Determining steady-state engine fuel maps and fuel consumption at idle.
§ 1036.535 Determining steady-state engine fuel maps and fuel consumption at idle.
This section describes how to determine an engine's steady-state fuel map and fuel consumption at idle for model year 2021 and later vehicles. Vehicle manufacturers may need these values to demonstrate compliance with emission standards under 40 CFR part 1037 as described in § 1036.510.
(a) General test provisions. Perform fuel mapping using the procedure described in paragraph (b) of this section to establish measured fuel-consumption rates at a range of engine speed and load settings. Measure fuel consumption at idle using the procedure described in paragraph (c) of this section. If you perform cycle-average mapping for highway cruise cycles as described in § 1036.540, omit mapping under paragraph (b) of the section and instead perform mapping as described in paragraph (d) of this section. Use these measured fuel-consumption values to declare fuel-consumption rates for certification as described in paragraph (e) of this section.
(1) Map the engine's torque curve and declare engine idle speed as described in § 1036.503(c)(1) and (3), and perform emission measurements as described in 40 CFR 1065.501 and 1065.530 for discrete-mode steady-state testing. This section uses engine parameters and variables that are consistent with 40 CFR part 1065.
(2) Measure NOX emissions for each specified sampling period in g/s. You may perform these measurements using a NOX emission-measurement system that meets the requirements of 40 CFR part 1065, subpart J. Include these measured NOX values any time you report to us your fuel consumption values from testing under this section. If a system malfunction prevents you from measuring NOX emissions during a test under this section but the test otherwise gives valid results, you may consider this a valid test and omit the NOX emission measurements; however, we may require you to repeat the test if we determine that you inappropriately voided the test with respect to NOX emission measurement.
(b) Steady-state fuel mapping. Determine fuel-consumption rates for each engine configuration over a series of steady-state engine operating points consisting of pairs of speed and torque points as described in this paragraph (b). You may use shared data across an engine platform to the extent that the fuel-consumption rates remain valid. For example, if you test a high-output configuration and create a different configuration that uses the same fueling strategy but limits the engine operation to be a subset of that from the high-output configuration, you may use the fuel-consumption rates for the reduced number of mapped points for the low-output configuration, as long as the narrower map includes at least 70 points. Perform fuel mapping as follows:
(1) Generate the sequence of steady-state engine operating points as follows:
(i) Determine the required steady-state engine operating points as follows:
(A) For engines with an adjustable warm idle speed setpoint, select the following speed setpoints: Minimum warm idle speed, fnidlemin, the highest speed above maximum power at which 70% of maximum power occurs, nhi, and eight (or more) equally spaced points between fnidlemin and nhi. (See 40 CFR 1065.610(c)). For engines without an adjustable warm idle speed replace minimum warm idle speed with warm idle speed, fnidle.
(B) Select the following torque setpoints at each of the selected speed setpoints: Zero (T = 0), maximum mapped torque, Tmax mapped, and eight (or more) equally spaced points between T = 0 and Tmax mapped. For each of the selected speed setpoints, replace any torque setpoints that are above the mapped torque at the selected speed setpoint, Tmax, minus 5 percent of Tmax mapped, with one test point at Tmax.
(ii) Select any additional (optional) steady-state engine operating points consistent with good engineering judgment. For example you may select additional points when linear interpolation between the defined points is not a reasonable assumption for determining fuel consumption from the engine. For each additional speed setpoint, increments between torque setpoints must be no larger than one-ninth of Tmax,mapped and we recommend including a torque setpoint of Tmax. If you select a maximum torque setpoint less than Tmax, use good engineering judgment to select your maximum torque setpoint to avoid unrepresentative data. Note that if the test points were added for the child rating, they should still be reported in the parent fuel map. We will select at least as many points as you.
(iii) Set the run order for all of the steady-state engine operating points (both required and optional) as described in this paragraph (b)(1)(iii). Arrange the list of steady-state engine operating points such that the resulting list of paired speed and torque setpoints begins with the highest speed setpoint and highest torque setpoint followed by decreasing torque setpoints at the highest speed setpoint. This will be followed by the next lowest speed setpoint and the highest torque setpoint at that speed setpoint continuing through all the steady-state engine operating points and ending with the lowest speed (fnidlemin) and torque setpoint (T = 0). The following figure provides an example of this array of points and run order.
