Commission Delegated Regulation (EU) 2017/654 of 19 December 2016 supplementing Regulation (EU) 2016/1628 of the European Parliament and of the Council with regard to technical and general requirements relating to emission limits and type-approval for internal combustion engines for non-road mobile machinery

• (a) The propane check shall be performed as follows:
• (i) For batch HC sampling, clean storage media, such as evacuated bags shall be connected;
• (ii) HC measurement instruments shall be operated according to the instrument manufacturer's instructions;
• (iii) If correction for dilution air background concentrations of HC is foreseen, background HC in the dilution air shall be measured and recorded;
• (iv) Any integrating devices shall be zeroed;
• (v) Sampling shall begin and any flow integrators shall be started;
• (vi) C3H8 shall be released at the rate selected. If a reference flow rate of C3H8 is used, the integration of this flow rate shall be started;
• (vii) C3H8 shall be continued to be released until at least enough C3H8 has been released to ensure accurate quantification of the reference C3H8 and the measured C3H8;
• (viii) The C3H8 cylinder shall be shut off and sampling shall continue until it has been accounted for time delays due to sample transport and analyzer response;
• (ix) Sampling shall be stopped and any integrators shall be stopped;

• (b) In case the metering with a critical flow orifice is used, the following procedure may be used for the propane check as the alternative method of point 8.1.8.5.5(a);
• (i) For batch HC sampling, clean storage media, such as evacuated bags shall be connected;
• (ii) HC measurement instruments shall be operated according to the instrument manufacturer's instructions;
• (iii) If correction for dilution air background concentrations of HC is foreseen, background HC in the dilution air shall be measured and recorded;
• (iv) Any integrating devices shall be zeroed;
• (v) The contents of the C3H8 reference cylinder shall be released at the rate selected;
• (vi) Sampling shall begin, and any flow integrators started after confirming that HC concentration is to be stable;
• (vii) The cylinder's contents shall be continued to be released until at least enough C3H8 has been released to ensure accurate quantification of the reference C3H8 and the measured C3H8;
• (viii) Any integrators shall be stopped;
• (ix) The C3H8 reference cylinder shall be shut off.

8.1.8.5.6.   Evaluation of the propane check

Post-test procedure shall be performed as follows:

• (a) If batch sampling has been used, batch samples shall be analyzed as soon as practical;

• (b) After analyzing HC, contamination and background shall be corrected for;

• (c) Total C3H8 mass based on the CVS and HC data shall be calculated as described in Annex VII, using the molar mass of C3H8, M C3H8, instead of the effective molar mass of HC, M HC;

• (d) If a reference mass (gravimetric technique) is used, the cylinder's propane mass shall be determined within ± 0,5 % and the C3H8 reference mass shall be determined by subtracting the empty cylinder propane mass from the full cylinder propane mass. If a critical flow orifice (metering with a critical flow orifice) is used, the propane mass shall be determined as flow rate multiplied by the test time;

• (e) The reference C3H8 mass shall be subtracted from the calculated mass. If this difference is within ± 3,0 % of the reference mass, the CVS passes this verification.

8.1.8.5.7.   PM secondary dilution system verification

When the propane check is to be repeated to verify the PM secondary dilution system, the following procedure from (a) to (d) shall be used for this verification:

• (a) The HC sampling system shall be configured to extract a sample near the location of the batch sampler's storage media (such as a PM filter). If the absolute pressure at this location is too low to extract an HC sample, HC may be sampled from the batch sampler pump's exhaust. Caution shall be used when sampling from pump's exhaust because an otherwise acceptable pump leak downstream of a batch sampler flow meter will cause a false failure of the propane check;

• (b) The propane check shall be repeated as described in this point, but HC shall be sampled from the batch sampler;

• (c) C3H8 mass shall be calculated, taking into account any secondary dilution from the batch sampler;

• (d) The reference C3H8 mass shall be subtracted from the calculated mass. If this difference is within ± 5 % of the reference mass, the batch sampler passes this verification. If not, corrective action shall be taken.

8.1.8.6.   Periodic calibration of the partial flow PM and associated raw exhaust gas measurement systems

8.1.8.6.1.   Specifications for differential flow measurement

For partial flow dilution systems to extract a proportional raw exhaust gas sample, the accuracy of the sample flow qm p is of special concern, if not measured directly, but determined by differential flow measurement as set out in equation (6-20):

qm p = qm dew – qm dw	(6-20)

Where:

• qm p is the sample mass flow rate of exhaust gas into partial flow dilution system

• qm dw is the dilution air mass flow rate (on wet basis)

• qm dew is the diluted exhaust gas mass flow rate on wet basis

In this case, the maximum error of the difference shall be such that the accuracy of qm p is within ± 5 % when the dilution ratio is less than 15. It can be calculated by taking root-mean-square of the errors of each instrument.

Acceptable accuracies of q mp can be obtained by either of the following methods:

• (a) The absolute accuracies of qm dew and qm dw are ± 0,2 % which guarantees an accuracy of qm p of ≤ 5 % at a dilution ratio of 15. However, greater errors will occur at higher dilution ratios;

• (b) Calibration of qm dw relative to qm dew is carried out such that the same accuracies for qm p as in (a) are obtained. For details see point 8.1.8.6.2;

• (c) The accuracy of q mp is determined indirectly from the accuracy of the dilution ratio as determined by a tracer gas, e.g. CO2. Accuracies equivalent to method (a) for q mp are required;

• (d) The absolute accuracy of qm dew and qm dw is within ± 2 % of full scale, the maximum error of the difference between qm dew and qm dw is within 0,2 % and the linearity error is within ± 0,2 % of the highest qm dew observed during the test.

8.1.8.6.2.   Calibration of differential flow measurement

The partial flow dilution system to extract a proportional raw exhaust gas sample shall be periodically calibrated with an accurate flow meter traceable to international and/or national standards. The flow meter or the flow measurement instrumentation shall be calibrated in one of the following procedures, such that the probe flow qm p into the tunnel shall fulfil the accuracy requirements of point 8.1.8.6.1.

• (a) The flow meter for qm dw shall be connected in series to the flow meter for qm dew, the difference between the two flow meters shall be calibrated for at least 5 set points with flow values equally spaced between the lowest qm dw value used during the test and the value of qm dew used during the test. The dilution tunnel may be bypassed;

• (b) A calibrated flow device shall be connected in series to the flowmeter for qm dew and the accuracy shall be checked for the value used for the test. The calibrated flow device shall be connected in series to the flow meter for qm dw, and the accuracy shall be checked for at least 5 settings corresponding to dilution ratio between 3 and 15, relative to qm dew used during the test;

• (c) The transfer line TL (see Figure 6.7) shall be disconnected from the exhaust system and a calibrated flow measuring device with a suitable range to measure qm p shall be connected to the transfer line. qm dew shall be set to the value used during the test, and qm dw shall be sequentially set to at least 5 values corresponding to dilution ratios between 3 and 15. Alternatively, a special calibration flow path may be provided, in which the tunnel is bypassed, but the total and dilution air flow is passed through the corresponding meters as in the actual test;

• (d) A tracer gas, shall be fed into the exhaust system transfer line TL. This tracer gas may be a component of the exhaust gas, like CO2 or NOx. After dilution in the tunnel the tracer gas component shall be measured. This shall be carried out for 5 dilution ratios between 3 and 15. The accuracy of the sample flow shall be determined from the dilution ratio r d by means of equation (6-21): qm p = qm dew / r d (6-21)

The accuracies of the gas analyzers shall be taken into account to guarantee the accuracy of qm p.

