Note: Descriptions are shown in the official language in which they were submitted.
CA 02789470 2012-09-07
AUXILIARY POWER UNIT BLEED CLEANING FUNCTION
BACKGROUND
This disclosure relates to an auxiliary power unit. Aircraft, commercial
vehicles, marine vehicles, aerospace vehicles and the like commonly include an
auxiliary power unit for purposes other than propulsion. As examples, the
auxiliary
power unit may provide supplemental power to start a main engine, provide
supplemental power to run electrical systems when a main engine is shut down,
or
provide air to a vehicle compartment.
SUMMARY
Disclosed is a method for controlling an auxiliary power unit. The auxiliary
power unit is operable to provide bleed air to a vehicle system. The method
includes
diverting substantially all of the bleed air to an exhaust for a selected time
period
commencing with startup of the auxiliary power unit. After the selected time
period,
at least a portion of the bleed air is diverted to the vehicle system.
In another aspect, a method for controlling an auxiliary power unit includes
diverting substantially all of the bleed air to an exhaust for a selected time
period
commencing with a command to purge odor in an inlet duct into a compressor
that
provides the bleed air. After the selected time period, at least a portion of
the bleed
air is diverted to the vehicle system.
Also disclosed is an auxiliary power unit that includes a compressor, a bleed
passage in fluid communication with the compressor to receive bleed air and a
bleed
control valve extending in the bleed passage. The bleed control valve includes
a first
state in which it is positioned to divert at least a portion of the bleed air
to a vehicle
system and a second state in which is positioned to divert substantially all
of the
bleed air to an exhaust. A controller is operable to command the bleed control
valve
to be in the second state for a selected time period commencing with startup
of the
auxiliary power unit.
BRIEF DESCRIPTION OF THE DRAWINGS
The various features and advantages of the present disclosure will become
apparent to those skilled in the art from the following detailed description.
The
drawings that accompany the detailed description can be briefly described as
follows.
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CA 02789470 2012-09-07
Figure 1 illustrates an example auxiliary power unit.
Figure 2 illustrates an example method for controlling an auxiliary power
unit.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 shows selected portions of an example auxiliary power unit 20. As
will also be described, the auxiliary power unit 20 exemplifies a method 22
(Figure
2). An "auxiliary power unit" is understood as used herein to refer to an
engine that is
configured for purposes other than propulsion.
In the illustrated example, the auxiliary power unit 20 includes a compressor
section 24 and a turbine section 26 that are mounted for rotation on a shaft
S. The
turbine section 26 is in communication with a combustor C, which produces
combustion gases that are expanded in the turbine section 26 to drive the
compressor
section 24 in a known manner. An exhaust gas temperature probe 26a is located
near
the turbine section 26 for monitoring exhaust gas temperature.
In this example, the compressor section 24 includes a primary compressor
24a and a secondary compressor 24b. The primary compressor 24a and the
secondary
compressor 24b include respective inlets 25a and 25b for air intake. The inlet
25b of
the secondary compressor 24b includes an inlet guide vane system 28 that is
operable
to modulate between a fully open position and closed or partially closed
positions to
control an amount of air intake into the secondary compressor 24b.
The auxiliary power unit 20 includes a bleed passage 30 in communication
with the secondary compressor 24b for receiving bleed air 32 there from. A
bleed
control valve 34 extends in the bleed passage 30 and is operable to control
flow of
the bleed air 32 into a delivery duct 36 and an exhaust duct 38. The bleed
control
valve 34 has a first state 341 in which the bleed control valve 34 is
positioned to
divert at least a portion of the bleed air 32 to the delivery duct 36 and
vehicle system
and a second state 342 in which the bleed control valve 34 is positioned to
divert all
or substantially all of the bleed air 32 to the exhaust duct 38.
The inlet guide vane system 28 includes at least one corresponding actuator
28a, and the bleed control valve 34 includes a corresponding bleed control
actuator
34a. The actuators 28a and 34a are in electrical communication with a
controller 40
for controlling operation of, respectively, the inlet guide vane system 28 and
the
bleed control valve 34. The controller 40 is operable to command the bleed
control
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valve 34 pursuant to the method 22 described below. In this regard, the
controller
may include hardware, software or both for implementing the method 22.
As shown, the controller 40 may be in communication with one or more other
controllers to receive input signals and provide output signals. Additionally,
the
controller 40 may receive feedback from the actuators 28a and 34a and other
controllers to facilitate operational control of the auxiliary power unit 20.
In operation, the compressor section 24 intakes air through the respective
inlets 25a and 25b for compression in the compressors 24a and 24b. The bleed
air 32
is provided through the bleed passage 30 and is selectively diverted by the
bleed
control valve 34 to the delivery duct 36, the exhaust duct 38 or a combination
of
both. In this example, the bleed air 32 that is diverted to the delivery duct
36 goes to
a vehicle system, such as a vehicle compartment. In a further example, the
vehicle
compartment is cabin compartment. The bleed air 32 that is diverted to the
exhaust
duct 38 is dumped overboard to the surrounding, exterior environment of the
vehicle.
