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A modified furnace, which burns diesel oil is adopted to study the combustion characteristics and the pollution of the exhausting products under certain designing and operating conditions. The different equivalence ratios and swirl numbers can be obtained by adjusting the flow rate of both axial air and tangential air. The controlling ranges of the various experimental parameters include the equivalence ratios from 0.8 to 1.1, the jet oil pressures from 7 kg/cm² to 9 kg/cm², the open angles of the plate 0¢X and 45¢X, the swirl numbers from 0 to 1.0, the flow rates of the recirculated flue gas from 0% to 12%. The effects of the controlling variables on the combustion characteristics and the formations of pollutants within combustion chamber are studied in this reseach. A photographic technology is used to study the flame structures for helping us to understand the behaviors of the flame under various operating conditions. Under the equivalence ratios from 0.8 to1.1, the concentrations of the average NO and CO decrease, at the lower equivalence ratio. However, the concentrations of the average NO and temperature increases monotonously when jet oil pressure increases. The plate open angle 45¢X is useful for the mixing of both fuel and air, so that the open angle of the plate have important effects on both the temperature of combusion gas and the formation of pollutant NO. When the plate open angle 45¢X and the swirl number is 0.6, the flow rate of NO in the exhaust duct is the lowest. At equivalence ratio 0.8, the average NO concentration in exhaust duct decrease, when the flow rate of the recirculated flue gas increase. Our experiments display that the optimized operating condition is at the plate open angle 45¢X, the swirl number 1.0 and the recirculation rate of the flue gas 12%. NO can be reduced to 32% in this condition, and heat efficiency is reduced only about 3.7%, so we can achieve the request of reducing efficiency to much, the formation of pollutant without influencing the combustion. Under the condition of swirl number 0 and the open angle of the plate at 0¢X and 45¢X the color of the flame in the primary combustion region are white-yellow. In the other hand, at the swirl number 1.0, the color of the flame out of the primary combustion region at the swirl number 1.0 exhibits the red color due to the formation of CO2 and water vapor. The red color region at the swirl number 1.0 is much larger than that at the swirl number 0.

The exhaust gas recirculation (EGR) system has been widely used to reduce nitrogen oxide (NOx) emission, improve fuel economy and suppress knock by using the characteristics of charge dilution. However, previous studies have shown that as the EGR rate at a given engine operating condition increases, the combustion instability increases. The combustion instability increases cyclic variations resulting in the deterioration of engine performance and increasing hydrocarbon emissions. Therefore, the optimum EGR rate should be carefully determined in order to obtain the better engine performance and emissions. A thermodynamic cycle simulation of the four-stroke spark-ignition engine was used to determine the effects of EGR on engine performance, emission characteristics and second law parameters, considering combustion instability issues as EGR level increases. A parameter, called 'Fuel Fraction Burned,' was introduced as a function of the EGR percentage and used in the simulation to incorporate the combustion instability effects. A comprehensive parametric investigation was conducted to examine the effects of variations in EGR, load and speed for a 5.7 liter spark-ignition automotive engine. Variations in the thermal efficiencies, brake specific NOx emissions, average combustion temperature, mean exhaust temperature, maximum temperature and relative heat transfer as functions of exhaust gas recycle were determined for both cooled and adiabatic EGR configurations. Also effects of variations in the load and speed on thermal efficiencies, relative heat transfers and destruction of availability due to combustion were determined for 0% EGR and 20% EGR cases with both cooled and adiabatic configurations. For both EGR configurations, thermal efficiencies first increase, reach a maximum at about 16% EGR and then decrease as the EGR level increases. Thermal efficiencies are slightly higher for cooled EGR configuration than that for adiabatic configuration. Concentration of nitric oxide emissions decreases from about 2950 ppm to 200 ppm as EGR level increases from 0% to 20% for cooled EGR configuration. The cooled EGR configuration results in lower nitric oxide emissions relative to the adiabatic EGR configuration. Also second law parameters show the expected trends as functions of EGR. Brake thermal efficiency is higher for the 20% EGR case than that for the no EGR case over the range of load (0 to WOT) and speed (600 rpm to 6000 rpm). Predictions made from the simulation were compared with some of the available experimental results. Predicted thermal efficiencies showed a similar trend when compared to the available experimental data. Also, percentage of unused fuel availability increases as the EGR level increases, and it can be seen as one of the effects of deteriorating combustion quality as the EGR level increases.

