barometric pressure timing controller. The
barometric pressure timing controller compares the instantaneous engine intake
air
parameter with a nominal value of the engine intake air parameter and
determines the
instantaneous barometric pressure from that comparison. The barometric
pressure
timing controller then adjusts the fuel injection timing by controlling the
fuel injection
pump and the fuel injector according to changes in barometric pressure, to
advance or
retard fuel injection timing to reduce untimely and incomplete combustion in
the
engine cylinders. Engine efficiency may therefore be optimized, and exhaust
emissions may be reduced, when the engine is operated at higher altitudes at a
desired
speed and power determined by a selected throttle position.
The barometric pressure timing controller is an electronic controller, such as
a
microprocessor with a memory of predetermined fuel injection timing values
that
have been found to minimize exhaust emissions while optimizing steady state
engine
operation under the corresponding barometric pressure, without exceeding a
maximum peak firing pressure in the engine cylinders. Thus, the engine may be
continuously and optimally operated under varying pressure conditions while
minimizing exhaust emissions and maintaining optimum engine performance. As
exhaust emissions are reduced, and combustion in the cylinders is more timely
and
complete, engine power deration due to turbocharger overspeed is largely
avoided.
The novel features of this invention, as well as the invention itself, will be
best
understood from the attached drawings, taken along with the following
description, in
which similar reference characters refer to similar parts, and in which:
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Figure 1 is a schematic view of a diesel engine system;
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Figure 2 is a simplified schematic view of the system shown in Figure 1; and
Figure 3 is a schematic view of a control system for use with the engine
system shown
in Figure 2.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 is a schematic illustration of a propulsion system 10 including a
diesel engine
12. Particularly, and in an exemplary embodiment, the system 10 is used in a
self
propelled locomotive. The engine 12 is mechanically coupled to a rotor of a
main
alternator 14 to power a plurality of traction motors 16 that are positioned
on each
side of an axle of the locomotive to propel the locomotive. While the present
invention is described in the context of a locomotive, it is recognized that
the benefits
of the invention accrue to other applications of diesel engines, and to other
varieties of
diesel engines beyond that specifically described. Therefore, this embodiment
of the
invention is intended solely for illustrative purposes and is in no way
intended to limit
the scope of application of the invention.
The engine 12 is a high horsepower, turbocharged, multiple-cylinder diesel
engine,
and includes a number of ancillary systems, such as a combustion air system
18, a
lube oil system 20, a cooling water system 22, and a fuel system 24. The
combustion
air system 18 includes an engine exhaust gas driven turbocharger for
compressing air
in a combustion air manifold of the engine 12. The lube oil system 20 includes
an oil
pump and associated piping for supplying suitable lubricating oil to the
various
moving parts of the engine 12. The cooling water system 22 includes a pump for
circulating relatively cool water from one or more air cooled radiators to a
lube oil
cooler, to a plurality of cylinder liners of the engine 12 for absorbing heat
generated in
the combustion process, and also to one or more "intercoolers" through which
combustion air passes after being compressed, and therefore heated, by the
turbocharger.
The fuel system 24 includes a fuel tank, fuel injection pumps, and fuel
injector
nozzles for injecting diesel fuel into a plurality of power cylinders. A fuel
pump
controller 28 controls the start and duration of fuel flow into each of the
cylinders. In
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a mechanically fuel injected engine, the fuel pump controller 28 is a governor
controller linked to fuel injection pump racks to control the start of and
duration of
fuel flow into an engine cylinder upon each actuation of the respective fuel
injectors.
In an electronically fuel injected engine, the fuel pump controller 28 is an
electronic
controller connected to electrically actuated valves in the fuel pump to
control when
and for how long fuel flows into a cylinder upon actuation of an associated
fuel
injector. The fuel pump controller 28 regulates engine speed by minimizing any
difference between a desired speed and an actual operating speed. The desired
speed
is set by a variable speed control signal received from an engine controller
30 in
response to a manually or automatically selected position or input of a
throttle 32
according to defined speed-load schedules.
