Craig Fairbridge

Fractal analysis of gas adsorption on Syncrude coke

Abstract Fractal dimension is an intrinsic, quantitative measure of surface irregularity and provides a convenient parameter for comparing surface physical properties. Several particle size ranges of Syncrude coke were studied by nitrogen and carbon dioxide adsorption. The apparent surface area, A, was observed to increase from 1 to 15 m2 g−1 for N2 and from 65 to 300m2 g−1 for CO2 data with decreased particle size. The fractal dimension, D, was determined from the proportionality: A∝RD-3, where the surface area is determined by BET or D-P (Dubinin-Polanyi) theories, R is the particle radius and 2⩽D⩽3. The value of D for Syncrude coke was determined to be 2.48 from both N2 and CO2 results.

Arrhenius behavior of hydrocarbon fuel photochemical reaction rates by thermal lens spectroscopy

The temperature dependence of thermo-optical and photochemical reaction properties of hydrocarbon fuels is investigated using thermal lens spectroscopy. We consider the time dependence of the absorption coefficient due to the photoinduced chemical reaction (PCR) and species diffusion to evaluate nonequilibrium characteristics of the samples. The measured temperature dependences of the reaction rates are found to follow the Arrhenius correlation. Experimental results for thermophysical properties of the samples and an analysis of the connection between PCR properties and the chemistry of the samples are also presented.

RemaRks on VaRious applications of micRowaVe eneRgy

Microwave energy is an alternative energy source that is receiving a considerable amount of attention from researchers for a wide spectrum of applications. The fundamentally different method of transferring energy from the source to the sample is the main benefit of utilizing microwave energy; by directly delivering energy to microwave-absorbing materials, conventional issues such as long heating periods, thermal gradients, and energy lost to the system environment can be minimized or avoided. Furthermore, the penetrating capacity of microwave allows volumetric heating of samples. These attributes of microwave energy make utilizing it very attractive for industrial applications as an alternative to conventional processing methods. The reality is otherwise however, and limited literature is found in any given area of work. Despite the lack of focus, in most published cases, the utilization of microwave energy has produced improved results compared to conventional methods with reduced heating times or reaction temperatures. This review provides a general overview of reported applications of microwave energy in the open literature. It also attempts to summarize the results obtained for various common uses and highlights some applications that have not gathered as much attention as anticipated.

Soret effect and photochemical reaction in liquids with laser-induced local heating

We report a theoretical model and experimental results for laser-induced local heating in liquids, and propose a method to detect and quantify the contributions of photochemical and Soret effects in several different situations. The time-dependent thermal and mass diffusion equations in the presence and absence of laser excitation are solved. The two effects can produce similar transients for the laser-on refractive index gradient, but very different laser-off behavior. The Soret effect, also called thermal diffusion, and photochemical reaction contributions in photochemically reacting aqueous Cr(VI)-diphenylcarbazide, Eosin Y, and Eosin Y-doped micellar solutions, are decoupled in this work. The extensive use of lasers in various optical techniques suggests that the results may have significance extending from physical-chemical to biological applications.

Thermal-lens study of photochemical reaction kinetics.

We consider the time dependence of the absorption coefficient due to the photoinduced chemical reaction (PCR) and species diffusion to calculate the temperature rise in the thermal-lens (TL) effect. The TL signal at the detector plane is also calculated. This theoretical approach removes the restriction that the PCR time constant is much greater than the characteristic TL time constant, which was assumed in a previously published model. Hydrocarbon fuel and aqueous Cr(VI) samples are investigated, and quantitative experimental results for the thermal, optical, and PCR properties are obtained. While similar results were obtained for the Cr(VI) solution using the previous and present models, the relative difference between the PCR time constants extracted from the same experimental data for a hydrocarbon fuel sample is found to be more than 220%. This demonstrates the significant difference of the two models.

