UBC Theses and Dissertations

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UBC Theses and Dissertations

Gain-scheduling and preview control of selective catalytic reduction systems in diesel engines Lim, Jihoon


Diesel engines have an excellent reputation due to higher torque and better fuel efficiency compared to gasoline engines. However, as a drawback, diesel combustion generates harmful nitrogen oxides (NOx) emissions. To reduce NOx emissions, the studies for selective catalytic reduction (SCR) control systems have been conducted. The SCR control system computes an optimal amount of liquid-reductant agent such as ammonia (NH₃) or urea and injects it upstream of the SCR catalyst. Thus, NOx emissions chemically react with NH₃ in the SCR catalyst resulting in ideally harmless gas coming out of the tailpipe. However, in practice, control challenges such as nonlinearity and unmeasurable catalyst conditions cause undesirable NOx and NH₃ downstream of the SCR catalyst. This thesis makes three contributions in designing the SCR controllers overcoming the control challenges. Firstly, this thesis proposes a new approach to designing a gain-scheduling (GS) SCR controller consisting of multiple linear time-invariant H infinity controllers, each of which provides satisfactory control performance for different operating points. Secondly, this thesis presents a GS linear parameter-varying SCR controller with a theoretical guarantee of stability and performance. Finally, this thesis introduces a preview-feedback SCR controller based on state augmentation techniques using previewed NOx information with a low computational requirement. The effectiveness of the proposed controllers is validated by the simulation tests using experimentally obtained data over the non-road transient driving cycle. It is shown that the proposed controllers significantly maximize NOx conversion efficiency with low ammonia out of the tailpipe even with model parameter variation and sensor noise.

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