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A Thermodynamic Study of Air Cycle Machine for Aeronautical Applications

TL;DR: In this paper, a thermodynamic study of an air cycle machine (ACM) for aircraft air-conditioning purposes is presented, where the energy to drive this machine comes from the compressed air bleed from the compressor of the aircraft propulsion turbine.
Abstract: This work focuses on a thermodynamic study of an air cycle machine (ACM) for aircraft air-conditioning purposes. The ACM configuration mainly includes two compact heat exchangers, a compressor and an expander. The energy to drive this machine comes from the compressed air bleed from the compressor of the aircraft propulsion turbine. Some design features that affect the ACM performance will be studied: aircraft Mach number, cabin altitude, cabin recirculated air temperature and the percentage of the turbine work absorbed by the exhaust fan. Results showed that the computational tool implemented to solve the ACM mathematical model allows an understanding of the air cycle machine performance when flight aircraft and cabin human comfort parameters are changed to attain an optimized aircraft environmental control system (ECS) design

Summary (2 min read)

1. Introduction

  • Environmental control system (ECS) is a generic term used in the aircraft industry for the systems and equipment associated with the ventilation, heating, cooling, humidity/contamination control, and pressurization in the occupied compartments, cargo compartments, and electronic equipment bays [1].
  • This includes a supply of conditioned air for heating and cooling the cockpit and cabin spaces [2].
  • Hence, the air cycle machine has evolved as a widely used means of providing cooling for aircraft and helicopters [5].
  • High flow rate of compressed air for cabin pressurization.

2. Flight Scenario and Air Cycle Machines

  • Cabin altitude and pressure changes are much smaller in magnitude on today’s high altitude pressurized jets than they were during past flights.
  • The partial pressure of oxygen decreases with increasing altitude.
  • The ACM must provide essentially dry, sterile, and dust free conditioned air to the airplane cabin at the proper temperature, flow rate, and pressure to satisfy pressurization and temperature control requirements [15].
  • (a) (b) 118 / Vol. 17 (No. 3) Int. Centre for Applied Thermodynamics (ICAT) A mixed configuration (simple/bootstrap) is achieved by sharing part of the ACM turbine useful work between the ACM compressor and the exhaust fan.

3. Thermodynamic Modeling

  • Point 1 represents the static temperature and pressure of external ambient air, while point 2i denotes the state after isentropic compression to pressure P2i and temperature T2i so that the authors have from the energy equation: 2 2 1 12 V hh += (1) where: h1 = static air enthalpy, V1 = aircraft velocity.
  • In the process 5-6 the working fluid (air) is cooled by the ACM secondary heat exchanger.
  • Pressure P5 (equal to P6) is determined solving the implicit equation obtained from the ACM work balancing: the ACM turbine work is equal to the sum of the secondary compressor work and the exhaust fan work.
  • This mixed air is then insufflated into the cabin through the ducting system.

4.1 Influence of Flight and Cabin Parameters

  • The present paper analyzed the influence of Mach number, exhaust fan power, cabin pressure and cabin temperature on the ACM coefficient of performance (COP).
  • The rejected heat in the secondary heat exchanger decreases and the pressure difference available to the turbine expansion is lower.
  • Figure 7 illustrates the “C test” results (Table 2) for the cabin pressure effect on the ACM performance.
  • When the remaining parameters do not change (“D test” in Table 2), the increase in the Tcabin value causes an elevation in the cooling effect Eq. (22) and, consequently, elevates both coefficients of performance.

4.2 Typical flight mission employing bootstrap ACM

  • In the present section, the air cycle machine coefficient of performance (COP), excluding the pressurization work, has been analyzed for a complete flight mission employing the bootstrap architecture .
  • Climb, cruise and descent modes totalize 4,000 seconds, as indicated Figure 10.
  • Simulations were carried using the parameters listed in Table 3.
  • Ambient temperature decreases along the climb mode and decreases as the aircraft descends.
  • Therefore, COP and COPP maximum levels correspond to the primary compressor work (Wpc) minimum level during the cruise flight mode.