8.1.8.6.3.   Special requirements for differential flow measurement

A carbon flow check using actual exhaust gas is strongly recommended for detecting measurement and control problems and verifying the proper operation of the partial flow system. The carbon flow check should be run at least each time a new engine is installed, or something significant is changed in the test cell configuration.

The engine shall be operated at peak torque load and speed or any other steady state mode that produces 5 % or more of CO2. The partial flow sampling system shall be operated with a dilution factor of about 15 to 1.

If a carbon flow check is conducted, Appendix 2 of Annex VII shall be applied. The carbon flow rates shall be calculated according to equations of Appendix 2 of Annex VII. All carbon flow rates shall agree to within 5 %.

8.1.8.6.3.1.   Pre-test check

A pre-test check shall be performed within 2 hours before the test run in the following way.

The accuracy of the flow meters shall be checked by the same method as used for calibration (see point 8.1.8.6.2) for at least two points, including flow values of qm dw that correspond to dilution ratios between 5 and 15 for the qm dew value used during the test.

If it can be demonstrated by records of the calibration procedure under point 8.1.8.6.2 that the flow meter calibration is stable over a longer period of time, the pre-test check may be omitted.

8.1.8.6.3.2.   Determination of the transformation time

The system settings for the transformation time evaluation shall be the same as during measurement of the test run. The transformation time, as defined in point 2.4 of Appendix 5 to this Annex and in figure 6-11, shall be determined by the following method:

An independent reference flowmeter with a measurement range appropriate for the probe flow shall be put in series with and closely coupled to the probe. This flowmeter shall have a transformation time of less than 100 ms for the flow step size used in the response time measurement, with flow pressure restriction sufficiently low as to not affect the dynamic performance of the partial flow dilution system according to good engineering judgment. A step change shall be introduced to the exhaust gas flow (or air flow if exhaust gas flow is calculated) input of the partial flow dilution system, from a low flow to at least 90 % of full scale. The trigger for the step change shall be the same one used to start the look-ahead control in actual testing. The exhaust gas flow step stimulus and the flowmeter response shall be recorded at a sample rate of at least 10 Hz.

From this data, the transformation time shall be determined for the partial flow dilution system, which is the time from the initiation of the step stimulus to the 50 % point of the flowmeter response. In a similar manner, the transformation times of the qmp signal (i.e. sample flow of exhaust gas into partial flow dilution system) and of the qmew,i signal (i.e. the exhaust gas mass flow rate on wet basis supplied by the exhaust flow meter) shall be determined. These signals are used in the regression checks performed after each test (see point 8.2.1.2).

The calculation shall be repeated for at least 5 rise and fall stimuli, and the results shall be averaged. The internal transformation time (< 100 ms) of the reference flowmeter shall be subtracted from this value. Where look-ahead control is required, the look-ahead value of the partial flow dilution system shall be applied in accordance with point 8.2.1.2.

8.1.8.7.   Vacuum-side leak verification

8.1.8.7.1.   Scope and frequency

Upon initial sampling system installation, after major maintenance such as pre-filter changes, and within 8 hours prior to each duty-cycle sequence, it shall be verified that there are no significant vacuum-side leaks using one of the leak tests described in this section. This verification does not apply to any full-flow portion of a CVS dilution system.

8.1.8.7.2.   Measurement principles

A leak may be detected either by measuring a small amount of flow when there shall be zero flow, by detecting the dilution of a known concentration of span gas when it flows through the vacuum side of a sampling system or by measuring the pressure increase of an evacuated system.

8.1.8.7.3.   Low-flow leak test

A sampling system shall be tested for low-flow leaks as follows:

• (a) The probe end of the system shall be sealed by taking one of the following steps:
• (i) The end of the sample probe shall be capped or plugged;
• (ii) The transfer line shall be disconnected at the probe and the transfer line capped or plugged;
• (iii) A leak-tight valve in-line between a probe and transfer line shall be closed;

• (b) All vacuum pumps shall be operated. After stabilizing, it shall be verified that the flow through the vacuum-side of the sampling system is less than 0,5 % of the system's normal in-use flow rate. Typical analyzer and bypass flows may be estimated as an approximation of the system's normal in-use flow rate.

8.1.8.7.4.   Dilution-of-span-gas leak test

Any gas analyzer may be used for this test. If a FID is used for this test, any HC contamination in the sampling system shall be corrected in accordance with sections 2 or 3 of Annex VII on HC determination. Misleading results shall be avoided by using only analyzers that have a repeatability of 0,5 % or better at the span gas concentration used for this test. The vacuum side leak check shall be performed as follows:

• (a) A gas analyzer shall be prepared as it would be for emission testing;

• (b) Span gas shall be supplied to the analyzer port and it shall be verified that the span gas concentration is measured within its expected measurement accuracy and repeatability;

• (c) Overflow span gas shall be routed to one of the following locations in the sampling system:
• (i) The end of the sample probe;
• (ii) The transfer line shall be disconnected at the probe connection, and the span gas overflown at the open end of the transfer line;
• (iii) A three-way valve installed in-line between a probe and its transfer line;

• (d) It shall be verified that the measured overflow span gas concentration is within ± 0,5 % of the span gas concentration. A measured value lower than expected indicates a leak, but a value higher than expected may indicate a problem with the span gas or the analyzer itself. A measured value higher than expected does not indicate a leak.

8.1.8.7.5.   Vacuum-decay leak test

To perform this test a vacuum shall be applied to the vacuum-side volume of the sampling system and the leak rate of the system shall be observed as a decay in the applied vacuum. To perform this test the vacuum-side volume of the sampling system shall be known to within ± 10 % of its true volume. For this test measurement instruments that meet the specifications of points 8.1 and 9.4 shall also be used.

A vacuum-decay leak test shall be performed as follows:

• (a) The probe end of the system shall be sealed as close to the probe opening as possible by taking one of the following steps:
• (i) The end of the sample probe shall be capped or plugged;
• (ii) The transfer line at the probe shall be disconnected and the transfer line capped or plugged;
• (iii) A leak-tight valve in-line between a probe and transfer line shall be closed;

- (b) All vacuum pumps shall be operated. A vacuum shall be drawn that is representative of normal operating conditions. In the case of sample bags, it is recommend that the normal sample bag pump-down procedure be repeated twice to minimize any trapped volumes;

• (c) The sample pumps shall be turned off and the system sealed. The absolute pressure of the trapped gas and optionally the system absolute temperature shall be measured and recorded. Sufficient time shall be allowed for any transients to settle and long enough for a leak at 0,5 % to have caused a pressure change of at least 10 times the resolution of the pressure transducer. The pressure and optionally temperature shall be recorded once again;

• (d) The leak flow rate based on an assumed value of zero for pumped-down bag volumes and based on known values for the sample system volume, the initial and final pressures, optional temperatures, and elapsed time shall be calculated. It shall be verified that the vacuum-decay leak flow rate is less than 0,5 % of the system's normal in-use flow rate by means of equation (6-22): Image omitted; see official source (6-22) Where: qV leak is the vacuum-decay leak rate, mol/s V vac is the geometric volume of the vacuum-side of the sampling system, m³ R is the molar gas constant, J/(mol · K) p 2 is the vacuum-side absolute pressure at time t 2, Pa T 2 is the vacuum-side absolute temperature at time t 2, K p 1 is the vacuum-side absolute pressure at time t 1, Pa T 1 is the vacuum-side absolute temperature at time t 1, K t 2 is the time at completion of vacuum-decay leak verification test, s t 1 is the time at start of vacuum-decay leak verification test, s

8.1.9.   CO and CO2 measurements

8.1.9.1.   H2O interference verification for CO2 NDIR analyzers

8.1.9.1.1.   Scope and frequency

If CO2 is measured using an NDIR analyzer, the amount of H2O interference shall be verified after initial analyzer installation and after major maintenance.

