Document ID: chunk:federal_register_of_legislation:F2023C00229:reg:9:p54
Version: federal_register_of_legislation:F2023C00229
Segment Type: reg
Provision Reference: reg 9 (pt 54/71)
Character Range: 361698–364694

signals. When using a pressurised air supply (Figure 18), FC2 directly controls the air flow.

              FM1 Flow measurement device (Figures 11, 12, 18, 19)

              Gas meter or other flow instrumentation to measure the dilution air flow. FM1 is optional if the pressure blower PB is calibrated to measure the flow.

              FM2 Flow measurement device (Figure 19)

              Gas meter or other flow instrumentation to measure the diluted exhaust gas flow. FM2 is optional if the suction blower SB is calibrated to measure the flow.

              PB Pressures blower (Figures 11, 12, 13, 14, 15, 16, 19)

              To control the dilution air flow rate, PB may be connected to the flow controllers FC1 or FC2. PB is not required when using a butterfly valve. PB may be used to to measure the dilution air flow, if calibrated.

              SB Suction blower (Figures 11, 12, 13, 16, 17, 19)

              For fractional sampling systems only. SB may be used to measure the diluted exhaust gas flow, if calibrated.

              DAF Dilution air filter (Figures 11 to 19)

              It is recommended that the dilution air be filtered and charcoal scrubbed to eliminate background hydrocarbons. At the engine manufacturers request the dilution air shall be sampled according to good engineering practice to determine the background particulate levels, which can then be subtracted from the values measured in the diluted exhaust.

              DT Dilution tunnel (Figures 11 to 19)

              The dilution tunnel:

                —    shall be of a sufficient length to cause complete mixing of the exhaust and dilution air under turbulent flow conditions;

                —    shall be constructed of stainless steel with:
                  —    thickness/diameter ratio of 0,025 or less for dilution tunnels with inside diameters greater than 75 mm;

                  —    a nominal thickness of no less then 1,5 mm for dilution tunnels with inside diameters of equal to or less than 75 mm;

                —    shall be at least 75 mm in diameter for the fractional sampling type;

                —    is recommended to be at least 25 mm in diameter for the total sampling type;

                —    may be heated to no greater than 325 K (52 °C) wall temperature by direct heating or by dilution air pre-heating, provided the air temperature does not exceed 325 K (52 °C) prior to the introduction of the exhaust in the dilution tunnel;

                —    may be insulated.

              The engine exhaust shall be thoroughly mixed with the dilution air. For fractional sampling systems, the mixing quality shall be checked after introduction into service by means of a CO2-profile of the tunnel with the engine running (at least four equally spaced measuring points). If necessary, a mixing orifice may be used.

                  Note: If the ambient temperature in the vicinity of the dilution tunnel (DT) is below 293K (20 °C), precautions