(44 pages)
CAEP.8.WP.018.2.en.doc 

### COMMITTEE ON AVIATION ENVIRO NMENTAL PROTECTION (CAEP)

EIGHTH MEETING

Montréal, 1 to 12 February 2010

Agenda Item 2: Review of technical proposals relating to aircraft engine emissions



### ENVIRONMENTAL TECHNICAL MANUAL (ETM), VOL II ON THE USE OF
PROCEDURES IN THE EMISSIONS CERTIFICATION OF AIRCRAFT
ENGINES

(Presented by WG3 Rapporteurs)

SUMMARY

The Working Paper describes the work of WG3 in development of the new Environmental Technical Manual (ETM), Vol II on the use of procedures in
the emissions certification of aircraft e ngines. This is in fulfilment of remit
E.07.

Action by the CAEP is in paragraph 3.

1. INTRODUCTION

1.1 As part of the CAEP/7 work programme, WG3 had been requested to develop a second
Volume of the Environmental Technical Manual (ETM) for emissions, consistent and compatible with the approach taken for noise (Vol I), including but no t limited to guidance material in support of Annex
16

, Vol II. WG3 had consequently agreed on the structur e, definitions of guidance material categories and principles to follow in developing the ETM. CAEP/7 endorsed the material developed thus far.

1.2 Regarding publication of this material, CA EP/7 accepted the Secretary’s proposal that since a revised version of Vol I of the ETM was anticip ated, and in view of the limited nature of the new material intended for Vol II at present, the plan was to delay formal publication until both Volumes could be produced together. However, so that the material de veloped for Vol II could be used in the interim, it was proposed to publish it as a guideline on the ICAO website. It was considered that this procedure would still allow national authorities to incorporate the material in their own regulations by reference to the CAEP/7 report, if they so desired. International Civil Aviation Organization



### WORKING PAPER CAEP/8-WP/18

24/11/09CAEP/8-WP/18 - 2 -

1.3 The CAEP/8 work programme included task E.07 which requested WG3 to further develop the Environmental Technical Manual (ETM ) Vol II as guidance to support the ICAO Annex 16, Vol II certification requirements for aircraft engine emissions.

1.4 WG3 remitted this to the Certification Task Group (CTG) that agreed to set up an ETM ad-hoc group to take forward this work principall y though telecons in between WG3 meetings. The adhoc group has held a total of 17 telecons and this pa per provides an overview of the main issues that have been considered since CAEP/7, with reference to the relevant part of Annex 16, Vol II (e.g. Chapter 2, Appendix 3, etc)

1.5 Appendix A provides the full text of the updated ETM.

2. OVERVIEW OF MAIN ISSUES DISCUSSED

2.1 Date of manufacture (Chapters 1 and 2)

2.1.1 The current Annex 16 Vol II applicability re quirements are related to the “date of manufacture of the first individual production engine”, while for NOx production cut-off requirements the date of manufacture refers to “date of issue of the document attesting that the individual.....engine....conforms to th e requirements of the type”. Explanatory information on this text and agreed interpretation has b een incorporated into the ETM.

2.2 Applicability of Certification Requirements (Chapter 2)

2.2.1 This item was carried across from CAEP/7 (modernization item MOD6) and deals with the applicability of Standards for derivative engine models. The current wording of Annex 16 Vol II could be interpreted to mean that any change in an engine design would require a full emissions certification test programme. This does not reflect the real world as many changes which are considered major, according to airworthiness considerations, ma y have no or very small effects on the emissions performance of that product.

2.2.2 Based on principles agreed to by WG3 th at take into account past and current certification practice, guidance has been developed on how to treat these changes which have no or very little effect on emission levels. It also includes guida nce on when new emissions levels would need to be determined, when a new certification test would be required, and whether the certification basis from the parent product would be retained or , due to substantial modifications , the latest standard applied.

2.3 Process and criteria for NOx production cut-off exemptions (Chapter 2)

2.3.1 In light of the ongoing discussions on a potential CAEP/6 production cut-off requirement,
WG3 identified the need to develo p guidance on the process and evaluation criteria for applications associated with NOx production cut-off exemptions.

2.3.2 Significant discussions have taken place since SG2009 in order to harmonise the approach on a global basis and the agreed gui dance has been incorp orated in the ETM.CAEP/8-WP/18 - 3 -

2.4 Validation of emissions sampling rakes (Chapter 2)

2.4.1 Annex 16 Vol II requires that “the applicant shall provide evidence to the certificating authority, by means of a detailed traverse, that the proposed probe design and position does provide a representative sample for each prescribed power setting” . This procedure is time consuming, costly and problematic with some engine designs. Further, the ab sence of a definition of the term “representative”, or an agreed test to demonstrate this, had resulted in a l ack of clarity in the application of the requirements.

2.4.2 ETM guidance has been agreed clarifying that a sample taken at the engine core exit plane, with a suitably designed rake, would provide more accurate and representative measurements than that from a rake measuring mixed flow (core and bypass). As such, future emissions certification projects should aim to measure at the core exit plane. Wher e mixed flow measurements are unavoidable, the ETM provides a default Smoke Number (SN) dilution corr ection based on the ICAO approved FOA. It was also agreed that, while 12 orifices is the minimum num ber for a sampling rake in Annex 16 Vol II, a more appropriate number would be 20 when validated by means of a detailed traverse.

2.4.3 The required traverse measurements to demonstrate representative sampling are dependent on the rake design, number of sampling or ifices and existing experience with similar engines or derivatives. These rake design requirements comple ment the system check performed in the carbon
balance criteria.

2.5 Status of supersonic engine emissions requirements (Chapter3)

2.5.1 The CAEP Secretariat highlighted that they had received questions regarding the current status of the Vol II certification requirements for e ngines intended for propulsion at supersonic spends.

2.5.2 WG3 has clarified their current position on this issue, which had previously been presented to CAEP/7, via the inclusion of text within the ETM.

2.6 Smoke emission evaluation (Appendix 2)

2.6.1 All engine manufacturers have confirmed that they use green tristimulus filters within their reflectometers, as per the requirements in SAE ARP 1179C on “Aircraft Gas Turbine Engine Exhaust Smoke Measurement”. This has been recognised as best practise in terms of ensuring an accurate
correlation between filter reflectance and SAE Smoke Number measurements. The filter requirement relates back to the ANSI PH2.17, wh ich has now been replaced by ISO 5- 4, and was introduced to ensure that the photosensitive receptor provid es for an effective spec tral sensitivity which is equivalent to the average human eye. ETM guidance has been agreed specifically referring to the use of the filter as best practice.

2.7 Instrumentation and measurement techniques for gaseous emissions (Appendix 3)

2.7.1 Based on existing FAA AC34-1B guidance mate rial, ETM guidance has been agreed for Annex 16 Vol II Appendix 3 on instrumentation and me asurement techniques for gaseous emissions. The
text includes a reference to SAE ARP 1256 on "Proce dure for the Continuous Sampling and Measurement of Gaseous Emissions from Aircraft Turbine Engines".CAEP/8-WP/18 - 4 -

2.7.2 This work included the need to clarify Section 7 on the post processing of measured emissions data taken during a certification test. A worked example of the calculation procedure for correcting measured Emissions Indices (EIs) to re ference conditions was produced by EASA, and validated by ICCAIA. It is based on combustor inle t conditions (T3, P3 and fuel flow) from a validated engine performance model and, again, makes referen ce to the relevant SAE ARP 1533 on “Procedure for the Analysis and Evaluation of Gaseous Emissions from Aircraft Engines”. In addition to being a method for calculating emissions data, this ARP also includ es two fully worked examples of the matrix method for solving the combustion chemical equation.

2.7.3 In coordination with SAE E-31, the ad-hoc group has also begun to develop guidance associated with the Attachments to Annex 16, Vol II, Appendix 3 which contain the specifications for all gaseous emissions analysers. This work has so far focused on Attachment A covering HC analysers.

2.8 Outstanding issues for CAEP/9

2.8.1 Several ongoing issues that have not been comple ted are expected to be carried over into the CAEP/9 work programme. These include evalua tion of Optical Smoke Meters (OSM) for use in certification tests, and development of fu rther guidance on Appendix 3 Attachments.

3. ACTION BY THE CAEP

3.1 The CAEP is invited to:

a) Review and approve the full text of the ETM Vol II, as presented in Appendix A; and

b) Recommend the publication of this document by ICAO.

— — — — — — — —CAEP/8-WP/18 Appendix English only

APPENDIX

ICAO EMISSIONS ENVIRONMENTAL TECHNICAL MANUAL

GUIDELINES ON THE USE OF PROCEDURES IN THE
EMISSIONS CERTIFICATION OF AIRCRAFT ENGINES



### TABLE OF CONTENTS

Nomenclature

S ECTION 

### 1. I NTRODUCTION

1.2 Purpose
1.3 Framework
1.4 Emissions Compliance Demonstration Plans
1.5 Emissions Certification Reports

1.



### S ECTION 

### 2. G UIDANCE 

### M ATERIAL



### Part I. D EFINITIONS AND 

### S YMBOLS



### P ART 

### II. V ENTED 

### F UEL 

### [ Reserved 

### ]

Part III. E MISSIONS 

### C ERTIFICATION

CHAPTER 1: Administration [Reserved]

CHAPTER 2: Turbo-jet and turbofan engines in tended for propulsion only at subsonic speeds

2.

