Document ID: chunk:federal_register_of_legislation:F2011C00805:reg:120:p6
Version: federal_register_of_legislation:F2011C00805
Segment Type: reg
Provision Reference: reg 120 (pt 6/23)
Character Range: 249681–252634

not fall below 5 litres per minute and shall not exceed 0.2 per cent of the flow rate of the dilute exhaust gases.

         2.3.4.2. Dilution air

         2.3.4.2.1. A sample of the dilution air shall be taken at a constant flow rate near the ambient air-inlet (after the filter if one is fitted).

         2.3.4.2.2.  The air shall not be contaminated by exhaust gases from the mixing area.

         2.3.4.2.3.  The sampling rate for the dilution air shall be comparable to that used in the case of the dilute exhaust gases.

         2.3.4.3. Sampling operations

         2.3.4.3.1. The materials used for the sampling operations shall be such as not to change the pollutant concentration.

         2.3.4.3.2. Filters may be used in order to extract the solid particles from the sample.

         2.3.4.3.3. Pumps are required in order to convey the sample to the sampling bag(s).

         2.3.4.3.4. Flow control valves and flow-meters are needed in order to obtain the flow-rates required for sampling.

         2.3.4.3.5. Quick-fastening gas-tight connections may be used between the three-way valves and the sampling bags, the connections sealing themselves automatically on the bag side. Other systems may be used for conveying the samples to the analyser (three-way stop valves, for example).

         2.3.4.3.6. The various valves used for directing the sampling gases shall be of the quick-adjusting and quick-acting type.

         2.3.4.4. Storage of the sample

         The gas samples shall be collected in sampling bags of adequate capacity so as not to reduce the sampling rate. The bags shall be made of a material such as will not change the concentration of synthetic pollutant gases by more than  2 per cent after 20 minutes.

         2.4.  Additional sampling unit for the testing of vehicles equipped with a compression-ignition engine

         2.4.1. Unlike the taking of gas samples from vehicles equipped with spark-ignition engines, the hydrocarbon and particulate sampling points are located in a dilution tunnel.

         2.4.2. In order to reduce heat losses in the exhaust gases between the exhaust outlet and the dilution tunnel inlet, the pipe may not be more than 3.6 m long, or 6.1 m long if heat insulated. Its internal diameter may not exceed 105 mm.

         2.4.3. Predominantly turbulent flow conditions (Reynolds number  4000) shall apply in the dilution tunnel, which shall consist of a straight tube of electrically-conductive material, in order to guarantee that the diluted exhaust gas is homogeneous at the sampling points and that the samples consist of representative gases and particulates. The dilution tunnel shall be at least 200 mm in diameter and the system shall be earthed.

         2.4.4. The particulate sampling system shall consist of a sampling probe in the dilution tunnel and two series-mounted filters. Quick-acting valves shall be located both up and downstream of the two