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App.03.en APPENDIX 3.    INSTRUMENTATION AND MEASUREMENT TECHNIQUES FOR GASEOUS EMISSIONS 1.    INTRODUCTION Note.— The procedures specified in this appendix are concerned with the acquisition of representative exhaust samples and their transmission to, and analysi...

App.03.en
APPENDIX 3.    INSTRUMENTATION AND MEASUREMENT TECHNIQUES FOR GASEOUS EMISSIONS 1.    INTRODUCTION Note.— The procedures specified in this appendix are concerned with the acquisition of representative exhaust samples and their transmission to, and analysis by, the emissions measuring system. The procedures do not apply to engines employing afterburning. The methods proposed are representative of the best readily available and most established practice. Variations in the procedure contained in this appendix shall only be allowed after prior application to and approval by the certificating authority. 2.    DEFINITIONS Where the following expressions are used in this appendix, they have the meanings ascribed to them below: Accuracy. The closeness with which a measurement approaches the true value established independently. Air/fuel ratio. The mass rate of airflow through the hot section of the engine divided by the mass rate of fuel flow to the engine. Calibration gas. A high accuracy reference gas to be used for alignment, adjustment and periodic checks of instruments. Concentration. The volume fraction of the component of interest in the gas mixture — expressed as volume percentage or as parts per million. Exhaust nozzle. In the exhaust emissions sampling of gas turbine engines where the jet effluxes are not mixed (as in some turbofan engines 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. Flame ionization detector. A hydrogen-air diffusion flame detector that produces a signal nominally proportional to the mass-flow rate of hydrocarbons entering the flame per unit of time — generally assumed responsive to the number of carbon atoms entering the flame. Interference. Instrument response due to presence of components other than the gas (or vapour) that is to be measured. Noise. Random variation in instrument output not associated with characteristics of the sample to which the instrument is responding, and distinguishable from its drift characteristics. Non-dispersive infra-red analyser. An instrument that by absorption of infra-red energy selectively measures specific components. Parts per million (ppm). The unit volume concentration of a gas per million unit volume of the gas mixture of which it is a part. Parts per million carbon (ppmC). The mole fraction of hydrocarbon multiplied by 106 measured on a methane-equivalence basis. Thus, 1 ppm of methane is indicated as 1 ppmC. To convert ppm concentration of any hydrocarbon to an equivalent ppmC value, multiply ppm concentration by the number of carbon atoms per molecule of the gas. For example, 1 ppm propane translates as 3 ppmC hydrocarbon; 1 ppm hexane as 6 ppmC hydrocarbon. Reference gas. A mixture of gases of specified and known composition used as the basis for interpreting instrument response in terms of the concentration of the gas to which the instrument is responding. Repeatability. The closeness with which a measurement upon a given, invariant sample can be reproduced in short-term repetitions of the measurement with no intervening instrument adjustment. Resolution. The smallest change in a measurement which can be detected. Response. The change in instrument output signal that occurs with change in sample concentration. Also the output signal corresponding to a given sample concentration. Stability. The closeness with which repeated measurements upon a given invariant sample can be maintained over a given period of time. Zero drift. Time-related deviation of instrument output from zero set point when it is operating on gas free of the component to be measured. Zero gas. A gas to be used in establishing the zero, or no-response, adjustment of an instrument. 3.    DATA REQUIRED 3.1    Gaseous emissions Concentrations of the following emissions shall be determined: a) Hydrocarbons (HC): a combined estimate of all hydro-carbon compounds present in the exhaust gas. b) Carbon monoxide (CO). c) Carbon dioxide (CO2). Note.— CO2 is not considered a pollutant but its concentration is required for calculation and check purposes. d) Oxides of nitrogen (NOx): an estimate of the sum of the two oxides, nitric oxide (NO) and nitrogen dioxide (NO2). e) Nitric oxide (NO). 