(iv) The steady-state engine operating points that have the highest torque setpoint for a given speed setpoint are optional reentry points into the steady-state-fuel-mapping sequence, should you need to pause or interrupt the sequence during testing.
(v) The steady-state engine operating points that have the lowest torque setpoint for a given speed setpoint are optional exit points from the steady-state-fuel-mapping sequence, should you need to pause or interrupt the sequence during testing.
(2) If the engine has an adjustable warm idle speed setpoint, set it to its minimum value, fnidlemin.
(3) During each test interval, control speed within ±1% of nhi and engine torque within ±5% of Tmax mapped except for the following cases where both setpoints cannot be achieved because the steady-state engine operating point is near an engine operating boundary:
(i) For steady-state engine operating points that cannot be achieved and the operator demand stabilizes at minimum; control the dynamometer so it gives priority to follow the torque setpoint and let the engine govern the speed (see 40 CFR 1065.512(b)(1)). In this case, the tolerance on speed control in paragraph (b)(3) of this section does not apply and engine torque is controlled to within ±25 N·m.
(ii) For steady-state engine operating points that cannot be achieved and the operator demand stabilizes at maximum and the speed setpoint is below 90% of nhi; control the dynamometer so it gives priority to follow the speed setpoint and let the engine govern the torque (see 40 CFR 1065.512(b)(2)). In this case, the tolerance on torque control given in paragraph (b)(3) of this section does not apply.
(iii) For steady-state engine operating points that cannot be achieved and the operator demand stabilizes at maximum and the speed setpoint is at or above 90% of nhi; control the dynamometer so it gives priority to follow the torque setpoint and let the engine govern the speed (see 40 CFR 1065.512(b)(1)). In this case, the tolerance on speed control given in paragraph (b)(3) of this section does not apply.
(iv) For the steady-state engine operating points at the minimum speed setpoint and maximum torque setpoint, you may select a dynamometer control mode that gives priority to speed and an engine control mode that gives priority to torque. In this case, if the operator demand stabilizes at minimum or maximum, the tolerance on torque control in paragraph (b)(3) of this section does not apply.
(4) You may select the appropriate dynamometer and engine control modes in real-time or at any time prior based on various factors including the operating setpoint location relative to an engine operating boundary. Warm-up the engine as described in 40 CFR 1065.510(b)(2).
(5) Within 60 seconds after concluding the warm-up, linearly ramp the speed and torque setpoints over 5 seconds to the first steady-state engine operating point from paragraph (b)(1) of this section.
(6) Operate the engine at the steady-state engine operating point for (70 ±1) seconds, and then start the test interval and record measurements using one of the following methods. You must also measure and report NOX emissions over each test interval as described in paragraph (a)(2) of this section. If you use redundant systems for the determination of fuel consumption, for example combining measurements of dilute and raw emissions when generating your map, follow the requirements of 40 CFR 1065.201(d).
(i) Indirect measurement of fuel flow. Record speed and torque and measure emissions and other inputs needed to run the chemical balance in 40 CFR 1065.655(c) for a (30 ±1) second test interval; determine the corresponding mean values for the test interval. For dilute sampling of emissions, in addition to the background measurement provisions described in 40 CFR 1065.140 you may do the following:
(A) If you use batch sampling to measure background emissions, you may sample periodically into the bag over the course of multiple test intervals and read them as allowed in paragraph (b)(7)(i) of this section. If you use this paragraph (b)(6)(i)(A), you must apply the same background readings to correct emissions from each of the applicable test intervals.
(B) You may determine background emissions by sampling from the dilution air during the non-test interval periods in the test sequence, including pauses allowed in paragraph (b)(7)(i) of this section. If you use this paragraph (b)(6)(i)(B), you must allow sufficient time for stabilization of the background measurement; followed by an averaging period of at least 30 seconds. Use the average of the most recent pre-test interval and the next post-test interval background readings to correct each test interval. The most recent pre-test interval background reading must be taken no greater than 30 minutes prior to the start of the first applicable test interval and the next post-test interval background reading must be taken no later than 30 minutes after the end of the last applicable test interval. Background readings must be taken prior to the test interval for each reentry point and after the test interval for each exit point or more frequently.
(ii) Direct measurement of fuel flow. Record speed and torque and measure fuel consumption with a fuel flow meter for a (30 ±1) second test interval; determine the corresponding mean values for the test interval.
