| dc.description.abstract | Given that burning conventional hydrocarbon fuels produces harmful carbon-based emissions contributing to global warming, recent environmental initiatives have focused on removing carbon-based fuels from the transportation, power generation and industrial sectors. Although eliminating all combustion devices are not immediately feasible, carbon-free alternative fuels provide a potential intermediate solution. Ammonia (NH3) is one such alternative, being relatively easy to store and transport in the liquid state, as well as having the ability to be produced from renewable sources without environmental damage. NH3 is usually mixed with other fuels to form combustible blends due to its lower flame speed and instability during combustion. The fuel blend of focus for this research was composed of H2:NH3:N2 in a 45:40:15 ratio by volume, which can be obtained from the partial cracking of NH3 and that has been observed to have similar adiabatic flame temperature and laminar flame speed to conventional methane (CH4) flames. Spectroscopic studies were used to identify the behavior of the following species of interest due to their importance in developing NH3 combustion kinematics: OH*, NO*, NH*, and NH2*. Given that a primary obstacle in the combustion of NH3 is the production of NOx and N2O emissions, focusing on these species can lead to improved overall performance of NH3-related combustion devices. Recent studies of NH3-H2 blend combustion have used tangential swirl burners to observe OH*, NO*, NH2*, and NH* in simulated internal combustion engine environments. However, the present work used a premixed Bunsen jet burner fitted with a H2-air pilot flame stabilized on a McKenna burner to study the NH3 blend combustion under laminar flow conditions. It was found that introducing a low-flow-rate pilot flame stabilized the NH3 blend sufficiently enough to reach equivalence ratios (ϕ) as lean as 0.58. Around this point the flame became unstable; however, doubling the pilot flow rate restabilized the NH3 blend combustion and caused a resurgence in key species production, allowing ϕ to be reduced further to 0.40 before experiencing lean blowout. Variations of OH*, NO*, NH*, and NH2* spectral profiles as functions of ϕ were generated, and OH* chemiluminescence imaging gave insight into the interactions between the main and pilot flames. It was discovered that the broadband emissions produced as a result of NH3 introduction into the fuel blend were occurring within the transmission range of the 315-nm bandpass filter used during imaging. Continued refinement of the experimental approach include additional filtration to prevent broadband interference, as well as quantitative diagnostics of such parameters as rate of heat release and laminar flame speed. | |