3.2    Other information In order to normalize the emissions measurement data and to quantify the engine test characteristics, the following additional information shall be provided: — inlet temperature; — inlet humidity; — atmospheric pressure; — hydrogen/carbon ratio of fuel; — other required engine parameters (for example, thrust, rotor speeds, turbine temperatures and gas-generator air flow). This data shall be obtained either by direct measurement or by calculation, as presented in Attachment F to this appendix. 4.    GENERAL ARRANGEMENT OF THE SYSTEM No desiccants, dryers, water traps or related equipment shall be used to treat the exhaust sample flowing to the oxides of nitrogen and the hydrocarbon analysis instrumentation. Requirements for the various component sub-systems are given in 5, but the following list gives some qualifications and variations: a) it is assumed that each of the various individual sub-systems includes the necessary flow control, conditioning and measurement facilities; b) the necessity for a dump and/or a hot-sample pump will depend on ability to meet the sample transfer time and analysis sub-system sample flow rate requirements. This in turn depends on the exhaust sample driving pressure and line losses. It is considered that these pumps usually will be necessary at certain engine running conditions; and c) the position of the hot pump, relative to the gas analysis sub-systems, may be varied as required. (For example, some HC analysers contain hot pumps and so may be judged capable of being used upstream of the system hot pump.) Note.— Figure 3-1 is a schematic drawing of the exhaust gas sampling and analytical system and typifies the basic requirements for emissions testing. 5.    DESCRIPTION OF COMPONENT PARTS Note.— A general description and specification of the principal elements in the engine exhaust emissions measurement system follows. Greater detail, where necessary, will be found in Attachments A, B and C to this appendix. 5.1    Sampling system 5.1.1    Sampling probe a) The probe shall be made of stainless steel. If a mixing probe is used, all sampling orifices shall be of equal diameter; 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; c) the number of sampling orifices shall not be less than 12; 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; and e) the applicant shall provide evidence 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. 5.1.2    Sampling lines The sample shall be transferred from the probe to the analysers via a line of 4.0 to 8.5 mm inside diameter, taking the shortest route practicable and using a flow rate such that the transport time is less than 10 seconds. The line shall be maintained at a temperature of 160°C ±15°C (with a stability of ±10°C), except for a) the distance required to cool the gas from the engine exhaust temperature down to the line control temperature, and b) the branch which supplies samples to the CO, CO2, and NOx analysers. This branch line shall be maintained at a temperature of 65°C ± 15°C (with a stability of ±10°C). When sampling to measure HC, CO, CO2 and NOx components the line shall be constructed in stainless steel or carbon-loaded grounded PTFE. 5.2    HC analyser The measurement of total hydrocarbon sample content shall be made by an analyser using the heated flame ionization detector (FID), between the electrodes of which passes an ionization current proportional to the mass rate of hydrocarbon entering a hydrogen flame. The analyser shall be deemed to include components arranged to control temperature and flow rates of sample, sample bypass, fuel and diluent gases, and to enable effective span and zero calibration checks. Note.— An over-all specification is given in Attachment A to this appendix. 5.3    CO and CO2 analysers Non-dispersive infra-red analysers shall be used for the measurements of these components, and shall be of the design which utilizes differential energy absorption in parallel reference and sample gas cells, the cell or group of cells for each of these gas constituents being sensitized appropriately. This analysis sub-system shall include all necessary functions for the control and handling of sample, zero and span gas flows. Temperature control shall be that appropriate to whichever basis of measurement, wet or dry, is chosen. Note.— An over-all specification is given in Attachment B to this appendix. 5.4    NOx analyser The measurement of NO concentration shall be by the chemiluminescent method in which the measure of the radiation intensity emitted during the reaction of the NO in the sample with added O3 is the measure of the NO concentration. The NO2 component shall be converted to NO in a converter of the requisite efficiency prior to measurement. The resultant NOx measurement system shall include all necessary flow, temperature and other controls and provide for routine zero and span calibration as well as for converter efficiency checks. Note.