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Title 40Chapter ISubchapter CPart 90 → Subpart E


Title 40: Protection of Environment
PART 90—CONTROL OF EMISSIONS FROM NONROAD SPARK-IGNITION ENGINES AT OR BELOW 19 KILOWATTS


Subpart E—Gaseous Exhaust Test Procedures


Contents
§90.401   Applicability.
§90.402   Definitions.
§90.403   Symbols, acronyms, and abbreviations.
§90.404   Test procedure overview.
§90.405   Recorded information.
§90.406   Engine parameters to be measured and recorded.
§90.407   Engine inlet and exhaust systems.
§90.408   Pre-test procedures.
§90.409   Engine dynamometer test run.
§90.410   Engine test cycle.
§90.411   Post-test analyzer procedures.
§90.412   Data logging.
§90.413   Exhaust sample procedure—gaseous components.
§90.414   Raw gaseous exhaust sampling and analytical system description.
§90.415   Raw gaseous sampling procedures.
§90.416   Intake air flow measurement specifications.
§90.417   Fuel flow measurement specifications.
§90.418   Data evaluation for gaseous emissions.
§90.419   Raw emission sampling calculations—gasoline fueled engines.
§90.420   CVS concept of exhaust gas sampling system.
§90.421   Dilute gaseous exhaust sampling and analytical system description.
§90.422   Background sample.
§90.423   Exhaust gas analytical system; CVS grab sample.
§90.424   Dilute sampling procedures—CVS calibration.
§90.425   CVS calibration frequency.
§90.426   Dilute emission sampling calculations—gasoline fueled engines.
§90.427   Catalyst thermal stress resistance evaluation.
Appendix A to Subpart E of Part 90—Tables
Appendix B to Subpart E of Part 90—Figures

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§90.401   Applicability.

(a) This subpart describes the procedures to follow in order to perform exhaust emission tests on new nonroad spark-ignition engines and vehicles subject to the provisions of subpart A of part 90. Provisions specific to raw gas sampling are in §90.414 through §90.419, provisions specific to constant volume sampling are in §90.420 through §90.426. All other sections in this subpart apply to both raw gas sampling and constant volume sampling except where indicated otherwise.

(b) Requirements for emission test equipment and calibrating this equipment are found in subpart D of this part.

(c) Certain text in this subpart is identified as pertaining to Phase 1 or Phase 2 engines. Such text pertains only to engines of the specified Phase. If no indication of Phase is given, the text pertains to all engines, regardless of Phase.

(d) For Phase 2 Class I, Phase 2 Class I-B, and Phase 2 Class II natural gas fueled engines, use the equipment specified in 40 CFR part 1065, subparts D and E, to measure nonmethane hydrocarbon (NMHC) exhaust emissions from Phase 2 Class I, Phase 2 Class I-B, and Phase 2 Class II natural gas fueled engines.

[60 FR 34598, July 3, 1995, as amended at 64 FR 15244, Mar. 30, 1999; 65 FR 24312, Apr. 25, 2000; 70 FR 40449, July 13, 2005]

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§90.402   Definitions.

The definitions in §90.3, §90.101, and §90.302 apply to this subpart.

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§90.403   Symbols, acronyms, and abbreviations.

(a) The acronyms and abbreviations in §90.5 apply to this subpart.

(b) The symbols in Table 1 in Appendix A to Subpart D apply to this subpart.

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§90.404   Test procedure overview.

(a) The test consists of prescribed sequences of engine operating conditions to be conducted on an engine dynamometer or equivalent load and speed measurement device. The exhaust gases generated during engine operation are sampled either raw or dilute and specific components are analyzed through the analytical system.

(b) The test is designed to determine the brake-specific emissions of hydrocarbons, carbon monoxide, carbon dioxide, and oxides of nitrogen and fuel consumption. For Phase 2 Class I-B, Class I, and Class II natural gas fueled engines the test is also designed to determine the brake-specific emissions of non-methane hydrocarbons. The test consists of three different test cycles which are application specific for engines which span the typical operating range of nonroad spark-ignition engines. Two cycles exist for Class I-B, I and II engines and one is for Class I-A, III, IV, and V engines (see §90.103(a) and §90.116(b) for the definitions of Class I-A, I-B, and I—V engines). The test cycles for Class I-B, I, and II engines consist of one idle mode and five power modes at one speed (rated or intermediate). The test cycle for Class I-A, III, IV, and V engines consists of one idle mode at idle speed and one power mode at rated speed. These procedures require the determination of the concentration of each pollutant, fuel flow, and the power output during each mode. The measured values are weighted and used to calculate the grams of each pollutant emitted per brake kilowatt hour (g/kW-hr).

(c)(1) When an engine is tested for exhaust emissions the complete engine must be tested, with all emission control devices installed and functioning.

(2) On air cooled engines, the cooling fan must be installed. For engines whose cooling fan serves a dual purpose, such as an air pump/blower, an external fan may be used to provide the engine with cooling air and the original cooling fan may be removed.

(d) All emission control systems installed on or incorporated in the application must be functioning during all procedures in this subpart. In case of component malfunction or failure, no maintenance is allowed without prior approval from the Administrator, in accordance with §90.119.

[60 FR 34598, July 3, 1995, as amended at 64 FR 15244, Mar. 30, 1999; 65 FR 24312, Apr. 25, 2000]

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§90.405   Recorded information.

(a) Record the information described in this section for each test, where applicable.

(b) Test data; general. (1) Engine identification number.

(2) Engine emission control system.

(3) Test operator(s).

(4) Number of hours of operation accumulated on the engine prior to beginning the warm-up portion of the test (to the nearest tenth hour).

(5) Fuel identification.

(6) For 2-stroke engines, fuel/oil mixture ratio.

(7) Date of most recent analyzer bench calibration.

(8) All pertinent instrument information such as tuning, gain, serial numbers, detector number, and calibration curve(s). As long as this information is traceable, it may be summarized by system number or analyzer identification numbers.

(c) Test data; pre-test. (1) Date and time of day.

(2) Test number.

(3) Barometric pressure; as an option, barometric pressure can be measured as a modal measurement instead of or in addition to a pre- and post-test measurement.

(4) Recorder chart or equivalent. Identify for each test segment zero traces for each range used, and span traces for each range used.

(d) Test data; modal. (1) Recorder chart or equivalent. Identify for each test mode the emission concentration traces and the associated analyzer range(s).

(2) Observed engine torque.

(3) Observed engine rpm.

(4) Intake air flow if applicable.

(5) Test cell temperature and humidity for each mode.

(6) For raw gas testing; fuel flow for each mode. Fuel flow measurement is not required for dilute testing, but is allowed. If the fuel flow measurement is a volume measurement system, record the fuel temperature in the measurement system for fuel density corrections to the mass flow rate. If the fuel temperature is within 3 °C of the calibration temperature, no density correction is required.

(7) Engine intake temperature and humidity, if applicable.

(8) Exhaust mixing chamber surface temperature, if applicable.

(9) Exhaust sample line temperature, if applicable.

(e) Test data; post-test. (1) Recorder chart or equivalent. Identify the hang-up check.

(2) Recorder chart or equivalent. Identify the zero traces for each range used and the span traces for each range used.

(3) Total number of hours of operation accumulated on the engine (to the nearest tenth hour).

(4) Barometric pressure, post-test segment.

[60 FR 34598, July 13, 1995, as amended at 70 FR 40449, July 13, 2005]

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§90.406   Engine parameters to be measured and recorded.

Measure or calculate, then record the engine parameters in table 1 in appendix A of this subpart.

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§90.407   Engine inlet and exhaust systems.

(a) The engine manufacturer is liable for exhaust emission compliance over the full range of air inlet filter systems and exhaust muffler systems.

(b) The air inlet filter system and exhaust muffler system combination used on the test engine must be the systems expected to yield the highest emission levels.

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§90.408   Pre-test procedures.

(a) Engine service accumulation and stabilization procedure. Use the service accumulation procedure determined by the manufacturer for exhaust emission stabilizing of an engine, consistent with good engineering practice (see §90.118).

(1) The manufacturer determines, for each engine family, the number of hours at which the engine exhaust emission control system combination is stabilized for emission testing. However, this stabilization procedure may not exceed 12 hours. The manufacturer must maintain, and provide to the Administrator upon request, a record of the rationale used in making this determination. If the manufacturer can document that at some time prior to the full 12 hour service accumulation period the engine emissions are decreasing for the remainder of the 12 hours, the service accumulation may be completed at that time. The manufacturer may elect to accumulate 12 hours on each test engine within an engine family without making this determination.

