The Non-Road Mobile Machinery (Emission of Gaseous and Particulate Pollutants) Regulations 1999

Figure 15 Dilution system (full flow system only)

A sample of the diluted exhaust gas is transferred from the dilution tunnel DT of a full flow dilution system through the particulate sampling probe PSP and the particulate transfer tube PTT to the secondary dilution tunnel SDT, where it is diluted once more. The sample is then passed through the filter holder(s) FH that contain the particulate sampling filters. The dilution air flow rate is usually constant whereas the sample flow rate is controlled by the flow controller FC3. If electronic flow compensation EFC (see Figure 13) is used, the total diluted exhaust gas flow is used as command signal for FC3.

— PTT particulate transfer tube (Figures 14 and 15)

The particulate transfer tube must not exceed 1020 mm in length, and must be minimised in length whenever possible.

The dimensions are valid for:

• the partial flow dilution fractional sampling type and the full flow single dilution system from the probe up to the filter holder,

• the partial flow dilution total sampling type from the end of the dilution tunnel to the filter holder,

• the full flow double dilution system from the probe tip to the secondary dilution tunnel.

The transfer tube:

• 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.

— SDT secondary dilution tunnel (Figure 15)

The second dilution tunnel should have a minimum diameter of 75mm and should be sufficient length so as to provide a residence time of at least 0.25 seconds for the doubly-diluted sample. The primary filter holder, FH, shall be located within 300 mm of the exit of the SDT.

The secondary dilution tunnel:

• 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.

— FH filter holder(s) (Figures 14 and 15)

For primary and back-up filters one filter housing or separate filter housings may be used. The requirements of Annex III, Appendix 1, section 1.5.1.3 have to be met.

The filter holder(s):

• 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),

• may be insulated.

— P sampling pump (Figures 14 and 15)

The particulate sampling pump shall be located sufficiently distant from the tunnel so that the inlet gas temperature is maintained constant (± 3 K), if flow correction by FC3 is not used.

— DP dilution air pump (Figure 15) (full flow double dilution only)

The dilution air pump shall be located so that the secondary dilution air is supplied at a temperature of 298 K (25°C) ± 5 K.

— FC3 flow controller (Figures 14 and 15)

A flow controller shall be used to compensate the particulate sample flow rate for temperature and backpressure variations in the sample path, if no other means are available. The flow controller is required if electronic flow compensation EFC (see Figure 13) is used.

— FM3 flow measurement device (Figures 14 and 15) (particulate sample flow)

The gas meter or flow instrumentation shall be located sufficiently distant from the sample pump so that the inlet gas temperature remains constant (± 3 K), if flow correction by FC3 is not used.

— FM4 flow measurement device (Figure 15) (dilution air, full flow double dilution only)

The gas meter or flow instrumentation shall be located so that the inlet gas tempertaure remains at 298 K (25°C) ± 5 K.

— BV ball valve (optional)

The ball valve shall have a diameter not less than the inside diameter of the sampling tube and a switching time of less than 0.5 seconds.

Note: If the ambient temperature in the vicinity of PSP, PTT, SDT, and FH is below 239 K (20°C), precautions should be taken to avoid particle losses onto the cool wall of these parts. Therefore, heating and/or insulating these parts within the limits given in the respective descriptions is recommended. It is also recommended that the filter face temperature during sampling be not below 293 K (20°C).

At high engine loads, the above parts may be cooled by a non-aggressive means such as a circulating fan, as long as the temperature of the cooling medium is not below 293 K (20°C).