8.1.9.1.2.   Measurement principles

H2O can interfere with an NDIR analyzer's response to CO2. If the NDIR analyzer uses compensation algorithms that utilize measurements of other gases to meet this interference verification, these other measurements shall be conducted simultaneously to test the compensation algorithms during the analyzer interference verification.

8.1.9.1.3.   System requirements

A CO2 NDIR analyzer shall have an H2O interference that is within (0,0 ± 0,4) mmol/mol (of the expected mean CO2 concentration).

8.1.9.1.4.   Procedure

The interference verification shall be performed as follows:

• (a) The CO2 NDIR analyzer shall be started, operated, zeroed, and spanned as it would be before an emission test;

• (b) A humidified test gas shall be created by bubbling zero air that meets the specifications set out in point 9.5.1 through distilled water in a sealed vessel. If the sample is not passed through a dryer, control the vessel temperature to generate an H2O content in the test gas at least as high as the maximum expected during testing. If the sample is passed through a dryer during testing, control the vessel temperature to generate an H2O content in the test gas at least as high as the maximum expected at the outlet of the dryer, in accordance with point 9.3.2.3.1.1;

• (c) The humidified test gas temperature shall be maintained at least 5 ^oK above its dew point downstream of the vessel;

• (d) The humidified test gas shall be introduced into the sampling system. The humidified test gas may be introduced downstream of any sample dryer, if one is used during testing;

• (e) The water mole fraction, x H2O, of the humidified test gas shall be measured, as close as possible to the inlet of the analyzer. For example, dew point, T dew, and absolute pressure p total, shall be measured to calculate x H2O;

• (f) Good engineering judgment shall be used to prevent condensation in the transfer lines, fittings, or valves from the point where x H2O is measured to the analyzer;

• (g) Time shall be allowed for the analyzer response to stabilize. Stabilization time shall include time to purge the transfer line and to account for analyzer response;

• (h) While the analyzer measures the sample's concentration, 30 s of sampled data shall be recorded. The arithmetic mean of this data shall be calculated. The analyzer meets the interference verification if this value is within (0,0 ± 0,4) mmol/mol.

8.1.9.2.   H2O and CO2 interference verification for CO NDIR analyzers

8.1.9.2.1.   Scope and frequency

If CO is measured using an NDIR analyzer, the amount of H2O and CO2 interference shall be verified after initial analyzer installation and after major maintenance.

8.1.9.2.2.   Measurement principles

H2O and CO2 can positively interfere with an NDIR analyzer by causing a response similar to CO. If the NDIR analyzer uses compensation algorithms that utilize measurements of other gases to meet this interference verification, simultaneously these other measurements shall be conducted to test the compensation algorithms during the analyzer interference verification.

8.1.9.2.3.   System requirements

A CO NDIR analyzer shall have combined H2O and CO2 interference that is within ± 2 % of the expected mean concentration of CO.

8.1.9.2.4.   Procedure

The interference verification shall be performed as follows:

• (a) The CO NDIR analyzer shall be started, operated, zeroed, and spanned as it would be before an emission test;

• (b) A humidified CO2 test gas shall be created by bubbling a CO2 span gas through distilled water in a sealed vessel. If the sample is not passed through a dryer, the vessel temperature shall be controlled to generate an H2O content in the test gas at least as high as the maximum expected during testing. If the sample is passed through a dryer during testing, the vessel temperature shall be controlled to generate an H2O content in the test gas at least as high as the maximum expected at the outlet of the dryer, in accordance with point 9.3.2.3.1.1. A CO2 span gas concentration shall be used at least as high as the maximum expected during testing;

• (c) The humidified CO2 test gas shall be introduced into the sampling system. The humidified CO2 test gas may be introduced downstream of any sample dryer, if one is used during testing;

• (d) The water mole fraction, x H2O, of the humidified test gas shall be measured, as close as possible to the inlet of the analyzer. For example, dew point, T dew, and absolute pressure p total, shall be measured to calculate x H2O;

• (e) Good engineering judgment shall be used to prevent condensation in the transfer lines, fittings, or valves from the point where x H2O is measured to the analyzer;

• (f) Time shall be allowed for the analyzer response to stabilize;

- (g) While the analyzer measures the sample's concentration, its output shall be recorded for 30 s. The arithmetic mean of this data shall be calculated;

• (h) The analyzer meets the interference verification if the result of paragraph (g) of this point meets the tolerance in point 8.1.9.2.3;

• (i) Interference procedures for CO2 and H2O may be also run separately. If the CO2 and H2O levels used are higher than the maximum levels expected during testing, each observed interference value shall be scaled down by multiplying the observed interference by the ratio of the maximum expected concentration value to the actual value used during this procedure. Separate interference procedures concentrations of H2O (down to 0,025 mol/mol H2O content) that are lower than the maximum levels expected during testing may be run, but the observed H2O interference shall be scaled up by multiplying the observed interference by the ratio of the maximum expected H2O concentration value to the actual value used during this procedure. The sum of the two scaled interference values shall meet the tolerance in point 8.1.9.2.3.

8.1.10.   Hydrocarbon measurements

8.1.10.1.   FID optimization and verification

8.1.10.1.1.   Scope and frequency

For all FID analyzers, the FID shall be calibrated upon initial installation. The calibration shall be repeated as needed using good engineering judgment. The following steps shall be performed for a FID that measures HC:

• (a) A FID's response to various hydrocarbons shall be optimized after initial analyzer installation and after major maintenance. FID response to propylene and toluene shall be between 0,9 and 1,1 relative to propane;

• (b) A FID's methane (CH4) response factor shall be determined after initial analyzer installation and after major maintenance as described in point 8.1.10.1.4;

• (c) Methane (CH4) response shall be verified within 185 days before testing.

8.1.10.1.2.   Calibration

Good engineering judgment shall be used to develop a calibration procedure, such as one based on the FID-analyzer manufacturer's instructions and recommended frequency for calibrating the FID. The FID shall be calibrated using C3H8 calibration gases that meet the specifications of point 9.5.1. It shall be calibrated on a carbon number basis of one (C1).

8.1.10.1.3.   HC FID response optimization

This procedure is only for FID analyzers that measure HC.

