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Design and Investigation of a Fuel-Flexible Injection System for Low-Emission Vehicles
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2017-06-01
[PDF-3.16 MB]
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Edition:Final Report, July 2016-June 2017
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Abstract:The transportation sector represented 27% of total U.S. greenhouse gas (GHG) emissions, all from fuel combustion, in 2013 according to the U.S. Greenhouse Gas Inventory Report: 1990-2013. The National Science Foundation (NSF) and Department of Energy (DOE) have urged researches on clean and efficient vehicles facing the ever increasing energy demand and aggravating GHG effect. Clean and complete combustion of liquid fuels highly relies on fine sprays evaporating quickly and mixing well with oxidizer and thus, burning cleanly and more completely. However, present fuel injection systems cannot finely atomize and thus cleanly combust viscous fuels. Also, the fluctuating oil price and high cost of biofuels obstructs the widespread utilization of renewable fuels. Recently, a novel flow-blurring (FB) injector has been developed by PI and collaborators and proved to generate fine sprays, instead of typical jets, immediately at the injector exit and result in ultra-low-emission combustion of fuels including conventional diesel and biodiesel and its source oil - vegetable oil (VO) as well as its waste byproduct - straight glycerol (about 200 times more viscous than diesel), without fuel-preheating and hardware modification. However, the detailed atomization mechanism is yet unknown limiting its practical application. Also for highly viscous glycerol, previous spray imaging has shown droplets and ligaments are generated at injector exit, resulting in extended pre-vaporization zone and lifted glycerol flame, that is easier to be blown off, and causing relatively higher emissions. The present research seeks to further enhance atomization and stabilize spray and thus combustion, especially for viscous fuels including VO and algae oil (AO). A novel swirl burst (SB) injector is successfully designed in the current work by incorporating a swirling atomizing air with the flow blurring concept. Results show clean lean premixed combustion of viscous and heavy source oils (VO and AO) of biodiesel have been achieved using the novel SB injection without fuel pre-heating. This signifies greatly saving the cost and energy of converting the source oils into biodiesel for conventional engines running on low viscosity fuels. Compared the FB injector, SB injection results in enhanced atomization, and thus faster fuel pre-vaporization, improved fuel-air mixing, hence less lifted flames with ultra-low emissions. Swirl number (SN) of 2.0 is found to give the optimum SB injector geometry with lowest emissions among three tested SNs of 1.5, 2.0 and 2.4. Spray characteristics using Particle Image Velocimetry quantitatively substantiate the further improved atomization of the SB injector. Pressure measurements in the flow line indicates the novel SB injection with high viscosity tolerance requires much lower energy input than the conventional AB injector, showing the promise of developing next-generation clean engines on heavy fuels with higher power-to-weight ratio. Compared to a FB injector, SB injection enhances the spray fineness without extra energy input. Overall, the novel SB injector indicates the promise for clean vehicles such as microturbine-driven hybrid vehicles (cars, trucks, and boats) and airplane powered by jet engines.
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