2.1 General
2.1.1 Applicability
2.1.2 Emissions involved [Reserved]
2.1.3 Units of measurement
2.1.4 Reference Conditions
2.1.4.1 Atmospheric conditions
2.1.4.2 Thrust settings [Reserved]
2.1.4.3 Reference emissions landing and take-off (LTO) cycle
2.1.4.4 Fuel specification
2.1.5 Test conditions [Reserved]

2.2 SmokeCAEP/8-WP/18 Appendix 18 A-2

2.2.1 Applicability [Reserved]
2.2.2 Regulatory smoke number [Reserved]

2.3 Gaseous Emissions
2.3.1 Applicability [Reserved]
2.3.2 Regulatory levels

2.4 Information Required
2.4.1 General information [Reserved]
2.4.2 Test information [Reserved]
2.4.3 Derived information

CHAPTER 3: Turbo-jet and turbofan engines intende d for propulsion at supersonic speeds [Reserved]

APPENDICES

APPENDIX 1. Measurement of reference pressure ratio [Reserved]

APPENDIX 2. Smoke emission evaluation

1. Introduction and Definitions [Reserved

2. Measurement of Smoke Emissions
2.1 Sampling probe for smoke emissions
2.2 Sampling line for smoke emissions
2.3 Smoke analysis system
2.4 Fuel specifications
2.5 Smoke measurement procedures
2.5.1 Engine operation
2.5.2 Leakage and cleanliness checks
2.5.3 Smoke measurement

3. Calculation of smoke number from measured data

4. Reporting of Data to the Certificating Authority [Reserved]

APPENDIX 3. Instrumentation and measurement techniques for gaseous emissions

1. Introduction

2. Definitions [Reserved]

3. Data Required
3.2 Gaseous Emissions
3.3 Other Information [Reserved]A-3 CAEP/8-WP/18 Appendix

4. General Arrangement of the System

5. Description of Component Parts
5.1 Sampling system
5.1.1 Sampling probe
5.1.2 Sampling lines [Reserved]
5.2 HC Analyser [Reserved]
5.3 CO and CO2 analysers [Reserved]
5.4 NOx analysers [Reserved]
5.5 Smoke analysis system [Reserved]

6. General Test Procedures
6.1 Engine operation [Reserved]
6.2 Major instrument calibration [Reserved]
6.3 Operation [Reserved]
6.4 Carbon balance check [Reserved]

7. Calculations
7.1 Gaseous emissions [Reserved]
7.1.1 General [Reserved]
7.1.2 Basic Parameters [Reserved]
7.1.3 Correction of emissions indices to reference conditions [Reserved]
7.2 Control parameter functions [Reserved]
7.3 Exceptions to the proposed procedures [Reserved]

Attachment A to Appendix 3: Specification for HC Analyser

1. General
2. Synergistic Effects
3. Optimisation of Detector Response and Alignment

3. APPENDIX 4. Specification for fuel to be used in aircraft turbine engine emission testing

4.

5. APPENDIX 5. Instrumentation and measurem ent techniques for gaseous emissions from afterburning gas turbine engines [Reserved]

6.

7. APPENDIX 6. Compliance procedures for g aseous emissions and smoke [Reserved]

8.CAEP/8-WP/18 Appendix 18 A-4

NOMENCLATURE

Symbols and Units

S YMBOLS AND ABBREVIATIONS EMPLOYED IN V OLUME II OF THIS MANUAL ARE CONSISTENT WITH

THOSE CONTAINED IN A NNEX 16

– E NVIRONMENTAL P ROTECTION , V OLUME II

– A IRCRAFT E NGINE
E

MISSIONS (T HIRD E DITION , J ULY 2008)

.A-5 CAEP/8-WP/18 Appendix



### S ECTION 

### 1

- I NTRODUCTION

3.2 Purpose

3.2.1 The aim of Volume II of this manual is to promote uniformity in the implementation of ICAO
Annex 16 – Environmental Protection

, Volume II – Aircraft Engine Emissions , by providing guidance to certificating authorities and applicants regarding the intended meaning of the current Annex 16, Volume II Emissions Standards and those specific procedur es that are deemed acceptable in demonstrating compliance to these Standards.

3.2.2 This manual also provides guidance in the wider a pplication of equivalent procedures that have been accepted as a technical means for demonstrati ng compliance with the emissions certification requirements of Annex 16, Volume II

. Such equivalent procedures are re ferred to in Annex 16, Volume II, but are not dealt with in the same detail as in the Appendices which describe the emissions evaluation methods for compliance with the releva nt Chapters of Annex 16, Volume II.

3.2.3 Annex 16, Volume II procedures must be used unles s an equivalent procedure is approved by the certificating authority. Procedures presented in this manual should not be considered as limited only to those described herein, as this manual will be expa nded as new procedures are developed. Also, their presentation does not infer limitation of their application or commitment by certificating authorities to
their further use.

3.2.4 References to Annex 16, Volume II relate to the Amendment 6 thereof.

3.3 Framework

3.3.1 The basic framework of Volume II of this manual is a replication of the ICAO Annex 16, Volume II structure in order to ensure easy reference betw een the requirements and guidance. References in the Table of Contents are only made to a part of the re quirements when there is associated guidance material, otherwise the relevant paragraph has been “Reserved” for future use. There is minimal repetition of the requirement text in order to simplify the ETM conten t, lower maintenance costs, and reduce the danger of
inconsistencies between Volume II and the ETM follo wing future revisions. The requirement text is
enclosed between 2 horizontal lines.

3.3.2 This first Section provides general informa tion while the second Section contains guidance material to ICAO Annex 16, Volume II. The format of the guidance material includes three types of information described as Explanatory Information, Equivalent Procedures and Technical Procedures. The Definitions of these three types of information are as follows:

Explanatory Information

• Explains ICAO Annex 16 Emissions Standards language

• States current policies of regulatory author ities regarding compliance with ICAO Annex 16
Emissions Standards

• Provides awareness of critical issues for approval of applicants’ compliance methodology proposalsCAEP/8-WP/18 Appendix 18 A-6

Equivalent Procedures

• An equivalent procedure is a test or anal ysis procedure which, while differing from one specified in Annex 16 Volume II, in the tec hnical judgement of the certificating authority yields effectively the same emissions levels as the specified procedure.

• The use of equivalent procedures may be requested by applicants for many reasons, including:

c) to make use of previously acquired certifi cation test data for the engine type; and

d) to minimize the costs of demonstrating complia nce with the requirements of ICAO Annex 16, Volume II by keeping engine test time, test be d usage, and equipment and personnel costs to
a minimum.

Technical Procedures

• A technical procedure is a test or analysis pr ocedure not defined in detail in ICAO Annex 16 Emissions Standards but which certificating au thorities have approved as being acceptable for compliance with the general provision s the Emissions Standards specify.

3.4 Emissions Compliance Demonstration Plan

3.4.1 Prior to undertaking an emissions certification de monstration, the applicant is normally required to submit to the certificating authority an emissions compliance demonstration plan. This plan contains the method by which the applicant proposes to show compliance with the emissions requirements. Approval of this plan and the proposed use of any equivalent procedure remains with the certificating authority. The determination of equivalency for any procedure or group of procedures must be based upon the consideration of all pertinent facts relating to the application.

3.4.2 Emissions compliance demonstration plans should include the following types of information:

Introduction:

description of the engine emissions certification basis, i.e. the applicable 

### Annex 16, Volume II Amendment and Chapter

e) engine description:

type, model number and specific details of the basic configuration to be certified

f) engine emissions certification methodology:

test concepts, equivalent pro cedures and technical procedures

g) test description:

test methods to comply with the emissions standardsA-7 CAEP/8-WP/18 Appendix

h) measurement system:

description of measurement and sampli ng system components and procedures, including calibration procedures, that ar e intended to be used to demonstrate compliance with the emissions standards

i) data evaluation procedures:

Emissions evaluation and adjustment proce dures (including equivalent and technical procedures such as those provided in this ma nual) to be used in compliance with the provisions of ICAO Annex 16, Volume II a ppropriate to the engine type being
certificated

3.5 Emissions Certification Reports

3.5.1 Following completion of an emissions certification demonstration test, an applicant is normally required to submit an emissions certification report. Th is report provides a complete description of the test process and the test results with respect to complia nce with the provisions of Annex 16, Volume II.

3.5.2 These reports should include the following types of information:

basis for test approval

the approved emissions certification complia nce plan for the engine type and model being certificated.

description of tests

actual configurations tested and non-confor ming items (with justification that they are not significant to emissions, or if significant, can be dealt with by an approved method), test methodology (including e quivalent procedures and technical procedures), tests conducted, test data valid ity, and data analysis and adjustment procedures used.

test results

data to demonstrate compliance with th e provisions of Annex 16, Volume II regarding maximum emissions levels fo r the engine type being certificated.

referencesCAEP/8-WP/18 Appendix 18 A-8



### S ECTION 

### 2

– G UIDANCE 

### M ATERIAL



### P ART 

### I

– D EFINITIONS AND 

### S YMBOLS



### C HAPTER 

### 1: D EFINITIONS

Exhaust nozzle

. In the exhaust emissions sampling of gas turbine engines where the jet effluxes are not mixed (as in some turbofan e ngines for example) the nozzle considered is that for the gas generator (core) flow only. Where, however, the jet efflux is mixed the
nozzle considered is the total exit nozzle.

Equivalent Procedure

Defining the exhaust nozzle in this manner, wher e the fan and core nozzles are not coplanar, is problematic. With imperfect knowledge of the fan fl ow characteristics when discharged upstream of the core exit nozzle, the effective nozzle size may be ambiguous. This affects the extreme downstream location of the sampling probe or rake and causes probl ems in terms of a detailed traverse of the total
exhaust nozzle. In order to obt ain equivalent, but more accurate gaseous emissions measurements and representative samples, it is considered best practise to arrange the engine configuration in such a way as to separate the fan and core flows, without affecti ng the engine performance, and sample just the core flow. The above is equally app licable to both gaseous and smoke emission measurements, however for smoke, the dilution and mixing of bypass air also need s to be taken into account and this is covered under Appendix 2 paragraph 2.1.