• (a) Instrument manufacturer requirements and good engineering judgment shall be used for initial instrument start-up and basic operating adjustment using FID fuel and zero air. Heated FIDs shall be within their required operating temperature ranges. FID response shall be optimized to meet the requirement of the hydrocarbon response factors and the oxygen interference check according to points 8.1.10.1.1(a) and 8.1.10.2 at the most common analyzer range expected during emission testing. Higher analyzer range may be used according to the instrument manufacturer's recommendation and good engineering judgment in order to optimize FID accurately, if the common analyzer range is lower than the minimum range for the optimization specified by the instrument manufacturer;

• (b) Heated FIDs shall be within their required operating temperature ranges. FID response shall be optimized at the most common analyzer range expected during emission testing.  With the FID fuel and airflow rates set at the manufacturer's recommendations, a span gas shall be introduced to the analyzer;

• (c) The following steps from (i) to (iv) or the procedure instructed by the instrument manufacturer shall be taken for optimization. The procedures outlined in SAE paper No 770141 may be optionally used for optimization;
• (i) The response at a given FID fuel flow shall be determined from the difference between the span gas response and the zero gas response;
• (ii) The fuel flow shall be incrementally adjusted above and below the manufacturer's specification.  The span and zero response at these FID fuel flows shall be recorded;
• (iii) The difference between the span and zero response shall be plotted and the fuel flow adjusted to the rich side of the curve. This is the initial flow rate setting which may need further optimization depending on the results of the hydrocarbon response factors and the oxygen interference check according to points 8.1.10.1.1(a) and 8.1.10.2;
• (iv) If the oxygen interference or the hydrocarbon response factors do not meet the following specifications, the airflow shall be incrementally adjusted above and below the manufacturer's specifications, repeating points 8.1.10.1.1(a) and 8.1.10.2 for each flow;

• (d) The optimum flow rates and/or pressures for FID fuel and burner air shall be determined, and they shall be sampled and recorded for future reference.

8.1.10.1.4.   HC FID CH4 response factor determination

Since FID analyzers generally have a different response to CH4 versus C3H8, each HC FID analyzer's CH4 response factor, RF CH4[THC-FID] shall be determined, after FID optimization. The most recent RF CH4[THC-FID] measured in accordance with this section shall be used in the calculations for HC determination described in section 2 of Annex VII (mass based approach) or section 3 of Annex VII (molar based approach) to compensate for CH4 response. RF CH4[THC-FID] shall be determined as follows:

• (a) A C3H8 span gas concentration shall be selected to span the analyzer before emission testing. Only span gases that meet the specifications of point 9.5.1 shall be selected and the C3H8 concentration of the gas shall be recorded;

• (b) A CH4 span gas that meets the specifications of point 9.5.1 shall be selected and the CH4 concentration of the gas shall be recorded,

• (c) The FID analyzer shall be operated according to the manufacturer's instructions;

• (d) It shall be confirmed that the FID analyzer has been calibrated using C3H8. Calibration shall be performed on a carbon number basis of one (C1);

• (e) The FID shall be zeroed with a zero gas used for emission testing;

• (f) The FID shall be spanned with the selected C3H8 span gas;

• (g) The CH4 span gas selected in accordance with paragraph (b) shall be introduced at the sample port of the FID analyzer;

• (h) The analyzer response shall be stabilized. Stabilization time may include time to purge the analyzer and to account for its response;

• (i) While the analyzer measures the CH4 concentration, 30 s of sampled data shall be recorded and the arithmetic mean of these values shall be calculated;

• (j) The mean measured concentration shall be divided by the recorded span concentration of the CH4 calibration gas. The result is the FID analyzer's response factor for CH4, RF CH4[THC-FID].

8.1.10.1.5.   HC FID methane (CH4) response verification

If the value of RF CH4[THC-FID] obtained in accordance with point 8.1.10.1.4 is within ± 5,0 % of its most recent previously determined value, the HC FID passes the methane response verification.

• (a) It shall be first verified that the pressures and / or flow rates of FID fuel, burner air, and sample are each within ± 0,5 % of their most recent previously recorded values, as described in point 8.1.10.1.3. If these flow rates have to be adjusted, a new RF CH4[THC-FID] shall be determined as described in point 8.1.10.1.4. It should be verified that the value of RF CH4[THC-FID] determined is within the tolerance specified in this point 8.1.10.1.5;

• (b) If RF CH4[THC-FID] is not within the tolerance specified in this point 8.1.10.1.5, the FID response shall be re-optimized as described in point 8.1.10.1.3;

• (c) A new RF CH4[THC-FID] shall be determined as described in point 8.1.10.1.4. This new value of RF CH4[THC-FID] shall be used in the calculations for HC determination, in section 2 of Annex VII (mass based approach) or section 3 of Annex VII (molar based approach).

8.1.10.2.   Non-stoichiometric raw exhaust gas FID O2 interference verification

8.1.10.2.1.   Scope and frequency

If FID analyzers are used for raw exhaust gas measurements, the amount of FID O2 interference shall be verified upon initial installation and after major maintenance.

8.1.10.2.2.   Measurement principles

Changes in O2 concentration in raw exhaust gas can affect FID response by changing FID flame temperature. FID fuel, burner air, and sample flow shall be optimized to meet this verification. FID performance shall be verified with the compensation algorithms for FID O2 interference that is active during an emission test.

8.1.10.2.3.   System requirements

Any FID analyzer used during testing shall meet the FID O2 interference verification according to the procedure in this section.

8.1.10.2.4.   Procedure

FID O2 interference shall be determined as follows, noting that one or more gas dividers may be used to create reference gas concentrations that are required to perform this verification:

• (a) Three span reference gases that meet the specifications set out in point 9.5.1 and contain C3H8 concentration shall be selected to span the analyzers before emissions testing.  ————— The three balance gas concentrations shall be selected such that the concentrations of O2 and N2 represent the minimum and maximum and intermediate O2 concentrations expected during testing. The requirement for using the average O2 concentration can be removed if the FID is calibrated with span gas balanced with the average expected oxygen concentration;

• (b) It shall be confirmed that the FID analyzer meets all the specifications of point 8.1.10.1;

• (c) The FID analyzer shall be started and operated as it would be before an emission test. Regardless of the FID burner's air source during testing, zero air shall be used as the FID burner's air source for this verification;

• (d) The analyzer shall be set at zero;

• (e) The analyzer shall be spanned using a span gas that is used during emissions testing;

• (f) The zero response shall be checked by using the zero gas used during emission testing. It shall be proceeded to the next step if the mean zero response of 30 s of sampled data is within ± 0,5 % of the span reference value used in paragraph (e) of this point, otherwise the procedure shall be restarted at paragraph (d) of this point;

• (g) The analyzer response shall be checked using the span gas that has the minimum concentration of O2 expected during testing. The mean response of 30 s of stabilized sample data shall be recorded as x O2minHC;

• (h) The zero response of the FID analyzer shall be checked using the zero gas used during emission testing. The next step shall be performed if the mean zero response of 30 s of stabilized sample data is within ± 0,5 % of the span reference value used in paragraph (e) of this point, otherwise the procedure shall be restarted at paragraph (d) of this point;

• (i) The analyzer response shall be checked using the span gas that has the average concentration of O2 expected during testing. The mean response of 30 s of stabilized sample data shall be recorded as x O2avgHC;

• (j) The zero response of the FID analyzer shall be checked using the zero gas used during emission testing. The next step shall be performed if the mean zero response of 30 s of stabilized sample data is within ± 0,5 % of the span reference value used in paragraph (e) of this point, otherwise the procedure shall be restarted at paragraph (d) of this point;

• (k) The analyzer response shall be checked using the span gas that has the maximum concentration of O2 expected during testing. The mean response of 30 s of stabilized sample data shall be recorded as x O2maxHC;

