Date of Publication :7th December 2016

Abstract: Diesel engines are advantageous in terms of lower fuel consumption, lower unburned HC* and better fuel efficiency. Counter side they are disadvantageous in terms of high particulate emissions that results from fuel pyrolysis at high temperatures. These particulate emissions have antagonistic effect on both environment and human health. To regulate these diesel particulates, government is imposing stringent emissions norms on diesel engine exhaust. Therefore, it is important for all engine manufacturers to design and develop a system that is capable of measuring these particulate emissions. Further, diesel particulate matter is very complex structure, primarily composed of solid carbon with several absorbed species like ash, metallic abrasion particles, sulfates and silicates, which cannot be measured directly by analytical instruments based on direct detection method. The best approach to measure diesel particulate matter is based on the gravimetric method by using the device known as dilution tunnel. The present work focuses on design and numerical analysis of partial flow isokinetic dilution tunnel in order to determine the optimum mixing length to achieve complete mixing between the dilution air and exhaust sample. A commercial ANSYS FLUENT software has been used to perform the numerical simulations. To find optimum mixing length, various simulation test were conducted which can be categorized in three broad divisions. The first test consists of 9 different conditions based on variation in duct diameter and dilution ratio (DR) for constant duct length of 2500 mm. Results from first test shows that the shortest mixing length of 1250 mm was obtained for duct diameter of 150 mm when dilution ratio of 20:1 is maintained. Further, in order to reduce the mixing length, test 2 and 3 were conducted by introducing number of perforated plates and grid of cylinders only to best design of test 1. Results from test 2 and 3 shows that mixture gets uniform within 1000 mm of duct length when perforated orifice plate was used. The introduction of a grid of cylinder does not influence quick mixing of exhaust sample with diluted air.

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