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Supersonic Engine Technology and Work by theCommittee on Aviation Environmental Protection (CAEP)
• Past alleviation seems to be based on Concorde emissionsperformance– Little reason for alleviation today, but the smaller BPR of supersonics does not
help within the CAEP LTO (Landing and Take-Off) emissions cycle.
– The supersonic LTO cycle times have small differences, and one question thegroup has struggled with is will supersonics operate similar to subsonics below3,000 feet.
Supersonic Engine Emissions CAEP Work
Figure 2. Comparison of HC Emissions Limits for Subsonic and Supersonic Aircraft
0
10
20
30
40
50
60
70
10 15 20 25 30 35 40 45 50
Pressure Ratio
Hyd
roca
rbo
n L
imit
(D
p/F
oo
)
Figure 3. Comparison of CO Emissions Regulations for Subsonic and Supersonic Aircraft
0
50
100
150
200
250
300
350
400
450
10 15 20 25 30 35 40 45 50
Pressure Ratio
CO
Em
issi
on
s L
imit
(D
p/F
oo
)
Taken from industry paperpresented to CAEPWorking Group 3.
• Industry has produced papers comparing subsonic and supersonicemissions regulations in Annex 16 Landing and Take-Off (LTO)standards.– Rolls-Royce led this work as our believe is that the sooner that we get
agreement that the subsonic airport emissions regulations should applyalso to supersonics the better (similar to the likely noise approach).
– The existing supersonic regulations have significant alleviation.
– An agreement this CAEP would enable work on the bigger issue of howsignificant cruise NOx emissions are for a supersonic.
Supersonic Engine Emissions CAEP Work
Figure 4. Comparison of NOx Emissions Regulations for Subsonic and Supersonic Aircraft
0
20
40
60
80
100
120
140
160
180
10 15 20 25 30 35 40 45 50
Pressure Ratio
NO
x E
mis
sio
ns
Lim
it (
Dp
/Fo
o)
Supersonic Rule
ICAO 86
CAEP 2
CAEP 4 CAEP 6
Taken from industrypaper presented toCAEP WorkingGroup 3.
Review of LTO Standards for Supersonic Engines• CAEP Working Group 3 has reviewed the history of the supersonic LTO
Standard• Development dates back to the 1970ies• Draft Standard was based on data from Concorde engine• There was no commercial development of SST aircraft when the Standard was
introduced• No changes have been made since the first introduction• The current supersonic standard seems to be outdated
First conclusions:-• Current supersonic standard should not be applied for new engine
projects• Any alleviation compared to the current subsonic Standard would
require detailed technical investigation
Taken from chair of taskgroups paper presented toCAEP Working Group 3.
What about cruise NOx performance?Effect of Forward Speed on Gas Turbine Inlet Temperature
0
50
100
150
200
250
300
350
400
450
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Mach Number
Tem
per
atu
re (
K)
Combustor Conditions for Subsonics and Supersonic Engines
This chart illustrates that the combustion design is heavilydictated by cruise conditions. This also makes NOx at cruisemore difficult and could drive combustion technology.
Comparison of Simple Subsonic and Supersonic Cycle Temperatures
1 2 3 4 5 6
Conditions
Tem
per
atu
re
TET
T3
Take-Off Climb Take-OffCruise CruiseClimb
Combustor Inlet Temperature (T3) Reduces
(T3) Increases due to Ram Effect
Turbine Entry Temperature (TET) Reduces
(TET) Increases due to Ram Effect
OPR is constrained due to increased temperatures at cruise
Subsonic Engine Supersonic Engine
Supersonic Engine Cruise Emissions
• Combustor conditions make controlling cruise NOx difficult.• When NASA were doing work on the HSST supersonic passenger
carrying programme then the targeted 5EINOx.• If combustion technology used is similar to the in-service technology
then the ram effects means cruise NOx could be greater than 30EI– NASA target implies an enormous reduction
• Lean combustion technologies will improve the cruise NOx as wellas LTO NOx but even they will probably not achieve the 5EINOxtarget– The 5EINOx target was for a Lean Premixed Prevapourised type concept
which none of the manufacturers are pursuing with any vigour due to auto-ignition and flashback concerns.
• If cruise NOx is proven to be a major concern then potentially amore sensible target could be 15EINOx as todays subsonic aircraft.– This is still a big improvement in combustion technology from that available
today.
Emissions TechnologiesConsidered in IPCC Report
Quiet Supersonic Transport PropulsionConflicting Requirements
• High thermal efficiency at supersonic cruise requires highcycle temperatures– High T30 and TET for the duration of cruise will
produce low hot component life– NOx generation is related directly to T30 (in
particular) and will be high at cruise
• Low takeoff (jet) noise requires high engine airflow– High airflow requires a large engine/nacelle/nozzle
diameter, implying high weight and drag– Supersonic aircraft are highly sensitive to both weight
and drag at supersonic cruise
1. Variable Cycle‘Conventional’Turbofan (VCT)
2. Mixed NozzleEjector (MNE)
3. Mid-Tandem Fan(MTF)
Variable exit nozzle used to help match airflows at take-off and supersonic cruise. Care needs to betaken on inlet geometry due to noise constraints and supersonic compatibility.
BPR ratio varied by mixed nozzle ejector to increase air-flow at take-off and reduce jet noise.Useful concept for high Mach speed engines due to sizing of inlet and exit engine proportions.
Added complexity with an attempt to help the engine inlet sizing for supersonic cruise by movingthe fan to a more mid engine position. Variable exit nozzle matching still required.