• (l) The zero response of the FID analyzer shall be checked using the zero gas used during emission testing. The next step shall be performed if the mean zero response of 30 s of stabilized sample data is within ± 0,5 % of the span reference value used in paragraph (e) of this point, otherwise the procedure shall be restarted at paragraph (d) of this point;

- (m) The % difference between x

O2maxHC and its reference gas concentration shall be calculated. The percent difference between x O2avgHC and its reference gas concentration shall be calculated. The % difference between x O2minHC and its reference gas concentration shall be calculated. The maximum % difference of the three shall be determined. This is the O2 interference;

• (n) If the O2 interference is within ± 3 %, the FID passes the O2 interference verification; otherwise one or more of the following need to be performed to address the deficiency:
• (i) The verification shall be repeated to determine if a mistake was made during the procedure;
• (ii) The zero and span gases for emission testing shall be selected that contain higher or lower O2 concentrations and the verification shall be repeated;
• (iii) The FID burner air, fuel, and sample flow rates shall be adjusted. Note that if these flow rates are adjusted on a THC FID to meet the O2 interference verification, the RF CH4 shall be reset for the next RF CH4 verification. The O2 interference verification shall be repeated after adjustment and RF CH4 shall be determined;
• (iv) The FID shall be repaired or replaced and the O2 interference verification shall be repeated.

8.1.10.3.   Non-methane cutter penetration fractions (Reserved)

8.1.11.   NOx measurements

8.1.11.1.   CLD CO2 and H2O quench verification

8.1.11.1.1.   Scope and frequency

If a CLD analyzer is used to measure NOx, the amount of H2O and CO2 quench shall be verified after installing the CLD analyzer and after major maintenance.

8.1.11.1.2.   Measurement principles

H2O and CO2 can negatively interfere with a CLD's NOx response by collisional quenching, which inhibits the chemiluminescent reaction that a CLD utilizes to detect NOx. This procedure and the calculations in point 8.1.11.2.3 determine quench and scale the quench results to the maximum mole fraction of H2O and the maximum CO2 concentration expected during emission testing. If the CLD analyzer uses quench compensation algorithms that utilize H2O and/or CO2 measurement instruments, quench shall be evaluated with these instruments active and with the compensation algorithms applied.

8.1.11.1.3.   System requirements

For dilute measurement a CLD analyzer shall not exceed a combined H2O and CO2 quench of ± 2 %. For raw measurement a CLD analyzer shall not exceed a combined H2O and CO2 quench of ± 2,5 %. Combined quench is the sum of the CO2 quench determined as described in point 8.1.11.1.4 and the H2O quench as determined in point 8.1.11.1.5. If these requirements are not met, corrective action shall be taken by repairing or replacing the analyzer. Before running emission tests, it shall be verified that the corrective action have successfully restored the analyzer to proper functioning.

8.1.11.1.4.   CO2 quench verification procedure

The following method or the method prescribed by the instrument manufacturer may be used to determine CO2 quench by using a gas divider that blends binary span gases with zero gas as the diluent and meets the specifications in point 9.4.5.6, or good engineering judgment shall be used to develop a different protocol:

• (a) PTFE or stainless steel tubing shall be used to make necessary connections;

• (b) The gas divider shall be configured such that nearly equal amounts of the span and diluent gases are blended with each other;

• (c) If the CLD analyzer has an operating mode in which it detects NO-only, as opposed to total NOx, the CLD analyzer shall be operated in the NO-only operating mode;

• (d) A CO2 span gas that meets the specifications of point 9.5.1 and a concentration that is approximately twice the maximum CO2 concentration expected during emission testing shall be used;

• (e) An NO span gas that meets the specifications of point 9.5.1 and a concentration that is approximately twice the maximum NO concentration expected during emission testing shall be used. Higher concentration may be used according to the instrument manufacturer's recommendation and good engineering judgement in order to obtain accurate verification, if the expected NO concentration is lower than the minimum range for the verification specified by the instrument manufacturer;

• (f) The CLD analyzer shall be zeroed and spanned. The CLD analyzer shall be spanned with the NO span gas from paragraph (e) of this point through the gas divider. The NO span gas shall be connected to the span port of the gas divider; a zero gas shall be connected to the diluent port of the gas divider; the same nominal blend ratio shall be used as selected in paragraph (b) of this point; and the gas divider's output concentration of NO shall be used to span the CLD analyzer. Gas property corrections shall be applied as necessary to ensure accurate gas division;

• (g) The CO2 span gas shall be connected to the span port of the gas divider;

• (h) The NO span gas shall be connected to the diluents port of the gas divider;

• (i) While flowing NO and CO2 through the gas divider, the output of the gas divider shall be stabilized. The CO2 concentration from the gas divider output shall be determined, applying gas property correction as necessary to ensure accurate gas division. This concentration, x CO2act, shall be recorded and it shall be used in the quench verification calculations in point 8.1.11.2.3. As an alternative to using a gas divider, another simple gas blending device may be used. In this case an analyzer shall be used to determine CO2 concentration. If a NDIR is used together with a simple gas blending device, it shall meet the requirements of this section and it shall be spanned with the CO2 span gas from paragraph (d) of this point. The linearity of the NDIR analyzer has to be checked before over the whole range up to twice of the expected maximum CO2 concentration expected during testing;

• (j) The NO concentration shall be measured downstream of the gas divider with the CLD analyzer. Time shall be allowed for the analyzer response to stabilize. Stabilization time may include time to purge the transfer line and to account for analyzer response. While the analyzer measures the sample's concentration, the analyzer's output shall be recorded for 30 seconds. The arithmetic mean concentration shall be calculated from these data, x NOmeas. x NOmeas shall be recorded and it shall be used in the quench verification calculations in point 8.1.11.2.3;

• (k) The actual NO concentration shall be calculated at the gas divider's outlet, x NOact, based on the span gas concentrations and x CO2act by means of equation (6-24). The calculated value shall be used in the quench verification calculations by means of equation (6-23);

• (l) The values recorded according to this points 8.1.11.1.4 and 8.1.11.1.5 shall be used to calculate quench as described in point 8.1.11.2.3.

8.1.11.1.5.   H2O quench verification procedure

The following method or the method prescribed by the instrument manufacturer may be used to determine H2O quench, or good engineering judgment shall be used to develop a different protocol:

• (a) PTFE or stainless steel tubing shall be used to make necessary connections;

• (b) If the CLD analyzer has an operating mode in which it detects NO-only, as opposed to total NOx, the CLD analyzer shall be operated in the NO-only operating mode;

• (c) A NO span gas shall be used that meets the specifications of point 9.5.1 and a concentration that is near the maximum concentration expected during emission testing. Higher concentration may be used according to the instrument manufacturer's recommendation and good engineering judgement in order to obtain accurate verification, if the expected NO concentration is lower than the minimum range for the verification specified by the instrument manufacturer;

• (d) The CLD analyzer shall be zeroed and spanned. The CLD analyzer shall be spanned with the NO span gas from paragraph (c) of this point, the span gas concentration shall be recorded as x NOdry, and it shall be used in the quench verification calculations in point 8.1.11.2.3;

