No abstract / Submitted to Bulletin of the Society of Rheology, May 2005

Via the viewpoint of fuel and oxidant supply in this study, we compare heterogeneous carbon fiber bipolar plates with graphite bipolar plates that apply to fuel cell. In operating condition with different gas inlet pressure and compressing pressure, we study the penetrability of reactant gases that come into the carbon cloth under the rib of a bipolar plate. Eventually the output voltage and power density are measured to prove the advantages of the new bipolar plate. The experimental results show that carbon fiber bipolar bunch in low compressing pressure 2bar already display high gas penetrability. Its dimensionless flow rate is about quadruple of graphite bipolar plates. The reactant gas can enter the carbon cloth either from the side or from the top of the penetrating carbon fiber bipolar bunch. In addition, carbon fiber bipolar plates are affected slightly by compressing pressure. Further, the total electrical resistant of carbon fiber bipolar plates with carbon cloth already decreases to 18.5mΩ*cm² in low compressing pressure 2bar. Therefore, by appling the new bipolar plate, the fuel cell in compressing pressure 2bar and inlet fuel pressure 1.15bar(absolute pressure) can developed a power rate 180mW/cm². Concerning graphite bipolar plates, we can find that compressing pressure increase from 1bar to 4bar due to the reduction in total resistance so the output voltage and power density can increase to maximum value 113mW/cm2. However, while we augment more compressing pressure, the influence in reducing total resistance is much smaller than that in reducing the porosity of carbon cloth. Therefore, the output power density decreases. Also, output voltage of carbon fiber bipolar plates at 0.5mA/cm2 is 0.38 V and is higher than that of graphite bipolar plate 0.2 V.

Diesel engine combustion has been studied during the last decades by researchers in terms of improving the performance of the engine. In order to improve the analysis of the diesel engine combustion, dimensionless parameters were used in this study. It was concluded that the newly introduced dimensionless parameters developed in this study facilitate understanding of diesel engine combustion process. A new method has been proposed to determine the values of the form factor (m) and efficiency factors (a) of the Wiebe equation. This is achieved by developing a modified form of Wiebe equation with only one constant. The modified version of Wiebe equation facilitates the determination of constants accurately, which enhances the accuracy of evaluating the burn fraction. The error induced on the burn fraction f with respect to the values of constants a and m obtained through different methods is discussed and compared. The form factor affects the burn fraction significantly compared to the efficiency factor. A new non-dimensional parameter ‘combustion burn factor (Ci)’ has been identified in the modified Wiebe equation. The burn fraction f was found to be a function of Ci only, thus the benefits of expressing heat release rate with respect to Ci have been presented. The errors associated with the determination of apparent heat release rate (AHRR) and the cumulative heat release (Cum.Hrr) from the measured cylinder pressure data and the assumed specific heat ratio (γ) was determined and compared. The γ affected the calculated AHRR more than the cylinder pressure. Overestimation of γ resulted in an underestimation of the peak value of the AHRR and vice versa, this occurred without any shift in the combustion phasing. A new methodology has been proposed to determine the instantaneous and mean value of γ for a given combustion. A two litre Ford puma Zetec diesel engine, four cylinder and 16 valves was employed to carry out this investigation. This new methodology has been applied to determine γ for a wide range of injection pressure (800 bar to 1200 bar), injection timing (9 deg BTDC to -2 deg BTDC) and engine loads at 2.7 BMEP and 5 BMEP. Standard ultra-low sulphur diesel fuel and two bio-diesels (Rapeseed Methyl Ester and Jatropha Methyl Ester) were studied in this investigation. Ignition delay is one the most important parameter that characterises the combustion and performance of diesel engines. The relation between ignition delay and combustion performance in terms of efficiency and emission was revealed by researchers. Ignition delay period measurements in diesel engine combustion along with the most used correlation for calculating ignition delay are discussed in this work. The effect of constants on accuracy in the correlation were discussed, and induced error on calculated ignition delay periods with respect to constants were calculated and compared. New techniques were proposed to calculate the constant values directly by using the experimental data. It was found that the calculated values for ignition delay using the new techniques matched well with the experimental data. These techniques can improve the accuracy of the ignition delay correlation. Also a new correlation without any constants was introduced in this work. This correlation can be used to predict ignition delay directly by using engine parameters only. The introduced correlation provides better results compared to Arrhenius type correlation presented by Wolfer. This new correlation can be used for feedback control engine combustion process.