(2) During service accumulation, the fuel and lubricants specified in §90.308 must be used.

(3) Engine maintenance during service accumulation is allowed only in accordance with §90.118.

(b) Engine pre-test preparation. (1) Drain and charge the fuel tank(s) with the specified test fuel (see §90.308(b)) to 50 percent of the tank's nominal capacity. If an external fuel tank is used, the engine fuel inlet system pressure must be typical of what the engine will see in use.

(2) An evaluation of the effects of test measurement systems on engine emissions shall be conducted using good engineering judgment to ensure that such test systems do not significantly impact exhaust emissions from the engine. For example, this would require evaluation of all types of emission sampling systems, and of fuel- and air-flow measurement systems for raw sampling. This can be accomplished by operating the engine at the highest engine torque value that will be encountered on the test cycle before and after such test systems are installed to ensure that the impact on measured torque is less than 5 percent. This may also be accomplished by measuring air-to-fuel ratio using a zirconia universal exhaust gas oxygen (UEGO) sensor to ensure that the impact on measured air-to-fuel ratio is less than 5 percent at the highest engine torque value that will be encountered on the test cycle before and after such test systems are installed. The impact of air- and fuel-flow measurement systems may be evaluated based on an engineering analysis of the impact of the change in pressure induced on air-intake pressure and fuel supply pressure by these measurement systems. While this would typically be done before testing, it may also be done as a post-test verification.

(c) Analyzer pre-test procedures. (1) If necessary, warm up and stabilize the analyzer(s) before calibrations are performed.

(2) Replace or clean the filter elements and then leak check the system as required by §90.324(a). If necessary, allow the heated sample line, filters, and pumps to reach operating temperature.

(3) Perform the following system checks:

(i) If necessary, check the sample-line temperature. Heated FID sample line temperature must be maintained between 110 °C and 230 °C; a heated NOX sample line temperature must be maintained between 60 °C and 230 °C.

(ii) Check that the system response time has been accounted for prior to sample collection data recording.

(iii) A HC hang-up check is permitted (see §90.413(e)).

(4) Check analyzer zero and span before and after each test at a minimum. Further, check analyzer zero and span any time a range change is made or at the maximum demonstrated time span for stability for each analyzer used.

(d) Check system flow rates and pressures and reset, if necessary.

[60 FR 34598, July 3, 1995, as amended at 65 FR 24312, Apr. 25, 2000; 70 FR 40449, July 13, 2005]

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§90.409   Engine dynamometer test run.

(a) Engine and dynamometer start-up. (1) Only adjustments in accordance with §90.119 may be made to the test engine prior to starting a test.

(2) If necessary, warm up the dynamometer as recommended by the dynamometer manufacturer or use good engineering practice.

(3) For Phase 1 engines, at the manufacturer's option, the engine can be run with the throttle in a fixed position or by using the engine's governor (if the engine is manufactured with a governor). In either case, the engine speed and load must meet the requirements specified in paragraph (b)(12) of this section. For Phase 2 Class I, Phase 2 Class I-B, and Phase 2 Class II engines equipped with an engine speed governor, the governor must be used to control engine speed during all test cycle modes except for Mode 1 or Mode 6, and no external throttle control may be used that interferes with the function of the engine's governor; a controller may be used to adjust the governor setting for the desired engine speed in Modes 2-5 or Modes 7-10; and during Mode 1 or Mode 6 fixed throttle operation may be used to determine the 100 percent torque value.

(b) Each test consists of the following steps.

(1) Record the general test data as specified in §90.405(b).

(2) Precondition the engine in the following manner;

(i) Operate the engine at a power greater than or equal to 50 percent maximum power at the appropriate speed (rated or intermediate) for 20 minutes;

(ii) Option. If the engine has been operating on service accumulation for a minimum of 40 minutes, the service accumulation may be substituted for step (i).

(3) Record all pre-test data specified in §90.405(c).

(4) Start the test cycle (see §90.410) within five minutes of the completion of the steps required by paragraph (b)(2) of this section.

(5) Modes are to be performed in the numerical order specified for the appropriate test cycle (see “Mode Points” Table 2 in Appendix A of this subpart).

(6) For Class I, I-B, and II engines, during the maximum torque mode calculate the torque corresponding to 75, 50, 25, and 10 percent of the maximum observed torque (see Table 2 in Appendix A to this subpart).

(7) Once engine speed and load are set for a mode, run the engine for a sufficient period of time to achieve thermal stability. At the manufacturer's option, determine and document the appropriate criterion for thermal stability for each engine family. If the manufacture chooses not to make this determination, an acceptable alternative is to run the engine at each mode until the cylinder head temperature remains within a 10 °C bandwidth for three minutes. Cylinder head temperature may be measured at the base of the spark plug. After stability is achieved, emission measurements are initiated.

(8) Record all modal data specified in §90.405(d) for a minimum time period of the last two minutes of each mode. Longer averaging periods are acceptable, but the data averaged must be from a continuous time period. The duration of time during which this data is recorded is referred to as the “sampling period.” The data collected during the sampling period is used for modal emission calculations.

(9) Continuously record the analyzer's response to the exhaust gas during each mode.

(10) Modes may be repeated.

(11) If a delay of more than one hour occurs between the end of one mode and the beginning of another mode, the test is void and must be restarted at paragraph (b)(1) of this section.

(12) The engine speed and load must be maintained within the requirements of §90.410 during the sampling period of each mode. If this requirement is not met, the mode is void and must be restarted.

(13) If at any time during a mode the test equipment malfunctions or the specifications in §90.410 can not be met, the test is void and must be aborted. Corrective action should be taken and the test restarted.

(14) If at any time during an operating mode the engine stalls, restart the engine immediately and continue the test starting with the steps required by paragraph (b)(6) of this section. If the engine will not restart within five minutes the test is void. If maintenance is required on the engine, advance approval from the Administrator is required as specified in §90.119. After corrective action is taken, the engine may be rescheduled for testing. Report the reason for the malfunction (if determined) and the corrective action taken.

(15) Fuel flow and air flow during the idle condition may be determined just prior to or immediately following the dynamometer sequence, if longer times are required for accurate measurements. If the dilute sampling method (Constant Volume Sampling) is used, neither fuel flow nor air flow measurements are required.

(c) Exhaust gas measurements. (1) Measure HC, CO, CO2, and NOX concentrations in the exhaust sample. Use the same units and modal calculations as for your other results to report a single weighted value for CO2; round CO2 to the nearest 1 g/kW-hr.

(2) Each analyzer range that may be used during a test mode must have the zero and span responses recorded prior to the start of the test. Only the range(s) used to measure the emissions during the test is required to have its zero and span recorded after the completion of the test. Depending on the stability of each individual analyzer, more frequent zero checks or spans between modes may be necessary.

(3) It is permitted to change filter elements between modes.

(4) A leak check is permitted between modes.

(5) A hang-up check is permitted between modes (see §90.413).

(6) If, during the emission measurement portion of a mode, the value of the gauges downstream of the NDIR analyzer(s) G3 or G4 (see Figure 1 in Appendix B of this subpart), differs by more than ±0.5kPa from the pretest value, the test mode is void.

[60 FR 34598, July 3, 1995, as amended at 64 FR 15244, Mar. 30, 1999; 65 FR 24313, Apr. 25, 2000; 70 FR 40449, July 13, 2005; 74 FR 56374, Oct. 30, 2009]

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§90.410   Engine test cycle.

(a) Follow the appropriate 6-mode test cycle for Class I, I-B and II engines and 2-mode test cycle for Class I-A, III, IV, and V engines when testing spark-ignition engines (see Table 2 in Appendix A of this subpart).

(b) For Phase 1 engines and Phase 2 Class I-A, III, IV, and V, and Phase 2 Class I and II engines not equipped with an engine speed governor, during each non-idle mode, hold both the specified speed and load within ±five percent of point. During the idle mode, hold speed within ±ten percent of the manufacturer's specified idle engine speed. For Phase 2 Class I, I-B, and II engines equipped with an engine speed governor, during Mode 1 or Mode 6 hold both the specified speed and load within ±five percent of point, during Modes 2-3, or Modes 7-8 hold the specified load with ±five percent of point, during Modes 4-5 or Modes 9-10, hold the specified load within the larger range provided by ±0.27 Nm (±0.2 lb-ft), or ±ten (10) percent of point, and during the idle mode hold the specified speed within ±ten percent of the manufacturer's specified idle engine speed (see Table 1 in Appendix A of this subpart for a description of test Modes). The use of alternative test procedures is allowed if approved in advance by the Administrator.

