2015-01-14
An Experimental Comparison of the Uniformity Index for Two Dual Stage Plate Mixers in a SCR system 2015-26-0109
As the number of vehicles and environment pollution is increasing day by day, the emission regulation gets more stringent by the emission regulation authorities. Vehicle manufacturers' develop new ways and technologies to meet the norms levied for cleaner vehicles. Especially in diesel engines, NOx emissions are considered an important pollutant to be treated. In EURO 5 regulation NOx emission value is 0.18g/km for passenger cars which is further reduced to 0.08 g/km in EURO 6 regulation for diesel engines. In order to meet such stringent emission norms without compromising on engine performance, Selective Catalytic Reduction (SCR) is one of the solution to achieve EURO 6 NOx emission levels from diesel engines.
In SCR technology the reduction of NOx is done through ammonia which is injected into exhaust stream in the form of Aqueous Urea solution known as DEF. To achieve better conversion efficiency, the injected DEF has to be uniformly distributed and mixed with the exhaust stream. In this system, a mixer is used for better mixing of ammonia with exhaust stream which in turn improve the NOx conversion efficiency. Mixer efficiency is measured through uniformity index of ammonia present in exhaust upstream SCR catalyst. The Uniformity Index of the ammonia up stream SCR catalyst can be calculated by the following equation [3].
Where ‘c’ is the value of ammonia upstream at the coordinate points of SCR catalyst, 
is the mean value of the ammonia values across the catalyst and ‘n’ is the total number of coordinate points.
is the mean value of the ammonia values across the catalyst and ‘n’ is the total number of coordinate points.Uniformity Index depends on the mixer plate angles, exhaust flow profile, mixing length, impingement of injected DEF on mixer plates. Better mixer design results in better uniformity index that in turn results in better NOx conversion efficiency.
This paper is an experimental comparison of the uniformity index for two dual stage plate mixers having different blade angles. At different engine operating points, the concentration of ammonia upstream SCR catalyst (at different co-ordinate points) is calculated which decides the uniformity index for the mixer and the effect of mixer design is analyzed
The objective of this paper is to study the performance of two different dual stage mixers with different blade angles and bring out experimental results to compare and conceive the best mixer design for the current application. The mixers under study are Mixer A and Mixer B, with a difference of 10°-15° in their blade angles.
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