Surface structure and oxidation reactivity of oil sand coke particles

Abstract Fractions of particles of varying mean diameter were isolated from coke obtained from the fluid coking of Athabasca bitumen. Correlations were established between the rate of oxygen sorption and the apparent surface area as measured by carbon dioxide adsorption. The rate of oxygen sorption, r0, could be related to particle radius, R, by the equation: r0 ∝ RD − 3 over a range of particle size where D is the fractal dimension of the coke. The existence of such correlations may be related to the iterative processes which form the particles.

Effects of different cetane number enhancement strategies on HCCI combustion and emissions

Cetane number is the accepted indicator for quantifying the autoignition characteristics of diesel fuels in compression ignition engines. Diesel fuel specifications typically require a minimum cetane number to achieve satisfactory combustion behaviour in conventional diesel engines. In contrast, a high cetane number fuel may not be beneficial for implementing high efficiency, clean combustion strategies such as homogeneous charge compression ignition (HCCI). The purpose of this study was to investigate cetane number effects on HCCI combustion and emissions. The experiments were conducted in a single-cylinder, variable compression ratio, cooperative fuel research engine operated in HCCI combustion mode. The fuels were finely atomized and partially vaporized in the intake manifold. The base fuel was a low cetane refining stream derived from oil sands sources. Three different methods were employed to increase the base fuel cetane number, namely hydroprocessing, cetane improver addition, and blending with a renewable fuel component. Results show that the three methods of cetane number enhancement produce significantly different HCCI combustion behaviour. The hydroprocessed fuels exhibited more stable and complete combustion than the base fuel, which resulted in a wider operating region, reduced carbon monoxide, unburned hydrocarbon, and nitrogen oxide (NO x ) emissions, and lower indicated specific fuel consumption (ISFC). The main disadvantages of the hydroprocessed fuels were the higher exhaust gas recirculation rates required to retard the combustion phasing, which limits the maximum indicated mean effective pressure for a given intake pressure, and increased knock intensity due to a faster combustion process. In comparison, the other two methods of fuel cetane enhancement increased ISFC compared to the base fuel. The addition of nitrate cetane improver resulted in higher NO x emissions, while blending with a renewable fuel component increased hydrocarbon emissions. The experimental data provide evidence that the magnitude and phasing of low temperature heat release, as well as fuel volatility, play important roles in HCCI combustion.

Fuels for Advanced Combustion Engines Research Diesel Fuels: Analysis of Physical and Chemical Properties

The CRC Fuels for Advanced Combustion Engines working group has worked to identify a matrix of research diesel fuels for use in advanced combustion research applications. Nine fuels were specified and formulated to investigate the effects of cetane number aromatic content and 90% distillation fraction. Standard ASTM analyses were performed on the fuels as well as GC/MS and /u1H//u1/u3C NMR analyses and thermodynamic characterizations. Details of the actual results of the fuel formulations compared with the design values are presented, as well as results from standard analyses, such as heating value, viscosity and density. Cetane number characterizations were accomplished by using both the engine method and the Ignition Quality Tester (IQT/sT) apparatus.

Various Approaches in Kinetics Modeling of Real Feedstock Hydrodesulfurization

Abstract This brief review discusses various important approaches in kinetics modeling of real feedstock hydrodesulfurization. These include analytical aspects of dealing with complicated real feedstock, structural approaches, linear-free energy relationships, and the continuum theory in hydrodesulfurization modeling.

Gasification reactivity of Canadian anthracite and semi-anthracite chars

Abstract This paper presents the gasification reactivity in air of untreated and demineralized chars derived from Canmore (semi-anthracite) and Mt. Klappan (anthracite) coals using a thermogravimetric analysis technique. The effects of mineral content, particle size and surface physical properties on the reactivity of these chars were investigated. It was found that the gasification reactivity of the char decreased with increased particle size and decreased mineral content. A reaction dimension, D R , was determined from logarithmic plots of gasification reactivity against particle size. This reaction rate/particle radius relationship is an example of a fractal scaling law where the exponent is a function of the effective fractal dimension of the process. The values determined for D R were 2.78 and 2.40 for Canmore and Mt. Klappan chars respectively. The specific surface area measured by carbon dioxide adsorption at 298 K did not correlate with reactivity or particle size data whereas the results from mercury porosimetry indicated possible correlations.