Supersonic Engine Technology

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

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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

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50

100

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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

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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

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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

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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


First Flight





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



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


First Flight





1

2

3

4

5

6


First Flight





1

2

3

4

5

6

Proposed Demonstrator Development Project

Design Tool Development and Validation Testing

2

43

6

Recommended Data Review Period *





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

Supersonic Engine Technology

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