Document ID: chunk:federal_register_of_legislation:F2024L00446:reg:16:p38
Version: federal_register_of_legislation:F2024L00446
Segment Type: reg
Provision Reference: reg 16 (pt 38/108)
Character Range: 991084–994119

hydrocarbon concentrations of ambient emissions in the dilution air;
                  (b) A connecting tube by which vehicle exhaust is admitted into a dilution tunnel;
                  (c) An optional heat exchanger as described in paragraph 3.3.5.1. of this annex;
                  (d) A mixing device in which exhaust gas and dilution air are mixed homogeneously, and which may be located close to the vehicle so that the length of the connecting tube is minimized;
                  (e) A dilution tunnel from which particulate and, if applicable, particles are sampled;
                  (f) Some form of protection for the measurement system may be used e.g. a cyclone separator, bulk stream filter, etc.;
                  (g) A suction device of sufficient capacity to handle the total volume of diluted exhaust gas.
              Exact conformity with these figures is not essential. Additional components such as instruments, valves, solenoids and switches may be used to provide additional information and co-ordinate the functions of the component system.
Figure A5/3
Exhaust dilution system
              3.3.6.1. Positive displacement pump (PDP)
              A positive displacement pump (PDP) full flow exhaust dilution system satisfies the requirements of this annex by metering the flow of gas through the pump at constant temperature and pressure. The total volume is measured by counting the revolutions made by the calibrated positive displacement pump. The proportional sample is achieved by sampling with pump, flow meter and flow control valve at a constant flow rate.
              3.3.6.2. Critical flow venturi (CFV)
              3.3.6.2.1. The use of a CFV for the full flow exhaust dilution system is based on the principles of flow mechanics for critical flow. The variable mixture flow rate of dilution and exhaust gas is maintained at sonic velocity that is directly proportional to the square root of the gas temperature. Flow is continually monitored, computed and integrated throughout the test.
              3.3.6.2.2. The use of an additional critical flow sampling venturi ensures the proportionality of the gas samples taken from the dilution tunnel. As both pressure and temperature are equal at the two venturi inlets, the volume of the gas flow diverted for sampling is proportional to the total volume of diluted exhaust gas mixture produced, and thus the requirements of this annex are fulfilled.
              3.3.6.2.3. A measuring CFV tube shall measure the flow volume of the diluted exhaust gas.
3.3.6.3. Subsonic flow venturi (SSV)
              3.3.6.3.1. The use of an SSV (Figure A5/4) for a full flow exhaust dilution system is based on the principles of flow mechanics. The variable mixture flow rate of dilution and exhaust gas is maintained at a subsonic velocity that is calculated from the physical dimensions of the subsonic venturi and measurement of the absolute temperature (T) and pressure (P) at the venturi inlet and the pressure in the throat of the venturi. Flow