6. Concluding Remarks

  • This paper presented a computational tool that solves the ACM mathematical model (thermodynamic cycle analysis) and allows an understanding of the ACM performance when flight aircraft and cabin human comfort parameters have been changed.
  • In addition, the bootstrap air cycle machine behavior has been tested during a typical flight mission showing that: i. The primary compressor work has the major impact on the ACM computed coefficient of performance.
  • The useful ACM turbine work is used to provide the cabin pressurization work and refrigerant effect and, during the cruise mode, these two last parcels have practically the same magnitude .
  • The opposite effect occurs during the descend mode.

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International Journal of Thermodynamics(IJoT) Vol. 17 (No. 3), pp. 117-126, 2014
ISSN 1301-9724 / e-ISSN 2146-1511 doi: 10.5541/ijot.538
www.ijoticat.com Published online:September 01, 2014
A Thermodynamic Study of Air Cycle Machine for Aeronautical Applications
A.P.P. Santos, C.R. Andrade
*
, E.L. Zaparoli
Instituto Tecnológico de Aeronáutica Aeronautical Division
Pça Marechal Eduardo Gomes, 50 - 12228-900 - São José dos Campos, SP, Brasil
Email:
*
claudia@ita.br
Abstract
This work focuses on a thermodynamic study of an air cycle machine (ACM) for aircraft air-conditioning purposes.
The ACM configuration mainly includes two compact heat exchangers, a compressor and an expander. The energy
to drive this machine comes from the compressed air bleed from the compressor of the aircraft propulsion turbine.
Some design features that affect the ACM performance will be studied: aircraft Mach number, cabin altitude, cabin
recirculated air temperature and the percentage of the turbine work absorbed by the exhaust fan. Results showed that
the computational tool implemented to solve the ACM mathematical model allows an understanding of the air cycle
machine performance when flight aircraft and cabin human comfort parameters are changed to attain an optimized
aircraft environmental control system (ECS) design.
Keywords: Air-conditioning; air cycle machine (ACM); environmental control system (ECS); coefficient of
performance (COP).
1. Introduction
Environmental control system (ECS) is a generic term
used in the aircraft industry for the systems and equipment
associated with the ventilation, heating, cooling,
humidity/contamination control, and pressurization in the
occupied compartments, cargo compartments, and
electronic equipment bays [1].
The primary function of the cabin air conditioning and
pressurization system is to maintain an aircraft environment
that will ensure the safety and comfort of the passengers
and crew during all flight operational conditions and
provide adequate avionics cooling. This includes a supply
of conditioned air for heating and cooling the cockpit and
cabin spaces [2]. Therefore, the aircraft air-conditioning
packs must provide essentially dry, sterile, and dust free
conditioned air to the airplane cabin at the proper
temperature, flow rate, and pressure to satisfy these
pressurization and temperature control requirements [3].
Also aircraft systems must be light, accessible for quick
inspection and servicing, highly reliable, tolerant of a wide
range of environmental conditions, able to withstand
aircraft vibratory and maneuver loads, and able to
accommodate failures occurring during flight [1]. Hence,
design conditions for aircraft purposes differ in several
ways from other air conditioning applications [4].
Air cycle refrigeration is a tried and tested technology
that has long been the basis of aircraft cabin cooling since
air is free, safe and harmless to the environment. The use of
air as a refrigerant is based on the principle that when a gas
expands isentropically from a given temperature, its final
temperature at the new pressure is much lower. The
resulting cold gas can then be used as a refrigerant, either
directly in an open system, or indirectly by means of a heat
exchanger in a closed system. The efficiency of such
systems is limited to a great extent by the efficiencies of
compression and expansion, as well as those of the heat
exchangers employed.
Hence, the air cycle machine has evolved as a widely
used means of providing cooling for aircraft and helicopters
[5]. Compressed air extracted from one or more stages of
the engine compressor expands through a turbine with the
power extracted used to drive a fan (simple cycle), a
compressor (bootstrap cycle), or both (simple/bootstrap
cycle). The power extraction and expansion of the
compressor air across the turbine results in a significant
temperature decrease. This air provides cooling for the
aircraft occupied compartments and avionics. Some of the
bleed air from the engines can be bypassed around the air-
conditioning pack if warm is need in the cabin [6].
It is well known that weight and space results in severe
fuel penalties for aircraft applications. Air cycle machine
presents lower coefficient of performance (refrigerating
effect unit per required power) than a vapor-compression
system but provides weight advantages due to no heat
exchanger required at the cold cycle end (low
pressure/temperature), as detailed in [7]. Moreover, a
common turbo compressor for both the propulsion turbine
and refrigeration plant results in a greater overall power
saving.
Some additional advantages of an air cycle with regard
to its application in aircraft refrigeration can be listed as
follows [8]:
i. High ventilation rate necessary for the pressurized
aircraft cabin.
ii. High flow rate of compressed air for cabin
pressurization.
iii. Part of compression work can be attributed to cabin
pressurization (also necessary if other refrigeration cycle is
used).
iv. One equipment for cooling/heating load (an
independent heating equipment is necessary for another
refrigeration cycle).
v. The cabin air-conditioning/pressurization integration
*Corresponding Author Vol. 17 (No. 3) / 117