(c) If the operating conditions specified in paragraph (b) of this section for Class I, I-B, and II engines using Mode Points 2, 3, 4, and 5 cannot be maintained, the Administrator may authorize deviations from the specified load conditions. Such deviations may not exceed 10 percent of the maximum torque at the test speed. The minimum deviations, above and below the specified load, necessary for stable operation shall be determined by the manufacturer and approved by the Administrator prior to the test run.

(d) Do not include power generated during the idle mode, Mode 11, in the calculation of emission results.

[60 FR 34598, July 3, 1995, as amended at 64 FR 15244, Mar. 30, 1999; 65 FR 24313, Apr. 25, 2000]

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§90.411   Post-test analyzer procedures.

(a) Perform a HC hang-up check within 60 seconds of the completion of the last mode in the test. Use the following procedure:

(1) Introduce a zero gas or room air into the sample probe or valve V2 (see Figure 2 in Appendix B of Subpart D) to check the “hangup zero” response. Simultaneously start a time measurement.

(2) Select the lowest HC range used during the test.

(3) Within four minutes of beginning the time measurement in paragraph (a)(1) of this section, the difference between the zero gas response and the hang-up zero response may not be greater than 5.0 percent of full scale or 10 ppmC, whichever is greater.

(b) Begin the analyzer span checks within six minutes after the completion of the last mode in the test. Record for each analyzer the zero and span response for each range used during the preceding test or test segment.

(c) If during the test, the filter element(s) were replaced or cleaned, a vacuum check must be performed per §90.324(a) immediately after the span checks. If the vacuum side leak check does not meet the requirements of §90.324(a), the test is void.

(d) Read and record the post-test data specified in §90.405(e).

(e) For a valid test, the analyzer drift between the before-segment and after-segment span checks for each analyzer must meet the following requirements:

(1) The span drift (defined as the change in the difference between the zero response and the span response) may not exceed two percent of full-scale chart deflection for each range used.

(2) The zero response drift may not exceed two percent of full-scale chart deflection for each range used above 155 ppm (or ppm C), or three percent of full-scale chart deflection for each range below 155 ppm (or ppm C).

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§90.412   Data logging.

(a) A computer or any other automatic data collection (ADC) device(s) may be used as long as the system meets the requirements of this subpart.

(b) Determine from the data collection records the analyzer responses corresponding to the end of each mode.

(c) Record data at a minimum of rate of one Hz (one time per second).

(d) Determine the final value for power by averaging the individually calculated power points for each value of speed and torque recorded during the sampling period. As an alternative, the final value for power can be calculated from the average values for speed and torque, collected during the sampling period.

(e) Determine the final value for CO2, CO, HC, and NOX concentrations by averaging the concentration of each point taken during the sample period for each mode.

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§90.413   Exhaust sample procedure—gaseous components.

(a) Automatic data collection equipment requirements. The analyzer response may be read by automatic data collection (ADC) equipment such as computers, data loggers, and so forth. If ADC equipment is used, the following is required:

(1) For dilute grab (“bag”) sample analysis, the analyzer response must be stable at greater than 99 percent of the final reading for the dilute exhaust sample. The ADC must store a single value representing the average chart deflection over a 10-second stabilized period. Alternatively, the ADC may store the individual instantaneous chart deflections collected over a 10-second stabilized period.

(2) For continuous analysis systems, the ADC must store a single value representing the average integrated concentration over a measurement period. Alternatively, the ADC may store the individual instantaneous values collected during the measurement period.

(3) The chart deflections or average integrated concentrations required in paragraphs (a)(1) and (a)(2) of this section may be stored on long-term computer storage devices such as computer tapes, storage discs, punch cards, or they may be printed in a listing for storage. In either case a chart recorder is not required and records from a chart recorder, if they exist, need not be stored.

(4) If ADC equipment is used to interpret analyzer values, the ADC equipment is subject to the calibration specifications of the analyzer as if the ADC equipment is part of analyzer system.

(b) Data records from any one or a combination of analyzers may be stored as chart recorder records.

(c) Grab sample analysis. For dilute grab sample analysis perform the following procedure:

(1) Calibrate analyzers using the procedure described in §90.326.

(2) Record the most recent zero and span response as the pre-analysis values.

(3) Measure and record HC, CO, CO2, and NOX concentrations in the exhaust sample bag(s) and background sample bag(s) using the same flow rates and pressures.

(4) Good engineering practice dictates that exhaust emission sample bag analyzer readings below 15 percent of full scale should generally not be used.

(5) A post-analysis zero and span calibration check of each range must be performed and the values recorded. The number of events that may occur between the pre- and post-checks is not specified. However, the difference between pre-analysis zero and span values (recorded in paragraph (c)(2) or (c)(3) of this section) versus those recorded for the post-analysis check may not exceed the zero drift limit or the span drift limit of two percent of full-scale chart deflection for any range used. Otherwise the analysis is void.

(d) Continuous sample analysis. For continuous sample analysis perform the following procedure:

(1) Calibrate analyzers using the procedure described in §90.326.

(2) Leak check portions of the sampling system that operate at negative gauge pressures when sampling and allow heated sample lines, filters, pumps, and so forth to stabilize at operating temperature.

(3) Option: Determine the HC hang-up for the FID or HFID sampling system:

(i) Zero the analyzer using zero gas introduced at the analyzer port.

(ii) Flow zero gas through the overflow sampling system. Check the analyzer response.

(iii) If the overflow zero response exceeds the analyzer zero response by two percent or more of the FID or HFID full-scale deflection, hang-up is indicated and corrective action must be taken (see paragraph (e) of this section).

(iv) The complete system hang-up check specified in paragraph (e) of this section is recommended as a periodic check.

(4) If necessary, recalibrate analyzer using the procedure specified in paragraph (d)(1) of this section.

(5) Good engineering practice dictates that analyzers used for continuous analysis should be operated such that the measured concentration falls between 15 percent and 100 percent of full scale.

(6) Record the most recent zero and span response as the pre-analysis values.

(7) Collect background HC, CO, CO2, and NOX in a sample bag (for dilute exhaust sampling only, see §90.422).

(8) Perform a post-analysis zero and span check for each range used at the conditions specified in paragraph (d)(1) of this section. Record these responses as the post-analysis values.

(9) Neither the zero drift nor the span drift between the pre-analysis and post-analysis checks on any range used may exceed three percent for HC, or two percent for NOX. CO, and CO2, of full-scale chart deflection, or the test is void. (If the HC drift is greater than three percent of full-scale chart deflection, HC hang-up is likely.)

(10) Determine background levels of HC, NOX. CO, or CO2 (for dilute exhaust sampling only) by the grab (“bag”) technique outlined in paragraph (c) of this section.

(e) Hydrocarbon hang-up. If HC hang-up is indicated, the following procedure may be performed:

(1) Fill a clean, evacuated sample bag with background air.

(2) Zero and span the HFID at the analyzer ports.

(3) Analyze the background air sample bag through the analyzer ports.

(4) Analyze the background air through the entire sample probe system.

(5) If the difference between the readings obtained is two ppm or more, clean the sample probe and the sample line.

(6) Reassemble the sample system, heat to specified temperature, and repeat the procedure in paragraphs (e)(1) through (e)(5) of this section.

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§90.414   Raw gaseous exhaust sampling and analytical system description.

(a) Schematic drawing. An example of a sampling and analytical system which may be used for testing under this subpart is shown in Figure 2 in appendix B of subpart D. All components or parts of components that are wetted by the sample or corrosive calibration gases must be either chemically cleaned stainless steel or inert material (e.g., polytetrafluoroethylene resin). The use of “gauge savers” or “protectors” with nonreactive diaphragms to reduce dead volumes is permitted.

(b) Sample probe. (1) The sample probe must be a straight, closed end, stainless steel, multi-hole probe. The inside diameter may not be greater than the inside diameter of the sample line + 0.03 cm. The wall thickness of the probe may not be greater than 0.10 cm. The fitting that attaches the probe to the exhaust pipe must be as small as practical in order to minimize heat loss from the probe.

