Engine and after-treatment modeling for controls

The low level of exhaust gas emissions from modern vehicles is a major achievement of automotive technology. Since the introduction of exhaust after-treatment catalysts, the emissions have been reduced by well over two orders of magnitude. Low emissions have to be maintained in the presence of hardware faults, degraded catalysts, and varying fuel composition such as ethanol content. Contributions to this achievement come from engine, chemical, and control engineering. The presentation will try to illuminate the role played by control and, in parallel, illustrate selection and application of models in control design. The models considered in this presentation range from very simple to very complex - from frequency domain to PDEs. Operation of the overall emission control system will be described and control designs for several subsystems explained in some detail. The subsystems that are covered in the presentation are the “inner” air-fuel ratio loop which features the Smith Predictor, catalyst modeling for control of the “outer” loop, and adaptive ethanol detection in flex fuel vehicles. Experimental vehicle traces and emission test results will be used to explain the results and illuminate benefits.