(7) After completing the test interval described in paragraph (b)(6) of this section, linearly ramp the speed and torque setpoints over 5 seconds to the next steady-state engine operating point.
(i) You may pause the steady-state-fuel-mapping sequence at any of the reentry points (as noted in paragraph (b)(1)(iv) of this section) to calibrate emission-measurement instrumentation; to read and evacuate background bag samples collected over the course of multiple test intervals; or to sample the dilution air for background emissions. This paragraph (b)(7)(i) allows you to spend more than the 70 seconds noted in paragraph (b)(6) of this section.
(ii) If an infrequent regeneration event occurs, interrupt the steady-state-fuel-mapping sequence and allow the regeneration event to finish. You may continue to operate at the steady-state engine operating point where the event began or, using good engineering judgment, you may transition to another operating condition to reduce the regeneration event duration. You may complete any post-test interval activities to validate test intervals prior to the most recent reentry point. Once the regeneration event is finished, linearly ramp the speed and torque setpoints over 5 seconds to the most recent reentry point described in paragraph (b)(1)(iv) of this section, and restart the steady-state-fuel-mapping sequence by repeating the steps in paragraphs (b)(6) and (7) of this section for all the remaining steady-state engine operating points. Operate at the reentry point for longer than the 70 seconds in paragraph (b)(6), as needed, to bring the aftertreatment to representative thermal conditions. Void all test intervals in the steady-state-fuel-mapping sequence beginning with the reentry point and ending with the steady-state engine operating point where the regeneration event began.
(iii) You may interrupt the steady-state-fuel-mapping sequence after any of the exit points described in paragraph (b)(1)(v) of this section. To restart the steady-state-fuel-mapping sequence; begin with paragraph (b)(4) of this section and continue with paragraph (b)(5) of this section, except that the steady-state engine operating point is the next reentry point, not the first operating point from paragraph (b)(1) of this section. Follow paragraphs (b)(6) and (7) of this section until all remaining steady-state engine operating points are tested.
(iv) If the steady-state-fuel-mapping sequence is interrupted due test equipment or engine malfunction, void all test intervals in the steady-state-fuel-mapping sequence beginning with the most recent reentry point as described in paragraph (b)(1)(iv) of this section. Complete any post-test interval activities to validate test intervals prior to the most recent reentry point. Correct the malfunction and restart the steady-state-fuel-mapping sequence as described in paragraph (b)(7)(iii) of this section.
(v) If any steady-state engine test interval is voided, void all test intervals in the steady-state-fuel-mapping sequence beginning with the most recent reentry point as described in paragraph (b)(1)(iv) of this section and ending with the next exit point as described in paragraph (b)(1)(v) of this section. Rerun that segment of the steady-state-fuel-mapping sequence. If multiple test intervals are voided in multiple speed setpoints, you may exclude the speed setpoints where all of the test intervals were valid from the rerun sequence. Rerun the steady-state-fuel-mapping sequence as described in paragraph (b)(7)(iii) of this section.
(8) If you determine fuel-consumption rates using emission measurements from the raw or diluted exhaust, calculate the mean fuel mass flow rate, ṁ̅fuel, for each point in the fuel map using the following equation:
Where:
ṁ̅fuel = mean fuel mass flow rate for a given fuel map setpoint, expressed to at least the nearest 0.001 g/s.
MC = molar mass of carbon.
wCmeas = carbon mass fraction of fuel (or mixture of test fuels) as determined in 40 CFR 1065.655(d), except that you may not use the default properties in Table 1 of 40 CFR 1065.655 to determine α, β, and wC for liquid fuels. You may not account for the contribution to α, β, γ, and δ of diesel exhaust fluid or other non-fuel fluids injected into the exhaust.
ṅ̅exh = the mean raw exhaust molar flow rate from which you measured emissions according to 40 CFR 1065.655.
xCcombdry = the mean concentration of carbon from fuel and any injected fluids in the exhaust per mole of dry exhaust as determined in 40 CFR 1065.655(c).
xH2Oexhdry = the mean concentration of H2O in exhaust per mole of dry exhaust as determined in 40 CFR 1065.655(c).
ṁ̅CO2DEF = the mean CO2 mass emission rate resulting from diesel exhaust fluid decomposition as determined in paragraph (b)(9) of this section. If your engine does not use diesel exhaust fluid, or if you choose not to perform this correction, set ṁ̅CO2DEF equal to 0.