— An over-all specification is given in Attachment C to this appendix. 6.    GENERAL TEST PROCEDURES 6.1    Engine operation 6.1.1    The engine shall be operated on a static test facility which is suitable and properly equipped for high accuracy performance testing. 6.1.2    The emissions tests shall be made at the power settings prescribed by the certificating authority. The engine shall be stabilized at each setting. 6.2    Major instrument calibration Note.— The general objective of this calibration is to confirm stability and linearity. 6.2.1    The applicant shall satisfy the certificating authority that the calibration of the analytical system is valid at the time of the test. 6.2.2    For the hydrocarbon analyser this calibration shall include checks that the detector oxygen and differential hydrocarbon responses are within the limits specified, as laid down in Attachment A to this appendix. The efficiency of the NO2/NO converter shall also be checked and verified to meet the requirements in Attachment C to this appendix. 6.2.3    The procedure for checking the performance of each analyser shall be as follows (using the calibration and test gases as specified in Attachment D to this appendix): a) introduce zero gas and adjust instrument zero, recording setting as appropriate; b) for each range to be used operationally, introduce calibration gas of (nominally) 90 per cent range full-scale deflection (FSD) concentration; adjust instrument gain accordingly and record its setting; c) introduce approximately 30 per cent, 60 per cent, and 90 per cent range FSD concentration and record analyser readings; d) fit a least squares straight line to the zero, 30 per cent, 60 per cent and 90 per cent concentration points. For the CO and/or CO2 analyser used in their basic form without linearization of output, a least squares curve of appropriate mathematical formulation shall be fitted using additional calibration points if judged necessary. If any point deviates by more than 2 per cent of the full scale value (or ±1 ppm*, whichever is greater) then a calibration curve shall be prepared for operational use. 6.3    Operation 6.3.1    No measurements shall be made until all instruments and sample transfer lines are warmed up and stable and the following checks have been carried out: a) leakage check: prior to a series of tests the system shall be checked for leakage by isolating the probe and the analysers, connecting and operating a vacuum pump of equivalent performance to that used in the smoke measurement system to verify that the system leakage flow rate is less than 0.4 L/min referred to normal temperature and pressure; b) cleanliness check: isolate the gas sampling system from the probe and connect the end of the sampling line to a source of zero gas. Warm the system up to the operational temperature needed to perform hydro-carbon measurements. Operate the sample flow pump and set the flow rate to that used during engine emission testing. Record the hydrocarbon analyser reading. The reading shall not exceed 1 per cent of the engine idle emission level or 1 ppm (both expressed as methane), whichever is the greater. Note 1.— It is good practice to back-purge the sampling lines during engine running, while the probe is in the engine exhaust but emissions are not being measured, to ensure that no significant contamination occurs. Note. 2.— It is also good practice to monitor the inlet air quality at the start and end of testing and at least once per hour during a test. If levels are considered significant, then they should be taken into account. 6.3.2    The following procedure shall be adopted for operational measurements: a) apply appropriate zero gas and make any necessary instrument adjustments; b) apply appropriate calibration gas at a nominal 90 per cent FSD concentration for the ranges to be used, adjust and record gain settings accordingly; c) when the engine has been stabilized at the requisite operating mode, continue to run it and observe pollutant concentrations until a stabilized reading is obtained, which shall be recorded; d) recheck zero and calibration points at the end of the test and also at intervals not greater than 1 hour during tests. If either has changed by more than ±2 per cent of range FSD, the test shall be repeated after restoration of the instrument to within its specification. 