Several features of air-cycle refrigeration machine have
been recently investigated. Leo and Perez-Grande [9]
performed a thermoeconomic analysis of a commercial
aircraft environmental control system. These authors
showed that a minimum cost can been found at a pressure
close to the ACM nominal bleed pressure. Conceição et al.
[10] developed a thermodynamic model of an air-cycle
machine under flight and ground operating conditions.
Their results showed that the thermodynamic advantages of
the four-wheel in relation to the three-wheel machine are
maximized when considering critical cooling conditions for
hot days. Al-Garni et al. [11] presented a tool for extracting
management information from field failures of aircraft
cooling systems. Their techniques allow engineers to
quickly identify failure trends, misbehaving systems,
unusual behaviors, and effects of environmental conditions,
maintenance practices, and repair actions for ECS system
maintenance.
In the work of Zhao et al. [12], an experimental study
on the off-design performance and dynamic response of an
aircraft environmental control system (ECS) has been
conducted. A bootstrap air cycle refrigeration system with
high pressure water separation was employed and both the
static and the dynamic tests were performed. Tu and Lin
[13] showed that the thermal dynamic responses of the air-
cycle cooling pack is sensible to the temperature and the
mass-flow-rate change of bleed air and ram air. Yoo et al.
[14] developed an air-cycle machine modeling program
including a phase change heat exchanger to estimate its
effect in various aircraft flight conditions such as take-off,
maneuver, cruise, and landing.
In this context, the present work focuses on the
numerical simulation of the air cycle machine changing
some aircraft flight and human comfort parameters as Mach
number, cabin altitude and cabin recirculated air
temperature. Results hereby obtained allow a better
understanding about the influence of these parameters on
the ACM performance, and leading to identification of
relevant conditions to attain an optimized ECS design.
2. Flight Scenario and Air Cycle Machines
Cabin altitude and pressure changes are much smaller in
magnitude on today’s high altitude pressurized jets than
they were during past flights. Although the percentage of
oxygen in cabin air remains virtually unchanged (21
percent) at all normal flight altitudes compared to sea level,
the partial pressure of oxygen decreases with increasing
altitude. This is because with increasing altitude air is less
densely packed, resulting in fewer molecules of oxygen
available for each occupant breathing cycle [15].
At a maximum cabin altitude of 8,000 feet, the partial
pressure of oxygen is about 74 percent of the sea level
value requiring an adequate pressurization system to
maintain a suitable comfort level to the passengers and
crew. A typical flight will cruise at 36,000 feet
(~11,000 m), resulting in a cabin altitude of 6,000 feet
(~1,800 m). Figure 1 shows a typical cabin and airplane
altitudes schedule.
An air-conditioning pack is an air cycle refrigeration
system that uses the air passing through and into the
airplane as the refrigerant fluid. Fresh air is bled from the
compression stages of the engine and supplied, after
conditioning, to the cabin to control such factors as
temperature, pressure, and contaminant level, which may
greatly influence passengers’ perceptions of the cabin
environment [16]. This is accomplished by a combined
turbine and compressor machine, valves for temperature
and flow control, and heat exchangers using outside air to
dispense waste heat. The ACM must provide essentially
dry, sterile, and dust free conditioned air to the airplane
cabin at the proper temperature, flow rate, and pressure to
satisfy pressurization and temperature control requirements
[15].
Figure 1. Typical cabin and airplane altitudes schedule.
There are three basic configurations of ACM where
compressed air extracted from one or more stages of the
propulsion turbine compressor is cooled (by one or more
heat exchangers) and expanded through a turbine. The
power supplied by the ACM turbine may be used to drive a
fan (simple cycle, Figure 2a), a compressor (bootstrap
cycle, Figure 2b), or both (simple/bootstrap cycle, Figure
2c).
(a)
(b)
118 / Vol. 17 (No. 3) Int. Centre for Applied Thermodynamics (ICAT)

