UC Berkeley

There has been a recent surge of interest in power generation for a variety of small-scale energy applications. However, as devices are scaled down, a variety of problems emerge from both a system and combustion perspective. Addressing the latter, as a machine gets smaller, the effects of heat losses and fluid interaction with walls can quench radical species, effecting the combustion reactions. Furthermore, boundary layer and friction effects which are normally predictable and small (compared to the system output) at high Reynolds numbers can play a large role in the flowfield development as the size of the combustor shrinks and moves from turbulent flow into the laminar and transitional regime.

Seeking to specifically address this gap in available small-scale combustion technology, a potential candidate exists, however, it has only been demonstrated in larger-scale (> 1.5”) applications. This combustion technology, named the low swirl burner (LSB), offers a variety of potential benefits such as ultra low NOx and CO emissions, low pressure drop, and high turndown ratios to suit these downscaled devices. This dissertation first seeks to understand whether the low swirl burner can be adapted to small scale (≈ 3 kW) combustors and, secondly, attempts to shed light on the flowfield evolution as the LSB is downscaled.

Addressing the first aspect, the LSB was successfully scaled down to a 14 mm diameter unit and tested both qualitatively and quantitatively. Results indicated that miniaturized LSBs exhibited all of the operational characteristics of their large-scale counterparts, indicating they are a perfect candidate for future small-scale energy systems.

Secondly, in order to gain an understanding of the flowfield evolution of the miniaturized LSBs, three different diameter LSBs (12, 14, and 25.4 mm) were probed using laser diagnostics over a wide range of bulk inlet velocities and equivalence ratios. Results indicate that while the effects of scaling are evident in certain parameters, the fundamental properties of the LSB are clearly observed. Additionally, the diagnostics employed proved to be ineffective at measuring a key parameter, the turbulent burning velocity indicating that further diagnostics and modeling efforts may be required.