Abstract:
Research on alternative fuel combustion systems is important to address global energy and environmental concerns. Renewable fuels, such as biofuels have attracted significant attention as potential sources to achieve energy security and to tackle environmental issues. However, these alternatives haven’t yet been fully utilized because much of the existing combustion systems are set up for traditional fossil-fuels. This study focuses on fuel-flexible combustion of diesel, vegetable oil (VO) and glycerol fuels by a novel technique of twin-fluid atomization known as Flow Blurring (FB) atomization, at different operating pressures. The first part of this study discusses scalability considerations of FB atomization, with an objective to develop a scaled-up fuel-flexible combustor. Several scaling parameters that affect the processes of atomization, fuel-air mixing, and combustion are analyzed to select scaling criteria for all components of the combustor. A scaled-up 60-kWth capacity combustor is developed and experimentally investigated using diesel and VO fuels. Results show that the scaled-up system’s performance is comparable to the small scale system in terms of flame appearance, emission levels, and static flame stability. Next, the scaled-up system’s combustion performance with glycerol fuel is investigated in laboratory and at industrial test site. Glycerol is extremely difficult to atomize because of its high viscosity. The lab combustor was able to burn glycerol cleanly, with low CO and NOx emissions. At industrial test site, combustion experiments with 40% methane and 60% glycerol resulted in stable flame. Next, effect of operating pressure on flame characteristics and injector pressure drop is experimentally investigated with diesel, at pressures ranging from 101.3 kPa to 450 kPa. Normalized pressure drop across the injector increased with increase in atomizing air flow rate and decreased with increase in pressure. An increase in chamber pressure resulted in increase in CO levels and decrease in NOx emissions. Increase in pressure also produced less lifted flames with increased yellow zones. Finally, combustion performance of VO is investigated at elevated pressures. Compared to diesel, VO produced larger flames exhibiting more distributed combustion and lower NOx emissions. At high pressures diesel flames contained significantly higher portions of yellow or sooty regions compared to VO.