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This thesis deals with turbulent mixing processes occurring in internal combustion engines, when applying exhaust gas recirculation (EGR). EGR is a very efficient way to reduce emissions of nitrogen oxides (NOx) in internal combustion engines. Exhaust gases are recirculated and mixed with the fresh intake air, reducing the oxygen con- centration of the combustion gas and thus the peak combustion temperatures. This temperature decrease results in a reduction of NOx emissions. When applying EGR, one is often faced with non-uniform distribution of exhaust among and inside the cylinders, deteriorating the emission performance. The mixing of exhaust gases and air is governed by the flow in the engine intake manifold, which is characterized by unsteadiness due to turbulence and engine pulsations. Moreover, the density cannot be assumed to be constant due to the presence of large temperature variations.Different flow cases having these characteristics are computed by compressible Large Eddy Simulations (LES). First, the stationary flows in two T-junction type geometries are investigated. The method is validated by comparison with experimental data and the accuracy of the simulations is confirmed by grid sensitivity studies. The flow structures and the unsteady flow modes are described for a range of mass flow ratios between the main and the branch inlet. A comparison to RANS computations showed qualitatively different flow fields.Thereafter, pulsating inflow conditions are prescribed on the branch inlet in or- der to mimic the large pulsations occurring in the EGR loop. The flow modes are investigated using Dynamical Mode Decomposition (DMD).After having established the simulation tool, the flow in a six-cylinder engine is simulated. The flow is studied by Proper Orthogonal Decomposition (POD) and DMD. The mixing quality is studied in terms of cylinder-to-cylinder non-uniformity and temporal and spatial variances. It was found that cycle-averaging of the concentration may give misleading results. A sensitivity study with respect to changes in the boundary conditions showed that the EGR pulsations, have large influence on the results. This could also be shown by POD of the concentration field showing the significance of the pulses for the maldistribution of exhaust gases.Finally, the flow in an intake manifold of a four-cylinder engine is investigated in terms of EGR distribution. For this geometry, pipe bends upstream of the EGR inlet were found to be responsible for the maldistribution. / <p>QC 20130207</p>

This study was concerned with the performance of biofuels in diesel engines. Generally, the basic combustion and emission characteristics of Rapeseed Oil (RSO) and Soya Oil (SO) result in a lower in-cylinder pressure peak than diesel. This led to the reduction of Nitrogen Oxides (NOx) emissions and to relatively high soot emissions. Further measurements of RSO were done in order to investigate the influence of injection pressure, injection timing and Exhaust Gas Recirculation (EGR) on combustion and emission characteristics. A high soot emission from RSO was reduced by increased injection pressure. Moreover, injection timing also had to be varied in order to reduce the soot emissions from RSO. The retarded injection timing (3 deg bTDC) and increased injection pressure (1200 bar) for the blend of 30% RSO resulted in a reduction of soot emission to the same level as from diesel fuel. Further investigation regarding the soot emissions was done for Rapeseed Methyl Ester (RME) under turbocharged engine operation. The application of the boost pressure resulted in stable engine operation at a late injection timing of 5 deg aTDC. A simultaneous reduction of soot and NOx emissions has been achieved for RME at an injection timing of TDC and high EGR percentage (40 – 50 %). The soot particles size distribution under different engine operating conditions for RME and diesel has also been investigated. Moreover, the characteristic of Electrostatic Mobility Spectrometer (EMS) and the design of primary dilution system have been provided in order to understand the influence of the dilution process and to obtain more real results. Generally, RME showed less particles concentration in the nucleation mode when compared to diesel. Moreover, high EGR caused a shift of the particles from the nucleation mode by agglomeration into the accumulation mode for both fuels. The effect of injection pressure could only be seen in the accumulation mode, where high injection pressure slightly reduced the concentration number. The soot emission was effectively reduced by the usage of the diesel particulate filter (DPF). For this purpose, the soot particles size distributions before and after the DPF have been measured at different engine speeds and loads. At low engine torque, the soot was effectively filtered while the operation under high engine loads resulted in low soot particle concentration especially in the nucleation mode, after the DPF.