(c)
Figure 2. Air cycle machines representation: (a) simple
cycle; (b) bootstrap cycle; (c) simple/bootstrap cycle.
In the simple cycle, all the ACM turbine work is
consumed by the heat exchanger exhaust fan while in the
full bootstrap cycle this power work is used only to drive
the ACM compressor. A mixed configuration
(simple/bootstrap) is achieved by sharing part of the ACM
turbine useful work between the ACM compressor and the
exhaust fan.
According to Wright et al [17], there is very little
publications specifically aimed to aircraft air-conditioning
systems. Details of air cycle machine architectures are
usually confidential information belonging to manufactures
and scarcely available within open literature. Thus, the
main contribution of the present work is to present a three-
wheel bootstrap ACM study by means of a well-known
thermodynamic modeling.
3. Thermodynamic Modeling
A typical open bootstrap air cycle machine processes (1-
7) can be plotted in a temperature x entropy diagram, as
schematized in Figure 3.
Figure 3. Processes of an aircraft bootstrap ACM.
where:
1 ambient static conditions;
2 state after ram air compression;
3a propulsion turbine compressor (primary
compressor) exit;
3b bleed pre-cooler (heat exchanger) exit;
4a bleed pressure control valve exit;
4b ACM primary heat exchanger exit;
5 ACM compressor (secondary compressor) exit;
6 ACM secondary heat exchanger exit;
7 ACM turbine exit;
i isentropic process exit;
cabin cabin pressure and cabin recirculated air temperature.
When the aircraft is flying, the initial compression of
the ambient air is due to ram effect. The ram effect is
shown by line 1-2. Point 1 represents the static temperature
and pressure of external ambient air, while point 2i denotes
the state after isentropic compression to pressure P
2i
and
temperature T
2i
so that we have from the energy equation:
2
2
1
12
V
hh
+
=
(1)
where: h
1
= static air enthalpy, V
1
= aircraft velocity.
Assuming air as a perfect gas with constant specific heat
[18] and using Eq.(1), the following result can be obtained:
p
i
C
V
TTT
2
2
1
122
+==
(2)
The above relation can be modified such that the Mach
number appears:
2
1
1
2
1
2
M)k(
T
T
+=
(3)
where:
k = C
p
/C
v
= specific heat at constant pressure to specific heat
at constant volume ratio;
M = Mach number of the aircraft flight = V
1
/a;
a = sound velocity.
The stagnation pressure after isentropic compression
P
2i
, is given by the relation:
1
1
2
1
2
=
k
k
i
i
T
T
P
P
(4)
erycovre
pressure
ideal
ery
cov
re
pressureactual
P
P
PP
i
r
=
=
1
2
1
2
η
(5)
The ram work (W
r
) which is obtained directly from the
engine (drag penalty) is evaluated by:
)
TT(CmW
pr 12
=
(6)
where
m
= mass flow rate.
The initial compressed air required to drive the ACM is
bleed of the aircraft engine, as shown in Figure 4. This first
compression occurs at the propulsion turbine compressor,
process 2-3a. For the ideal isentropic process 2-3i the
temperature at the point 3i is calculated as:
k
k
ai
P
P
T
T
1
2
3
2
3
=
(7)
where P
3
= compressor bleed port pressure.
Int. J. of Thermodynamics (IJoT) Vol. 17 (No. 3) / 119