MCO2 = molar mass of carbon dioxide.
Example:
MC = 12.0107 g/mol
wCmeas = 0.869
ṅ̅exh = 25.534 mol/s
xCcombdry = 0.002805 mol/mol
xH2Oexhdry = 0.0353 mol/mol
ṁ̅CO2DEF = 0.0726 g/s
MCO2 = 44.0095 g/mol
(9) If you determine fuel-consumption rates using emission measurements with engines that utilize diesel exhaust fluid for NOX control, correct for the mean CO2 mass emissions resulting from diesel exhaust fluid decomposition at each fuel map setpoint using the following equation:
Where:
ṁ̅DEF = the mean mass flow rate of injected urea solution diesel exhaust fluid for a given sampling period, determined directly from the electronic control module, or measured separately, consistent with good engineering judgment.
MCO2 = molar mass of carbon dioxide.
wCH4N2O = mass fraction of urea in diesel exhaust fluid aqueous solution. Note that the subscript “CH4N2O” refers to urea as a pure compound and the subscript “DEF” refers to the aqueous urea diesel exhaust fluid as a solution of urea in water. You may use a default value of 32.5% or use good engineering judgment to determine this value based on measurement.
MCH4N2O = molar mass of urea.
Example:
ṁ̅DEF = 0. 304 g/s
MCO2 = 44.0095 g/mol
wCH4N2O = 32.5% = 0.325
MCH4N2O = 60.05526 g/mol
(c) Fuel consumption at idle. Determine fuel-consumption rates for engines certified for installation in vocational vehicles for each engine configuration over a series of engine-idle operating points consisting of pairs of speed and torque points as described in this paragraph (c). You may use shared data across engine configurations, consistent with good engineering judgment. Perform measurements as follows:
(1) Determine the required engine-idle operating points as follows:
(i) Select the following two speed setpoints:
(A) Engines with an adjustable warm idle speed setpoint: Minimum warm idle speed, fnidlemin, and the maximum warm idle speed, fnidlemax.
(B) Engines without an adjustable warm idle speed setpoint: Warm idle speed (with zero torque on the primary output shaft), fnidle, and 1.15 times fnidle.
(ii) Select the following two torque setpoints at each of the selected speed setpoints: 0 and 100 N·m.
(iii) You may run these four engine-idle operating points in any order.
(2) Control speed and torque as follows:
(i) Engines with an adjustable warm idle speed setpoint. For the warm-up in paragraph (c)(3) of this section and the transition in paragraph (c)(4) of this section control both speed and torque. At any time prior to reaching the next engine-idle operating point, set the engine's adjustable warm idle speed setpoint to the speed setpoint of the next engine-idle operating point in the sequence. This may be done before or during the warm-up or during the transition. Near the end of the transition period control speed and torque as described in paragraph (b)(3)(i) of this section. Once the transition is complete; set the operator demand to minimum to allow the engine governor to control speed; and control torque with the dynamometer as described in paragraph (b)(3) of this section.
(ii) Engines without an adjustable warm idle speed setpoint. Control speed and torque with operator demand and the dynamometer for the engine-idle operating points at the higher speed setpoint as described in paragraph (b)(3) of this section. Both the speed and torque tolerances apply for these points because they are not near the engine's operating boundary and are achievable. Control speed and torque for the engine-idle operating points at the lower speed setpoint as described in paragraph (c)(2)(i) of this section except for setting the engine's adjustable warm idle speed setpoint.
(3) Warm-up the engine as described in 40 CFR 1065.510(b)(2).
(4) After concluding the warm-up procedure, linearly ramp the speed and torque setpoints over 20 seconds to operate the engine at the next engine-idle operating point from paragraph (c)(1) of this section.
(5) Operate the engine at the engine-idle operating point for (180 ±1) seconds, and then start the test interval and record measurements using one of the following methods. You must also measure and report NOX emissions over each test interval as described in paragraph (a)(2) of this section. If you use redundant systems for the determination of fuel consumption, for example combining measurements of dilute and raw emissions when generating your map, follow the requirements of 40 CFR 1065.201(d).
