Document ID: chunk:federal_register_of_legislation:F2024C00356:reg:21:p6
Version: federal_register_of_legislation:F2024C00356
Segment Type: reg
Provision Reference: reg 21 (pt 6/35)
Character Range: 303638–306672

within 0.25 kPa may be used if               a written request from a manufacturer to the Technical Service               substantiates the need for the closer tolerance;

                 (c) Shall not change the nature of the exhaust gas;

                 (d) Any elastomer connectors employed shall be as thermally stable as   possible and have minimum exposure to the exhaust gases.

1.3.2.  Dilution Air Conditioning
                The dilution air used for the primary dilution of the exhaust in the CVS  tunnel shall be passed through a medium capable of reducing particles in               the most penetrating particle size of the filter material by ≥ 99.95 per cent,               or through a filter of at least class H13 of EN 1822:1998. This represents the specification of High Efficiency Particulate Air (HEPA) filters. The dilution air may optionally be charcoal scrubbed before being passed to the HEPA filter. It is recommended that an additional coarse particle filter is situated before the HEPA filter and after the charcoal scrubber, if used.
                At the vehicle manufacturer's request, the dilution air may be sampled according to good engineering practice to determine the tunnel contribution to background particulate mass levels, which can then be subtracted from the values measured in the diluted exhaust.
1.3.3.  Dilution Tunnel
  Provision shall be made for the vehicle exhaust gases and the dilution air   to be mixed. A mixing orifice may be used.
                In order to minimise the effects on the conditions at the exhaust outlet and to limit the drop in pressure inside the dilution-air conditioning device, if any, the pressure at the mixing point shall not differ by more than ±0.25 kPa from atmospheric pressure.
                The homogeneity of the mixture in any cross-section at the location of the sampling probe shall not vary by more than ±2 per cent from the average of the values obtained for at least five points located at equal intervals on the diameter of the gas stream.
                For particulate and particle emissions sampling, a dilution tunnel shall be used which:
                (a) Shall consist of a straight tube of electrically-conductive material,  which shall be earthed;

                (b) Shall be small enough in diameter to cause turbulent flow  (Reynolds number  4000) and of sufficient length to cause               complete mixing of the exhaust and dilution air;

                (c) Shall be at least 200 mm in diameter;

                (d) May be insulated.

              1.3.4.  Suction Device
                This device may have a range of fixed speeds to ensure sufficient flow to prevent any water condensation. This result is generally obtained if the flow is either:

                (a) Twice as high as the maximum flow of exhaust gas produced by                accelerations of the driving cycle; or

               (b) Sufficient to ensure that the CO2 concentration in the dilute- exhaust sample bag is less than 3