(2) The probe must have a minimum of three holes. The spacing of the radial planes for each hole in the probe must be such that they cover approximately equal cross-sectional areas of the exhaust duct. See Figure 2 in appendix B of subpart D. The angular spacing of the holes must be approximately equal. The angular spacing of any two holes in one plane may not be 180° ±20° (i.e., section view C-C of Figure 2 in appendix B of subpart D). The holes should be sized such that each has approximately the same flow. If only three holes are used, they may not all be in the same radial plane.

(3) The exhaust gas probe must be located in a position which yields a well mixed, homogenous sample of the engine exhaust. The probe must extend radially across the exhaust gas stream. The probe must pass through the approximate center and must extend across at least 80 percent of the exhaust gas stream. The exact position of the probe may vary from engine family to engine family.

(c) Mixing chamber. The exhaust mixing chamber is located in the exhaust system between the muffler and the sample probe. The mixing chamber is an optional component of the raw gas sampling equipment.

(1) The internal volume of the mixing chamber may not be less than ten times the cylinder displacement of the engine under test. The shape of the mixing chamber must be such that it provides a well mixed, homogenous sample at the sample probe location.

(2) Couple the mixing chamber as closely as possible to the engine muffler.

(3) Maintain the inner surface of the mixing chamber at a minimum temperature of 179 °C.

(4) Thermocouple temperature monitoring of the mixing chamber inner surface is required to assure wall temperatures specified in paragraph (c)(3) of this section. The temperature measurement must be accurate to within ±5 °C.

(5) The sample probe must extend radially across the exit of the mixing chamber. The probe must pass through the approximate center and must extend across at least 80 percent of the diameter of the exit. The exact position of the probe may vary from engine family to engine family. The probe must be located in a position which yields a well mixed, homogenous sample of the exhaust.

(d) Sample transfer line. (1) The maximum inside diameter of the sample line may not exceed 1.32 cm.

(2) If valve V2 in Figure 1 of appendix B of this subpart is used, the sample probe must connect directly to valve V2. The location of optional valve V2 in Figure 1 of appendix B of subpart D may not be greater than 1.22 m from the exhaust duct.

(3) The location of optional valve V16, Figure 1 of appendix B of this subpart, may not be greater than 61 cm from the sample pump. The leakage rate for this section on the pressure side of the sample pump may not exceed the leakage rate specification for the vacuum side of the pump.

(e) Venting. All vents, including analyzer vents, bypass flow, and pressure relief vents, of regulators should be vented in such a manner as to avoid endangering personnel in the immediate area.

(f) Any variation from the specifications in this subpart, including performance specifications and emission detection methods, may be used only with prior approval by the Administrator.

(g) Additional components, such as instruments, valves, solenoids, pumps, switches, and so forth, may be employed to provide additional information and coordinate the functions of the component systems.

(h) The following requirements must be incorporated in each system used for raw testing under this subpart.

(1) Take the sample for all components with one sample probe and split it internally to the different analyzers.

(2) Heat the sample transport system from the engine exhaust pipe to the HC analyzer for the raw gas sampling method as indicated in Figure 1 in appendix B of this subpart. The NOX analyzer for the raw gas sampling method may be heated as indicated in Figure 1 in appendix B of this subpart. The HC analyzer and the NOX analyzer for the dilute sampling method may be heated as indicated in Figure 1 in appendix B of this subpart.

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§90.415   Raw gaseous sampling procedures.

Fit all heated sampling lines with a heated filter to extract solid particles from the flow of gas required for analysis. The sample line for HC measurement must be heated. The sample line for CO, CO2 and NOX analysis may be heated or unheated.

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§90.416   Intake air flow measurement specifications.

(a) If used, the engine intake air flow measurement method used must have a range large enough to accurately measure the air flow over the engine operating range during the test. Overall measurement accuracy must be two percent of full-scale value of the measurement device for all modes except the idle mode. For the idle mode, the measurement accuracy must be ±five percent or less of the full-scale value. The Administrator must be advised of the method used prior to testing.

(b) When an engine system incorporates devices that affect the air flow measurement (such as air bleeds, air injection, pulsed air, and so forth) resulting in understated exhaust emission results, make corrections to the exhaust emission results to account for such effects.

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§90.417   Fuel flow measurement specifications.

(a) Fuel flow measurement is required only for raw testing. Fuel flow is allowed for dilute testing.

(b) The fuel flow measurement instrument must have a minimum accuracy of one percent of full-scale flow rate for each measurement range used. An exception is allowed for the idle mode. For this mode, the minimum accuracy is ±five percent of full-scale flow rate for the measurement range used. The controlling parameters are the elapsed time measurement of the event and the weight or volume measurement. You may apply the accuracy specifications of 40 CFR part 1065, subpart C, instead of those in this paragraph (b).

[70 FR 40449, July 13, 2005]

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§90.418   Data evaluation for gaseous emissions.

For the evaluation of the gaseous emissions recording, record the last two minutes of each mode and determine the average values for HC, CO, CO2 and NOX during each mode from the average concentration readings determined from the corresponding calibration data. Longer averaging times are acceptable, but the reported sampling period must be a continuous set of data.

[70 FR 40449, July 13, 2005]

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§90.419   Raw emission sampling calculations—gasoline fueled engines.

(a) Derive the final weighted brake-specific mass emission rates (g/kW-hr) through the steps described in this section.

(b) Air and fuel flow method. If both air and fuel flow mass rates are measured, use the following equations to determine the weighted emission values for the test engine:

eCFR graphic er03jy95.016.gif

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Where:

WHC = Mass rate of HC in exhaust [g/hr],

GAIRD = Intake air mass flow rate on dry basis [g/hr],

GFUEL = Fuel mass flow rate [g/hr],

MHCexh = Molecular weight of hydrocarbons in the exhaust, see the following equation:

eCFR graphic er03jy95.017.gif

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Where:

α = Hydrogen/carbon atomic ratio of the fuel

β = Oxygen/carbon atomic ratio of the fuel

Mexh = Molecular weight of the total exhaust, see the following equation:

eCFR graphic er03jy95.018.gif

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Where:

WHC = HC volume concentration in exhaust, ppmC wet

WCO = CO percent concentration in the exhaust, wet

DCO = CO percent concentration in the exhaust, dry

WCO2 = CO2 percent concentration in the exhaust, wet

DCO2 = CO2 percent concentration in the exhaust, dry

WNOX = NO volume concentration in exhaust, ppm wet

WO2 = O2 percent concentration in the exhaust, wet

WH2 = H2 percent concentration in exhaust, wet

K = correction factor to be used when converting dry measurements to a wet basis. Therefore, wet concentration = dry concentration × K,

where K is:

eCFR graphic er03jy95.019.gif

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DH2 = H2 percent concentration in exhaust, dry, calculated from the following equation:

eCFR graphic er03jy95.020.gif

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Wco = Mass rate of CO in exhaust, [g/hr]

Mco = Molecular weight of CO = 28.01

WNOx = Mass rate of NOX in exhaust, [g/hr]

MNO2 = Molecular weight of NO2 = 46.01

KH = Factor for correcting the effects of humidity on NO2 formation for 4-stroke gasoline small engines, as follows:

KH = (9.953 × H + 0.832)

Where:

H = the amount of water in an ideal gas; 40 CFR 1065.645 describes how to determine this value (referred to as xH2O).

KH = 1 for two-stroke gasoline engines.

(c) Fuel flow method. The following equations are to be used when fuel flow is selected as the basis for mass emission calculations using the raw gas method.

eCFR graphic er03jy95.022.gif

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Where:

WHC = Mass rate of HC in exhaust, [g/hr]

MHCexh = Molecular weight of hydrocarbons in the exhaust, see following equation:

eCFR graphic er03jy95.023.gif

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MC = Molecular weight of carbon = 12.01 [g/mole]

MH = Molecular weight of hydrogen = 1.008 [g/mole]

MO = Molecular weight of oxygen = 16.00 [g/mole]

α = Hydrogen to carbon ratio of the test fuel

β = Oxygen to carbon ratio of the test fuel

MF = Molecular weight of test fuel

GFUEL = Fuel mass flow rate, [g/hr]

TC = Total carbon in exhaust, see following equation:

eCFR graphic er03jy95.024.gif

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WCO = CO percent concentration in the exhaust, wet

WCO2 = CO2 percent concentration in the exhaust, wet

DCO = CO percent concentration in the exhaust, dry

DCO2 = CO2 percent concentration in the exhaust, dry

WHC = HC volume concentration in exhaust, ppmC wet

WNOX = NOX volume concentration in exhaust, ppm wet

K = correction factor to be used when converting dry measurements to a wet basis. Therefore, wet concentration = dry concentration × K, where K is:

eCFR graphic er03jy95.025.gif

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DH2 = H2 percent concentration in exhaust, dry, calculated from the following equation:

eCFR graphic er03jy95.026.gif

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WCO = Mass rate of CO in exhaust, [g/hr]

MCO = Molecular weight of CO = 28.01

WNOX = Mass rate of NOX in exhaust, [g/hr]

MNO2 = Molecular weight of NO2 = 46.01

KH = Factor for correcting the effects of humidity on NO2 formation for 4-stroke gasoline small engines, as follows:

KH = (9.953 × H + 0.832)

Where:

H = the amount of water in an ideal gas; 40 CFR 1065.645 describes how to determine this value (referred to as xH2O).