Figure 2 is a schematic illustration of the exemplary diesel engine 12. A
turbocharger
40 in the combustion air system 18 includes a turbine 42, the output of which
drives a
centrifugal air compressor 44. Air is collected in a plenum, passed through an
array
of air filters 46, and delivered to a central inlet of the compressor 44 and
discharged
from the compressor 44 at elevated temperature and pressure to an air-water
heat
exchanger 48, known as an aftercooler or intercooler. From the intercooler 48,
compressed air passes into a combustion air intake manifold 50. Compressed air
is
supplied to the power cylinders 54 from the combustion air intake manifold 50.
Gases produced during combustion are exhausted from each of the power
cylinders
into an exhaust manifold 56. The exhaust gases drive the rotor of the turbine
42 prior
to their discharge through an exhaust stack 58 to the atmosphere. The speed of
the
turbine 42 typically increases as the engine 12 develops more power. With the
engine
running at or near full power, the compressor 44 compresses combustion air to
more
than twice atmospheric pressure. One or more intercoolers 48 lower the
temperature
of the compressed air, which is heated appreciably during the compression
process,
thereby enlarging the amount of the air charge by filling the cylinders with
higher
density air, and lowering the thermal loading of the engine 12.
Hot engine oil is pumped by an oil pump 60 to an inlet of an oil-water heat
exchanger
64, and cooled oil flows from the oil-water heat exchanger 64 through an oil
filter 66
and to an oil supply header. Oil is distributed from the supply header to
various
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bearings, valves, pistons, gears, and other moving parts of the engine 12 for
lubricating and cooling purposes. A thermistor 72 is exposed to oil flowing in
a pipe
62 near an inlet of the oil cooler.
The cooling water system 22 comprises a water storage tank 74 from which
relatively
cool water flows, via heat exchanger tubes inside the oil cooler 64, to a
water pump
76. The water pump 76 raises the pressure of the water which flows through the
cylinder jackets of the cylinders 54 to a common water discharge header 80.
Cooling
water is also pumped through the intercooler 48 to extract heat from the
combustion
air discharged from the compressor 44 at an elevated temperature. The system
is
balanced hydraulically so that the flow rate to one or more intercoolers is in
a desired
flow rate to the cylinder jackets.
Hot water leaving the engine from the discharge header 80 flows through at
Ieast one
fluid valve 86. The fluid valve 86 is typically coupled to a thermistor that
diverts
water to the water storage tank 74 when the temperature of the water in the
valve 86 is
below a predetermined temperature or when the water pressure is below a
predetermined pressure. When cooling water is above a predetermined
temperature, or
above a predetermined pressure, water flows into one or more water-air heat
exchangers, or radiators 94. After being cooled in the radiators 94, water is
discharged into the water tank 74.
Figure 3 schematically illustrates a control system 70 for the exemplary
engine 12
including a plurality of pistons 72 operating in a plurality of cylinders 54.
A fuel
injection pump 76 and a fuel injector 78 are operable to inject fuel into each
cylinder
54 for combustion to produce energy for driving the pistons 72 in a downward
direction. As the fuel is injected, it is mixed with cylinder-compressed air
in each
cylinder 54 supplied by the combustion air manifold 50 and the turbocharger
40. Air
is supplied to the turbocharger 40 through an appropriate air intake unit (not
shown)
that includes the air filters 46 to filter particulate matter from the air.
The fuel injection pump 76 and the fuel injector 78 are controlled by a
barometric
pressure timing controller 88 to control fuel injection timing, i.e., when
fuel injection
into the cylinders 54 begins. The barometric pressure timing controller 88 can
be
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integral with the fuel pump controller 28, a discrete component of the engine
controller 30, or a separate controller cooperating with the fuel pump
controllers 28
and the engine controller 30. The barometric pressure timing controller 88, by
altering fuel injection timing at the corresponding engine throttle input or
throttle
position, reduces exhaust emissions and increases engine efficiency at higher
altitudes, i.e., at lower barometric pressure.