Temperature at the point 3a (primary compressor bleed
port) is determined knowing the value of the primary
compressor isentropic efficiency, defined by:
(8)
The actual primary compressor work can be calculated
by:
==
1
1
2
3
2
23
k
k
pc
apc
P
P
CpT
m
)TT(
CpmW
η
(9)
The aircraft bleed system initially controls the
temperature and pressure of the compressed air as shown in
Figure 4. The state of compressed air supplied to the air
cycle machine is represented by point 4a in T vs s diagram
shown in Figure 3 and also in Figure 4 (primary heat
exchanger entry). The temperature drop in the pneumatic
system pre-cooler (3a-3b) does not represent a performance
penalty but the pressure reduction through the pneumatic
pressure control valve (3b-4a) causes a lost in the cooling
effect.
In the process 4a-4b the working fluid (air) is cooled by
the ACM primary heat exchanger. Pressure P
4a
is equal to
P
4b
if the fluid friction process is neglected. So, the amount
of heat rejected in the ACM primary heat exchanger
(Q
phx
) is:
)TT(
CmQ
bap
phx 44
=
(10)
Temperature state T
4b
is calculated taking account the
primary heat exchanger effectiveness (
ε
phx
) given by:
24
44
TT
TT
a
ba
phx
=
ε
(11)
assuming that the heat sink (ram air) temperature of the
primary heat exchanger is equal to T
2
. Remember that the
temperature after the cooling process 4a-4b must be higher
than the stagnation temperature T
2
of the ambient air. It
implies that the working fluid cannot be cooled by heat
exchange to a temperature bellow T
2
.
Temperature at the point 5i, after the isentropic
compression through the ACM secondary compressor, is
calculated as:
k
k
bb
i
P
P
T
T
1
4
5
4
5
=
(12)
Given the value of the secondary compressor isentropic
efficiency, the temperature at the point 5 can be determined
as:
Figure
4. Typical architecture of the ACM and the gas turbine (GT) bleed system showing the pre-
cooler and the pressure
regulator valve.
120 / Vol. 17 (No. 3) Int. Centre for Applied Thermodynamics (ICAT)