• (e) The NO span gas shall be humidified by bubbling it through distilled water in a sealed vessel. If the humidified NO span gas sample does not pass through a sample dryer for this verification test, the vessel temperature shall be controlled to generate an H2O content in the span gas approximately equal to the maximum mole fraction of H2O expected during emission testing. If the humidified NO span gas sample does not pass through a sample dryer, the quench verification calculations in point 8.1.11.2.3 scale the measured H2O quench to the highest mole fraction of H2O expected during emission testing. If the humidified NO span gas sample passes through a dryer for this verification test, the vessel temperature shall be controlled to generate an H2O content in the span gas at least as high as the maximum expected at the outlet of the dryer in accordance with point 9.3.2.3.1.1. In this case, the quench verification calculations set out in point 8.1.11.2.3 do not scale the measured H2O quench;

• (f) The humidified NO test gas shall be introduced into the sample system. It may be introduced upstream or downstream of a sample dryer that is used during emission testing. Depending on the point of introduction, the respective calculation method of paragraph (e) of this point shall be selected.  Note that the sample dryer shall meet the sample dryer verification check in point 8.1.12;

• (g) The mole fraction of H2O in the humidified NO span gas shall be measured. In case a sample dryer is used, the mole fraction of H2O in the humidified NO span gas shall be measured downstream of the sample dryer, x H2Omeas. It is recommended to measure x H2Omeas as close as possible to the CLD analyzer inlet. x H2Omeas may be calculated from measurements of dew point, T dew, and absolute pressure, p total;

• (h) Good engineering judgment shall be used to prevent condensation in the transfer lines, fittings, or valves from the point where x H2Omeas is measured to the analyzer. It is recommended that the system is designed so the wall temperatures in the transfer lines, fittings, and valves from the point where x H2Omeas is measured to the analyzer are at least 5 K above the local sample gas dew point;

• (i) The humidified NO span gas concentration shall be measured with the CLD analyzer. Time shall be allowed for the analyzer response to stabilize. Stabilization time may include time to purge the transfer line and to account for analyzer response. While the analyzer measures the sample's concentration, the analyzer's output shall be recorded for 30 seconds. The arithmetic mean shall be calculated of these data, x NOwet. x NOwet shall be recorded and used in the quench verification calculations in point 8.1.11.2.3.

8.1.11.2.   CLD quench verification calculations

CLD quench-check calculations shall be performed as described in this point.

8.1.11.2.1.   Amount of water expected during testing

The maximum expected mole fraction of water during emission testing, x H2Oexp shall be estimated. This estimate shall be made where the humidified NO span gas was introduced in point 8.1.11.1.5(f). When estimating the maximum expected mole fraction of water, the maximum expected water content in combustion air, fuel combustion products, and dilution air (if applicable) shall be considered. If the humidified NO span gas is introduced into the sample system upstream of a sample dryer during the verification test, it is not needed to estimate the maximum expected mole fraction of water and x H2Oexp shall be set equal to x H2Omeas.

8.1.11.2.2.   Amount of CO2 expected during testing

The maximum expected CO2 concentration during emission testing, x CO2exp shall be estimated. This estimate shall be made at the sample system location where the blended NO and CO2 span gases are introduced according to point 8.1.11.1.4(j). When estimating the maximum expected CO2 concentration, the maximum expected CO2 content in fuel combustion products and dilution air shall be considered.

8.1.11.2.3.   Combined H2O and CO2 quench calculations

Combined H2O and CO2 quench shall be calculated by means of equation (6-23):

Image omitted; see official source	(6-23)

Where:

• quench = amount of CLD quench

• x NOdry is the measured concentration of NO upstream of a bubbler, in accordance with point 8.1.11.1.5(d)

• x NOwet is the measured concentration of NO downstream of a bubbler, in accordance with point 8.1.11.1.5(i)

• x H2Oexp is the maximum expected mole fraction of water during emission testing in accordance with point 8.1.11.2.1.

• x H2Omeas is the measured mole fraction of water during the quench verification in accordance with point 8.1.11.1.5(g)

• x NOmeas is the measured concentration of NO when NO span gas is blended with CO2 span gas, in accordance with point 8.1.11.1.4(j)

• x NOact is the actual concentration of NO when NO span gas is blended with CO2 span gas, in accordance with point 8.1.11.1.4(k) and calculated by means of equation (6-24)

• x CO2exp is the maximum expected concentration of CO2 during emission testing, in accordance with point 8.1.11.2.2.

• x CO2act is the actual concentration of CO2 when NO span gas is blended with CO2 span gas, in accordance with point 8.1.11.1.4(i)

Image omitted; see official source	(6-24)

Where:

• x NOspan is the NO span gas concentration input to the gas divider, in accordance with point 8.1.11.1.4(e)

• x CO2span is the CO2 span gas concentration input to the gas divider, in accordance with point 8.1.11.1.4(d)

8.1.11.3.   NDUV analyzer HC and H2O interference verification

8.1.11.3.1.   Scope and frequency

If NOx is measured using an NDUV analyzer, the amount of H2O and hydrocarbon interference shall be verified after initial analyzer installation and after major maintenance.

8.1.11.3.2.   Measurement principles

Hydrocarbons and H2O can positively interfere with a NDUV analyzer by causing a response similar to NOx. If the NDUV analyzer uses compensation algorithms that utilize measurements of other gases to meet this interference verification, simultaneously such measurements shall be conducted to test the algorithms during the analyzer interference verification.

8.1.11.3.3.   System requirements

A NOx NDUV analyzer shall have combined H2O and HC interference within ± 2 % of the mean concentration of NOx.

8.1.11.3.4.   Procedure

The interference verification shall be performed as follows:

• (a) The NOx NDUV analyzer shall be started, operated, zeroed, and spanned according to the instrument manufacturer's instructions;

• (b) It is recommended to extract engine exhaust gas to perform this verification. A CLD shall be used that meets the specifications of point 9.4 to quantify NOx in the exhaust gas. The CLD response shall be used as the reference value. Also HC shall be measured in the exhaust gas with a FID analyzer that meets the specifications of point 9.4. The FID response shall be used as the reference hydrocarbon value;

• (c) Upstream of any sample dryer, if one is used during testing, the engine exhaust gas shall be introduced into the NDUV analyzer;

• (d) Time shall be allowed for the analyzer response to stabilize. Stabilization time may include time to purge the transfer line and to account for analyzer response;

• (e) While all analyzers measure the sample's concentration, 30 s of sampled data shall be recorded, and the arithmetic means for the three analyzers calculated;

• (f) The CLD mean shall be subtracted from the NDUV mean;

• (g) This difference shall be multiplied by the ratio of the expected mean HC concentration to the HC concentration measured during the verification. The analyzer meets the interference verification of this point if this result is within ± 2 % of the NOx concentration expected at the emission limit value, as set out in equation (6-25):

Image omitted; see official source	(6-25)

Where:

• Image omitted; see official source is the mean concentration of NOx measured by CLD [μmol/mol] or [ppm]

• Image omitted; see official source is the mean concentration of NOx measured by NDUV [μmol/mol] or [ppm]

• Image omitted; see official source is the mean concentration of HC measured [μmol/mol] or [ppm]

• Image omitted; see official source is the mean concentration of HC expected at the standard [μmol/mol] or [ppm]

• Image omitted; see official source is the mean concentration of NOx expected at the standard [μmol/mol] or [ppm]

8.1.11.4   Sample dryer NO2 penetration

8.1.11.4.1.   Scope and frequency

If a sample dryer is used to dry a sample upstream of a NOx measurement instrument, but no NO2-to-NO converter is used upstream of the sample dryer, this verification shall be performed for sample dryer NO2 penetration. This verification shall be performed after initial installation and after major maintenance.

