Construction And Application Of High Temperature And High Pressure Combustion Bomb For Flame Propagation Of Some Transportation Fuel Components

Reducing pollutant emissions and improving energy efficiency are the main objective of combustion. In various fossil fuels, liquid transportation fuels, such as gasoline, jet fuel and diesel fuel, are widely used in various combustors due to their high energy density and convenience of transportation. The hydrocarbon-based transportation fuels consist of hundreds of different species, including linear alkanes, cycloalkanes, aromatics and so on. The complexity of these components makes it impossible to directly simulate their specfic combustion chemistry. Therefore, surrogates are usually built using 3-5 representative components to imitate the physico-chemical and combustion properties of real fuels. Different kinds of combustion research could be performed for the surrogates. So it is essential to study the combustion characteristics of the representative compoents in transportation fuels.Laminar burning velocity is one of the most important macro-parameters in premixed combustion. It can be measured over wide pressures, temperatures and equivalence ratios. It plays an irreplaceable role in the engine design and turbulent combustion. Laminar burning velocity has been widely used to validate combustion kinetics models. However, most studies on the laminar burning velocities of representative components in transportation fuels focus on atmospheric pressure because the boiling points of these fuels are usually higher than 100℃. Laminar burning velocities of these representative components at elevated pressures are deficient. In this work, an electrically heated single cylindrical combustion vessel is developed for measuring burning velocities at high temperature and high pressure. The combustion kinetic models are validated and developed by using the present experimental results. The dissertation consists of four chapters.In chapter 1, theoretical basis and experimental techniques for laminar burning velocity are introduced. The status and developing trends of laminar burning velocity are reviewed. It is clear that study on the laminar burning velocities of high boiling points fuels at elevated pressures is of significance.In chapter 2, design objectives and design process of the new high temperature and high pressure combustion bomb are introduced, including the mechanical structure, combustible preparation system, heating system, ignition system and schlieren system. Laminar burning velocities at pressure up to 20 atm are measured. A Matlab based processing program is also developed to automatically process the flame videos.In chapter 3, comprehensive validation and uncertainty evaluation are performed for the new apparatus. The validation experiments of methane and ethanol indicate that reproducible and precise experimental data can be derived from this apparatus. Different sources of uncertainty are systematically analyzed. The uncertainties of initial temperature, initial pressure, equivalence ratio and laminar burning velocity are evaluated.In chapter 4, laminar burning velocities of the representative components in transportation fuels, including alkanes, cycloalkanes, aromatics and oxygenated fuels, are measured at atmospheric pressure to engine-relevant pressures. Simulations are performed using detailed combustion kinetic models. For alkanes and cycloalkanes, the most sensitive reactions are the kinetics of small species in flame. Benzene ring in aromatics makes some large intermediates very stable in the combustion of aromatics. So flame propagations of aromatics are sensitive to the molecular structures of fuels. Laminar burning velocities of oxygenated fuels are also different from traditional hydrocarbons. The oxygen atom in the molecular structure of oxygenated fuels improves the importance of oxygen-containing functional groups in flame propagation. The sensitive reactions of oxygenated fuels are slightly different from alkanes. In general, the kinetics of small intermediates dominate in most flame propagation due to the extreme high temperature of laminar premixed flame. Reaction rates and branching ratio can be largely changed by the increase of initial pressures. Three-body reactions are more important at elevated pressure. The predictive ability of combustion kinetic models are still need to improve over wide pressure ranges. Finally, we summarize our work and give some perpectives for future research.