Document ID: chunk:federal_register_of_legislation:F2024L00446:reg:16:p36
Version: federal_register_of_legislation:F2024L00446
Segment Type: reg
Provision Reference: reg 16 (pt 36/108)
Character Range: 985672–988668

between the vehicle exhaust and the connecting tube.
              3.3.2. Dilution air conditioning
              3.3.2.1. The dilution air used for the primary dilution of the exhaust in the CVS tunnel shall pass through a medium capable of reducing particles of the most penetrating particle size in the filter material by ≤ 99.95 per cent, or through a filter of at least Class H13 of EN 1822:2009. 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 be situated before the HEPA filter and after the charcoal scrubber, if used.
              3.3.2.2. 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 and particle levels, which can be subsequently subtracted from the values measured in the diluted exhaust. See paragraph 2.1.3. of Annex B6.
              3.3.3. Dilution tunnel
              3.3.3.1. Provision shall be made for the vehicle exhaust gases and the dilution air to be mixed. A mixing device may be used.
              3.3.3.2. 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 arithmetic average of the values obtained for at least five points located at equal intervals on the diameter of the gas stream.
              3.3.3.3. For PM and PN emissions sampling, a dilution tunnel shall be used that:
                  (a) Consists of a straight tube of electrically-conductive material that is grounded;
                  (b) Causes turbulent flow (Reynolds number  4,000) and be of sufficient length to cause complete mixing of the exhaust and dilution air;
                  (c) Is at least 200 mm in diameter;
                  (d) May be insulated and/or heated.
              3.3.4. Suction device
              3.3.4.1. This device may have a range of fixed speeds to ensure sufficient flow to prevent any water condensation. This result is 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 per cent by volume for petrol and diesel, less than 2.2 per cent by volume for LPG and less than 1.5 per cent by volume for NG/biomethane.
              3.3.4.2. Compliance with the requirements in paragraph 3.3.4.1. of this annex may not be necessary if the CVS system is designed to inhibit condensation by such techniques, or combination of techniques, as:
                  (a) Reducing water content in the dilution air (dilution air dehumidification);
                  (b) Heating of the CVS dilution air and of all components up to the diluted exhaust