Full Flow Dilution Tunnel

In the full flow system, entire exhaust of the engine/vehicle is diluted with the filtered room air. The full flow system is quite large in size and expensive. A full-flow double dilution tunnel is shown schematically in Fig. 4.16 . For small engines/vehicles only the primary dilution tunnel is used. For the large engines to provide the desired dilution ratio, the gas is diluted again in the secondary dilution tunnel. The sample is withdrawn for measurements from the secondary dilution tunnel in the large engines. The dilution ratio is maintained around 10:1. The temperature of the diluted exhaust gases at the primary filter is maintained at 325º K or less by a heat exchanger. The flow rate of diluted gas is kept constant during the test by a CVS system.

After thorough mixing of exhaust and air in the dilution tunnel, a constant flow rate sample is extracted that is filtered through a Teflon coated glass fibre filter. The mass of particulate is determined by weighing the particulate mass collected on the filter. A reference filter is used to determine the particulate mass in the dilution air for correction of PM measurement for the background PM. The filter papers are conditioned before and after filtration to prevent condensation of any moisture or deposition of foreign particulate matter from atmosphere. With the full flow dilution tunnel and CVS system, gaseous pollutants are also measured simultaneously with particulates