KH = 1 for two-stroke gasoline engines.

(d) Calculate the final weighted brake-specific emission rate for each individual gas component using the following equation:

eCFR graphic er03jy95.028.gif

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Where:

AWM = Final weighted brake-specific mass emission rate (HC, CO, NOX) [g/kW-hr]

Wi = Mass emission rate during mode i [g/hr]

WFi = Weighting factors for each mode according to §90.410(a)

Pi = Gross average power generated during mode i [kW], calculated from the following equation,

eCFR graphic er03jy95.029.gif

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Where:

speed = average engine speed measured during mode i [rev./minute]

torque = average engine torque measured during mode i [N-m]

[60 FR 34598, July 13, 1995, as amended at 70 FR 40449, July 13, 2005]

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§90.420   CVS concept of exhaust gas sampling system.

(a) A dilute exhaust sampling system is designed to directly measure the true mass of emissions in engine exhaust without the necessity of measuring either fuel flow or intake air flow. This is accomplished by diluting the exhaust produced by a test engine with ambient background air and measuring the total diluted exhaust flow rate and the concentration of emissions within the dilute flow. Total mass flow of an emission is then easily calculated.

(b) A constant volume sampler (CVS) is typically used to control the total amount of dilute flow through the system. As the name implies, a CVS restricts flow to a known value dependent only on the dilute exhaust temperature and pressure.

(c) For the testing described in this subpart, a CVS must consist of: a mixing tunnel into which the engine exhaust and dilutant (background) air are dumped; a dilute exhaust flow metering system; a dilute exhaust sample port; a background sample port; a dilute exhaust sampling system; and a background sampling system.

(1) Mixing tunnel. The mixing tunnel must be constructed such that complete mixing of the engine exhaust and background air is assured prior to the sampling probe.

(2) Exhaust flow metering system. A dilute exhaust flow metering system must be used to control the total flow rate of the dilute engine exhaust as described in §90.421.

(3) Exhaust sample port. A dilute exhaust sample port must be located in or downstream of the mixing tunnel at a point where complete mixing of the engine exhaust and background air is assured.

(4) Background sample port. A dilute exhaust sample port must be located in the stream of background air before it is mixed with the engine exhaust. The background probe must draw a representative sample of the background air during each sampling mode.

(5) Exhaust sampling system. The dilute exhaust sampling system controls the flow of samples from the mixing tunnel to the analyzer system. This could be either a continuous sampling system or grab (bag) sampling system. If a critical flow venturi (CFV) is used on the dilute exhaust sample probe, this system must assure that the sample CFV is in choke flow during testing. If no CFV is used, this system must assure a constant volumetric flow rate through the dilute exhaust sample probe or must incorporate electronic flow compensation.

(6) Background sampling system. The background sampling system controls the flow of samples from the background air supply to the analyzer system. This could be either a continuous sampling system or grab (bag) sampling system. This system must assure a constant volumetric flow rate through the background sample probe.

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§90.421   Dilute gaseous exhaust sampling and analytical system description.

(a) General. The exhaust gas sampling system described in this section is designed to measure the true mass of gaseous emissions in the exhaust of nonroad small spark-ignition engines. This system utilizes the Constant Volume Sampling (CVS) concept (described in §90.420) of measuring mass emissions of HC, NOX. CO, and CO2. Grab sampling for individual modes is an acceptable method of dilute testing for all constituents, HC, NOX. CO, and CO2. Continuous dilute sampling is not required for any of the exhaust constituents, but is allowable for all. Heated sampling is not required for any of the constituents, but is allowable for HC and NOX. The mass of gaseous emissions is determined from the sample concentration and total flow over the test period. As an option, the measurement of total fuel mass consumed over a cycle may be substituted for the exhaust measurement of CO2. General requirements are as follows:

(1) This sampling system requires the use of a Positive Displacement Pump—Constant Volume Sampler (PDP-CVS) system with a heat exchanger, or a Critical Flow Venturi—Constant Volume Sampler (CFV-CVS) system with CFV sample probes and/or a heat exchanger or electronic flow compensation. Figure 2 in Appendix B of this subpart is a schematic drawing of the PDP-CVS system. Figure 3 in Appendix B of this subpart is a schematic drawing of the CFV-CVS system.

(2) The HC analytical system requires:

(i) Grab sampling (see §90.420, and Figure 2 or Figure 3 in Appendix B of this subpart) and analytical capabilities (see §90.423, and Figure 4 in Appendix B of this subpart), or

(ii) Continuously integrated measurement of diluted HC meeting the minimum requirements and technical specifications contained in paragraph (b)(2) of this section.

(iii) The dilute HC analytical system for nonroad small spark-ignition engines does not require a heated flame ionization detector (HFID).

(iv) If used, the HFID sample must be taken directly from the diluted exhaust stream through a heated probe and integrated continuously over the test cycle.

(v) The heated probe must be located in the sampling system far enough downstream of the mixing area to ensure a uniform sample distribution across the CVS duct at the sampling zone.

(3) The CO and CO2 analytical system requires:

(i) Grab sampling (see §90.420, and Figure 2 or Figure 3 in Appendix B of this subpart) and analytical capabilities (see §90.423, and Figure 4 in Appendix B of this subpart), or

(ii) Continuously integrated measurement of diluted CO and CO2 meeting the minimum requirements and technical specifications contained in paragraph (b)(4) of this section.

(4) The NOX analytical system requires:

(i) Grab sampling (see §90.420, and Figure 2 or Figure 3 in Appendix B of this subpart) and analytical capabilities (see §90.423, and Figure 4 in Appendix B of this subpart), or

(ii) A continuously integrated measurement of diluted NOX meeting the minimum requirements and technical specifications contained in paragraph (b)(4) of this section.

(5) Since various configurations can produce equivalent results, exact conformance with these drawings is not required. Additional components such as instruments, valves, solenoids, pumps, and switches may be used to provide additional information and coordinate the functions of the component systems. Other components, such as snubbers, which are not needed to maintain accuracy on some systems, may be excluded if their exclusion is based upon good engineering judgment.

(6) Other sampling and/or analytical systems may be used if shown to yield equivalent results and if approved in advance by the Administrator.

(b) Component description. The components necessary for exhaust sampling must meet the following requirements:

(1) Exhaust dilution system. The PDP-CVS must conform to all of the requirements listed for the exhaust gas PDP-CVS in §90.420 of this chapter. The CFV-CVS must conform to all of the requirements listed for the exhaust gas CFV-CVS in §90.420 of this chapter. In addition, the CVS must conform to the following requirements:

(i) The flow capacity of the CVS must be sufficient to maintain the diluted exhaust stream in the dilution system at a temperature of 190 °C or less at the sampling zone for hydrocarbon measurement and as required to prevent condensation at any point in the dilution system. Gaseous emission samples may be taken directly from this sampling point.

(ii) For the CFV-CVS, either a heat exchanger or electronic flow compensation is required (see Figure 3 in Appendix B of this subpart).

(iii) For the CFV-CVS when a heat exchanger is used, the gas mixture temperature, measured at a point immediately ahead of the critical flow venturi, must be within ±11 °C of the average operating temperature observed during the test with the simultaneous requirement that condensation does not occur. The temperature measuring system (sensors and readout) must have an accuracy and precision of ±2 °C. For systems utilizing a flow compensator to maintain proportional flow, the requirement for maintaining constant temperature is not necessary.

