The system, which is shown diagrammatically below, consists of a dilution air filter, exhaust inlet mixer section, particulate formation tunnel, throttle valve and fan together with a twin mode particulate filter and a gas flow metering system. The system is housed in a cubicle with the particulate formation tunnel mounted horizontally.

Dilution air enters vertically downwards through an 18" square horizontal sandwich filter via a transition section into a 90º bend, which leads into the horizontal o.d. 135.7 mm diameter 1345 mm long flange to flange particulate formation tunnel. Exhaust gas enters through a horizontal 60 mm diameter exhaust pipe, which terminates at a mixing orifice trapped between the 90º bend and the tunnel.

A raw exhaust gas sampling probe is located in the 60 mm exhaust pipe. The tunnel terminates at its exit end in a 180º stainless steel bend, into which are fitted a particulates probe and a dilute exhaust gas sampling probe. From the 180º bend flexible plastic trunking connects to the manual butterfly valve at the entry to the centrifugal fan and from the fan to the discharge port.

The twin particulate filter bank is located in a 19" rack mounted recess at the opposite end to the exhaust entry. Above this recess are located the flow control module and the mode select and display module, both of which are 19" rack modules. The sample pump and the gas meter are located on the base of the cabinet.

Legislative requirements for particulate sampling systems for engine exhaust utilise the constant volume sampling system handling the whole exhaust flow whilst the engine or vehicle is operated over the prescribed ‘drive’ cycle. Such particulate and constant volume sampling systems are expensive capital items, particularly for heavy duty engines.
For engine development studies measurement of particulate emissions are required at various individual engine conditions and it is therefore possible to conduct these measurements during steady state tests. Constant volume techniques are not necessary for such steady state testing and it also possible to make measurements based on a fraction of the total exhaust flow. Consequently Cussons have developed a mini variable split particulate sampling system which is being successfully used by a number of  client companies.

Particulate Tunnel: Stainless steel construction 113 mm bore with 10 x diameters between exhaust inlet and sample point and 100 mm mixing orifice at exhaust gas inlet. Reynolds number at 2860 l/m = 31,400.
Exhaust Inlet: 52 mm bore with ‘V’ flange connections to variable exhaust flow splitter.
Tunnel Particulate Probe: 14.0 mm bore stainless steel.

Tunnel Particulate
Sampling: Dual sampling lines each with Gelman 2220, 47 mm dia. filter with 35 mm dia. effective filtration area.
Sample Pump: Metbel MB 602
Sample Flow: By variable area flowmeter 0.05 -0.06 l/sec. Total sample flow by dry gas meter 3200 l/hr rating converted to provide digital display of total flow.
Tunnel Fan: Centrifugal fan providing turbulent flow conditions may be throttled by manual butterfly valve at fan inlet.
Temperature
Indications: Two digital indicators providing continuous monitoring of tunnel at sampling point and gas meter temperatures.