6.4    Carbon balance check Each test shall include a check that the air/fuel ratio as estimated from the integrated sample total carbon concentration exclusive of smoke, agrees with the estimate based on engine air/fuel ratio within ±15 per cent for the taxi/ground idle mode, and within 10 per cent for all other modes (see 7.1.2). 7.    CALCULATIONS 7.1    Gaseous emissions 7.1.1    General The analytical measurements made shall be the concentrations of the various classes of pollutant, as detected at their respective analysers for the several engine operation modes, and these values shall be reported. In addition, other parameters shall be computed and reported, as follows**. 7.1.2    Basic parameters EIp (emission index = mass of p produced in g for component p) mass of fuel used in kg EI(CO) =  (1 + T(P0/m)) EI(HC) =  (1 + T(P0/m)) EI(NOx) =  (1 + T(P0/m)) (as NO2) Air/fuel ratio = (P0/m) where P0/m = 2Z – (n/m) 4(1 + h – TZ/2) and Z = 2 – [CO] – ( 2/x – y/2x) [HC} + [NO2] [CO2] + [CO] + [HC] MAIR molecular mass of dry air = 28.966 g or, where appropriate, = (32 R + 28.156 4 S + 44.011 T)g MHC molecular mass of exhaust hydrocarbons, taken as CH4 = 16.043 g MCO molecular mass of CO = 28.011 g MNO2 molecular mass of NO2 = 46.008 g MC atomic mass of carbon = 12.011 g MH atomic mass of hydrogen = 1.008 g R concentration of O2 in dry air, by volume = 0.209 5 normally S concentration of N2 + rare gases in dry air, by volume = 0.709 2 normally T concentration of CO2 in dry air, by volume = 0.000 3 normally [HC] mean concentration of exhaust hydrocarbons vol/vol, expressed as carbon [CO] mean concentration of CO vol/vol, wet [CO2] mean concentration of CO2 vol/vol, wet [NOx] mean concentration of NOx vol/vol, wet = [NO + NO2] [NO] mean concentration of NO in exhaust sample, vol/vol, wet [NO2] mean concentration of NO2 in exhaust sample, vol/vol, wet = [NOx]c mean concentration of NO in exhaust sample after passing through the NO2/NO converter, vol/vol, wet  efficiency of NO2/NO converter h humidity of ambient air, vol water/vol dry air m number of C atoms in characteristic fuel molecule n number of H atoms in characteristic fuel molecule x number of C atoms in characteristic exhaust hydrocarbon molecule y number of H atoms in characteristic exhaust hydrocarbon molecule The value of n/m, the ratio of the atomic hydrogen to atomic carbon of the fuel used, is evaluated by fuel type analysis. The ambient air humidity, h, shall be measured at each set condition. In the absence of contrary evidence as to the characterization (x,y) of the exhaust hydrocarbons, the values x = 1, y = 4 are to be used. If dry or semi-dry CO and CO2 measurements are to be used then these shall first be converted to the equivalent wet concentration as shown in Attachment E to this appendix, which also contains interference correction formulas for use as required. 7.1.3    Correction of emission indices to reference conditions Corrections shall be made to the measured engine emission indices for all pollutants in all relevant engine operating modes to account for deviations from the reference conditions (ISA at sea level) of the actual test inlet air conditions of temperature and pressure. The reference value for humidity shall be 0.00634 kg water/kg dry air. Thus, EI corrected = K × EI measured, where the generalized expression for K is: K = (PBref/PB)a  (FARref/FARB)b K  exp ( |TBref – TB|/c)  exp (d|h – 0.00634| ) PB Combustor inlet pressure, measured TB Combustor inlet temperature, measured FARB Fuel/air ratio in the combustor h Ambient air humidity Pref ISA sea level pressure Tref ISA sea level temperature PBref Pressure at the combustor inlet of the engine tested (or the reference engine if the data is corrected to a reference engine) associated with TB under ISA sea level conditions. TBref Temperature at the combustor inlet under ISA sea level conditions for the engine tested (or the reference engine if the data is to be corrected to a reference engine). This temperature is the temperature associated with each thrust level specified for each mode. FARref Fuel/air ratio in the combustor under ISA sea level conditions for the engine tested (or the reference engine if the data is to be corrected to a reference engine). a,b,c,d Specific constants which may vary for each pollutant and each engine type. The combustor inlet parameters shall preferably be measured but may be calculated from ambient conditions by appropriate formulas. 