Document ID: chunk:federal_register_of_legislation:F2023C00229:reg:10:p20
Version: federal_register_of_legislation:F2023C00229
Segment Type: reg
Provision Reference: reg 10 (pt 20/30)
Character Range: 575386–578221

shall especially not be affected by the installation of the device.

              The accuracy of exhaust flow determination shall be at least ± 2,5 % of reading or ± 1,5 % of engine's maximum value, whichever is the greater.

        4.2.3. Air and fuel measurement method

              This involves measurement of the air flow and the fuel flow. Air flowmeters and fuel flowmeters shall be used that meet the total exhaust flow accuracy requirement of section 4.2.2. The calculation of the exhaust gas flow is as follows:

qmew  = qmaw  + qmf

        4.2.4. Tracer measurement method

              This involves measurement of the concentration of a tracer gas in the exhaust. A known amount of an inert gas (e.g. pure helium) shall be injected into the exhaust gas flow as a tracer. The gas is mixed and diluted by the exhaust gas, but shall not react in the exhaust pipe. The concentration of the gas shall then be measured in the exhaust gas sample.

              In order to ensure complete mixing of the tracer gas, the exhaust gas sampling probe shall be located at least 1 m or 30 times the diameter of the exhaust pipe, whichever is larger, downstream of the tracer gas injection point. The sampling probe may be located closer to the injection point if complete mixing is verified by comparing the tracer gas concentration with the reference concen- tration when the tracer gas is injected upstream of the engine.

              The tracer gas flow rate shall be set so that the tracer gas concentration at engine idle speed after mixing becomes lower than the full scale of the trace gas analyser.

              The calculation of the exhaust gas flow is as follows:

where:

qmew,i  =  instantaneous exhaust mass flow, kg/s
qvt     =  tracer gas flow, cm3/min
cmix.i  =  instantaneous concentration of the tracer gas after mixing, ppm
ρe      =  density of the exhaust gas, kg/m3 (cf. table 3)
ca      =  background concentration of the tracer gas in the intake air, ppm

              When the background concentration is less than 1 % of the concentration of the tracer gas after mixing (cmix.i) at maximum exhaust flow, the background concentration may be neglected.

              The total system shall meet the accuracy specifications for the exhaust gas flow, and shall be calibrated according to section 1.7 of Appendix 5 to this Annex.

        4.2.5. Air flow and air-to-fuel ratio measurement method

              This involves exhaust mass calculation from the air flow and the air to fuel ratio. The calculation of the instantaneous exhaust gas mass flow is as follows:

              with:

where:
A/Fst   =  stoichiometric air to fuel ratio, kg/kg
λ       =  excess air ratio
cCO2    =  dry CO2 concentration, %
cCO     =  dry CO concentration, ppm
cHC     =  HC concentration, ppm