### .........................

CHAPTER 2. SYMBOLS

[Reserved]



### .........................

PART II. VENTED FUEL

[Reserved]



### .........................A-9 CAEP/8-WP/18 Appendix



### P ART 

### III – E MISSIONS 

### C ERTIFICATION

Chapter 1. Administration [Reserved]

Chapter 2. Turbo-jet and turbofan engines in tended for propulsion only at subsonic speeds

2.1 General

2.1.1 Applicability

Explanatory Information

Part I of Annex 16 Vol. II defines a derivative version 1 in terms of emissions certification, but this definition is only referred to in the Annex in the c ontext of granting exemptions and does not specify how the rule should be applied to modifications of al ready certificated engine types. Many changes to a certificated engine, which are considered to be ma jor from an airworthiness perspective, require an amendment or supplement to the Type Certificate (TC). However, this same modification(s) may have no or very little effect on the emissions characteristics of that engine. If Annex 16 is interpreted literally, these small effects would require a full investigatio n of compliance against the emissions certification requirements. This may not be necessary in many cases. The following guidelines have been developed in order to help determine whether a modification coul d be classified as a “no emission change” or if it
would affect the emissions levels to such an extent th at the engine type would need to be re-certificated against Annex 16 Vol. II requirements. Of course manufacturers may elect to recertify to the latest requirements at any time.

Technical procedure

9. 1. No emissions change

The principle of a “no emissions change” criteria is that an engine would not need to be re-certified against the emissions requirements if the manufacturer could demonstrate that the modification(s) would result in a small cumulative change to the current certified engine emission levels. Cumulative change could be as a result of more than one change at a given time or multiple changes from more than one
derivative version of the same engine being developed.

The potential determination of a “no emissions ch ange” is limited to the following conditions:

i) If all of the characteristic levels prior to any modification are greater than or equal to 95% of the existing ICAO standard, the manufacturer must provide new engine emissions test data to demonstrate that the resulting charact eristic levels after the cumulative changes since original emission testing will not exceed the existing ICAO exhaust emission
standard.

1 Derivative version. An aircraft gas turbine engine of the same ge neric family as an originally ty pe certificated engine and hav ing features which

retain the basic core engine and combustor design of the origin al model and for which other factors as judged by the certificat ing authority, have not changed.CAEP/8-WP/18 Appendix 18 A-10

ii) If all of the characteristic levels are less than 95% of the existing ICAO exhaust emission standards, then new or related emissions test data and good engineering judgment based on substantive analysis may be an acceptabl e means to demonstrate that the resulting emission levels after the cumulative chang es since original emission testing will not exceed the existing ICAO exhaust emission standard. 2 Analyses should consider areas such as cycle changes, combustor and fuel no zzle design, or large changes in combustor inlet velocity profile or turbine coolin g flows as discussed in paragraph 5 below. iii) Any new emissions test data and/or engi neering/technical analysis under subparagraphs (i) and (ii) must demonstrate that the cumulative changes in absolute emission levels, as compared to those of the orig inal certification, are within: 3 NOx ± 3 g/kN HC ± 1 g/kN CO ± 5 g/kN
Smoke ± 2 SN

With respect to the tracking of cu mulative changes, an applicant s hould maintain formal documentation of the technical basis for all approved “no emissions changes” for an engine model. The tracking list will be reproduced in each emissions certification dossier demonstration.



### If a modification is classified as a “no emissions change”, the characteristic levels for the
derivative version will be considered the same as the parent engine.

2. Changes requiring new emissions levels

A change, or cumulative set of changes to the type design, which is/are not considered a “no emissions change” and thus affects the characteristic levels woul d require new characteristic levels to be determined during the certification program. This would normally be done through a new emissions certification test.

3. Existing emissions certification basis retained

If a modified engine remains on the existing type certif icate, it may retain the existing certification basis of the parent engine 4 if the modification(s):
i. meets the demonstration criteria of 1(i) or 1(ii);
ii. results in a decrease of the absolute emissions levels;

iii. results in an increase of the absolute emi ssions levels below those prescribed in 1(iii);

iv. are necessary for improved safety and continued airworthiness (e.g. ADs).

4. Latest emissions standards applied

An engine type should demonstrate compliance with the latest emissions standards when: i) The engine requires a new TC; ii) The engine modification(s) involves significant technical modifications and where, in the judgment of the certificating authority, the engine would not meet the definition of a derivative engine as defined in Annex 16 Vol. II;

2 Good engineering judgment means judgments ma de consistent with generally accepted sc ientific and engineer ing principles and

all available relevant information.

3 Absolute emission level refers to the av erage of the measured emission levels corr ected to reference conditions. This does no t

include application of the Append ix 6 statistical factors used to determine characteristic levels.

4 In terms of emissions certification the pare nt engine must have demons trated emissions compliance and is not considered to be a derivative of

an even earlier standard itself.A-11 CAEP/8-WP/18 Appendix

iii) The engine modification(s) does not meet th e demonstration criteria of 1(i) or 1(ii); iv) The engine modification(s) results in an in crease in any of the absolute emissions levels below those prescribed in 1(iii) but which resu lts in an exceedance of the existing ICAO standard; v) The engine modification(s) results in an in crease in any of the absolute emissions levels in excess of those prescribed in 1(iii); or v) There are significant future environmental impacts 5

.

10. 5. Engineering analysis examples

The basic premise in assessing emissions effects of design changes from an engineering analysis perspective is that emissions are mainly affected by cycle changes, combustor and fuel nozzle design, or large changes in combustor inlet velocity profile or turbine cooling flows. A number of examples are provided below for illustration.

Cycle change Annex 16 Vol. II only requires the measurement of fuel mass flow by direct measurement to an accuracy of ±2% (Attachment F to Appendix 3, d.) and thrust to an accuracy of ±1% at take-off power and ±5% at the minimum thrust. It may be that no affect on emissions beyond those prescribed in paragraph 1(iii) would be expected unless changes in air fuel ratio (AFR) result in a specific fuel consumption (SFC) change of more than 1%.

Regarding combustor inlet temperature (T3), th e Annex also states that the combustor inlet parameters shall preferably be measured but may be calculated from ambient conditions by appropriate formulas. Following a comparison on T3 detailed traverses versus typical certification test measurements, it was concluded that measurements are within ±6°F (ca. 3.5°C) of theoretical calculations. It may be that no affect on emissions beyond those prescribed in paragraph 1(iii) would be expected if the cycle T3 change is within ±6°F.

Combustor and fuel nozzle Combustor and fuel nozzle changes include some ke y design characteristics that can significantly affect emissions (e.g. swirl cup fl ow, primary hole flow, front end coo ling flow, injector atomization). Changes within or outside of production tolerances or part-to-part variation may indicate when a change would be important for emissions or else c onsidered to be not measurable. No affect on emissions beyond those in prescribed paragraph 1(iii) might be expected if the changes are within current part-to-part variation or prescribed production tolerances.

Boundary conditions Similar limitations to that for key design character istics can be applied to that resulting from changes in boundary conditions. For example, if turbine cooling changes by 2%, one could look at the resulting change in combustor flow distribution, and ifthe change is of the same order as typical partto-part variation, it may be acceptable to conc lude that no affect on emissions beyond those prescribed in paragraph 1(iii) would be expected.

5 The application of an old engine type to a new aircraft design could mean a life time of 30 years or more and thereby have a m ore serious

impact on the environment than if the engine was produced for spares only.CAEP/8-WP/18 Appendix 18 A-12

2.1.1.1 The provisions of this chapter shall apply to all turbo-jet and turbofan engines as further specified in 2.2 and 2.3, intended for propulsion only at subsonic speeds, except when certificating authorities make exemptions for:

a) specific engine types and derivative vers ions of such engines for which the type certificate of the first basic type was issued or other equivalent prescribed procedure was carried out before 1 January 1965; and

b) a limited number of engines beyond the dates of applicability specified in 2.2 and 2.3 for the manufacture of the individual engine.

2.1.1.2 In such cases, an exemption document sh all be issued by the certificating authority, the identification plates on the engines sha ll be marked “EXEMPT,” and the grant of exemption shall be noted in the permanent engine record.

Technical Procedure

1. Introduction

1.1 The current ICAO Annex 16, Volume II contai ns two different references to applicability
dates:

• “date of manufacture for the first individual production model” which re fers to the engine type certification; and

• “date of manufacture for the individual engine” which refers to the production date of a specific engine serial number.

1.2 The second reference is used in the appli cation of global engine NOx production cut-off standards which specify a date after which all in-p roduction engine models must meet a certain NOx emission standard. For example, all engines manufactured after 31 st December 1999 must be compliant
with the CAEP/2 NOx standard. It should be noted that these requirements are applicable to complete new “engine units” released into service as spares or for new aircraft installations, as discussed below, and not engine components required for maintenance aspects, overhaul, parts, etc.

1.3 It is recognized that there may be certain circumstances where it is justified to permit manufacturers to continue to produce new non-complia nt engine units after a production cut-off date. These take the form of exemptions against the relevant Annex 16 Vol. II provisions.

1.4 In order to promote a harmonized global approach to the granting, implementing and monitoring of these exemptions, this section provid es guidelines on the process and criteria for issuing exemptions against a NOx production cut-off standard.A-13 CAEP/8-WP/18 Appendix

11. 2. Exemption Process

12.

13. 2.1 Application

2.1.1 The applicant should submit a formal a pplication letter to the competent authority 6 for the manufacture of the exempted engines, signed by an appr opriate manager, and copied to all other relevant organizations and involved competent authorities. Th e letter should include the following information in order for the competent authority to be in a position to review the application:

a) Administration

 Name, address and contact details of the applicant.

b) Scope of application for exemptions

 Engine type (model designation, type certif icate (TC) number, TC date, emission TC basis, ICAO Engine Emissions Databank Un ique Identification (UID) Number).