HSCT Propulsion: Performance Comparison, M2.4 & M2.0VCT vs MTF vs MNE
Mach 2.0 Mach 2.4
0.96
1
0.95
0.5
1
CTF MTF MNE
Re
lati
ve
Ra
ng
e
0.8650.9
1
0.5
1
CTF MTF MNER
ela
tiv
e R
an
ge
VCT VCT
Relative range of optimised aircraft designed at fixed MTOW
Variable Cycle TurbofanConcept Design Philosophy, Characteristics
• Core can be based on existing technology (eg ANTLE)• Core size and OPR defined to achieve required cruise thrust within T30 & TET limits
consistent with life and emissions targets• Fan sized to achieve required takeoff thrust with a jet velocity consistent with the noise
target– Intent is to meet current subsonic noise regulations with some margin
• Airflow schedule can be controlled to optimise overall propulsion system characteristics– Match preferred intake characteristics (fixed vs variable geometry, 2D vs Axi etc)– Match fan aerodynamic characteristics– Minimise intake and nozzle size and weight– Optimise overall nacelle shape for low drag and low sonic boom
Research focal point for supersonic boom requested in the CAEP process.
Supersonic Cruise Industry Alliance Proposed Program Schedule
FY 2009CY 2009
FY 2010CY 2010
FY 2005CY 2005
FY 2006CY 2006
FY 2007CY 2007
FY 2008CY 2008
Small Low Boom Demonstrator Phase
Regulatory Change Process
ROM Funding Estimates ($M)
CDR FFRR
Flight Test
Design
PDRSRR
Fabrication
Flight Test Planning
En
v. E
xpan
.R
ang
e D
ata
Co
llec
tio
n
IDR
Tooling/Procurement
20 20 22 15 10 102016753
AdditionalTesting
(as req’d)
PublicAcceptance
Testing
2
RFP
DesignProduceConceptual
Design +Cost/SchedEstimates
ICAO CAEP 7 ICAO CAEP 8
Ongoing NASA Activities
Co
ntr
act
Aw
ard
Pro
po
sals
Du
e
CAEP Working Group Meetings
ConceptStudies
Comp.Phase
5
Milestones:Milestones:Initial Boom Acceptability Criteria
First Flight
Validate Low Boom Design
Deliver Public Acceptance Data
Validate Acceptability Criteria
Regulatory Acceptance
1
2
3
4
5
6
Milestones:Milestones:Initial Boom Acceptability Criteria
First Flight
Validate Low Boom Design
Deliver Public Acceptance Data
Validate Acceptability Criteria
Regulatory Acceptance
1
2
3
4
5
6
Low Boom Technology Development
Design Tool Development and Validation Testing
2
1
43
6DATA DATA DATA
Recommended Data Review Period *
DATA
* Data Review Period Supports Four CAEP Working Group Meetings Prior
to ICAO CAEP 8 Meeting
* Data Review Period Supports Four CAEP Working Group Meetings Prior
to ICAO CAEP 8 Meeting
FY 2009CY 2009
FY 2010CY 2010
FY 2005CY 2005
FY 2006CY 2006
FY 2007CY 2007
FY 2008CY 2008
Small Low Boom Demonstrator Phase
Regulatory Change Process
CDR FFRR
Flight Test
Design
PDRSRR
Fabrication
Flight Test Planning
En
v. E
xpan
.R
ang
e D
ata
Co
llec
tio
n
IDR
Tooling/Procurement
AdditionalTesting
(as req’d)
PublicAcceptance
Testing
RFP
DesignProduceConceptual
Design +Cost/SchedEstimates
ICAO CAEP 7 ICAO CAEP 8
Co
ntr
act
Aw
ard
Pro
po
sals
Du
e
CAEP Working Group Meetings
ConceptStudies
Comp.Phase
Milestones:Milestones:Initial Boom Acceptability Criteria
First Flight
Validate Low Boom Design
Deliver Public Acceptance Data
Validate Acceptability Criteria
Regulatory Acceptance
1
2
3
4
5
6
Milestones:Milestones:Initial Boom Acceptability Criteria
First Flight
Validate Low Boom Design
Deliver Public Acceptance Data
Validate Acceptability Criteria
Regulatory Acceptance
1
2
3
4
5
6
Proposed Demonstrator Development Project
Design Tool Development and Validation Testing
2
43
6
Recommended Data Review Period *
* Data Review Period Supports Four CAEP Working Group Meetings Prior
to ICAO CAEP 8 Meeting
* Data Review Period Supports Four CAEP Working Group Meetings Prior
to ICAO CAEP 8 Meeting
DATA DATA DATADATA DATA
NASA / FAA / Partner COE Boom Acceptability Studies 5NASA / FAA / Partner COE Boom Acceptability Studies 5
Multiple Industry InitiativesMultiple Industry Initiatives
Ongoing NASA Activities 1
Summary and Food for Thought in Discussion• It is likely that a supersonic will have to meet the subsonic emissions
and noise airport standards and no alleviation will be allowed.– Noise level v cruise performance give conflicts in design of engine BPR, and could
involve some variable geometry.
• During the U.S. HSST programme it was believed that an EINOx of5g/Kg were required for a passenger carrying supersonic– Understanding at that time was that at higher altitudes NOx depletes ozone– 5EINOx would be an extremely hard target for a supersonic jet.
• Typical subsonic emissions are 15EINOx at cruise– This may be a sensible target for a supersonic business jet if there is a serious concern for
NOx emissions? although even this is a stepped improvement in combustion technology– Atmospheric science studies need to consider the range of 5-35EINOx
• We are encouraging work in CAEP to understand the issue ofsupersonic cruise emissions especially NOx
• Water vapour is important to global warming along with CO2. Thismay be more of an important issue than NOx and ozone?
• Acceptance of some level of sonic boom overland will be the maintrigger to new supersonic technology development.– Airframe manufacturers believe it may be possible to shape sonic boom.
Thank You