8.1.11.4.2.   Measurement principles

A sample dryer removes water, which can otherwise interfere with a NOx measurement. However, liquid water remaining in an improperly designed  sample dryer can remove NO2 from the sample. If a sample dryer is used without an NO2-to-NO converter upstream, it could therefore remove NO2 from the sample prior NOx measurement.

8.1.11.4.3.   System requirements

The sample dryer shall allow for measuring at least 95 % of the total NO2 at the maximum expected concentration of NO2.

8.1.11.4.4.   Procedure

The following procedure shall be used to verify sample dryer performance:

• (a) Instrument setup. The analyzer and sample dryer manufacturers' start-up and operating instructions shall be followed. The analyzer and sample dryer shall be adjusted as needed to optimize performance;

• (b) Equipment setup and data collection.
• (i) The total NOx gas analyzer(s) shall be zeroed and spanned as it would be before emission testing;
• (ii) NO2 calibration gas (balance gas of dry air) that has an NO2 concentration that is near the maximum expected during testing shall be selected. Higher concentration may be used in accordance with the instrument manufacturer's recommendation and good engineering judgement in order to obtain accurate verification, if the expected NO2 concentration is lower than the minimum range for the verification specified by the instrument manufacturer;
• (iii) This calibration gas shall be overflowed at the gas sampling system's probe or overflow fitting. Time shall be allowed for stabilization of the total NOx response, accounting only for transport delays and instrument response;
• (iv) The mean of 30 s of recorded total NOx data shall be calculated and this value recorded as x NOxref;
• (v) The flowing the NO2 calibration gas shall be stopped;
• (vi) Next the sampling system shall be saturated by overflowing a dew point generator's output, set at a dew point of 323 K (50 °C), to the gas sampling system's probe or overflow fitting. The dew point generator's output shall be sampled through the sampling system and sample dryer for at least 10 minutes until the sample dryer is expected to be removing a constant rate of water;
• (vii) It shall be immediately switched back to overflowing the NO2 calibration gas used to establish x NOxref. It shall be allowed for stabilization of the total NOx response, accounting only for transport delays and instrument response. The mean of 30 s of recorded total NOx data shall be calculated and this value recorded as x NOxmeas;
• (viii) x NOxmeas shall be corrected to x NOxdry based upon the residual water vapour that passed through the sample dryer at the sample dryer's outlet temperature and pressure;

• (c) Performance evaluation. If xNOxdry is less than 95 % of xNOxref, the sample dryer shall be repaired or replaced.

8.1.11.5.   NO2-to-NO converter conversion verification

8.1.11.5.1.   Scope and frequency

If an analyzer is used that measures only NO to determine NOx, an NO2-to-NO converter shall be used upstream of the analyzer. This verification shall be performed after installing the converter, after major maintenance and within 35 days before an emission test. This verification shall be repeated at this frequency to verify that the catalytic activity of the NO2-to-NO converter has not deteriorated.

8.1.11.5.2.   Measurement principles

An NO2-to-NO converter allows an analyzer that measures only NO to determine total NOx by converting the NO2 in exhaust gas to NO.

8.1.11.5.3.   System requirements

An NO2-to-NO converter shall allow for measuring at least 95 % of the total NO2 at the maximum expected concentration of NO2.

8.1.11.5.4   Procedure

The following procedure shall be used to verify the performance of a NO2-to-NO converter:

• (a) For the instrument setup the analyzer and NO2-to-NO converter manufacturers' start-up and operating instructions shall be followed. The analyzer and converter shall be adjusted as needed to optimize performance;

• (b) An ozonator's inlet shall be connected to a zero-air or oxygen source and its outlet shall be connected to one port of a 3-way tee fitting. An NO span gas shall be connected to another port and the NO2-to-NO converter inlet shall be connected to the last port;

- (c) The following steps shall be taken when performing this check:

• (i) The ozonator air shall be set off and the ozonator power shall be turned off and the NO2-to-NO converter shall be set to the bypass mode (i.e., NO mode). Stabilization shall be allowed for, accounting only for transport delays and instrument response;
• (ii) The NO and zero-gas flows shall be adjusted so the NO concentration at the analyzer is near the peak total NOx concentration expected during testing. The NO2 content of the gas mixture shall be less than 5 % of the NO concentration. The concentration of NO shall be recorded by calculating the mean of 30 s of sampled data from the analyzer and this value shall be recorded as x NOref. Higher concentration may be used according to the instrument manufacturer's recommendation and good engineering judgement in order to obtain accurate verification, if the expected NO concentration is lower than the minimum range for the verification specified by the instrument manufacturer;
• (iii) The ozonator O2 supply shall be turned on and the O2 flow rate adjusted so that the NO indicated by the analyzer is about 10 percent less than x NOref. The concentration of NO shall be recorded by calculating the mean of 30 s of sampled data from the analyzer and this value recorded as x NO+O2mix;
• (iv) The ozonator shall be switched on and the ozone generation rate adjusted so that the NO measured by the analyzer is approximately 20 percent of x NOref, while maintaining at least 10 % unreacted NO. The concentration of NO shall be recorded by calculating the mean of 30 s of sampled data from the analyzer and this value shall be recorded as x NOmeas;
• (v) The NOx analyzer shall be switched to NOx mode and total NOx measured. The concentration of NOx shall be recorded by calculating the mean of 30 s of sampled data from the analyzer and this value shall be recorded as x NOxmeas;
• (vi) The ozonator shall be switched off but gas flow through the system shall be maintained. The NOx analyzer will indicate the NOx in the NO + O2 mixture. The concentration of NOx shall be recorded by calculating the mean of 30 s of sampled data from the analyzer and this value shall be recorded as x NOx+O2mix;
• (vii) O2 supply shall be turned off. The NOx analyzer will indicate the NOx in the original NO-in-N2 mixture. The concentration of NOx shall be recorded by calculating the mean of 30 s of sampled data from the analyzer and this value shall be recorded as x NOxref. This value shall be no more than 5 % above the x NOref value;

• (d) Performance evaluation. The efficiency of the NOx converter shall be calculated by substituting the concentrations obtained into equation (6-26): Image omitted; see official source (6-26)

• (e) If the result is less than 95 %, the NO2-to-NO converter shall be repaired or replaced.

8.1.12.   Sample dryer verification

If a humidity sensor for continuous monitoring of dew point at the sample dryer outlet is used this check does not apply, as long as it is ensured that the dryer outlet humidity is below the minimum values used for quench, interference, and compensation checks.

If a sample dryer is used as allowed in point 9.3.2.3.1 to remove water from the sample gas, the performance shall be verified upon installation, after major maintenance, for thermal chillers. For osmotic membrane dryers, the performance shall be verified upon installation, after major maintenance, and within 35 days of testing.

Water can inhibit an analyzer's ability to properly measure the exhaust component of interest and thus is sometimes removed before the sample gas reaches the analyzer. For example water can negatively interfere with a CLD's NOx response through collisional quenching and can positively interfere with an NDIR analyzer by causing a response similar to CO.

The sample dryer shall meet the specifications as determined in point 9.3.2.3.1 for dew point, T dew, and absolute pressure, p total, downstream of the osmotic-membrane dryer or thermal chiller.