 Number of engine exemptions requested.

 Duration (end date) of continued production of exempted engines.

 Designate whether the proposed exem pted engines are “spares” or “new” 7 and to whom the engines will be originally delivered.

c) Justification for exemptions In applying for an exemption, an applicant should, to the extent possible, address the following factors, with quantification, in order to support the merits of the exemption request:

 Technical issues, from an environmental and airworthiness perspective, which may have delayed compliance with a production cut-off.

 Economic impacts on the manufacturer, operato r(s) and aviation industry at large.

 Environmental effects. This should consider the amount of additional NOx that will be emitted as a result of the exemption. This coul d include consideration of items such as:

- the amount that the engine model exceed s the standard, taking into account any other engine models in the engine fami ly covered by the same type certificate and their relation to the standard;

- the amount of NOx that would be emitted by an alternative engine for the same application;

- impact of changes to reduce NOx on other environmental factors, including community noise and CO2 emissions.

 Impact of unforeseen circumstances and hard ship due to business circumstances beyond the manufacturer’s control (e.g. employee st rike, supplier disruption or calamitous events)

 Projected future production volumes and plans for producing a compliant version of the engine model seeking exemption.

 Equity issues in administering the production cut-off among economically competing parties (e.g. provide rationale for granting th is exemption when another manufacturer has a compliant engine and does not need an exemption, taking into account the implications

6 In most cases this will be the Certificating Authority alt hough it may vary depending on individual Member State processes. 7 In the case that engines are to be “new” (installed on new ai rcraft), and would thus result in a larger negative environmenta l impact compared to spare engines, greater justification could be required to approve this application.CAEP/8-WP/18 Appendix 18 A-14

for operator fleet composition, commonality and related issues in the absence of the engine for which exemptions are sought)

 Any other relevant factors

2.2 Evaluation

2.2.1 The evaluation of an exemption application s hould be based on the justification provided and the following definitions and criteria:

a) Use of engines

“ Spare engines ” are defined as complete new engine units which are to be installed on inservice aircraft for maintenance and replacement. It can be presumed that applications associated with engines for this purpose would be granted as long as the emissions were equal to or better than those engines they are repl acing. The application should also include the other items described in paragraphs 2.1.1 (a) and (b), but it would not need to include the items specified in paragraph 2.1.1(c). For sp are engines, the evaluation of the exemption application would be conducted for recordkeep ing and reporting purposes, but it would not be done for approval of an exemption.

“ New engines ” are defined as complete new engine un its which are to be installed on new aircraft. They can only be exempted from a NOx production cut-off requirement if they already meet the previous standard (e.g. ex emption from a CAEP/6 NOx production cut-off is only possible if an engine type already meets the CAEP/4 NOx standard). Also, in order to gain approval for this type of exemption the applicant must clearly demonstrate that they meet the criteria for an exemption by including items described in paragraphs 2.1.1(a), (b), and (c). The competent authority may re quire additional information regarding the appropriateness of the potential exemption.

b) Number of New Engine exemptions

Exemptions should be based on a total number of engines and time period for delivery of these engines, which would be agreed at time the application is approved and based on the considerations explained in 2.1.1.c) above. The number of engines exempted would normally not exceed 75 per engine type certificate and the duration would not exceed 4 years from the effective date of the production cut-off. Exemptions would only apply to non-compliant engine models on an engine type certificate.

Exemptions for new engines should be processed and approved by the competent authorities for both the manufacture of the exempted engin es and the initial operator of the aircraft to which they are to be fitted. Given the inte rnational nature of aviation, civil aviation authorities of member states should attempt to collaborate and consult on the details of exemptions. In the case where engine type cer tification is done through a reciprocity agreement between or among member states, the states involved should coordinate on the processing of exemptions and concur before approval is granted.

As part of the review and approval pro cess for exemptions from any production cut-off requirement associated with the CAEP/6 NOx st andard, competent authorities may in some cases require a form of NOx emissions offse tting, as appropriate within the context of aviation and considering an applicant's ability to utilize such measures. However, offsettingA-15 CAEP/8-WP/18 Appendix

measures should be applied only when necessary in view of the number of engines for which exemptions are sought (e.g. greater than 30), dur ation and/or percent exceedance described in an application.

c) Exceptions

Unlimited exemptions should be granted for spar e engines having emissions equivalent to or better than the engines they replace. Engines fo r use on state aircraft (e.g. military, customs and police) are not covered by the Chicago Convention and therefore excluded from these civil aircraft NOx production cut-off requirements.

2.3 Review

14.

The competent authority should review, in a timel y manner, the application using the information provided in para. 2.1 and against the definitions/criteria in para. 2.2.

The analysis and the conclusions from the review sh ould be communicated to the applicant in a formal response. If the application is approved, the respon se should clearly state the scope of the exemptions which have been granted. If the application is rejected, then the response should include a detailed justification.

3. Registration and Communication

3.1 Oversight of the granted exemptions should include the following elements:

• The competent authority should publish details of the exempted engines in an official public register, including engine model, max. number of permitted exemptions and use of engines.

• The applicant should have a quality control process for maintaining oversight of and managing the production of engines which have been granted exemptions against a NOx emissions production cut-off standard.

• Exempted engine plates should be mark ed with “EXEMPT [SPARE] or [NEW]”.

• An exemption should be recorded in the e ngine release to service document which states conformity with the Type Certificate (e.g. EASA Form 1, FAA Form 8130-3). Proposed
standard text - “ [New] or [Spare] Engine exempted fr om NOx emissions production cut-off requirement ”.

• The applicant should provide, on a regular basis and appropriate to the limitation of the approval, details to the competent authority on the actual exempted engines which have been produced (e.g. model, serial number, use of e ngine, aircraft type and serial number on which new engines are installed).CAEP/8-WP/18 Appendix 18 A-16

2.1.1.3 The provisions of this chapter shall al so apply to engines designed for applications

that otherwise would have been fulfilled by turbo-jet and turbofan engines.

Explanatory Information

This sentence anticipates the introduction of future engine technologies. The emissions Standards in Chapter 2 would also be applicable to future engine types not categorized as a turbo-jet or turbofan but intended for use in international air transport services . The provision above is not directly applicable to turbo-prop engines for example.

2.1.2 Emissions involved [reserved]

2.1.3 Units of measurement

Explanatory Information

Smoke level is determined indirectly, by means of th e loss of reflectance of a filter used to trap smoke particles from a prescribed mass of exhaust per unit area of filter. The result is a dimensionless smoke number “SN” which acts as a surrogate for, or indicator of, plume opacity. These smoke sampling and measurement procedures standardized in Anne x 16 Appendix 2 are derived from SAE Aerospace Recommended Practice (ARP) 1179, Aircraft Gas Turbine Exhaust Smoke Measurement.

The smoke measurement standard was developed for engi nes that generated smoke at considerably higher levels than are seen today. This affects the rela tive accuracy of the method. The measurement is considered (by the SAE E-31 committee that developed th e method) to be no more accurate than ±3 SN. At smoke levels of SN 50-60 this represents an accu racy of 6%-5%. At regulatory standards of 30 and below, relative accuracy becomes 10%-20% or more.

2.1.4 Reference conditions

2.1.4.1 Atmospheric conditions

15.A-17 CAEP/8-WP/18 Appendix

Explanatory Information

The reference atmospheric conditions to which the gaseous emissions (HC, CO and NOx) are to be corrected are the reference day conditions, as follows: Temperature = 15 o C, Humidity = 0.00634 kg

H 2 O/kg of dry air, Pressure = 101.325 kPa.

2.1.4.2 Thrust settings [Reserved]

2.1.4.3 Reference emissions landing and take-off (LTO) cycle

Explanatory Information

The exhaust emissions test is designed to me asure hydrocarbons, carbon monoxide, carbon dioxide and oxides of nitrogen concen trations, and to determine mass emi ssions through calculations during a simulated aircraft landing-takeoff cycle (LTO). Th e LTO cycle is based on times in mode data during high activity periods at major airports for four modes of engine operation: taxi/id le, takeoff, climbout, and approach. The mass emissions for these modes are comb ined to yield the reported emissions certification
levels.

2.1.4.4 Fuel specifications

Explanatory Information

Aircraft gas turbine engines use a va riety of fuels. The specific fuel type and composition can and often does have a significant effect on engine emissions. Hence it is an important factor when comparing emissions levels from one engine with those from anot her. It is particularly important in evaluating engine emission levels relative to a regulation that w as based, in part, on an assumed fuel specification. The ICAO fuel specification defined in Appendix 4 is typical, but tighter, than the general Jet A aviation fuel specification. The requirement for emissions certification testing with a fuel that meets a particular specification provides a fixed point of reference for th e engine. It provides for some degree of control over the effect of fuel composition on smoke formation and emission. It also helps in the assessment of the effects of changing technology.

2.1.5 Test Conditions [Reserved]

2.2 Smoke

2.2.1 Applicability [Reserved]CAEP/8-WP/18 Appendix 18 A-18

2.2.2 Regulatory Smoke Number [Reserved]

2.3 Gaseous Emissions

2.3.1 Applicability [Reserved]

2.3.2 Regulatory levels

Explanatory Information

The date when a standard in paragraph 2.2 and 2.3 becomes applicable within a certification project is
related to the “..date of manufacture of the first indivi dual production model..”. As this date is not always clear, certificating authorities have used the date of issue of the engine type certificate (TC) as a surrogate. The date is transparent as it is recorded on the TC and has therefore proven a useful approach in defining the certification basis for an engine type or model.

