No description available.

<p>Diesel engines emit toxic gases like NOx and hydrocarbons. These gases need to be treated before they are released out the tailpipe. Thus, an aftertreatment system is installed which comprises of DOC, DPF and SCR. The DOC oxidizes the hydrocarbons and NO, the DPF traps the particulate matter and SCR reduces the NOx by reacting with NH3 at high temperatures. However, since NH3 is also a toxic gas, it cannot be released out the tailpipe in excess. It is important to inject an appropriate amount of NH3 so that it does not slip out the tailpipe. With increasingly stringent regulations on the emission limits of these toxic gases, control of SCR has become more necessary than before.</p> <p>In this thesis, the work done by previous members of the lab research group was improved upon. The objective remained the same, namely, keeping the NH3 slip under 50 ppm while maximizing NOx reduction. On initial inspection, it was realized that the entire controller had been designed and implemented in continuous time. Since the controller would be implemented digitally, with limited hardware sampling time, a discrete-time implementation as done via a DCU was created. The controller switched between two controllers – slip-based and storage-based. The slip-based controller was modified to include a feedforward term in the system so that the response time could be improved along with a feedback controller to eliminate any disturbances and steady-state error, using ammonia slip feedback as measured by an NH3 sensor. It aims at keeping the maximum ammonia slip under 50 ppm. The storage controller is a feedback controller which tries to limit the ammonia storage based on the values fed by a lookup table. This lookup table is a simplified table that determines the maximum ammonia storage at any given instant based on the catalyst bed temperature. The feedback controller gains for both controllers were determined based on a linearized plant model since the initial gains were ineffective with the discretized model. The initial switching mode controller that switches between slip control and storage control switched too frequently between the controllers, thereby affecting controller performance. A switching logic was implemented to limit the number of switches. A switch will be permitted only if the previous switch occurred over a certain time. By implementing all the subparts together in the controller, incremental improvements were prominent. In the end, the performance by implementing the proposed idea was distinctly better. The metrics considered for performance comparison are the number of switches and the ability to maximize slip up to 50 ppm. Parameter error was also studied as well and its effect on the controller performance was analyzed. The data when tested against sets of underestimated, overestimated and mixed estimates for the plant parameters resulted in the underestimated parameters to work within the scope of the objective. The controller was able to compensate for the underdosing. Overestimation caused overdosing in the system which led to spikes in the NH3 slip. Thus, it is better to underestimate the plant parameters than overestimate them.</p>

One major aspect of environmental pollution affecting human life and climate is air pollution. The harmful pollutants in the air include mostly hydrocarbons, carbon monoxide, carbon dioxide, nitrogen oxides as well as soot and other particulate matter. These pollutants result in several damaging effects on environment and living beings which include acid rain, photochemical smog, global warming and various health hazards in human beings even cancer. Major contribution of these pollutants is from man-made sources such as industrial and automotive emissions that employ fossil fuels. In our country, diesel constitutes more than 40% of the fossil fuel consumption. Studies show that diesel engine emissions contribute to 80% of nitrogen oxides amongst other air pollutants. In the context of stringent emission regulations being implemented all over the world, exhaust emission control, in general and nitrogen oxide emission in particular, is gaining significant importance. A review of recent literature indicates the significance and popularity of electrical discharge based non thermal plasma for exhaust cleaning applications in general, and NOx cleaning in particular. While the existing pre-combustion and catalyst based post-combustion nitrogen oxides (NOx) abatement techniques have inherent disadvantages owing to short shelf life, saturated engine modifications, cost concerns etc., the electrical discharge based non- thermal plasma techniques offer certain advantages in terms of cost and life factors. Several non-thermal plasma techniques viz., pulsed plasma, surface plasma, dielectric barrier discharge plasma etc., have been studied under different laboratory conditions. Interestingly, due to the high oxidizing environment that prevails in the discharge plasma zone, complete reduction of NOx by the plasma alone is becoming a challenging task. This has led the researchers to utilize additional processing techniques in cascade with discharge plasma. This additional gas cleaning technique may involve the use of adsorbents, catalysts or some other secondary treatment for eliminating the nitrogen oxides produced due to oxidizing reactions in the plasma chamber. One such additive can be an adsorbent, which can be commercially obtained or prepared from industrial wastes. In this thesis the adsorption properties of two industrial wastes were explored for the first time in conjunction with discharge plasma. The synergistic effect of plasma combined with an adsorbent shows promising results in NOx removal thus offering an effective solution to two environmental issues namely air pollution and open waste dumping. While the plasma, generally, refers to direct plasma treatment of exhaust, it can also be used for generation of ozone in a separate reactor which can subsequently be injected into the exhaust stream resulting in indirect plasma treatment. The current work focuses on both direct and indirect dielectric barrier discharge plasma treatment for NOx reduction in diesel engine exhaust cascaded with either oyster shells, a mariculture waste or lignite ash from lignite coal fired plant. Instead of conventional petro-diesel, biodiesel produced from the seeds of pongamia pinnata is used as the fuel. This biofuel, on one hand, causes considerable reduction in volatile organic compounds, particulate matter, soot, oil mist etc., but on the other hand may have higher concentrations of nitrogen oxides, an aspect that has motivated us to take up the research work envisaged in this thesis. It was observed in the laboratory environment that for a given power, both direct and indirect plasma treatments have resulted in NOx removal to the tune of 85 to 95% when cascaded with the adsorbents studied.