The following sample dryer verification procedure method shall be used to determine sample dryer performance, or good engineering judgment shall be used to develop a different protocol:

• (i) polytetrafluoroethylene (‘PTFE’) or stainless steel tubing shall be used to make necessary connections;

• (ii) N2 or purified air shall be humidified by bubbling it through distilled water in a sealed vessel that humidifies the gas to the highest sample dew point that is estimated during emission sampling;

• (iii) The humidified gas shall be introduced upstream of the sample dryer;

• (iv) The humidified gas temperature downstream of the vessel shall be maintained at least 5 K (5 °C) above its dew point;

- (v) The humidified gas dew point, T

dew, and pressure, p total, shall be measured as close as possible to the inlet of the sample dryer to verify that the dew point is the highest that was estimated during emission sampling;

• (vi) The humidified gas dew point, T dew, and pressure, p total, shall be measured as close as possible to the outlet of the sample dryer;

• (vii) The sample dryer meets the verification if the result of point (d)(vi) of this section is less than the dew point corresponding to the sample dryer specifications as determined in point 9.3.2.3.1 plus 2 K (2 °C) or if the mol fraction from (d)(vi) is less than the corresponding sample dryer specifications plus 0,002 mol/mol or 0,2 volume %. Note for this verification, sample dew point is expressed in absolute temperature, Kelvin.

8.1.13.   PM measurements

8.1.13.1.   PM balance verifications and weighing process verification

8.1.13.1.1.   Scope and frequency

This section describes three verifications.

• (a) Independent verification of PM balance performance within 370 days prior to weighing any filter;

• (b) Zero and span of the balance within 12 h prior to weighing any filter;

• (c) Verification that the mass determination of reference filters before and after a filter weighing session be less than a specified tolerance.

8.1.13.1.2.   Independent verification

The balance manufacturer (or a representative approved by the balance manufacturer) shall verify the balance performance within 370 days of testing in accordance with internal audit procedures.

8.1.13.1.3.   Zeroing and spanning

Balance performance shall be verified by zeroing and spanning it with at least one calibration weight, and any weights that are used shall meet the specifications in point 9.5.2 to perform that verification. A manual or automated procedure shall be used:

• (a) A manual procedure requires that the balance shall be used in which the balance shall be zeroed and spanned with at least one calibration weight. If normally mean values are obtained by repeating the weighing process to improve the accuracy and precision of PM measurements, the same process shall be used to verify balance performance;

• (b) An automated procedure is carried out with internal calibration weights that are used automatically to verify balance performance. These internal calibration weights shall meet the specifications in point 9.5.2 to perform that verification.

8.1.13.1.4.   Reference sample weighing

All mass readings during a weighing session shall be verified by weighing reference PM sample media (e.g. filters) before and after a weighing session. A weighing session may be as short as desired, but no longer than 80 hours, and may include both pre- and post-test mass readings. Successive mass determinations of each reference PM sample media shall return the same value within ± 10 μg or ± 10 % of the expected total PM mass, whichever is higher. Should successive PM sample filter weighing events fail that criterion, all individual test filter mass readings mass readings occurring between the successive reference filter mass determinations shall be invalidated. These filters may be re-weighed in another weighing session. Should a post-test filter be invalidated then the test interval is void. That verification shall be performed as follows:

• (a) At least two samples of unused PM sample media shall be kept in the PM-stabilization environment. These shall be used as references. Unused filters of the same material and size shall be selected for use as references;

• (b) References shall be stabilized in the PM stabilization environment. References shall be considered stabilized if they have been in the PM-stabilization environment for a minimum of 30 min, and the PM-stabilization environment has been within the specifications of point 9.3.4.4 for at least the preceding 60 min;

• (c) The balance shall be exercised several times with a reference sample without recording the values;

• (d) The balance shall be zeroed and spanned. A test mass shall be placed on the balance (e.g. calibration weight) and then removed ensuring that the balance returns to an acceptable zero reading within the normal stabilization time;

• (e) Each of the reference media (e.g. filters) shall be weighed and their masses recorded. If normally mean values are obtained by repeating the weighing process to improve the accuracy and precision of reference media (e.g. filters) masses, the same process shall be used to measure mean values of sample media (e.g. filters) masses;

• (f) The balance environment dew point, ambient temperature, and atmospheric pressure shall be recorded;

• (g) The recorded ambient conditions shall be used to correct results for buoyancy as described in point 8.1.13.2. The buoyancy-corrected mass of each of the references shall be recorded;

• (h) Each of the reference media's (e.g. filter's) buoyancy-corrected reference mass shall be subtracted from its previously measured and recorded buoyancy-corrected mass;

• (i) If any of the reference filters' observed mass changes by more than that allowed under this section, all PM mass determinations made since the last successful reference media (e.g. filter) mass validation shall be invalidated. Reference PM filters may be discarded if only one of the filters mass has changed by more than the allowable amount and a special cause for that filter's mass change can be positively identified which would not have affected other in-process filters. Thus the validation can be considered a success. In that case, the contaminated reference media shall not be included when determining compliance with paragraph (j) of this point, but the affected reference filter shall be discarded and replaced;

• (j) If any of the reference masses change by more than that allowed under point 8.1.13.1.4, all PM results that were determined between the two times that the reference masses were determined shall be invalidated. If reference PM sample media is discarded in accordance with point (i), at least one reference mass difference that meets the criteria set out in point 8.1.13.1.4 shall be available. Otherwise, all PM results that were determined between the two times that the reference media (e.g. filters) masses were determined shall be invalidated.

8.1.13.2.   PM sample filter buoyancy correction

8.1.13.2.1.   General

PM sample filter shall be corrected for their buoyancy in air. The buoyancy correction depends on the sample media density, the density of air, and the density of the calibration weight used to calibrate the balance. The buoyancy correction does not account for the buoyancy of the PM itself, because the mass of PM typically accounts for only (0,01 to 0,10) % of the total weight. A correction to this small fraction of mass would be at the most 0,010 %. The buoyancy-corrected values are the tare masses of the PM samples. These buoyancy-corrected values of the pre-test filter weighing are subsequently subtracted from the buoyancy-corrected values of the post-test weighing of the corresponding filter to determine the mass of PM emitted during the test.

8.1.13.2.2.   PM sample filter density

Different PM sample filter have different densities. The known density of the sample media shall be used, or one of the densities for some common sampling media shall be used, as follows:

• (a) For PTFE-coated borosilicate glass, a sample media density of 2 300 kg/m³ shall be used;

• (b) For PTFE membrane (film) media with an integral support ring of polymethylpentene that accounts for 95 % of the media mass, a sample media density of 920 kg/m³ shall be used;

• (c) For PTFE membrane (film) media with an integral support ring of PTFE, a sample media density of 2 144 kg/m³ shall be used.

8.1.13.2.3.   Air density

Because a PM balance environment shall be tightly controlled to an ambient temperature of 295 ± 1 K (22 ± 1 °C) and a dew point of 282,5 ± 1 K (9,5 ± 1 °C), air density is primarily function of atmospheric pressure. Therefore a buoyancy correction is specified that is only a function of atmospheric pressure.

8.1.13.2.4.   Calibration weight density

The stated density of the material of the metal calibration weight shall be used.

8.1.13.2.5.   Correction calculation

The PM sample filter shall be corrected for buoyancy by means of equation (6-27):

Image omitted; see official source	(6-27)

Where: