Document ID: chunk:federal_register_of_legislation:F2012C00283:reg:21:p7
Version: federal_register_of_legislation:F2012C00283
Segment Type: reg
Provision Reference: reg 21 (pt 7/39)
Character Range: 275606–278713

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.

              1.3.5.  Volume Measurement in the Primary Dilution System
                The method of measuring total dilute exhaust volume incorporated in the constant volume sampler shall be such that measurement is accurate to 2 per cent under all operating conditions. If the device cannot compensate for variations in the temperature of the mixture of exhaust gases and dilution air at the measuring point, a heat exchanger shall be used to maintain the temperature to within ±6 K of the specified operating temperature.
                If necessary, some form of protection for the volume measuring device may be used e.g. a cyclone separator, bulk stream filter, etc.
                A temperature sensor shall be installed immediately before the volume measuring device. This temperature sensor shall have an accuracy and a precision of ±1 K and a response time of 0.1 s at 62 per cent of a given temperature variation (value measured in silicone oil).
                The measurement of the pressure difference from atmospheric pressure shall be taken upstream from and, if necessary, downstream from the volume measuring device.
                The pressure measurements shall have a precision and an accuracy of ±0.4 kPa during the test.

              1.4.  Recommended System Descriptions
               Figure 6 and Figure 7 are schematic drawings of two types of recommended exhaust dilution systems that meet the requirements of this annex.
                Since various configurations can produce accurate results, 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.
              1.4.1.  Full Flow Dilution System with Positive Displacement Pump

Figure 6
Positive Displacement Pump Dilution System

               The positive displacement pump (PDP) full flow 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. The collecting equipment consists of:
              1.4.1.1. A filter (DAF) for the dilution air, which can be preheated if necessary. This filter shall consist of the following filters in sequence: an optional activated charcoal filter (inlet side), and a high efficiency particulate air (HEPA) filter (outlet side). It is recommended that an