Amonyak'ın alternatif bir yakıt olarak yanma karakteristikleri

With its high hydrogen density and already existing infrastructure, ammonia (NH3) is believed to be an excellent alternative fuel that can be used in energy generation and transportation systems. Combustion of ammonia has two main challenges that need to be addressed before its widespread use in practical systems: low flame speed (or weak flame stability) and its potential of generating fuel bond NOx. The primary goal of the present research is to find a method to combust ammonia in an efficient and environmentally benign way. For this aim, the research is conducted in two parallel frameworks; chemical kinetics study and experimental investigation. First we have investigated the combustion characteristics of NH3/H2/air mixtures at elevated pressure and lean conditions which are encountered in practical systems such as gas turbine combustors. Laminar premixed freely propagating flame model is used to calculate the combustion properties. The results of sensitivity study of total NOx formation with respect to the equivalence ratio indicates the possibility of localized rich combustion as an effective way to reduce the NOx concentration down to levels that are the same order as the modern gas turbine engines. One of the main objectives of the chemical kinetics study is to develop a reduced reaction mechanism for the combustion of ammonia which can be used to expedite the design of effective ammonia combustors through numerical simulations of realistic combustor geometries with accurate kinetics models. Accordingly by considering a wide range of conditions in terms of pressure, fuel mixture, and equivalence ratio we have developed two reduced mechanisms based on the well known Konnov mechanism. The reduced mechanisms are capable of predicting the total NOx emission level and the laminar flame speed at an acceptable accuracy over a wide range of conditions. Evaluating the performance of the reduced mechanisms with respect to the full mechanism and experimental data shows that the mechanisms are able to predict the combustion properties almost at the same accuracy level as the Konnov mechanism, but at a nearly five times less CPU time expense. The experimental study focuses on premixed ammonia-hydrogen-air flames under standard temperature and pressure conditions using an inert silicon-carbide (SiC) porous block as a practical and effective medium for flame stabilization. Combustion experiments conducted using a lab scale burner resulted in stable flames with high combustion efficiencies at very high ammonia concentration levels over a wide range of equivalence ratios. Effects of some major influential parameters including equivalence ratio, ammonia mixture fraction, and diameter of the burner on flame stability have been investigated. Noticeable power output densities have also been achieved in the experiments. Results of NOx emission measurements indicate NOx concentrations as low as 35 ppm under rich conditions. The remarkable capability of this specific burner to operate efficiently and cleanly at high ammonia concentration levels, which can easily be achieved by partial cracking of NH3, is believed to be a key accomplishment in the development of ammonia fired power generation systems.