workcompressorondarysecactual
workcompressorondarysecideal
TT
TT
b
bi
sc
=
=
45
45
η
(13)
The actual secondary compressor work can be
calculated by:
==
1
1
4
5
4
45
k
k
sc
bp
bpsc
P
P
T
Cm
)TT(CmW
η
(14)
In the process 5-6 the working fluid (air) is cooled by
the ACM secondary heat exchanger. If the fluid friction
process is neglected, pressure P
5
is equal to P
6
. The amount
of heat rejected in the ACM secondary heat exchanger
(Q
shx
) is:
)TT(CmQ
pshx 65
=
(15)
where T6 is calculated taking account the secondary heat
exchanger effectiveness (
ε
shx
) given by:
25
65
T
T
TT
shx
=
ε
(16)
assuming that the minimum attainable temperature for the
working fluid is the ram air temperature.
The largest temperature drop occurs when the air
expands in the turbine (expander) of the air cycle machine.
(see Figure 4). In the isentropic process the state at the end
of expansion process is represented by point 7i in T vs s
diagram (Figure 3). For the actual conditions, the pressure
P
7i
= P
7
is slightly above the pressure of aircraft
pressurized cabin (P
cabin
) that is higher than the external
ambient pressure. So, in the present work, it is assumed that
P
7
= P
cabin
, neglecting the pressure drop in the air
distribution ducts.
Pressure P
5
(equal to P
6
) is determined solving the
implicit equation obtained from the ACM work balancing:
the ACM turbine work is equal to the sum of the secondary
compressor work and the exhaust fan work.
Temperature T
7i
can be calculated by the isentropic
relation:
k
k
i
P
P
T
T
1
6
7
6
7
=
(17)
Due to expansion irreversibilities, temperature T
7
is
greater than T
7i
reducing the expander temperature drop.
The temperature T
7
at the end of the actual expansion
process can be calculated knowing the turbine isentropic
efficiency (
η
t
):
workturbineisentropic
workturbineactual
TT
TT
i
t
=
=
76
76
η
(18)
The ACM turbine useful work is calculated as:
t
k
k
ppt
P
P
TCm)TT(CmW
η
==
1
5
7
676
1
(19)
The implicit equation resultant from the ACM work
balance is given by:
)W(W
tsc
α
=
(20)
where
α
indicates the percentage of the ACM turbine work
absorbed by the secondary compressor. The available work to
drive the heat exchanger exhaust fan is equal to (1 -
α
) W
t
.
Inserting Eq. (14) and Eq.(19) into Eq. (20), the implicit
equation that provides the P
5
value is determined as:
1
1
4
5
4
k
k
sc
bp
P
P
TCm
η
01
1
5
7
6
=
t
k
k
p
P
P
TCm
ηα
(21)
when
α
= 0, the exhaust fan consumes all the ACM turbine
work (simple cycle) and for
α
= 1, the secondary compressor
absorbs the whole turbine work (bootstrap cycle).
Typically, the aircraft air conditioning system has a
mixture chamber, where the cool air at temperature T
7
provided by the air cycle machine is mixed with the cabin
recirculated air, which has been cleaned with high
efficiency filters. This mixed air is then insufflated into the
cabin through the ducting system. Therefore, the cooling
effect of the air cycle machine (Q
c
) can be calculated as:
)TT(CmQ
cabinpc 7
=
(22)
where
T
cabin
is the cabin recirculated air temperature.
A portion of the primary compressor work must be
attributed to the cabin pressurization system. This power
work is used to increase the external air pressure to an
adequate value that satisfies the human breathing
requirements attaining a desirable occupants comfort level
(usually a pressure value in the 8,000 feet level in the
standard atmosphere, Figure 1). Hence, the cabin
pressurization work (W
p
) is expressed by:
r
k
k
pc
p
p
W
P
P
TCm
W +
=
1
1
2
7
2
η
(23)
The coefficient of performance (COPP) for the
simple/bootstrap cycle, including the pressurization work,
can be evaluated as:
pcr
c
WW
Q
COPP
+
=
(24)
Int. J. of Thermodynamics (IJoT) Vol. 17 (No. 3) / 121

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Cites background from "A Thermodynamic Study of Air Cycle ..."

  • ...In commercial aircraft, a comfortable and healthy cabin environment for the passengers is created by the supplying of conditioned air through an environmental control system (ECS) (Pérez-Grande and Leo, 2002; Santos et al., 2014) The source of the conditioned air is compressed outside air that is drawn from the engine or auxiliary power unit (APU) when the aircraft is in the air or on the ground, respectively (Supplee and Murawski, 2008)....

    [...]

  • ...5 mass concentration 22 deposition in the ECSs of these airplanes ranged from 50% to 90%, which was much higher 23 than that measured in an airplane with a ground air-conditioning unit....

    [...]

  • ...AC CE PT ED 1 Severe air pollution and low on-time performance of c mmercial flights in China could 15 increase particle deposition in the environmental control systems (ECSs) of commercial 16 airliners....

    [...]

  • ...The particles deposited in the ECSs could negatively affect the performance of the 17 airplanes....

    [...]

