Semester

Fall

Date of Graduation

2008

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Mridul Gautam.

Abstract

Selective Catalytic Reduction (SCR) has been shown to be the most promising exhaust aftertreatment system for reducing oxides of nitrogen in near term in-use applications. SCRs use the ammonia containing compound urea, as a reducing agent. In order to control the urea dosage during transient operation of the engine, sophisticated control strategies are needed. The goal of this study was to design a controller to achieve the maximum NO x emission reduction possible in the transient mode of engine operation, without causing ammonia slip. The development of an open loop, non-sensor based fuzzy logic urea dosage controller is discussed in this thesis. Urea injection values were controlled with 'maps' based upon the engine speed and engine load, and fuzzy logic was employed as a robust artificial intelligence technique to allow for the development of these maps. Fuzzy logic was utilized to model the complex SCR system and predict the efficiency of NOx conversion. In order to aid in the development of the fuzzy logic SCR model, other methods for generating urea maps were investigated, as well. The first method was an optimization technique, which involved manual testing of the engine to find the optimal urea injection amount. The other method involved injection of urea based upon the average NOx produced. A correction factor was developed and applied to this map to account for losses of ammonia.;The open loop urea map control strategy was implemented without the use of NOx or NH3 sensors. The final fuzzy logic urea map created was able to reduce NOx by 57% over the FTP cycle and 60% over the ETC cycle. This reduction was achieved without causing any significant ammonia slip. The optimized and average NOx urea maps reduced NO x by 67% and 66% over the FTP cycle, but also resulted in large peaks of ammonia slip during the LAFY section. The average NH3 slip seen during the FTP was less than 10 ppm, which was deemed acceptable. The optimized map was also used on the ETC cycle and NOx was reduced by 65% with no significant NH3 slip. The urea maps created for this study appeared to be cycle independent and could be used to control NOx emissions for any transient mode of engine operation.

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