Evidence based performance of novel ventilation systems in existing low energy buildings is invaluable as it provides data on the system operation in a real dynamic environment. This thesis presents the outcomes from research involving a number of experimental field studies of a single sided ventilation system installed in a single cell office space as part of a building retrofit pilot project in Cork, Ireland. The solution consists of a purpose provided, multi configuration opening, comprising a narrow slotted architectural louvre component split across a low level manual opening section and a high level automated opening section. A review of published research found that little experimental data exists on the performance of such systems and air flow rate correlations developed for plain openings are currently used by designers to make predictions about their performance. Three experimental campaigns were designed and carried out. First, in order to quantify performance of the system, long term and short term monitoring of the internal thermal and air flow environment at the experimental building was completed. Second, ventilation rate measurements in existing and retrofit spaces were completed using a tracer gas concentration decay technique. Thirdly, air flow through the single sided slot louvre opening was investigated. In addition, the annual cooling potential of the multi-configuration system was investigated computationally. Results show there was a significant difference between both thermal environments with the retrofit space consistently displaying lower air temperatures over the cooling season and throughout all Air Change Rate measurement periods. Lower levels of vertical thermal stratification and diurnal temperature variation were also observed. On average, across a wide range of boundary conditions, lower ventilation rates were observed for the slotted louvre system with a narrower spread of values when compared with the existing building. The dominant driving force was either buoyancy or wind depending on the opening configuration adopted in the slotted louvre system. The slot louvre was found to be wind dominant for lower opening heights when compared with a plain opening of the same dimensions. Existing single sided correlations were found to perform better when predicting airflow rates through a plain opening when compared with the slot louvre system and a new dimensionless exchange rate parameter is proposed for predicting wind driven airflow through the slot louvre. Simulations indicate that 80% of annual occupied hours required an enhanced ventilative cooling airflow rate to achieve internal thermal comfort. Using a combination of configurations the system was able to provide the required cooling airflow rate for 93% of the occupied hours.

This dissertation presents analytical solutions to address several unresolved issues on the modeling of CO₂ flow in permeable media. Analytical solutions are important as numerical simulations do not yield explicit expressions in terms of the model parameters. In addition, simulations that provide the most comprehensive solutions to multiphase flow problems are computationally intensive. Accordingly, we address the following topics in this dissertation. The method of characteristics (MOC) solution of the overall mass conservation equation of CO₂ in two-phase flow through permeable media is derived in the presence of compressibility. The formally developed MOC solutions rely on the incompressible fluid and rock assumptions that are rarely met in practice; hence, the incompressible assumption is relaxed and the first semi-analytic MOC solution for compressible flow is derived. The analytical solution is verified by simulation results. Fractional flow theory is applied to evaluate the CO2 storage capacity of one-dimensional (1D) saline aquifers. Lack of an accurate estimation of the CO₂ storage capacity stands in the way of the fully implementation of CO₂ storage in aquifers. The notion of optimal solvent-water-slug size is incorporated into the graphical solution of combined geochemical front propagation and fractional flow theory to determine the CO₂ storage capacity of aquifers. The analytical solution is verified by simulation results. The limits of the Walsh and Lake (WL) method to predict the performance of CO₂ injection is examined when miscibility is not achieved. The idea of an analogous first-contact miscible flood is implemented into the WL method to study miscibly-degraded simultaneous water and gas (SWAG) displacements. The simulation verifies the WL solutions. For the two-dimensional (2D) displacements, the predicted optimal SWAG ratio is accurate when the permeable medium is fairly homogeneous with a small cross-flow or heterogeneous with a large lateral correlation length (the same size or greater than the interwell spacing). We conclude that the WL solution is accurate when the mixing zone grows linearly with time. We examine decoupling of large and small-scale heterogeneity in multilayered reservoirs. In addition, using an analytical solution derived in this research, the fraction of layers in which the channeling occurs is determined as a function of the Koval factor and input dispersivity. We successfully present a simulation configuration to verify the off-diagonal elements of the numerical dispersion tensor. Numerical dispersion is inevitably introduced into the finite difference approximations of the 2D convection-dispersion equation. We show that the off-diagonal elements of the numerical dispersion tensor double when the flow velocity changes with distance. In addition, the simulation results reveal that the flow becomes more dispersive with distance travelled if there is convective cross-flow. In addition, local mixing increases with the convective cross-flow between layers. A numerical indicator is presented to describe the nature of CO₂ miscible displacements in heterogeneous permeable media. Hence, the quantitative distinction between flow patterns becomes possible despite the traditionally qualitative approach. The correlation coefficient function is adopted to assign numerical values to flow patterns. The simulation results confirm the accuracy of the descriptive flow pattern values. The order-of-one scaling analysis procedure is implemented to provide a unique set of dimensionless scaling groups of 2D SWAG displacements. The order-of-one scaling analysis is a strong mathematical approach to determine approximations that are allowed for a particular transport phenomenon. For the first time, we implement the scaling analysis of miscible displacements while considering effects of water salinity, dissolution of CO₂ in the aqueous phase, and complex configurations of injection and production wells. / text

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