7.1.4    Using the recommended curve fitting technique to relate emission indices to combustor inlet temperature effectively eliminates the exp ((TBref – TB)/c) term from the generalized equation and for most cases the (FARref /FARB) term may be considered unity. For the emissions indices of CO and HC many testing facilities have determined that the humidity term is sufficiently close to unity to be eliminated from the expression and that the exponent of the (PBref /PB) term is close to unity. Thus, EI(CO) corrected = EI derived from (PB /PBref)  EI(CO) v. TB curve EI(HC) corrected = EI derived from (PB /PBref)  EI(HC) v. TB curve EI(NOx) corrected = EI derived from EI(NOx) (PBref /PB)0.5 exp (19 | h – 0.00634 | ) v. TB curve If this recommended method for the CO and HC emissions index correction does not provide a satisfactory correlation, an alternative method using parameters derived from component tests may be used. Any other methods used for making corrections to CO, HC and NOx emission indices shall have the approval of the certificating authority. 7.2    Control parameter functions (Dp, Foo, ) 7.2.1    Definitions Dp The mass of any gaseous pollutant emitted during the reference emissions landing and take-off cycle. Foo The maximum thrust available for take-off under normal operating conditions at ISA sea level static conditions, without the use of water injection, as approved by the applicable certificating authority.  The ratio of the mean total pressure at the last compressor discharge plane of the compressor to the mean total pressure at the compressor entry plane when the engine is developing take-off thrust rating at ISA sea level static conditions. 7.2.2    The emission indices (EI) for each pollutant, corrected for pressure and humidity (as appropriate) to the reference ambient atmospheric conditions as indicated in 7.1.4 and if necessary to the reference engine, shall be obtained for the required LTO engine operating mode settings (n) of idle, approach, climb-out and take-off, at each of the equivalent corrected thrust conditions. A minimum of three test points shall be required to define the idle mode. The following relationships shall be determined for each pollutant: a) between EI and TB ; and b) between Wf (engine fuel mass flow rate) and TB ; and c) between Fn (corrected to ISA sea level conditions) and TB (corrected to ISA sea level conditions); Note.— These are illustrated, for example, by Figure 3-2 a), b) and c). When the engine being tested is not a “reference” engine, the data may be corrected to “reference” engine conditions using the relationships b) and c) obtained from a reference engine. A reference engine is defined as an engine substantially configured to the description of the engine to be certificated and accepted by the certificating authority to be representative of the engine type for which certification is sought. The manufacturer shall also supply to the certificating authority all of the necessary engine performance data to substantiate these relationships and for ISA sea level ambient conditions: d) maximum rated thrust (Foo); and e) engine pressure ratio () at maximum rated thrust. Note.— These are illustrated by Figure 3-2 d). 7.2.3    The estimation of EI for each pollutant at each of the required engine mode settings, corrected to the reference ambient conditions, shall comply with the following general procedure: a) at each mode ISA thrust condition Fn, determine the equivalent combustor inlet temperature (TB) (Figure 3-2 c)); b) from the EI/TB characteristic (Figure 3-2 a)), determine the EIn value corresponding to TB; c) from the Wf /TB characteristic (Figure 3-2 b)), determine the Wfn value corresponding to TB; d) note the ISA maximum rated thrust and pressure ratio values. These are Foo and  respectively (Figure 32 d)); e) calculate, for each pollutant Dp =  (EIn) (Wfn) (t) where: t time in LTO mode (minutes) Wfn fuel mass flow rate (kg/min)  is the summation for the set of modes comprising the reference LTO cycle. 7.2.4    While the methodology described above is the recommended method, the certificating authority may accept equivalent mathematical procedures which utilize mathematical expressions representing the curves illustrated if the expression have been derived using an accepted curve fitting technique. 7.3    Exceptions to the proposed procedures In those cases where the configuration of the engine or other extenuating conditions exist which would prohibit the use of this procedure, the certificating authority, after receiving satisfactory technical evidence of equivalent results obtained by an alternative procedure, may approve an alternative procedure.
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