(2) Continuous HC measurement system. (i) The continuous HC sample system (as shown in Figure 2 or 3 in Appendix B of this subpart) uses an “overflow” zero and span system. In this type of system, excess zero or span gas spills out of the probe when zero and span checks of the analyzer are made.

(ii) No other analyzers may draw a sample from the continuous HC sample probe, line, or system, unless a common sample pump is used for all analyzers and the sample line system design reflects good engineering practice.

(iii) The overflow gas flow rates into the sample line must be at least 105 percent of the sample system flow rate.

(iv) The overflow gases must enter the sample line as close as practical to the outside surface of the CVS duct or dilution system.

(v) The continuous HC sampling system consists of a probe (which for a HFID analyzer must raise the sample to the specified temperature) and, where used, a sample transfer system (which for a HFID must maintain the specified temperature). The HFID continuous hydrocarbon sampling system (exclusive of the probe) must:

(A) Maintain a wall temperature of 190 ±11 °C as measured at every separately controlled heated component (that is, filters, heated line sections), using permanent thermocouples located at each of the separate components.

(B) Have a wall temperature of 190 ±11 °C over its entire length. The temperature of the system is demonstrated by profiling the thermal characteristics of the system where possible at initial installation and after any major maintenance performed on the system. The profiling is to be accomplished using the insertion thermocouple probing technique. The system temperature must be monitored continuously during testing at the locations and temperature described in §90.421(b)(2).

(C) Maintain a gas temperature of 190 ±11 °C immediately before the heated filter and HFID. Determine these gas temperatures by a temperature sensor located immediately upstream of each component.

(vi) The continuous hydrocarbon sampling probe:

(A) Is defined as the first 25.4 to 76.2 cm of the continuous hydrocarbon sampling system.

(B) Has a 0.483 cm minimum inside diameter.

(C) Is installed in the dilution system at a point where the dilution air and exhaust are well mixed and provide a homogenous mixture.

(D) Is sufficiently distant (radially) from other probes and the system wall so as to be free from the influence of any wakes or eddies.

(E) For a continuous HFID sample probe, the probe must increases the gas stream temperature to 190 ±11 °C at the exit of the probe. Demonstrate the ability of the probe to accomplish this using the insertion thermocouple technique at initial installation and after any major maintenance. Demonstrate compliance with the temperature specification by continuously recording during each test the temperature of either the gas stream or the wall of the sample probe at its terminus.

(vii) The response time of the continuous measurement system must be taken into account when logging test data.

(3) Sample mixing. (i) Configure the dilution system to ensure a well mixed, homogeneous sample prior to the sampling probe(s).

(ii) Make the temperature of the diluted exhaust stream inside the dilution system sufficient to prevent water condensation.

(iii) Direct the engine exhaust downstream at the point where it is introduced into the dilution system.

(4) Continuously integrated NOX, CO, and CO2 measurement systems—(i) Sample probe requirements:

(A) The sample probe for continously intergrated NOX. CO, and CO2 must be in the same plane as the continuous HC probe, but sufficiently distant (radially) from other probes and the tunnel wall so as to be free from the influences of any wakes or eddies.

(B) The sample probe for continously intergrated NOX. CO, and CO2 must be heated and insulated over the entire length, to prevent water condensation, to a minimum temperature of 55 °C. Sample gas temperature immediately before the first filter in the system must be at least 55 °C.

(ii) Conform to the continuous NOX, CO, or CO2 sampling and analysis system to the specifications of 40 CFR 1065.145, with the following exceptions and revisions:

(A) Heat the system components requiring heating only to prevent water condensation, the minimum component temperature is 55 °C.

(B) Coordinate analysis system response time with CVS flow fluctuations and sampling time/test cycle offsets, if necessary.

(C) Use only analytical gases conforming to the specifications of §90.312 of this subpart for calibration, zero and span checks.

(D) Use a calibration curve conforming to §90.321 for CO and CO2 and §90.318 for NOX for any range on a linear analyzer below 155 ppm.

(iii) Convert the chart deflections or voltage output of analyzers with non-linear calibration curves to concentration values by the calibration curve(s) specified in §90.321 of this chapter before flow correction (if used) and subsequent integration takes place.

[60 FR 34598, July 3, 1995, as amended at 70 FR 40450, July 13, 2005]

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§90.422   Background sample.

(a) Background samples are produced by drawing a sample of the dilution air during the exhaust collection phase of each test cycle mode.

(1) An individual background sample may be produced and analyzed for each mode. Hence, a unique background value will be used for the emission calculations for each mode.

(2) Alternatively, a single background sample may be produced by drawing a sample during the collection phase of each test cycle mode. Hence, a single cumulative background value will be used for the emission calculations for each mode.

(b) For analysis of the individual sample described in paragraph (a)(1) of this section, a single value representing the average chart deflection over a 10-second stabilized period must be stored. All readings taken during the data logging period must be stable within ±one percent of full scale.

(c) Measure HC, CO, CO2, and NOX exhaust and background concentrations in the sample bag(s) with approximately the same flow rates and pressures used during calibration.

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§90.423   Exhaust gas analytical system; CVS grab sample.

(a) Schematic drawings. Figure 4 in Appendix B of this subpart is a schematic drawing of the exhaust gas analytical systems used for analyzing CVS grab “bag” samples from spark-ignition engines. Since various configurations can produce accurate results, exact conformance with the drawing is not required. Additional components such as instruments, valves, solenoids, pumps and switches may be used to provide additional information and coordinate the functions of the component systems. Other components such as snubbers, which are not needed to maintain accuracy in some systems, may be excluded if their exclusion is based upon good engineering judgment.

(b) Major component description. The analytical system, Figure 4 in Appendix B of this subpart, consists of a flame ionization detector (FID) or a heated flame ionization detector (HFID) for the measurement of hydrocarbons, non-dispersive infrared analyzers (NDIR) for the measurement of carbon monoxide and carbon dioxide, and a chemiluminescence detector (CLD) (or heated CLD (HCLD)) for the measurement of oxides of nitrogen. The exhaust gas analytical system must conform to the following requirements:

(1) The CLD (or HCLD) requires that the nitrogen dioxide present in the sample be converted to nitric oxide before analysis. Other types of analyzers may be used if shown to yield equivalent results and if approved in advance by the Administrator.

(2) If CO instruments are used which are essentially free of CO2 and water vapor interference, the use of the conditioning column may be deleted. (See §90.317 and §90.320.)

(3) A CO instrument is considered to be essentially free of CO2 and water vapor interference if its response to a mixture of three percent CO2 in N2, which has been bubbled through water at room temperature, produces an equivalent CO response, as measured on the most sensitive CO range, which is less than one percent of full-scale CO concentration on ranges above 300 ppm full scale or less than three ppm on ranges below 300 ppm full scale. (See §90.317.)

(c) Alternate analytical systems. Analysis systems meeting the specifications and requirements of this subpart for dilute sampling may be used upon approval of the Administrator.

(d) Other analyzers and equipment. Other types of analyzers and equipment may be used if shown to yield equivalent results and if approved in advance by the Administrator.

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§90.424   Dilute sampling procedures—CVS calibration.

(a) The CVS is calibrated using an accurate flowmeter and restrictor valve.

(1) The flowmeter calibration must be traceable to the National Institute for Standards and Testing (NIST) and serves as the reference value (NIST “true” value) for the CVS calibration. (Note: In no case should an upstream screen or other restriction which can affect the flow be used ahead of the flowmeter unless calibrated throughout the flow range with such a device.)

(2) The CVS calibration procedures are designed for use of a “metering venturi” type flowmeter. Large radius or American Society of Mechanical Engineers (ASME) flow nozzles are considered equivalent if traceable to NIST measurements. Other measurement systems may be used if shown to be equivalent under the test conditions in this section and traceable to NIST measurements.

(3) Measurements of the various flowmeter parameters are recorded and related to flow through the CVS.

(4) Procedures using both PDP-CVS and CFV-CVS are outlined in the following paragraphs. Other procedures yielding equivalent results may be used if approved in advance by the Administrator.

(b) After the calibration curve has been obtained, verification of the entire system may be performed by injecting a known mass of gas into the system and comparing the mass indicated by the system to the true mass injected. An indicated error does not necessarily mean that the calibration is wrong, since other factors can influence the accuracy of the system (for example, analyzer calibration, leaks, or HC hangup). A verification procedure is found in paragraph (e) of this section.

