No description available.

No description available.

Combustion has been used for a long time as a means of energy extraction. However, in the recent years there has been further increase in air pollution, through pollutants such as nitrogen oxides, acid rain etc. To solve this problem, there is a need to reduce carbon and nitrogen oxides through lean burning, fuel dilution and usage of bi-product fuel gases. A numerical analysis has been carried out to investigate the effectiveness of several reduced mechanisms, in terms of computational time and accuracy. The cases were tested for the combustion of hydrocarbons diluted with hydrogen, syngas, and bi-product fuel in a cylindrical combustor. The simulations were carried out using the ANSYS Fluent 19.1. By solving the conservations equations, several global reduced mechanisms (2-5-10 steps) were obtained. The reduced mechanisms were used in the simulations for a 2D cylindrical tube with dimensions of 40 cm in length and 2.0 cm diameter. The mesh of the model included a proper fine quad mesh, within the first 7 cm of the tube and around the walls. By developing a proper boundary layer, several simulations were performed on hydrocarbon/air and syngas blends to visualize the flame characteristics. To validate the results “PREMIX and CHEMKIN” codes were used to calculate 1D premixed flame based on the temperature, composition of burned and unburned gas mixtures. Numerical calculations were carried for several hydrocarbons by changing the equivalence ratios (lean to rich) and adding small amounts of hydrogen into the fuel blends. The changes in temperature, radical formation, burning velocities and the reduction in NOx and CO2 emissions were observed. The results compared to experimental data to study the changes. Once the results were within acceptable range, different fuels compositions were used for the premixed combustion through adding H2/CO/CO2 by volume and changing the equivalence ratios and preheat temperatures, in the fuel blends. The results on flame temperature, shape, burning velocity and concentrations of radicals and emissions were observed. The flame speed was calculated by finding the surface area of the flame, through the mass fractions of fuel components and products conversions that were simulated through the tube. The area method was applied to determine the flame speed. It was determined that the reduced mechanisms provided results within an acceptable range. The variation of the inlet velocity had neglectable effects on the burning velocity. The highest temperatures were obtained in lean conditions (0.5-0.9) equivalence ratio and highest flame speed was obtained for Blast Furnace Gas (BFG) at elevated preheat temperature and methane-hydrogen fuels blends in the combustor. The results included; reduction in CO2 and NOx emissions, expansion of the flammable limit, under the condition of having the same laminar flow. The usage of diluted natural gases, syngas and bi-product gases provides a step in solving environmental problems and providing efficient energy.

Mass spectrometers have proven to be vital to understanding the Solar System and the planets within it. Spacecraft containing mass spectrometers have been sent to numerous remote places and have determined important information about the atmospheric composition of Venus, Earth, Mars, Jupiter, and Saturn, along with other celestial bodies. Such results have shown a variety of small neutral molecules, such as CH4 NH3, H2O, CO2, and CO, neutral radicals such as atomic O, H, and N, and a host of small ions, such as H+, N+, and NH4+. Closed ion source inlets, which allow for the detection of these small neutral molecules, contain a spherical antechamber that allows the neutrals to thermalize with the walls of the chamber through many successive collisions before they are introduced into the ionization region of the spacecraft mass spectrometer. These collisions, however, energetically excite neutral molecules and lead to many chemical changes, such as racemization, ionization, or even dissociation. When these changes occur, smaller neutrals can be produced, even if they were not in the original sample from the atmosphere or surface. As a result, the determination of the true composition of an atmosphere or a surface is cast into doubt. Herein is given a brief description of mass spectrometry in space research and how the closed ion source has greatly assisted this process. Dissociation and other chemical changes caused by the high velocity impacts that occur in closed source antechambers is also addressed. A theoretical approach to understanding such dissociative processes that occur after high energy collisions in closed source antechambers is described and undertaken. Chapter 2 describes a proof-of-concept study using hexane as a representative molecule and determines the velocity at which widespread dissociation of hexane molecules is likely to occur in closed source antechambers. This same theoretical process is then utilized in Chapter 3 with many more members of the n-alkane family to probe what effect molecular weight has on the amount of dissociation. Alkanes of both higher and lower molecular weight than hexane (C6H14) are used to show the effect as a function of molecular weight. In all cases, it was found that the velocity at which half of the incoming neutral n-alkane molecules dissociate is roughly the same for all molecular weights studied. This result is then applied to current and future space research through a proposed hardware solution, which will reduce the amount of dissociation and a discussion of how this effect may be seen in the results obtained from future mission instruments. Lastly, future work with different molecular weights and with successive collisions (the second, third, fourth, etc.) is described. This future work will further expand the present study to show how different functional groups, which may be partly responsible for higher-than-expected levels of NH3 and CO2, are affected after a high velocity, high energy impact.