Evaluation of the Performance of a Variable Geometry Low-Swirl Burner Operated on Simulated Renewable Fuels in a Boiler Environment
This thesis evaluates a variable blockage low-swirl injector operated on digester gas in a simulated boiler environment to understand how such a device can impact combustion performance as fuel composition varies. California, like many other states, is requiring a reduction in emissions from primary sources of electricity generation. As emission regulations become stricter, novel strategies for achieving the reductions required are required. The current energy policy in California specifically promotes the use of renewable and carbon neutral fuels such as digester gas. The future generations of burners must be fuel flexible in order to meet these emission laws while providing continual operation. To address this, a variable geometry low-swirl injector was developed and its emissions and stability performance assessed using a variety of diagnostics. It was found that a fiber optic probe, integrated into the injector head, was able to provide a reliable measure of emissions and stability. One key result from the optical probe is that the recorded radiation emitted by the reaction corresponding to the lean blow off limits of any composition of digester gas remains constant, implying it could serve as a robust stability sensor with minimal signal processing. Evaluating the role of the variable geometry found that (1) variable center blockage in a low-swirl injector has no effect on the lean blow off limits, (2) as the center blockage becomes less restrictive the NOx emissions will increase, and (3) incorporation of a quarl expansion rather than a sudden expansion increased the lean blow off limits and gave a 50% reduction in NOx emissions. Utilizing a low-swirl injector with high blockage in the central flow, high swirl number, can reduce the NOx emissions across the range of lean operating conditions.