(c) PDP-CVS calibration. (1) The following calibration procedure outlines the equipment, the test configuration, and the various parameters which must be measured to establish the flow rate of the CVS pump.

(i) All the parameters related to the pump are simultaneously measured with the parameters related to a flowmeter which is connected in series with the pump.

(ii) The calculated flow rate, in cm3/s, (at pump inlet absolute pressure and temperature) can then be plotted versus a correlation function which is the value of a specific combination of pump parameters.

(iii) The linear equation which relates the pump flow and the correlation function is then determined.

(iv) In the event that a CVS has a multiple speed drive, a calibration for each range used must be performed.

(2) This calibration procedure is based on the measurement of the absolute values of the pump and flowmeter parameters that relate the flow rate at each point. Two conditions must be maintained to assure the accuracy and integrity of the calibration curve:

(i) The temperature stability must be maintained during calibration. (Flowmeters are sensitive to inlet temperature oscillations; this can cause the data points to be scattered. Gradual changes in temperature are acceptable as long as they occur over a period of several minutes.)

(ii) All connections and ducting between the flowmeter and the CVS pump must be absolutely void of leakage.

(3) During an exhaust emission test the measurement of these same pump parameters enables the user to calculate the flow rate from the calibration equation.

(4) Connect a system as shown in Figure 5 in Appendix B of this subpart. Although particular types of equipment are shown, other configurations that yield equivalent results may be used if approved in advance by the Administrator. For the system indicated, the following measurements and accuracies are required:

Calibration Data Measurements

Parameter Symbol Units Sensor-readout tolerances
Barometric pressure (corrected)PBkPa±.340 kPa.
Ambient temperatureTA°C±.28 °C.
Air temperature into metering venturiETI°C±1.11 °C.
Pressure drop between the inlet and throat of metering venturiEDPkPa±0.012 kPa.
Air flowQSm3/min.±0.5 percent of NIST value.
Air temperature at CVS pump inletPTI°C±1.11 °C.
Pressure depression at CVS pump inletPPIkPa±0.055 kPa.
Pressure head at CVS pump outletPPOkPa±0.055 kPa.
Air temperature at CVS pump outlet (optional)PTO°C±1.11 °C.
Pump revolutions during test periodNRevs±1 Rev.
Elapsed time for test periodts±0.5 s.

(5) After the system has been connected as shown in Figure 5 in Appendix B of this subpart, set the variable restrictor in the wide open position and run the CVS pump for 20 minutes. Record the calibration data.

(6) Reset the restrictor valve to a more restricted condition in an increment of pump inlet depression that will yield a minimum of six data points for the total calibration. Allow the system to stabilize for three minutes and repeat the data acquisition.

(7) Data analysis:

(i) The air flow rate, Qs, at each test point is calculated in standard cubic feet per minute 20 °C, 101.3 kPa from the flowmeter data using the manufacturer's prescribed method.

(ii) The air flow rate is then converted to pump flow, Vo, in cubic meter per revolution at absolute pump inlet temperature and pressure:

eCFR graphic er03jy95.031.gif

View or download PDF

Where:

Vo = Pump flow, m3/rev at Tp, Pp.

Qs = Meter air flow rate in standard cubic meters per minute, standard conditions are 20 °C, 101.3 kPa.

n = Pump speed in revolutions per minute.

Tp = Absolute pump inlet temperature in Kelvin, = PTI + 273 [°K]

Pp = Absolute pump inlet pressure, kPa. = PB−PPI

Where:

PB = barometric pressure, kPa

PPI = Pump inlet depression, kPa.

(iii) The correlation function at each test point is then calculated from the calibration data:

eCFR graphic er03jy95.032.gif

View or download PDF

Where:

Xo = correlation function.

Δp = The pressure differential from pump inlet to pump outlet [kPa]

Δp = Pe−Pp.

Where:

Pe = Absolute pump outlet pressure [kPa], Pe = PB + PPI

(iv) A linear least squares fit is performed to generate the calibration equation which has the form:

eCFR graphic er03jy95.033.gif

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Where:

Do and M are the intercept and slope constants, respectively, describing the regression line.

(8) A CVS system that has multiple speeds should be calibrated on each speed used. The calibration curves generated for the ranges will be approximately parallel and the intercept values, Do, will increase as the pump flow range decreases.

(9) If the calibration has been performed carefully, the calculated values from the equation will be within ±0.50 percent of the measured value of Vo. Values of M will vary from one pump to another, but values of Do for pumps of the same make, model, and range should agree within ±three percent of each other. Calibrations should be performed at pump start-up and after major maintenance to assure the stability of the pump slip rate. Analysis of mass injection data will also reflect pump slip stability.

(d) CFV-CVS calibration. (1) Calibration of the CFV is based upon the flow equation for a critical venturi. Gas flow is a function of inlet pressure and temperature:

eCFR graphic er03jy95.034.gif

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Where:

Qs = flow rate [m3/min.]

Kv = calibration coefficient

P = absolute pressure [kPa]

T = absolute temperature [°K]

The calibration procedure described in paragraph (d)(3) of this section establishes the value of the calibration coefficient at measured values of pressure, temperature, and air flow.

(2) The manufacturer's recommended procedure must be followed for calibrating electronic portions of the CFV.

(3) Measurements necessary for flow calibration are as follows:

Calibration Data Measurements

ParameterSymbolUnitsTolerances
Barometric Pressure (corrected)PBkPa±.34 kPa
Air temperature, into flowmeterETI°C±.28 °C
Pressure drop between the inlet and throat of metering venturiEDPin. H2 O±.05 in H2 O
Air flowQSm3/min±.5 percent of NIST value
CFV inlet depressionPPI(kPa)±.055 kPa
Temperature at venturi inletTV°C±2.22 °C

(4) Set up equipment as shown in Figure 6 in Appendix B of this subpart and eliminate leaks. (Leaks between the flow measuring devices and the critical flow venturi will seriously affect the accuracy of the calibration.)

(5) Set the variable flow restrictor to the open position, start the blower, and allow the system to stabilize. Record data from all instruments.

(6) Vary the flow restrictor and make at least eight readings across the critical flow range of the venturi.

(7) Data analysis. The data recorded during the calibration are to be used in the following calculations:

(i) Calculate the air flow rate (designated as Qs) at each test point in standard cubic feet per minute from the flow meter data using the manufacturer's prescribed method.

(ii) Calculate values of the calibration coefficient for each test point:

eCFR graphic er03jy95.035.gif

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Where:

Qs = Flow rate in standard cubic meters per minute, at the standard conditions of 20 °C, 101.3 kPa.

Tv = Temperature at venturi inlet, °K.

Pv = Pressure at venturi inlet, kPa = PB − PPI

Where:

PPI = Venturi inlet pressure depression, kPa.

(iii) Plot Kv as a function of venturi inlet pressure. For choked flow, Kv will have a relatively constant value. As pressure decreases (vacuum increases), the venturi becomes unchoked and Kv decreases. (See Figure 7 in Appendix B to Subpart D.)

(iv) For a minimum of eight points in the critical region, calculate an average Kv and the standard deviation.

(v) If the standard deviation exceeds 0.3 percent of the average Kv , take corrective action.

(e) CVS system verification. The following “gravimetric” technique may be used to verify that the CVS and analytical instruments can accurately measure a mass of gas that has been injected into the system. (Verification can also be accomplished by constant flow metering using critical flow orifice devices.)

(1) Obtain a small cylinder that has been charged with 99.5 percent or greater propane or carbon monoxide gas (CAUTION—carbon monoxide is poisonous).

(2) Determine a reference cylinder weight to the nearest 0.01 grams.

(3) Operate the CVS in the normal manner and release a quantity of pure propane into the system during the sampling period (approximately five minutes).

(4) The calculations are performed in the normal way except in the case of propane. The density of propane (0.6109 kg/m3/carbon atom) is used in place of the density of exhaust hydrocarbons.

(5) The gravimetric mass is subtracted from the CVS measured mass and then divided by the gravimetric mass to determine the percent accuracy of the system.

(6) Good engineering practice requires that the cause for any discrepancy greater than ±two percent must be found and corrected.

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§90.425   CVS calibration frequency.

Calibrate the CVS positive displacement pump or critical flow venturi following initial installation, major maintenance, or as necessary when indicated by the CVS system verification (described in §90.424(e)).

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§90.426   Dilute emission sampling calculations—gasoline fueled engines.