(i) Indirect measurement of fuel flow. Record speed and torque and measure emissions and other inputs needed to run the chemical balance in 40 CFR 1065.655(c) for a (600 ±1) second test interval; determine the corresponding mean values for the test interval. We will use an average of indirect measurement of fuel flow with dilute sampling and direct sampling. For dilute sampling of emissions, measure background according to the provisions described in 40 CFR 1065.140, but read the background as described in paragraph (c)(7)(i) of this section. If you use batch sampling to measure background emissions, you may sample periodically into the bag over the course of multiple test intervals and read them as allowed in paragraph (b)(7)(i) of this section. If you use this paragraph (c)(5)(i), you must apply the same background readings to correct emissions from each of the applicable test intervals. Note that the minimum dilution ratio requirements for PM sampling in 40 CFR 1065.140(e)(2) do not apply. We recommend minimizing the CVS flow rate to minimize errors due to background correction consistent with good engineering judgment and operational constraints such as minimum flow rate for good mixing.
(ii) Direct measurement of fuel flow. Record speed and torque and measure fuel consumption with a fuel flow meter for a (600 ±1) second test interval; determine the corresponding mean values for the test interval.
(6) After completing the test interval described in paragraph (c)(5) of this section, repeat the steps in paragraphs (c)(3) through (5) of this section for all the remaining engine-idle operating points. After completing the test interval on the last engine-idle operating point, the fuel-consumption-at-idle sequence is complete.
(7) The following provisions apply for interruptions in the fuel-consumption-at-idle sequence in a way that is intended to produce results equivalent to running the sequence without interruption:
(i) You may pause the fuel-consumption-at-idle sequence after each test interval to calibrate emission-measurement instrumentation and to read and evacuate background bag samples collected over the course of a single test interval. This paragraph (c)(7)(i) allows you to shut-down the engine or to spend more time at the speed/torque idle setpoint after completing the test interval before transitioning to the step in paragraph (c)(3) of this section.
(ii) If an infrequent regeneration event occurs, interrupt the fuel-consumption-at-idle sequence and allow the regeneration event to finish. You may continue to operate at the engine-idle operating point where the event began or, using good engineering judgment, you may transition to another operating condition to reduce the regeneration event duration. If the event occurs during a test interval, void that test interval. Once the regeneration event is finished, restart the fuel-consumption-at-idle sequence by repeating the steps in paragraphs (c)(3) through (5) of this section for all the remaining engine-idle operating points.
(iii) You may interrupt the fuel-consumption-at-idle sequence after any of the test intervals. Restart the fuel-consumption-at-idle sequence by repeating the steps in paragraphs (c)(3) through (5) of this section for all the remaining engine-idle operating points.
(iv) If the fuel-consumption-at-idle sequence is interrupted due to test equipment or engine malfunction, correct the malfunction and restart the fuel-consumption-at-idle sequence by repeating the steps in paragraphs (c)(3) through (5) of this section for all the remaining engine-idle operating points. If the malfunction occurred during a test interval, void that test interval.
(v) If any idle test intervals are voided, repeat the steps in paragraphs (c)(3) through (5) of this section for each of the voided engine-idle operating points.
(8) Correct the measured or calculated mean fuel mass flow rate, ṁ̅fuel at each of the engine-idle operating points to account for mass-specific net energy content as described in paragraph (b)(13) of this section.
(d) Steady-state fuel maps used for cycle-average fuel mapping of the cruise cycles. Determine fuel-consumption rates for each engine configuration over a series of steady-state engine operating points near idle as described in this paragraph (d). You may use shared data across an engine platform to the extent that the fuel-consumption rates remain valid.
(1) Perform steady-state fuel mapping as described in paragraph (b) of this section with the following exceptions:
(i) All the required steady-state engine operating points as described in paragraph (b)(1)(i) of this section are optional.
(ii) Select speed setpoints to cover the range of idle speeds expected as follows:
(A) The minimum number of speed setpoints is two.
(B) For engines with an adjustable warm idle speed setpoint, the minimum speed setpoint must be equal to the minimum warm idle speed, fnidlemin, and the maximum speed setpoint must be equal to or greater than the maximum warm idle speed, fnidlemax. The minimum speed setpoint for engines without an adjustable warm idle speed setpoint, must be equal to the warm idle speed (with zero torque on the primary output shaft), fnidle, and the maximum speed setpoint must be equal to or greater than 1.15 times the warm idle speed, fnidle.