A sensor 82 senses a parameter related to the engine intake air, such as the
pressure in
the intake manifold or the turbocharger speed. This engine intake air
parameter
sensor 82 is coupled to the barometric pressure timing controller 88. An
engine
intake air parameter signal 86 is supplied to the barometric pressure timing
controller
88 from the sensor 82 for adjusting operation of the fuel injection pump 76
and the
fuel injector 78 to reduce exhaust emissions, enhance engine efficiency, and
maintain
engine power capacity at higher altitudes. The barometric pressure timing
controller
88 includes a microcomputer (not shown) and electronic controls (not shown),
which
are well known in the art.
A table of values of expected or nominal levels of the engine intake air
parameter are
empirically determined, at a nominal barometric pressure, at various throttle
notch
settings, and for various sets of engine performance characteristics. The
table can be
integral with the barometric pressure timing controller 88. The engine
performance
characteristics can include characteristics such as horsepower output, rpm,
injection
timing, and manifold air temperature. For example, an expected or nominal
value of
engine intake air pressure can be accessed from this table, for a nominal
barometric
pressure, at a given throttle notch setting, and for various sets of engine
performance
characteristics. Alternatively, an expected or nominal value of turbocharger
speed
can be accessed from this table, for a nominal barometric pressure, at a given
throttle
notch setting, and for various sets of engine performance characteristics.
At least one throttle position sensor 84 is connected to the engine 12 and to
an engine
input, such as the throttle 32, to assess the selected engine throttle
position, or the
desired speed and load of the engine. A throttle position signal 90 is
supplied to a
loading device, such as an alternator (not shown) mechanically coupled to the
engine
to generate a desired engine power corresponding to the selected throttle
position.
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The fuel injection controller 28 controls fuel injection timing by operating
the fuel
injection pump 76 and the fuel injector 78 to begin fuel injection at an
optimal time in
the injection cycle in response to the barometric pressure and throttle
position.
The barometric pressure of the engine air supply is monitored by the control
system
70 to distinguish high altitude operation from normal altitude operation, and
the
barometric pressure timing controller 88 adjusts fuel injection timing as a
function of
air to fuel ratios at elevated altitudes. Therefore, exhaust emissions can be
reduced,
and engine performance comparable to normal altitude performance is achieved.
The engine intake air parameter sensor senses an instantaneous or known value
of the
engine intake air parameter, such as the pressure in the engine intake air
manifold.
The barometric pressure timing controller 88 compares this sensed
instantaneous
value with the nominal value of the engine intake air parameter which was
accessed
from the aforementioned table. If an exact set of engine performance
characteristics
and throttle notch setting is not available in the table, if desired,
interpolation can be
performed by the barometric pressure timing controller 88. Based on the
difference
between the instantaneous value and the nominal value of the engine intake air
parameter, the barometric pressure timing controller 88 adjusts the nominal
barometric pressure to determine the instantaneous barometric pressure.
If the engine intake air parameter being sensed is turbocharger speed, rather
than
engine intake air pressure, a second table can be provided, which stores
empirically
determined values of the difference between nominal and instantaneous engine
intake
air pressure for various differences between nominal and instantaneous
turbocharger
speed, at various throttle notch settings and for various sets of engine
performance
characteristics. Once the sensor 82 senses the instantaneous turbocharger
speed, the
barometric pressure timing controller 88 looks up the expected or nominal
value of
turbocharger speed for the known throttle notch setting and the known set of
engine
performance characteristics. Then, the barometric pressure timing controller
88 looks
up the difference between nominal and instantaneous engine intake air
pressure, from
the second table, based on the difference between the known and instantaneous
turbocharger speed. As with the first table, if desired, interpolation of the
values in
the second table can be performed by the barometric pressure timing controller
88.
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Finally, then, the difference between nominal and instantaneous engine intake
air
pressure, from the second table, is used by the barometric pressure timing
controller
$8 to adjust the nominal barometric pressure to determine the instantaneous
barometric pressure.
