Halon 1301 (CF3Br), or bromotrifluoromethane, had been widely used as fire-extinguishing agent for many years before its production and consumption were severely regulated by the Montreal Protocol due to its hazardous depletion effect to the stratospheric ozone layer. It is therefore imperative to find an effective replacement fire-fighting agent before the mandated deadline of the complete phase out of CF3Br. Currently there are intensive efforts in searching for an environmentally acceptable fire suppression replacement. This, however, is hampered by a lack of fundamental understanding of how CF3Br suppresses the chemical reactions in a flame environment so effectively. Recent experimental evidence has shown that the addition of CF3Br significantly reduced the burning velocity of premixed H2/Air flames by depleting the important radical species that are important to sustain chemical reactions. Extending this finding to understand the suppression of more complicated diffusion flames and unsteady three dimension turbulent flames in the presence of Halon 1301, however, still faces enormous challenge because of the prohibitive requirement of the computational power. The present chemical reaction mechanism for even the simplest hydrocarbon fuel (CH4) combustion involves more than 300 elemental reactions and the addition of CF3Br adds approximately 70 more elemental reactions. This large number of reactions and the associated large number of reaction species, many of which still involve uncertain reaction coefficients and thermodynamics properties, present significant computing challenges for applications in multidimensional non-premixed flames that are often encountered in practice. Therefore, it is of interest to systematically reduce the full chemical mechanism to a few global reactions while still maintaining the accuracy of the original mechanism. The present research systematically reduced the complex H2/Air/CF3Br chemical reaction mechanism with 94 initial elemental reactions to 5 global reaction steps. The reduced mechanism results in dramatic savings in computer time and is capable of predicting the major species and important steady state species with high accuracy. Through detailed sensitivity and production rate analysis the present research was able to find the key elemental reactions that are responsible for the fire suppression behavior of CF3Br. Predicted maximum concentrations of H and OH were found to correlate closely with the existing laminar burning velocity data measured for the premixed H2/Air/CF3Br flames. Better agreement with the experimental data was found when two activation energies for the two most important elementary reactions from QRRK calculations were adopted. The reduced mechanism developed through this research can be used to assist in the calculation and the understanding of fire suppression of CF3Br for more practical multidimensional nonpremixed laminar and turbulent flames, and the effort in searching for other effective fire suppressing agents.

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.