(iii) Select torque setpoints at each speed setpoint to cover the range of idle torques expected as follows:
(A) The minimum number of torque setpoints at each speed setpoint is three. Note that you must meet the minimum torque spacing requirements described in paragraph (b)(1)(ii) of this section.
(B) The minimum torque setpoint at each speed setpoint is zero.
(C) The maximum torque setpoint at each speed setpoint must be greater than or equal to the estimated maximum torque at warm idle (in-drive) conditions, Tidlemaxest, using the following equation. For engines with an adjustable warm idle speed setpoint, evaluate Tidlemaxest at the maximum warm idle speed, fnidlemax. For engines without an adjustable warm idle speed setpoint, use the warm idle speed (with zero torque on the primary output shaft), fnidle.
Where:
Tfnstall = the maximum engine torque at fnstall.
fnidle = the applicable engine idle speed as described in this paragraph (d).
fnstall = the stall speed of the torque converter; use fntest or 2250 r/min, whichever is lower.
Pacc = accessory power for the vehicle class; use 1500 W for Vocational Light HDV, 2500 W for Vocational Medium HDV, and 3500 W for Tractors and Vocational Heavy HDV.
Example:
Tfnstall = 1870 N·m
fntest = 1740.8 r/min = 182.30 rad/s
fnstall = 1740.8 r/min = 182.30 rad/s
fnidle = 700 r/min = 73.30 rad/s
Pacc = 1500 W
(2) Remove the points from the default map that are below 115% of the maximum speed and 115% of the maximum torque of the boundaries of the points measured in paragraph (d)(1) of this section.
(3) Add the points measured in paragraph (d)(1) of this section.
(e) Carbon balance verification. The provisions related to carbon balance verification in § 1036.543 apply to test intervals in this section.
(f) Correction for net energy content. Correct the measured or calculated mean fuel mass flow rate, ṁ̅fuel at each engine operating condition as specified in paragraphs (b), (c), and (d) of this section to a mass-specific net energy content of a reference fuel using the following equation:
Where:
Emfuelmeas = the mass-specific net energy content of the test fuel as determined in § 1036.530(b)(1).
EmfuelCref = the reference value of carbon-mass-specific net energy content for the appropriate fuel. Use the values shown in Table 1 of § 1036.530 for the designated fuel types, or values we approve for other fuel types.
wCref = the reference value of carbon mass fraction for the test fuel as shown in Table 1 of § 1036.530 for the designated fuels. For other fuels, use the reference carbon mass fraction of diesel fuel for engines subject to compression-ignition standards, and use the reference carbon mass fraction of gasoline for engines subject to spark-ignition standards.
Example:
ṁ̅fuel = 0.933 g/s
Emfuelmeas = 42.7984 MJ/kgC
EmfuelCref = 49.3112 MJ/kgC
wCref = 0.874
(g) Measured vs. declared fuel-consumption rates. Select fuel-consumption rates in g/s to characterize the engine's fuel maps. These declared values may not be lower than any corresponding measured values determined in paragraphs (b) through (d) of this section. This includes if you use multiple measurement methods as allowed in paragraph (b)(7) of this section. You may select any value that is at or above the corresponding measured value. These declared fuel-consumption rates, which serve as emission standards under § 1036.108, are the values that vehicle manufacturers will use for certification under 40 CFR part 1037. Note that production engines are subject to GEM cycle-weighted limits as described in § 1036.301. If you perform the carbon balance error verification in § 1036.543, for each fuel map data point:
(1) If you pass the ∈rC verification, you must declare fuel-consumption rates no lower than the average of the direct and indirect fuel measurements.
(2) If you pass either the ∈aC verification or ∈aCrate verification and fail the ∈rC verification, you must declare fuel-consumption rates no lower than the indirect fuel measurement.
(3) If you don't pass the ∈rC, ∈aC, and ∈aCrate verifications, you must declare fuel-consumption rates no lower than the highest rate for the direct and indirect fuel measurements.
(h) EPA measured fuel-consumption rates. If we pass the carbon mass relative error for a test interval (∈rC) verification, the official fuel-consumption rate result will be the average of the direct and indirect fuel measurements. If we pass either the carbon mass absolute error for a test interval (∈aC) verification or carbon mass rate absolute error for a test interval (∈aCrate) verification and fail the ∈rC verification, the official fuel-consumption rate result will be the indirect fuel measurement.
[86 FR 34388, June 29, 2021]
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