If a low barometric pressure representing a high altitude is determined, fuel
injection
timing is advanced, i.e., fuel injection starts at an earlier point in time in
the piston
cycle, according to a predetermined value selected from a table, or tables, of
fuel
injection timing values stored in memory of the barometric pressure timing
controller
88 and corresponding to the instantaneous barometric pressure and engine speed
and
load, which is dictated by throttle position. Because the engine speed 92, and
the
amount of fuel to be injected at each injection cycle to maintain the desired
engine
speed and power, is dictated by the throttle position, an optimum fuel
injection timing
value can be selected based on the barometric pressure and the throttle
position. Of
course, other known indicators of engine speed and load may be used to select
a fuel
injection timing value. If necessary, or as desired, the barometric pressure
timing
controller 88 may interpolate between values in the tables to calculate a
desired fuel
injectian timing value, or to fine tune fuel injection timing.
Each of the stored fuel injection timing values minimizes exhaust emissions
and
optimized engine efficiency while preventing cylinder pressures above the
allowable
peak firing pressure in the cylinders 54. By advancing fuel injection timing
by the
predetermined value, the peak firing pressure of the cylinder 54 is increased
to be
closer to the designed maximum allowable peak firing pressure of the cylinder
during
high engine loads at higher altitudes so that the engine 12 generates
sufficient power.
Also, as a result of the fuel injection timing being advanced, the air-fuel
mixing is
prolonged to allow a more complete and timely combustion with an improved
timeliness of heat release. Further, as untimely and late combustion is
reduced,
exhaust emission temperatures are reduced. Consequently, the speed of the
turbocharger 40 is reduced, and the need for power deration to prevent
turbocharger
damage is minimized.
As barometric pressure changes, the barometric pressure timing controller 88
adjusts
fuel injection timing accordingly, so that the engine 12 may be continuously
operated
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under different pressure conditions with minimal deterioration of engine
performance.
Thus, fuel injection timing is advanced from normal altitude values during
high
elevation operation, and retarded or returned to normal altitude values when
the
engine 12 is returned to normal altitude. Of course, the same principles can
be
applied to operate the engine 12 and maintain peak firing pressure at or below
the
maximum allowable pressure value when operating an engine at or below sea
level.
Fuel injection timing can be adjusted by the barometric pressure timing
controller 88
either continuously with changes in barometric pressure, or in steps with
specified
levels of pressure change. For example, the barometric pressure timing
controller 88
may adjust fuel injection timing when barometric pressure increases or
decreases by
two pressure units from a given operating pressure.
At lower engine loads in high altitude operation, fuel injection timing is
adjusted by
the barometric pressure timing controller 88 to optimize steady state
operation of the
engine 12. More specifically, advancing the fuel injection timing has
significant
benefits at lower engine loads because the turbocharger 40 is relatively
sluggish.
When the engine operates under partial load, the turbocharger turbine 42
rotates
slower than when the engine 12 operates at full load. Consequently, the
turbocharger
turbine 42 does not rotate as fast, so less pressure is developed in the
cylinders 54 and
the deterioration of exhaust emissions is more pronounced. Because of the
relatively
low cylinder firing pressure at lower engine loads, exceeding a maximum firing
pressure by adjusting the fuel injection timing advance is of little practical
concern.
Thus, the injection timing can be freely set for optimum emissions and fuel
efficiency
performance for a given air supply pressure and engine throttle position.
Based on the
barometric pressure and throttle position, the barometric pressure timing
controller 88
selects fuel injection timing values from predetermined values stored in the
altitude
timing controller memory and found to achieve optimum fuel efficiency and
emission
reductions without exceeding the maximum peak allowable firing pressure in the
cylinders 54 for a given engine speed and engine load.
Thus, a diesel engine fuel injection timing control is provided that allows
for optimal
engine efficiency and performance with reduced emissions despite changes in
barometric pressure, without having to measure actual barometric pressure.
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While the particular invention as herein shown and disclosed in detail is
fully capable
of obtaining the objects and providing the advantages hereinbefore stated, it
is to be
understood that this disclosure is merely illustrative of the presently
preferred
embodiments of the invention and that no limitations are intended other than
as
described in the appended claims.
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