Journal ArticleDOI
TL;DR: A review of the various aeronautical air conditioning systems that are currently available and discusses possible system configurations in the context of the aeronuclear environmental control systems is presented in this paper.
Abstract: This paper presents a review of the various aeronautical air conditioning systems that are currently available and discusses possible system configurations in the context of the aeronautical environmental control systems. Descriptions of the standard vapor compression cycle and air cycles are provided. The latter includes, simple-cycle, bootstrap-cycle, simple-bootstrap cycle (3-wheel) and condensing cycle (4-wheel). Water separation and air recirculation systems are also explored. A comparison between vapor compression cycles and air cycles is provided, as well as a comparison between different air cycles. Air cycle units are far less efficient than vapor compression cycle units, but they are lighter and more reliable for an equivalent cooling capacity. Details regarding the aircraft conceptual design phase along with general criteria for the selection of an air conditioning system are provided. Additionally, industry trends and technological advances are examined. Conclusions are compiled to guide the systems engineer in the search for the most appropriate design for a particular application.

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  • ...In addition, in most cases, some of the system development aspects are subject to proprietary and/or confidential information(5,6)....

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01 Jan 1983

244 citations


"A Thermodynamic Study of Air Cycle ..." refers background in this paper

  • ...Some additional advantages of an air cycle with regard to its application in aircraft refrigeration can be listed as follows [8]: i....

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Journal ArticleDOI
Hongli Zhao1, Yu Hou1, Yongfeng Zhu, Liang Chen1, Shuangtao Chen1 
TL;DR: In this paper, the experimental study on the off-design performance and dynamic response of an aircraft environmental control system (ECS) was presented, where a bootstrap air cycle refrigeration system with high-pressure water separation was employed in the ECS.

49 citations


"A Thermodynamic Study of Air Cycle ..." refers background in this paper

  • ...[12], an experimental study on the off-design performance and dynamic response of an aircraft environmental control system (ECS) has been conducted....

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Journal ArticleDOI
TL;DR: In this paper, the authors investigated the unsteady air supply method and found that the averaged temperature and CO2 concentration levels under periodic air supplies were lower within the whole domain and in typical breath zones than the conventional steady-supply condition with the same amount of fresh air.
Abstract: Maintaining a suitable cabin environment for an aircraft at cruise requires constant extraction of fresh air from the engine, resulting in a loss of thrust. An effective air delivery method for ventilating the cabin will minimize such loss and thus improve the fuel economy of an aircraft. This study investigated the unsteady air supply method and found that the averaged temperature andCO2 concentration levels under periodic air supplies were lowerwithin the whole domain and in typical breath zones than the conventional steady-supply condition with the same amount of fresh air. The dynamic flow pattern observed inside the cabin was found to be themain reason for this improvement. Unsteady air supply has shown great potential in improving the fresh air delivery efficiency and the air quality inside the cabin.

48 citations


"A Thermodynamic Study of Air Cycle ..." refers background in this paper

  • ...Fresh air is bled from the compression stages of the engine and supplied, after conditioning, to the cabin to control such factors as temperature, pressure, and contaminant level, which may greatly influence passengers’ perceptions of the cabin environment [16]....

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Journal ArticleDOI
TL;DR: In this paper, the authors present a focused literature review to understand the common problem of fouling of air-conditioning heat exchangers aboard aircraft, with the academic consideration to employ electrostatic precipitation to remove airborne particulate matter.

34 citations


"A Thermodynamic Study of Air Cycle ..." refers background in this paper

  • ...According to Wright et al [17], there is very little publications specifically aimed to aircraft air-conditioning systems....

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Frequently Asked Questions (1)
Q1. What are the contributions mentioned in the paper "A thermodynamic study of air cycle machine for aeronautical applications" ?

This work focuses on a thermodynamic study of an air cycle machine ( ACM ) for aircraft air-conditioning purposes. Some design features that affect the ACM performance will be studied: aircraft Mach number, cabin altitude, cabin recirculated air temperature and the percentage of the turbine work absorbed by the exhaust fan.