With an increased urgency for global action towards climate change mitigation, this research was undertaken with the aim of evaluating post-combustion CO2 capture as an emission abatement strategy for gas-fired power plants. A dynamic rate-based model of a capture plant with MEA solvent was built, with imposed chemical equilibrium, and validated at pilot scale under transient conditions. The model predicted plant behaviour under multiple process inputs and disturbances. The validated model was next used to analyse the process and it was found that CO2 absorption is mass transfer limited. The model was then improved by explicitly adding reactions rate in the model continuity, the first such dynamic model to be reported for the capture process. The model is again validated and is observed to provide better predictions than the previous model. Next, high fidelity models of a gas-fired power plant, a scaled-up capture plant and a compression train were built and integrated for 90% CO2 capture. Steam for solvent regeneration is extracted from the power plant IP/LP crossover pipe. Net efficiency drops from 59% to 49%, with increased cooling water demand. A 40% exhaust gas recirculation resulted in a recovery of 1% efficiency, proving that enhanced mass transfer in the capture plant reduces solvent regeneration energy demands. Economic analysis reveals that overnight cost increases by 58% with CO2 capture, and cost of electricity by 30%. While this discourages deployment of capture technology, natural gas prices remain the largest driver for cost of electricity. Other integration approaches – using a dedicated boiler and steam extraction from the LP steam drum – were explored for operational flexibility, and their net efficiencies were found to be 40 and 45% respectively. Supplementary firing of exhaust gas may be a viable option for retrofit, as it is shown to minimise integrated plant output losses at a net efficiency of 43.5%. Areas identified for further study are solvent substitution, integrated plant part load operation, flexible control and use of rotating packed beds for CO2 capture.

With an increased urgency for global action towards climate change mitigation, this research was undertaken with the aim of evaluating post-combustion CO2 capture as an emission abatement strategy for gas-fired power plants. A dynamic rate-based model of a capture plant with MEA solvent was built, with imposed chemical equilibrium, and validated at pilot scale under transient conditions. The model predicted plant behaviour under multiple process inputs and disturbances. The validated model was next used to analyse the process and it was found that CO2 absorption is mass transfer limited. The model was then improved by explicitly adding reactions rate in the model continuity, the first such dynamic model to be reported for the capture process. The model is again validated and is observed to provide better predictions than the previous model. Next, high fidelity models of a gas-fired power plant, a scaled-up capture plant and a compression train were built and integrated for 90% CO2 capture. Steam for solvent regeneration is extracted from the power plant IP/LP crossover pipe. Net efficiency drops from 59% to 49%, with increased cooling water demand. A 40% exhaust gas recirculation resulted in a recovery of 1% efficiency, proving that enhanced mass transfer in the capture plant reduces solvent regeneration energy demands. Economic analysis reveals that overnight cost increases by 58% with CO2 capture, and cost of electricity by 30%. While this discourages deployment of capture technology, natural gas prices remain the largest driver for cost of electricity. Other integration approaches – using a dedicated boiler and steam extraction from the LP steam drum – were explored for operational flexibility, and their net efficiencies were found to be 40 and 45% respectively. Supplementary firing of exhaust gas may be a viable option for retrofit, as it is shown to minimise integrated plant output losses at a net efficiency of 43.5%. Areas identified for further study are solvent substitution, integrated plant part load operation, flexible control and use of rotating packed beds for CO2 capture.

This diploma dissertation focuses on the constructional solutions of EGR exchangers in the form of a CAD model, on their CFD simulation, on the drawing of relevant conclusions, and also on the comparison of two developmental types of these exchangers.

Anaerobic digestion is one of the most promising management options for dairy manure treatment. Manure wastewater from dairy farms has been used for methane production for decades. However, performance failure due to inadequate mixing is routine. In general, the mixng of anaerobic digester is achived throguh mechnical stirring, liquid circulation, and gas circulation, among which the gas circulation proves to be the most effcient way. In this work, we studied the liquid flow pattern of two differetn type of gas-circualtion based anaerobic digesters, with the aim to understand the effects of hydrodynamic behavior of the digesting liquid on the anaerobic digestion performance, so a better mixing strategy can be provided. We used two 20-L gas circulation based anaerobic digesters with confined (gas-lift) and unconfined (bubble column) design. The anaerobic digestion performance and mixing behaviors were studied at different gas recirculation rate. It was found that the biogas production from the bubble column was constantly higher than that from gas-lift digester. However, the overall flow of the two digesters, which is indicated by residence time distribution (RTD), showed a similar pattern. Furhter investigation of local liquid flow behavior using Computational Fluid Dynamic (CFD) indicate that the bubble column accumulated higher portion of sludge in the bottom of the digester, which has a higher TS and VS, COD, and biomethane production potential than those from the gas-lift digester. This is the reason that the biogas production from the bubble column is higher than the gas-lift digester. Through this study, a thorough characterization of the flow behavior of the anaerobic digester were developed, and provided a deep insight of its influence on the anaerobic digestion performance. / Master of Science