Division 9.2.3.1 Description of partial flow system

A schematic of a PFD system is shown in Figure 6.7. It is a general schematic showing principles of sample extraction, dilution and PM sampling. It is not meant to indicate that all the components described in the Figure are necessary for other possible sampling systems that satisfy the intent of sample collection. Other configurations which do not match these schematics are allowed under the condition that they serve the same purpose of sample collection, dilution, and PM sampling. F1These need to satisfy other criteria such as in points 8.1.8.6 (periodic calibration) and 8.2.1.2 (validation) for varying dilution PFD, and point 8.1.4.5 as well as Table 6.5 (linearity verification) and point 8.1.8.5.7 (verification) for constant dilution PFD.

As shown in Figure 6.7, the raw exhaust gas or the primary diluted flow is transferred from the exhaust pipe EP or from CVS respectively to the dilution tunnel DT through the sampling probe SP and the transfer line TL. The total flow through the tunnel is adjusted with a flow controller and the sampling pump P of the particulate sampling system (PSS). For proportional raw exhaust gas sampling, the dilution air flow is controlled by the flow controller FC1, which may use q_{m ew} (exhaust gas mass flow rate on wet basis) or q_{m aw} (intake air mass flow rate on wet basis) and q_{m f} (fuel mass flow rate) as command signals, for the desired exhaust gas split. The sample flow into the dilution tunnel DT is the difference of the total flow and the dilution air flow. The dilution air flow rate is measured with the flow measurement device FM1, the total flow rate with the flow measurement device of the particulate sampling system. The dilution ratio is calculated from these two flow rates. For sampling with a constant dilution ratio of raw or diluted exhaust gas versus exhaust gas flow (e.g.: secondary dilution for PM sampling), the dilution air flow rate is usually constant and controlled by the flow controller FC1 or dilution air pump.

The dilution air (ambient air, synthetic air, or nitrogen) shall be filtered with a high-efficiency PM air (HEPA) filter.

Components of Figure 6.7:

DAF

Dilution air filter

DT

Dilution tunnel or secondary dilution system

EP

Exhaust pipe or primary dilution system

FC1

Flow controller

FH

Filter holder

FM1

Flow measurement device measuring the dilution air flow rate

P

Sampling pump

PSS

PM sampling system

PTL

PM transfer line

SP

Raw or diluted exhaust gas sampling probe

TL

Transfer line

Mass flow rates applicable only for proportional raw exhaust gas sampling PFD:

q_{m ew}

is the exhaust gas mass gas flow rate on wet basis

q_{m aw}

is the intake air mass flow rate on wet basis

q_{m f}

is the fuel mass flow rate