Particulate Emission Measurement

For measurement of particulate emissions, the gas is diluted with air in a dilution tunnel and, a sample is continuously collected from the diluted gas and filtered to collect particulate matter. The mass of the collected PM is measured to determine specific PM emissions in terms of g/km or g/kWh.

The dilution tunnels are of two types

• Partial flow, and
• Full flow dilution tunnel

Partial Flow Dilution Tunnel

In the partial-flow system, only a small part of the exhaust stream is diluted. To withdraw a true representative of the exhaust gas the following systems have been developed;

• Isokinetic sampling systems
• Flow controlled systems with concentration measurement, and
• Flow controlled systems with flow measurement

In an isokinetic system, the gas velocity in the sampling tube which leads the sampled exhaust gas to dilution tunnel is kept same in magnitude as the velocity of the bulk exhaust gas stream. In this way, an undisturbed and uniform exhaust gas sample flow at the inlet of sampling probe is obtained.

An isokinetic system is shown schematically in Fig. 4.15. Raw exhaust gas is transferred from the exhaust pipe to the dilution tunnel (DT) through isokinetic sampling probe (ISP) and the transfer tube. The differential pressure of the exhaust gas between exhaust pipe and inlet to the probe is measured with a pressure transducer. The signal is fed to a flow controller that controls the suction blower and, a differential pressure of zero at the tip of probe is maintained. Under these conditions, exhaust gas velocities in the exhaust pipe and probe are identical and the flow through isokinetic probe is a constant fraction of the exhaust flow. The sampling rate can be obtained by the ratio of cross sectional areas of probe and the exhaust pipe. The dilution airflow rate is measured with the flow meter. The dilution ratio is calculated from the dilution air flow rate and exhaust sample to total exhaust flow ratio.