The Part 1, Chapter 1 definition of “Date of manufactur e” refers to the date of the document issued to an individual production engine which attests compliance with the type certificate.

2.4 Information Required

2.4.1 General information [Reserved]

2.4.2 Test information [Reserved]

2.4.3 Derived information

Explanatory Information

The “maximum Smoke Number” is formally defined as the greatest value of SN measured at any of the
four thrust levels defined in 2.1. 4.2. However, if a higher smoke number is measured at any other test
condition between 7% and 100% of rated thrust duri ng emissions certification tests, it is recommended that the higher value be reported as the “Maximum Smoke Number”.A-19 CAEP/8-WP/18 Appendix

Chapter 3. Turbo-jet and turbofan engines intended for propulsion at supersonic speeds

Explanatory Information

During the CAEP/7 work programme, Working Gr oup 3 reviewed the historic background on the development of the emissions standards for turbo-je t and turbofan engines intended for propulsion at supersonic speeds and discussed general technology asp ects of supersonic engines in comparison to those for subsonic applications. The output of this work was reported in CAEP/7-WP/10 in February 2007.

While further work, taking into account aircraft and e ngine development, was c onsidered to be necessary to give clear recommendations on future changes to Chapter 3, the following preliminary observations and conclusions were agreed:

The current supersonic Standa rd seems to be outdated.

The Standard should not be applied for new engine projects.

Part III, Chapter 3 of ICAO Annex 16, Volume II would need to be revised.

The timescale for updating should take into account the technological development of any new SST engine project and be in line with the work to be undertaken on development of revised
noise standards.

Any alleviation compared to the current subs onic Standard would require detailed technical investigation.

In order for these conclusions to become reco mmendations work needs to be completed on whether the current subsonic LTO regulatory approach can be applied to supersonic.

Effects from cruise emissions from a potential fleet of supersonic business jets require more scientific understanding.

WG3 continues to monitor developments within the aviation industry and scientific community on this issue. WG3 has also agreed not to update Chapter 3 until a new SST engine project reaches a sufficiently
mature level such that it can inform discussions on potential future revisions.CAEP/8-WP/18 Appendix 18 A-20

Appendix 2: Smoke Emission Evaluation

Explanatory Information

The procedure for evaluating smoke emissions is an i ndirect measure of smoke plume visibility which is obtained by using a filter to trap smoke particles co ntained in a predetermined mass of exhaust gas and measuring the loss of reflectance, i.e., degree of staini ng, of this filter relative to the absolute reflectance
of the filter when clean or free of stain. The uncerta inty of the smoke emission evaluation is estimated to be within ±3 SN (smoke numbers).

1. Introduction and Definitions [Reserved]

16.

2. Measurement of Smoke Emissions

2.1 Sampling probe for smoke emissions

2.1.a) The probe shall be made of stainless steel or any other non reactive metal. If a probe with multiple sampling orifices is used, all sampling orifices shall be of equal diameter.

Equivalent Procedures

Stainless steel is the preferred probe material but ot her non-reacting materials may be more suitable under specific circumstances, e.g. engine exhaust temperat ures which exceed the physical specification limits of stainless steel. Inconel 625 and Nimonic 75 alloys ha ve previously been accep ted as a non-reactive probe material in the context of the regulated species. Othe r materials may be suitable but need to be approved by the certificating authority.

2.1.b) The probe design shall be such that at least 80 per cent of the pressure drop through the probe assembly is taken at the orifices.

Explanatory Information

Smoke particles are submicron in size which, for sam pling from gas turbine engines, precludes the need for isokinetic sampling. Never-the-less good practice would suggest sampling as close to isokinetic as possible. Taking an 80 per cent pressure drop at the probe orifices is a reasonable compromise. Further information on probe design is provided within the section on Appendix 3, paragraph 5.1.1.

2.1.c) The number of locations sampled shall not be less than 12. [Reserved]A-21 CAEP/8-WP/18 Appendix

2.1.d) The sampling plane shall be as cl ose to the engine exhaust nozzle exit plane as permitted by considerations of engine performance but in any case shall be within 0.5 nozzle diameters of the exit plane.

Explanatory Information

The definition of the engine exhaust nozzle is contained in Part 1, Chapter 1, Definitions.

Equivalent Procedure (for mixed flow engine configurations)

For accurate gaseous emissions measurements and represen tative samples, it is considered best practise to arrange the engine configuration in such a way as to separate the fan and core flows, without affecting the engine performance, and to sample just the core flow . This is equally applicable to smoke emission measurements, however for mixed flow engine designs, the dilution and mixing of bypass air also needs to be taken into account with respec t to the exhaust nozzle location. Th is means that the measured core SN would need to be corrected analytically for dilution and mixing in order to compare against the original visibility criteria.

Currently Annex 16 Vol. II does not contain any met hod or procedure for these corrections which has led to inconsistent application of the requirements. Wher e no specific engine data is available, version 3 of the First Order Approximation (FOA) for estimati ng Particulate Matter emissions, which contains correlations between SN and non-volatile PM, is provid ed as a generic dilution correction in the technical procedure below. If it can be shown that an improved correlation is available for a given engine type, or the FOA is developed further, then the improved co rrelation shall be used with the approval of the certificating authority. No generic mixing correctio n procedure has yet been identified, and as such, certificating authorities need to address this issue on a project by project basis. Ideally the measured core SN would already meet the SN limit. Where this is not the case, further evidence may be required to inform a technically based engineering judgement as to whether the plume could still considered to be
invisible. This could include a detailed traverse at the mi xed exhaust nozzle plane in order to perform a contour analysis and determine the level of mixing,

Technical Procedure

The following procedure is provided as guidance mate rial on how to correct core Smoke Numbers for dilution at a mixed flow engine exhaust nozzle:CAEP/8-WP/18 Appendix 18 A-22

Step 1: Convert measured core smoke numbe r to equivalent carbon mass concentration

Figure1: SN plotted against carbon concentration

Based on various research studies, the following F OA carbon correlation equation has been established: CI = 0.0694(SN) 1.23357 for SN < 30

Example: From an engine with a maximum measured core smoke number of 20, the FOA reference curve provides an equivalent carbon mass concentrat ion of 2.8 mg/m3 at the core exit plane.

Step 2: Adjust carbon mass conc entration for mixed stream equivalent

The carbon concentration can now be corrected fo r the amount of bypass air using the following
formulae:



### Ratio Bypass Mass

Carbon Core Mass Carbon Mixed

+ = 1

Example : Assuming a bypass ratio of 5, the mixed carbon mass concentration is 2.8/(1+5) = 0.47 mg/m 3 at the mixed nozzle exit plane.

Step 3: Convert mixed stream carbon mass back to a smoke number Using the FOA reference curve, the mixed flow carbon ma ss (calculated in the previous step) is converted to an equivalent smoke number.

Example : The diluted smoke number, accounting for the fa n air using the FOA reference curve, is 4.8 at the mixed nozzle exit plane. 0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5

0 5 10 15 20 25 30

SNCarbon Conc. mg/m3 FOA 3 curve for SN < 30A-23 CAEP/8-WP/18 Appendix

2.1.e) The applicant shall provide eviden ce to the certificating authority, by means of detailed traverses, that the proposed probe design and position does provide a representative sample for each prescribed power setting.

Explanatory information

Smoke measurements can be performed by means of a single point probe which is traversed through the sampling plane in sufficient detail to provide a repr esentative sample. This measurement can also be made using a multi-orifice probe which has been de monstrated to provide a representative sample by comparison with those of the single point traverse. Work sponsored by the SAE E-31 committee has shown that the best agreement between a detailed tr averse, used to establish the mean value of smoke emissions in the sampling plane, and a multi-point sa mpling probe is achieved when this probes sampling orifices are located on centres of equal area. The most common configuration is that of a cruciform with the individual orifices equally distribute d and located on centres of equal area.

2.2 Sampling line for smoke emissions

17. 2.2.2 Note. Stainless steel or carbon loaded grounded PTFE meet these requirements

Explanatory Information

If carbon-loaded grounded poly-tetra-fluoro-ethylene (PTFE) is used special care must be taken to allow sufficient cooling of the exhaust sample from the probe to the PTFE line to prevent damaging the PTFE line and possibly compromising the sample.

2.3 Smoke analysis system

18.

a) sample size measurement: [Reserved]

b) sample flow rate measurement: [Reserved]

c) filter and holder: [Reserved]

d) valves: [Reserved]

19.

e) vacuum pump:CAEP/8-WP/18 Appendix 18 A-24

[Reserved]

f) temperature control: [Reserved]

g) If it is desired to draw a higher sample flow rate through the probe than through the filter holder, an optional flow splitter may be located between the probe and valve A (Figure 2-1), to dump excess flow. The dump line shall be as close as possible to probe off-take and shall not aff ect the ability of the sampling system to maintain the required 80 per cent pressure drop across the probe assembly. The dump flow may also be sent to the CO 2 analyser or complete emissions analysis system.

Explanatory Information

Achieving an 80% pressure drop across the probe assembly can result in an un acceptably high sample flow rate through the filter holder due to the pressure drop taken across the filter. In these instances, a flow splitter may be required.

h) If a flow splitter is used, a test shall be conducted to demonstrate that the flow

splitter does not change the smoke level pass ing to the filter holder. This may be accomplished by reversing the outlet lines fro m the flow splitter and showing that, within the accuracy of the method, the smoke level does not change.