The inlet 25b, or duct work that the inlet 25b is in communication with, may
include one or more fluids that produce vapors within the air that is taken
into the
secondary compressor 24b. The fluids are not limited to any particular kind
but may
include hydrocarbons, for example, that are present from maintenance. Thus,
especially upon startup of the auxiliary power unit 20 after vapors from the
fluid may
have accumulated, vapors are transported in the bleed air 32. If the bleed air
32
containing such vapors is permitted to go to the delivery duct 36 and
subsequently
into a cabin compartment, the vapors may cause an odor in the cabin
compartment.
As will be described below with reference to the method 22, the operation of
the
auxiliary power unit 20 can be controlled to reduce or avoid such odors.
With reference to Figure 2, the method 22 for controlling the auxiliary power
unit 20 includes step 50 of diverting the bleed air 32 to the exhaust duct 38
for a
selected time period, followed by step 52 of diverting at least a portion of
the bleed
air 32 to the delivery duct 36 after the selected time period. By diverting
the bleed air
32 to the exhaust duct 38 rather than the delivery duct 36, any vapors in the
bleed air
32 that may cause an odor are not permitted to go into the vehicle or cabin
compartment. Thus, the method 22 provides a "cleaning" or "purging" function
for
discharging vapors that may enter into the auxiliary power unit 20 through the
inlet
25b.
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In one example, the controller 40 causes substantially all of the bleed air 32
to
be diverted to the exhaust duct 38 for a selected time period, commencing with
startup of the auxiliary power unit 20, as represented at 54. That is, in
response to
startup of the auxiliary power unit 20, the controller 40 commands the bleed
control
valve 34 to be in the second state 342 to divert substantially all of the
bleed air to the
exhaust duct 38. Thus, if the bleed control valve 34 is not in the second
state 342, it
moves into the second state 342 and if the bleed control valve 34 is already
in the
second state 342, it remains the second state 342 for the selected time
period. After
the selected time period, the controller 40 commands the bleed control valve
34 to
move to the first state 341 in which the bleed control valve 34 is positioned
to divert
at least a portion of the bleed air 32 to the delivery duct 36. Alternatively,
the
controller 40 may command the bleed control valve 34 to remain in the first
state 34,
but move the inlet guide vane system 28 to a different position. Such as
response can
be automatic with every startup or particular number of startups of the
auxiliary
power unit 20, or alternatively can be selected manually with startup, for
example.
In another embodiment, the controller 40 commands the bleed control valve
34 to divert substantially all of the bleed air 32 into the exhaust duct 38
commencing
with a command to purge odor in the inlet 25b, as represented at 56. For
example, the
command to purge odor may correspond with the startup of the auxiliary power
unit
20 when it is known that there are vapors that may cause an odor or,
alternatively,
may be initiated at another time during the operation of the auxiliary power
unit 20.
To facilitate operation of the auxiliary power unit 20 during the method 22,
the controller 40 can also modulate the inlet guide vane system 28 during the
selected
time period to provide a reduced an amount of air intake with respect to a
full air
intake into the compressor 24b. In one example, the controller 40 modulates
the inlet
guide vane system 28 to 50%-75% of fully opened during the selected time
period to
control the amount of air intake into the compressor 24b. The modulating of
the inlet
guide vane system 28 to reduce or control the amount of air intake facilitates
mitigation of loads on the compressor 24b. Additionally, the exhaust duct 38
is of a
finite size and can only accommodate a given amount of bleed air 32. To ensure
that
the amount of bleed air 32 does not exceed the capacity of the exhaust duct
38, the
inlet guide vane system 28 is modulated to reduce the amount of intake air.
Further,
the modulation of the inlet guide vane system 28 can be used to vary the value
of the
selected time period. For example, lower airflow may require a higher selected
time
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period to purge the vapors to a desired degree while higher airflow may
require a
lower selected time period to purge the vapors to a desired degree. In one
example,
the selected time period may be 15 seconds but may alternatively be anywhere
between a couple of seconds up to any desired time to purge the vapors to a
desired
degree.
Although a combination of features is shown in the illustrated examples, not
all of them need to be combined to realize the benefits of various embodiments
of
this disclosure. In other words, a system designed according to an embodiment
of this
disclosure will not necessarily include all of the features shown in any one
of the
Figures or all of the portions schematically shown in the Figures. Moreover,
selected
features of one example embodiment may be combined with selected features of
other example embodiments.
The preceding description is exemplary rather than limiting in nature.
Variations and modifications to the disclosed examples may become apparent to
those skilled in the art that do not necessarily depart from the essence of
this
disclosure. The scope of legal protection given to this disclosure can only be
determined by studying the following claims.
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