(a) The final reported emission test results must be computed by use of the following formula:

eCFR graphic er03jy95.036.gif

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Where:

AWM = Final weighted brake-specific mass emission rate for an emission (HC, CO, CO2, or NOX) [g/kW-hr]

Wi = Average mass flow rate of an emission (HC, CO, CO2, NOX) from a test engine during mode i [g/hr]

WFi = Weighting factor for each mode i as defined in §90.410(a).

Pi = Gross average power generated during mode i [kW], calculated from the following equation,

eCFR graphic er03jy95.037.gif

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Where:

speed = average engine speed measured during mode i [rev./minute]

torque = average engine torque measured during mode i [N-m]

KHi = NOX humidity correction factor for mode i. This correction factor only affects calculations for tion factor only affects calculations for NOX and is equal to one for all other emissions. KHi is also equal to 1 for all two-stroke engines.

(b) The mass flow rate, Wi in g/hr, of an emission for mode i is determined from the following equation:

eCFR graphic er08oc08.081.gif

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Where:

QI = Volumetric flow rate [m3/HR at stp].

Density = Density of a specific emission (DensityHC, DensityCO, DensityCO2, Density NOX) [g/m3].

DFi = Dilution factor of the dilute exhaust during mode i.

CDi = Concentration of the emission (HC, CO, NOX) in dilute exhaust extracted from the CVS during mode i [ppm].

CBi = Concentration of the emission (HC, CO, NOX) in the background sample during mode i [ppm].

STP = Standard temperature and pressure. All volumetric calculations made for the equations in this section are to be corrected to a standard temperature of 20 °C and a standard pressure of 101.3 kPa.

(c) Densities for emissions that are to be measured for this test procedure are:

DensityHC = 576.8 g/m3

DensityNOX = 1912 g/m3

DensityCO = 1164 g/m3

DensityCO2 = 1829 g/m3

(1) The value of DensityHC above is calculated based on the assumption that the fuel used has a hydrogen to carbon ratio of 1:1.85. For other fuels DensityHC can be calculated from the following formula:

eCFR graphic er08oc08.082.gif

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Where:

MHC = The molecular weight of the hydrocarbon molecule divided by the number of carbon atoms in the molecule [g/mole].

RSTP = Ideal gas constant for a gas at STP = 0.024065 [m3·mole]

(2) The idealized molecular weight of the exhaust hydrocarbons, i.e., the molecular weight of the hydrocarbon molecule divided by the number of carbon atoms in the molecule, MHC, can be calculated from the following formula:

eCFR graphic er03jy95.040.gif

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Where:

MC = Molecular weight of carbon = 12.01 [g/mole]

MH = Molecular weight of hydrogen = 1.008 [g/mole]

MO = Molecular weight of oxygen = 16.00 [g/mole]

α = Hydrogen to carbon ratio of the test fuel

β = Oxygen to carbon ratio of the test fuel

(3) The value of DensityNOX above assumes that NOX is entirely in the form of NO2

(d) The dilution factor, DF, is the ratio of the volumetric flow rate of the background air to that of the raw engine exhaust. The following formula is used to determine DF:

eCFR graphic er08oc08.083.gif

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Where:

CDHC = Concentration of HC in the dilute sample [ppm].

CDCO = Concentration of CO in the dilute sample [ppm].

CDCO2 = Concentration of CO2 in the dilute sample [ppm].

(e) The humidity correction factor KH is an adjustment made to measured NOX values. This corrects for the sensitivity that a spark-ignition engine has to the humidity of its combustion air. The following formula is used to determine KH for NOX calculations:

KH = (9.953 H + 0.832)

Where:

H = the amount of water in an ideal gas; 40 CFR 1065.645 describes how to determine this value (referred to as xH2O).

KH = 1 for two-stroke gasoline engines.

(f)-(g) [Reserved]

(h) The fuel mass flow rate, Fi, can be either measured or calculated using the following formula:

eCFR graphic er03jy95.046.gif

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Where:

MFUEL = Mass of fuel consumed by the engine during the mode [g]

T = Duration of the sampling period [hr]

(i) The mass of fuel consumed during the mode smpling period, MFUEL, can be calculated from the following equation:

eCFR graphic er08oc08.084.gif

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Where:

GS = Mass of carbon measured during the mode sampling period [g].

R2 = The fuel carbon weight fraction, which is the mass of carbon in fuel per mass of fuel [g/g].

(j) The grams of carbon measured during the mode, GS, can be calculated from the following equation:

eCFR graphic er08oc08.085.gif

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Where:

HCmass = mass of hydrocarbon emissions for the mode sampling period [grams].

COmass mass of carbon monoxide emissions for the mode sample period [grams].

CO2mass = mass of carbon dioxide emissions for the mode sample period [grams].

α = The atomic hydrogen-to-carbon ratio of the fuel.

[60 FR 34598, July 3, 1995, as amended at 70 FR 40450, July 13, 2005; 73 FR 59182, Oct. 8, 2008]

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§90.427   Catalyst thermal stress resistance evaluation.

(a) The purpose of the evaluation procedure specified in this section is to determine the effect of thermal stress on catalyst conversion efficiency for Phase 1 engines. The thermal stress is imposed on the test catalyst by exposing it to quiescent heated air in an oven. The evaluation of the effect of such stress on catalyst performance is based on the resultant degradation of the efficiency with which the conversions of specific pollutants are promoted. The application of this evaluation procedure involves the several steps that are described in the following paragraphs.

(b) Determination of initial conversion efficiency. (1) A synthetic exhaust gas mixture having the composition specified in §90.329 is heated to a temperature of 450 °C ±5 °C and passed through the new test catalyst or, optionally, a test catalyst that has been exposed to temperatures less than or equal to 500 °C for less than or equal to two hours, under flow conditions that are representative of anticipated in-use conditions.

(2) The concentration of each pollutant of interest, that is, hydrocarbons, carbon monoxide, or oxides of nitrogen, in the effluent of the catalyst is determined by means of the instrumentation that is specified for exhaust gas analysis in subpart D of this part.

(3) The conversion efficiency for each pollutant is determined by:

(i) Subtracting the effluent concentration from the initial concentration;

(ii) Dividing this result by the initial concentration; and

(iii) Multiplying this result by 100 percent.

(c) Imposition of thermal stress. (1) The catalyst is placed in an oven that has been pre-heated to 1000 °C and the temperature of the air in the oven is maintained at 1000 °C ±10 °C for six hours.

(2) The catalyst is removed from the oven and allowed to cool to room temperature.

(d) Determination of final conversion efficiency. The steps listed in paragraph (b) of this section are repeated.

(e) Determination of conversion efficiency degradation. (1) The final conversion efficiency determined in paragraph (c) of this section is subtracted from the initial conversion efficiency determined in paragraph (b) of this section.

(2) This result is divided by the initial conversion efficiency.

(3) This result is multiplied by 100 percent.

(f) Determination of compliance with degradation limit. The percent degradation determined in paragraph (e) of this section must not be greater than 20 percent.

[60 FR 34598, July 3, 1995, as amended at 64 FR 15244, Mar. 30, 1999]

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Appendix A to Subpart E of Part 90—Tables

Table 1—Parameters to be Measured or Calculated and Recorded

Parameter Units
Airflow rate (dry), if applicableg/h
Fuel flow rateg/h
Engine Speedrpm
Engine Torque OutputN m
Power OutputkW
Air inlet temperature°C
Air humiditymg/kg
Coolant temperature (liquid cooled)°C
Exhaust mixing chamber surface temperature, if applicable°C
Exhaust sample line temperature, if applicable°C
Total Accumulated hours of Engine Operationh
Barometric PressurekPa

Table 2—Test Cycles for Class I-A, I-B, and Class I-V Engines

Mode Speed1234567891011
   Rated SpeedIntermediate SpeedIdle
Mode Points—A Cycle123456
Load Percent—A Cycle100755025100
Weighting9%20%29%30%7%5%
Mode Points—B Cycle123456
Load Percent—B Cycle100755025100
Weighting9%20%29%30%7%5%
Mode Points—C Cycle12
Load Percent—C Cycle1000
Weighting for Phase 1 Engines90%10%
Weighting for Phase 2 Engines85%15%

[60 FR 34598, July 3, 1995, as amended at 65 FR 24313, Apr. 25, 2000]

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Appendix B to Subpart E of Part 90—Figures

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eCFR graphic ec01mr92.088.gif

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eCFR graphic ec01mr92.008.gif

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