Explanatory Information

Smoke from gas turbine engines, although consisting of sub-micron particles, can be particularly sensitive to flow splitter design or other flow el ements in the sampling stream due to inertial separation at very high flow velocities. This test addresses these concerns and ensures that the splitter design does not adversely impact the smoke emissions evaluation.

i) leak performance: [Reserved]

j) reflectometer:

Equivalent Procedure

ARP 1179 Rev. C requires the use of a green tristimulus filter to adjust for the effect of various light sources from different reflectometer manufacturers. While this is not a requirement in Annex 16 Vol. II, it is considered best practice to follow this approach.

2.1 Fuel specifications [Reserved]A-25 CAEP/8-WP/18 Appendix

2.2 Smoke measurement procedures

2.5.1 Engine operation [Reserved]

2.5.2 Leakage and cleanliness checks

Explanatory Information

Leakage checks are to ensure clean air does not leak into the system thereby diluting the sample and lowering the smoke number. Cleanliness checks ensure that the sampling system is acceptably clean and the collecting filter will not be contaminated. If th e probe cannot be removed from the sampling stream during engine start-up, the probe a nd lines should be back pressured with a suitably clean gas, such as dry nitrogen, to minimize contamination problems.

2.5.3 Smoke measurement

Explanatory information:

It is common practice, while sampling for smoke, to also measure levels of CO 2 as an operational check of the sampling system. The engine fuel -air ratio is calculated from the measured CO 2 and compared to the fuel-air ratio obtained fro m engine performance data. These should be in agreement within ±10% at engine power above idle and within ±15% at idle.

Paragraphs a) through d) provides for adjusting an d setting the sample flow rate through the filter holder. To duplicate the pressure drop through the filter holder during actual sampling conditions a clean filter is clamped into the holder. This filter should be removed and discarded before clamping a clean filter into the holder as described in d).

3. Calculation of Smoke Number from Measured Data

Explanatory Information

The absolute reflectance of each clean filter should be determined as well as that of the stained filter. Work performed by Dieck, et al, “Aircraft Gas Turbin e Smoke Measurement Uncertainty Using the SAE/EPA Method”, Journal of Aircraft, Vol. 15, No. 4, Apri l 1978, concluded that “The major instrument-related source of error in SAE/EPA smoke measurement is clean-filter reflectance precision. It is a direct result of the variability in filter reflectanc e about the average value used”.

The backing material should be flat and provide equal pressure across the surface of the filter.

4. Reporting of Data to the Certificating Authority [Reserved]CAEP/8-WP/18 Appendix 18 A-26

Appendix 3: Instrumentation and Measur ement Techniques for Gaseous Emissions

1. Introduction

Explanatory Information

The sampling and analysis procedures prescribed in ICAO Annex 16 Volume II, Second Edition, 1993 were adopted from SAE Aerospace Recommended Prac tice ARP 1256, "Procedure for the Continuous Sampling and Measurement of Gaseous Emissions from Aircraft Turbine Engines". The calculation procedures were derived from ARP 1533 ‘Procedure for the Analysis and Evaluation of Gaseous Emissions from Aircraft Engines”. ARP 1256 and AR P 1533 were developed and are maintained by SAE committee E-31, Aircraft Exhaust Emission Measurement.

2. Definitions [Reserved]

3. Data Required

3.1 Gaseous Emissions

a) Hydrocarbons (HC): a combined estimate of all hydrocarbon compounds present in the exhaust gas.

Explanatory information

Gas turbine engine exhaust gases typically cont ain a variety of hydrocarbon compounds. The specific compounds present and their relative concentrations ar e usually unknown. Flame Ionization Detectors, used to measure hydrocarbons, do not respond equa lly to all hydrocarbon compounds. Although this differential hydrocarbon response is to be held with in specific bounds, the resulting measurement is an estimate of the hydrocarbon compounds present in the exhaust gas.

3.2 Other information

20. [Reserved]

21.

4. General Arrangement of the System

Explanatory information

Water is a major product of combustion. Its removal ups tream of the measuring instruments is attractive. Removal would minimize possible interference effects where the instrument responds to the water present as well as to the gas or vapour being measured. It would also prevent or minimize water condensing inA-27 CAEP/8-WP/18 Appendix

the instruments which could cause erratic flow and/or contamination. In the worst case, the instrument would be rendered inoperable until thoroughly cleaned . However, devices which remove water are known to remove hydrocarbons and oxides of nitrogen , and are therefore only permitted for CO and CO2 measurements. If the sample is dried, an appropria te dry/semi-dry to wet correction must be made.

For most aircraft gas turbine engines, and most engine running modes, supplemental pumps will be needed to meet the probe system pressure drop requi rement (80% at the probe entrance orifices), the sample line residence time and pressure drop, and the need to remove excess flow from the sampling system. Any pump used for the purpose of sample transfer must be heated. Usually, because of the sample gas physical properties and the need to main tain temperature and flow control within the Flame Ionization Detector used for hydrocarbon analysis, th ese instruments utilize intern al heated, inert sample transfer pumps. The use of an upstream flow sp litter to dump a portion of the sample is also an acceptable procedure to assist in controlling flow to the analytical sampling train.

If loss of hydrocarbons in the sampling system is a concern, the FID can be, when configured with a heated transfer pump, located upstream of the system hot pump as close as physical constraints will allow (e.g. temperature, noise, vibration). The necessity for a dump and/or a hot-sample pump will depend on the ability to meet the sample transfer time and analys is sub-system sample flow rate requirements. This in turn depends on the exhaust sample driving pressure and line losses. Therefore, in general, the size and location of the pumps, and the associated flow cont rol devices, are determined from the particular sampling system configuration.

5. Description of Component Parts

5.1 Sampling system

5.1.1 Sampling probe a) The probe shall be made of stainless steel or any other non-reactive metal. If a probe with multiple orifices is used, all sa mpling orifices shall be of equal diameter;

Equivalent Procedures

Stainless steel is the preferred probe material but other non-reacting materials may be more suitable under specific circumstances, e.g. engine e xhaust temperatures which exceed the physical specification limits of stainless steel. Inconel 625 and Nimonic 75 alloys have previously been accepted as a non-reactive probe material in the cont ext of the regulated species. Other materials may be suitable but need to be approved by the certificating authority.

Explanatory Information

A probe design with multiple orifices (mixing probe) could include either several sampling orifices leading into a single plenum, or several sampling orifices leading into individual sample lines which are mixed external to the probe, as shown in Figure App. 3-1. The sampling orifices should be equal in size and located on centres of equal area for all mixing pr obes. If a multi-armed probe is used, then there should be an equal number of orifices on each arm. Considerations for probe design leading to these
criteria can be found in “Gas/Turbine Emission Pr obe Factors”, SAE Aerospace Information Report AIR4068A, 1996.The most common configuration is that of cruciform with individual orifices located on centres of equal area.CAEP/8-WP/18 Appendix 18 A-28

b) the probe design shall be such that at l east 80 per cent of the pressure drop through the probe assembly is taken at the orifices;

Explanatory Information

The pressure drop is needed to isokinetically sample flows at the different orifices. The orifice is supposed to be the minimum area right at the probe entrance. To achieve the pressure drop criterion, there must be a rapid expansion into the sampling tube.

The pressure drop refers to the dynamic head , not the total pressure, and is needed to ensure that each orifice takes a flow rate that is proportional to the dynamic head present at the sampling orifice. Thus, when the samples taken by the individual sampling orif ices are mixed together within the probe, the total sample is representative of the mass flux of emissi ons through the engine exhaust sampling plane.



### 8

. 0

0 ) ( 0 

### 〉

− −

sout t i n s t



### p P p P

o

sout t i n s t 

### p P p P

o 

### − 〉

− 0 ) ( 0 

### 8

. 0

Figure App.3-1. Sampling probe designs

c) the number of sampling orifices shall not be less than 12;

Explanatory Information

While 12 orifices is the minimum number for a sampli ng rake in Annex 16 Vol. II, a more appropriate number would be 20 when validated by means of a detailed traverse. 5mm 

### Pt0

Ps(n°i)

Psout
Averaging of individual samplings

Multi-hole non mixing probe
Mixing at the probe exit (before entering the line) Multi-hole mixing probe
(Mixing in the probe) 

### Pt0

Ps(n°i)

Psout 5mm 

### Pt0

Ps(n°i)

Psout
Averaging of individual samplings

Multi-hole non mixing probe
Mixing at the probe exit (before entering the line) Multi-hole mixing probe
(Mixing in the probe) 

### Pt0

Ps(n°i)

PsoutA-29 CAEP/8-WP/18 Appendix

d) the sampling plane shall be as close to the engine exhaust nozzle exit plane as permitted by considerations of engine performance but in any case shall be within 0.5 nozzle diameter of the exit plane;

Explanatory information

Further guidance on the issue of “Exhaust Nozzle“ is av ailable under the Definitions in Part 1, Chapter 1.

e) the applicant shall provide evidence to the certificating auth ority, by means of detailed traverses, that the proposed probe design and position does provide a representative sample for each prescribed power setting.

Explanatory information

Detailed traverse measurements, although expensive, c ould be performed with a single hole probe which measures stabilized concentrations at various positions . These individual measurements will then be used to derive average values and demonstrate represen tative sampling. The carbon balance check is also derived in the same way. The “80% pressure drop” condition which has been in troduced in the past to guarantee the sample is representative, is no more justified for the purpose of a single hole probe.

Technical procedure

There is no standard definition of a “representativ e sample” for emissions from aircraft gas turbine engines, nor is there a specification for “detailed tr averse”. Representative and detailed are, in this instance, matters of opinion to be negotiated betwee n the manufacturer and the certificating authority. The issue is to do with how much the measured averag ed sample can deviate from the true sample mean before it is no longer considered to be representative. The most commonly used definition, arrived at from decades of testing and collaborative analytical exercises by user groups, is 10% for engine modes above idle (i.e., approach, decent, climb and take -off), and ± 15% for idle, as per the carbon balance check in section 6.4 of Appendix 3. There is a significant difference however. For the carbon balance check a comparison is made between sets of indepe ndently related measured values. With knowledge about the combustion process and the hydrogen to carbon ratio of the fuel used, an estimate can be made from the measured carbon containing species, most of which is CO 2 , of the engine average fuel to air ratio. The actual engine fuel to air ratio can be i ndependently arrived at from measured fuel and airflow. These two values can be compared to provide an es timate of how well the exhaust stream was sampled for carbon containing compounds. However, as CO 2 far outweighs the influence of any other carbon bearing species in the calculation of fuel to air ratios, the spatial variability of CO 2 will determine how many sampling points are required and how th ese sampling points should be distributed. CO 2 has been found to consistently exhibit the least variability of all the species of interest, which include CO, HC, NO

x and smoke. This suggests that it would be possibl e to meet the 10 and 15% criteria for carbon balance without having obtained a representative sample, using th e same 10 and 15% criteria, of the other species. In other words, obtaining a carbon balance, while a necessary pre-condition for a representative sample,
could not be considered to be a sufficient dem onstration of representative sampling on its own.

Historically engine manufacturers, or testing agenci es, have addressed this problem in different ways. Recognizing that gas turbine engines are predominat ely axi-symmetric, one acceptable method (for fixed rake designs) has been to sample the exhaust plume, point by point, with a sufficient number of points to be able to estimate, by statistical means, the true engine average species concentration for each of theCAEP/8-WP/18 Appendix 18 A-30

species of interest. Engine exhaust species seem almost normally (Gaussian) distributed, thus making simple statistical tools acceptable. Using these samp ling points, and the measured concentration values for each of the species of interest, contour plots of constant concentration (isopleths) have been analytically generated at each power setting tested. There are a number of computer programs available for workstations or desktop computers to do this. A probe or rake design is then overlaid on the contour plots in order to estimate the average probe/rake valu es and compare to the estimated true average arrived at from the detailed traverse. If the comparisons matc h the carbon balance criteria, within 10% for engine powers above idle and ± 15% at idle, the probe/rake can be consid ered to provide representative sampling. This process may have to be repeated several ti mes before an acceptable design is found.

Equivalent Procedure

When applying this analytical technique, for core fl ow only, multi-orifice rake designs which have proven most robust seem to have four sampling arms spa ced 90 degrees apart with sampling orifices located on centres of equal area. The sampling orifices are equally distributed across the sampling arms and the contour analysis will determine the minimum number of sampling ports necessary to yield a representative sample.

A detailed traverse was not required for rotating rake designs as they provide, in normal use, as many or more sampling points than the typical single point traverse thus ensuring a representative sample. However, in order to demonstrate that a fixed rake d esign is orientated in the right position to collect a representative sample, traverse measurements were necessary. The detail (single point, number of rake orientations, number of different power settings) of traverse measurements may depend on the number of sampling orifices on the rake and exis ting experience of similar engines or derivatives. These rake design requirements were recognized as being complement ed by the system check performed in the carbon balance criteria. Where a sample has low EIs and relatively large % variations between the detailed traverse and the fixed rake measurements, it co uld be accepted as representative without having demonstrated NOx, CO and HC to be within 10 % (15% for idle) as long as ther e is a sufficient large
number of orifices and an AFR matc h within 10% (15% at idle).

All data used in arriving at a probe/rake design shoul d be made available to the certificating authority.

5.1.2 Sampling lines [Reserved]

5.1.3 HC Analyser [Reserved]

5.1.4 CO and CO2 analysers [Reserved]

5.1.5 NOx analysers [Reserved]

5.1.6 Smoke analysis system [Reserved]

6. General Test ProceduresA-31 CAEP/8-WP/18 Appendix

6.1 Engine operation [Reserved]

6.2 Major instrument calibration [Reserved]

6.3 Operation [Reserved]

6.4 Carbon balance check [Reserved]

7. Calculations

Technical Procedure

This technical procedure provides guidance on th e processing of measured data from an emissions
certification test in the form of a simplified worked example.

Definitions:

Reference engine – For this example, the emi ssions certification values are calculated based on combustor inlet conditions (T3, P3, and fuel flow) from a validated engine performance model.

Test engine(s) – Recommended practice is to use an engine which conforms to the production build standard. If differences exist, these differen ces must be documented for approval by the certificating authorities. If any of these non conformances are predicted to impact engine performance, gaseous emissions or smoke levels, then an explan ation and quantification of the impacts will be provided to the certificating author ities for approval. Generally manufacturers will keep deviations from the production standard to a minimum. Measured emissions levels will be corrected to reference engine (production build standard) and standard day conditions.

Detailed traverse – For a new engine type, the next step prior to the actual emission certification test is to conduct a detailed traverse of the engine exhaust to show that a representative sample is being obtained (further guidance in the ETM on detailed traverse see ETM Appendix 3, 5.1.1).

Emissions tests – Emissions are typically measured at more than the four required thrust levels (typically 8-16 conditions) between gr ound idle and maximum rated thrust.

Instrument calibration curves for the different analyzer s may need to be established in order to translate instrument readings to calibrated concentration values. These gas con centrations will be recorded and emission indices will be calculated from that using the equations in 7.1.2 of the Annex 16 Vol. II. The following simple example shows how to derive EI(CO) . Assuming the measured values all on a wet basis:

n/m = H/C = 2; CO = 500 ppm(v) wet = 0,0005; HC = 800 ppm(v) wet = 0,0008;
CO 2 = 2,25% = 0,0225;CAEP/8-WP/18 Appendix 18 A-32

NO 2 = 20 ppm(v) wet = 0,00002;
h amb = 0,0025 vol water /vol dryair CxHy = CH 4 Æ x=1, y=4

The equation in 7.1.2 for EI(CO) would then read:

EI(CO) = (CO/(CO + CO 2 + HC)) * (10 3 * 28,011g / ( 12,011g + n/m* 1,008g) * (1 + (0,0003 * (P 0 /m)))

Where: (P 0 /m) = (2*Z - n/m) = 2*Z – 2 Z = {2 – CO – (2/1 – 4/2*1) * HC + NO2}/ {CO + CO 2 + HC} = 2 – 0,0005 – 0 * HC + 0,00002 = 1,99952 (P 0 /m) = 1,99904

Hence, from the equation above:

EI(CO) = (0,0005/0,0225+0,0005+0,0008) * (28011/(12,011 + 2,016)) * (1 + (0,0003*1,99904)) = 0,021008 * 1996,934483 * 1,000056 = 41,98 g/kg fuel

EI(HC) and EI(NO

x ) are calculated in a similar manner using the other two equations in 7.1.2. For EI(NO

x ) the NO 2 /NO converter efficiency must also be taken into account. EIs are calculated for each measurement point (thrust c ondition) and engine run.

Attachment E of Appendix 3 contains a comprehensiv e and precise numerical method which is often used by engine manufacturers software programs. Further information is contained in SAE ARP 1533 Procedure for the Analysis and Evaluation of Gaseous Emissions from Aircraft Engines which contains two fully worked examples of the Matrix met hod solving the combustion chemical equation.

To correct these EIs from measured to reference engi ne and ambient conditions, a curve fitting technique is recommended. One acceptable alternative method of plotting measured test data is to plot the following:

EI(CO) * P3 v. T3

EI(HC) * P3 v. T3

EI(NO

x ) * P3 ^-0.5 * exp (19 [ h

mass – 0.006 34 ] ) v. T3

A best fit of each of the data curves can then be obt ained, typically using a polynomial function. In some cases, two curve fit equations are needed, one for lo w power data and one for high power data. When more than one engine test has been conducted on an engine, data may be plotted for each test run or a single correlation may be used for the multiple runs. However, if multiple engi nes are tested, a separate set of plots should be made for each test engine.

The procedure for calculating the corrected EI(CO) at values of Fn corresponding to the four LTO operating modes includes the following steps (as shown in Figure A3.1) [Reserved] :

1. Use validated engine performance model to determ ine T3ref, P3ref and reference fuel flow
2. Starting with T3ref, determine EI(CO) * P3 from the EI(CO) * P3 v. T3 curveA-33 CAEP/8-WP/18 Appendix

3. Divide by the corresponding P3ref to get: Corrected EI(CO) = EI(CO) * P3 / P3ref

Calculation of corrected EI(HC) follows exactly th e same process as EI (CO), as does the calculation of corrected EI(NOx) except step 3 i nvolves multiplying by P3ref ^ 0.5 rather than dividing by P3ref.

Once the Corrected EI(CO), EI(HC) and EI(NOx) have been calculated for each operating mode, Dp is calculated using the standard LTO times in mode and corresponding values of reference fuel flow from the validated engine performance model.EI (CO) * P3EI (HC) * P3EI (NOx) * P3-0.5* exp(19(hmass-0.00634)) T3

T3 T3ref

P3refF00refF00ref

100% Foo 100% Foo

Example:

EI (CO) korr = EI (CO) * P3 / P3ref Step 1

Step 2 Step 3

Step 4 From measured data From performance modelEI (CO) * P3EI (HC) * P3EI (NOx) * P3-0.5* exp(19(hmass-0.00634)) T3

T3 T3ref

P3refF00refF00ref

100% Foo 100% Foo

Example:

EI (CO) korr = EI (CO) * P3 / P3ref Step 1

Step 2 Step 3

Step 4 From measured data From performance model

Figure A3.1 – Gaseous Emissions Calculation Procedure

7.1 Gaseous emissions [Reserved]

7.1.1 General [Reserved]

7.1.2 Basic Parameters [Reserved]

7.1.3 Correction of emissions indices to reference conditions [Reserved]CAEP/8-WP/18 Appendix 18 A-34

7.2 Control parameter functions [Reserved]

7.3 Exceptions to the proposed procedures [Reserved]A-35 CAEP/8-WP/18 Appendix

Appendix 3: Attachment A: Specification for HC Analyser

1. General

Precautions: The performance specifications indicat ed are generally for analyser full scale. Errors at part scale may be a significantly great er percentage of reading. The relevance and importance of such increases shall be considered when preparing to make measurements. If better performance is necessary, then a ppropriate precautions shall be taken.

Explanatory Information

The performance specifications for these analyzers, gi ven in terms of full scale response, can have a significant and adverse impact on part scale measurements. In extreme instances, concentrations of HC at high power, such as take-off, can differ from concentrations at idle by orders of magnitude. In general it is always good practice to use a multi-range instrume nt and to adjust ranges such as to keep the measurement in the upper 30% of the instrument re sponse range. Calibrations should be performed on each range used as required.

The instrument to be used shall be such as to maintain the temperature of the detector and sample-handling components at a set point temp erature not less than 155oC to a ability of
±2°C.

Explanatory Information

ICAO Annex 16 Volume II previously (Amendment 6 a nd before) had a set point temperature within the range of 155oC to 165oC to a stability of +/- 2°C. This was adopted from SAE ARP1256, “Procedure For The Continuous Sampling and Measurement of Gase ous Emissions From Aircraft Turbine Engines - 1971. ARP1256 specified this range to meet the need for minimising the condensation of hydrocarbons in the instrument and in recognition of the operating ch aracteristics of then commercially available total hydrocarbon analysers (THAs). Si nce then the ARP has been revised, and now requires a single temperature set point of not less than 160oC but w ith no temperature stability requirement. Commercially
available THAs have evolved and the more common detector housing temperatures approach 200oC. This increase in temperature does not effect the emissions certification measurements but does place an unnecessary constraint on the test procedure.

a) Total range: 0 to 5 000 ppmC in appropriate ranges.

Explanatory Information

A total range of 0 to 5,000 ppmC, while appropriate for the engines in use wh en Annex 16 Vol. II was published in 1981, is broader than needed for today' s engines where concentrations are much lower. Appropriate instruments should be used to ensure best practice measurements in the upper 30% of the range. Thus an instrument with a range upper limit of 5000ppmC may not be necessary and may, in fact, negatively affect the ability to ensure suitable range span due to instrument design limitations.CAEP/8-WP/18 Appendix 18 A-36

b) Resolution: better than 0.5 per cent of full scale of range used or 0.5 ppmC, whichever is greater. [Reserved]

c) Repeatability: better than ±1 per cent of full scale of range used. or ±0.5 ppmC. whichever is greater. [Reserved]

d) Stability: better than ±2 per cent of full scale of range used or ±l.0 ppmC, whichever is greater, in a period of 1 hour.

Explanatory Information

Stability, taken to be span stability and sometimes re ferred to as repeatability or reproducibility, is the maximum variation in instrument output over a specif ied time period and within specified environmental conditions when identical concentration samples, n ear FSD, are passed through the instrument and after zero corrections have been made. Stability is the sum of time dependent drift, i.e., the change in output under invariant laboratory conditions, and changes in output due to other factors such as environmental temperature and/or variations in FID enclosure te mperature. Stability is highly dependent on how, and under what environmental conditions the analyzer is u sed. As such it is out of their control and they choose to specify a value for time dependent drift along with a range of environmental temperatures, i.e., basically under laboratory conditions. Due to improveme nt of instruments using solid state electronics the drift specifications from modern THC Analysers quot e better drift performance(< 1% FS over 8 hours in laboratory conditions) than the stability requirements of the standard. Errors associated with this factor are small to negligible. As measurements are not taken under laboratory condition and as changes in
environmental conditions are the norm rather than th e exception operational procedures, as described in 6.3.2 d of Appendix 3 are required.

e) Zero drift: less than ±1 per cent of full scale of range used or ±0.5 ppmC, whichever is greater , in a period of 1 hour. [Reserved]

f) Noise: 0.5 Hz and greater, less than ±1 per cent of full scale of range used or ±0.5 ppmC, whichever is greater, in a period of 1 hour.

Explanatory Information

The FID requires fuel and oxidant gases for operation. The fuel gas is typically either a mixture of hydrogen/nitrogen, or hydrogen/helium. If the noise sp ecification cannot be met, and a hydrogen/nitrogen mixture is being used as the fuel gas, it can be helpful to change to a hydrogen/helium mixture.

g) Response time: shall not exceed 10 sec onds from inlet of the sample to the analyser system, to the achievement of 90% of the final reading [Reserved]A-37 CAEP/8-WP/18 Appendix

h) Linearity: response with propane in air shall be linear for each range within ±2 per cent of full scale, otherwise calibration corrections shall be used. [Reserved]

2. Synergistic Effects

Oxygen response: Measure the response with two blends of propane, at approximately 500 ppmC
concentration known to a relative accu racy of ±1 per cent, as follows: 1) propane in 10 ± 1 per cent 02, balance N2 2) propane in 21 ± 1 per cent 02, balance N2

If R1 and R2 are the respec tive normalized responses then (R1 - R2) shall be less than 3 per cent of R1.

Explanatory Information

The typical range of O2 concentrations in the core exhaust gas is 18% at idle to 15% at take-off. The specification for a response of <3% between samples of 10% and 21% is conservative and effectively limits the differential response to <1% over the range of interest. If needed the O2 response can be minimized by adjusting the FID burner fuel/air ratio.

Differential hydrocarbon response: measure the response with four blends of different hydrocarbons in air, at concen trations of approximately 500 ppmC, known to a relative accuracy of ±l per cent, as follows: a) propane in zero air b) propylene in zero air c) toluene in zero air d) n-hexane in zero air.

If Ra, Rb, Rc and Rd are, respectively, the normalized responses (with respect to propane), then (Ra - Rb), (Ra - Rc) and (Ra - Rd) shall each be less than 5 per cent
of Ra.

Explanatory Information

While the FID response is assumed to respond in a manner proportional to carbon number, it does vary somewhat with the particular hydrocarbon or class of hydrocarbons being measured. For example, three molecules of methane (CH4) will not necessarily result in the same instrument response as one molecule of propane (C3H8). Due to this differential response, it is useful to think of the FID as responding to an “effective” carbon number. It is important that th e instrument responses are acceptable for all of the hydrocarbons in the engine exhaust. The group of hy drocarbons (propylene, toluene, and n-hexane), with propane as a reference, was chosen to represent, in terms of differential response, the range of hydrocarbons expected in the engine exhaust.CAEP/8-WP/18 Appendix 18 A-38

3. Optimisation of Detector Response and Alignment

3.1 The manufacturer's instructions for initia l setting up procedures and ancillary services and supplies required shall be implemented, and the instrument allowed to stabilize. All setting adjustments shall involve iterative zero checking, and correction as necessary. Using as sample a mixture of approximately 500 ppmC of propane in air, the response
characteristics for variations first in fuel fl ow and then, near an optimum fuel flow, for
variations in dilution air flow to select its optimum shall be determined. The oxygen and differential hydrocarbon responses shall then be determined as indicated above.

Explanatory Information

The FID detector response and alignment can be optimized by adjusting the FID burner fuel and air flow while sampling a mixture containing approximately 500 ppmC propane. Care should be taken when changing fuel flow that the instrument zero does not shift. If it does, the instrument zero should be reset. Response curves illustrating this process are shown in Figures A3-3 and A3-4, and were taken from SAE ARP1256, "Procedure for the Continuous Sampling and Measurement of Gaseous Emissions from Aircraft Turbine Engines".

Figure A3-3 Typical Fuel Flow Response CurveA-39 CAEP/8-WP/18 Appendix

Figure A3-4 Typical Airflow Response Curve



### The objective of this procedure is to select operating flow rates which will give near maximum response with least variation for minor fuel flow variations. It may be necessary to repeat this operation in an iterative fashion:

• Adjust the fuel flow to maximize output;

• Adjust zero if necessary;

• Adjust the air flow to maximize output;

• Readjust the fuel flow, if necessary; and

• Repeat until the burner output is optimized.CAEP/8-WP/18 Appendix 18 A-40

Appendix 4: Specification for Fuel to be used in Aircraft Turbine Engine Emission Testing

The fuel used during tests shall meet the specifications of this Appendix 4, unless a deviation and any necessary corrections have b een agreed by the certificating authority.

Additives used for the purpose of smoke suppression (such as organo-metallic compounds) shall not be present.

Equivalent Procedure

Appropriate evidence should be provided to the certifi cating authority to substantiate any deviation from the fuel specification of Appendix 4 as early as possible.

A deviation may be accepted when it can be shown th at the locally available fuel does not meet the specification. In such a case, use of the available fuel may be acceptable, subject to the substantiation of corrections to compensate for the effect of the de viation on the measured emissions levels. The measured data should then be corrected to reflect the limiting values of the fuel specification of Appendix 4. Corrections will normally be accepted when the magnitude of the correction to the measured data is small in relation to the margin to the certification limits.

The corrections to the declared emission levels resu lting from the deviation in test fuel properties should be based upon engine or rig test data which can be related to the specific combustor type, supported by validated analysis where necessary. The corrections woul d need to be conservative, particularly when test data is not available for the specific combustor type being certificated. Manufactu rers should avoid use of fuels that have been heavily hydro-treated , or produced using synthetic processes.

The deviations from the fuel specification, and the associated corrections, require the agreement of the certificating authority.

..............................

22.

Appendix 5: Instrumentation and measurement techniques for gaseous emissions from afterburning gas turbine engines [Reserved]

................................

Appendix 6: Compliance procedures for gaseous emissions and smoke [Reserved]

................................

— END —