| Mesoscale burner arrays allow combustion to be conducted in a distributed fashion at a millimeter (meso) scale. At this scale, diffusive processes are fast, but not yet dominant, such that numerous advantages over conventional gas turbine combustion can be achieved without giving up the possibility to use fluid inertia to advantage. Since the scale of the reaction zone follows from the scale at which the reactants are mixed, very compact flames result. This compact, distributed form of combustion can provide the opportunity of inter-turbine reheat as well as the potential for lean premixed or highly vitiated combustion to suppress NOx emissions.; As a proof-of-concept, a 4x4 array with burner elements on 5-mm centers was fabricated in silicon nitride via assembly mold SDM. Each burner element was designed in a single monolithic unit with its own combination of reactant inlets, fuel plenum and injection nozzles, and swirler to induce flame stabilization. Results using methane, including pressure drop, flame stability, temperature distribution in the burnt gas, and NO emissions are reported for both fully premixed (mixing prior to injection) and nonpremixed (mixing in the array) configurations. These results demonstrate the degree to which premixed performance can be achieved with this design and pointed to ways in which the array design could be improved over this first-generation unit.; Given what was learned from the 4x4 array, a next-generation 6x6 array was developed. Major design changes include addition of a bluff-body stabilizer to each burner element to improve stability and use of a multilayer architecture to enhance the degree of reactant mixing. Tests using methane in both operating conditions were performed for two stabilization configurations---with and without the bluff bodies. The results for nonpremixed operation show that nearly complete air/fuel mixing was achieved using the 6x6 design, leading to NO emission levels obtainable under fully premixed conditions. However, the results also indicate that element-to-element fuel maldistribution of the array remains significant such that additional efforts to resolve manufacturing difficulties should be made in future applications. Elimination of maldistribution will reduce NO emissions even further as well as improve stability characteristics of the array. |
