Research Terms
Mechanical Engineering Aerospace Engineering
This highly compact gas turbine airplane engine recirculates most of the post-combustion flow to join with air coming into the engine. The design increases engine performance and reduces the environmental impact of flight by limiting contrail formation. Contrails contribute to global warming more than CO2 emissions from planes; they form when water vapor condenses around soot from the exhaust. Recirculating part of the post-combustion flow can reduce contrail formation via water capture, soot suppression, and total exhaust flow reduction. Semi-closed cycle gas turbine engines have been demonstrated but not applied to airplanes. Normally the addition of a heat exchanger increases the engine weight significantly; however, semi-closed cycle engines provide the dual benefits of low weight and high efficiency, in addition to contrail suppression.
Researchers at the University of Florida have demonstrated a semi-closed cycle engine that employs a heat exchanger that operates at high pressures, allowing high overall engine compactness. The design enables the application of a semi-closed cycle gas turbine engine in airplanes.
Semi-closed gas turbine airplane engine that increases engine performance and limits contrail formation
This engine design for application in airplanes employs a semi-closed cycle that allows for capture of water vapor produced by combustion. The exhaust is nearly soot-free, which also reduces contrail formation, and the total exhaust flow is only one quarter of the normal flow. These three effects combine to produce a dramatic reduction in contrail formation. Further, the design improves engine performance and reduces the engine propulsion system weight as compared to conventional airplane engines.
Retrofitting gas turbine engines with inlet air dilution enables hydrogen gas combustion for power generation without excessive nitrous oxide emissions. Hydrogen utilization in gas turbine engines is an intense focus in the energy industry. Efforts are underway by global original equipment manufacturers of terrestrial gas turbines to meet the mandates for decarbonization goals set by the European Union and other countries. While the industry has made progress in allowing increased percentages of hydrogen in fuel blends, the use of 100% hydrogen in practical, flexible systems remains rare, preventing the achievement of zero-carbon generation. There is a need to replace hydrocarbon fuels with hydrogen in legacy systems to reduce greenhouse gas emissions.
The primary challenge associated with hydrogen combustion is the production of large amounts of nitrous oxides (NOx), which plays a significant role in atmospheric pollution. When hydrogen reacts with pure air, it causes excessively high local temperatures, rapidly creating nitrous oxide unless it is premixed or diluted. However, premixing hydrogen increases the likelihood of dangerous flame flashback due to its rapid ignition time, still generating nitrous oxide and damaging equipment. Meanwhile, dilution requires a diluent gas, such as a steam of nitrogen, burdening the system and decreasing plant efficiency. A different strategy is necessary to suppress nitrous oxide production using hydrogen fuel.
A researcher at the University of Florida has developed a design methodology for retrofitting natural gas turbines to burn hydrogen with minimal nitrous oxide (NOx) emissions. The retrofitted system recirculates its own exhaust to lower emissions, especially applicable to gas turbines with simple diffusion burners.
Retrofits natural gas turbines for diffusion burning of hydrogen and diluted air with minimal nitrous oxide emissions
This system for retrofitting gas turbine engines enables them to run on pure hydrogen without exceeding the regulated nitrous oxide limits. Dilution of combustion air with an inert gas reduces nitrous oxide emissions in gas turbines. The turbine exhaust gas is a natural source of the inert gas. Dilution with exhaust, also known as exhaust gas recirculation (EGR), occurs by cooling some of the turbine outflow to mix with incoming air, providing efficiency benefits and external heat.
The turbine design approach straightforwardly retrofits conventional natural gas turbines to utilize EGR and reduce nitrous oxide pollution without requiring a fully redesigned combustor. The retrofit modifies the external ductwork to capture a part of the exhaust gas and pass it through a heat exchanger or absorption refrigeration system. After cooling, the captured exhaust mixes with fresh air before re-entering the engine. This accomplishes the dilution of the fresh air necessary for reduced nitrogen oxide formation and the prevention of hot regions when the diluted air combusts with hydrogen fuel. The overall process requires no fuel premixing, avoids dangerous flashback, and operates as a simple diffusion burner.
This humid air turbine is a combined cooling, heat, and power system that provides increased power grid efficiency and stability by providing flexible distributed electricity generation (~1 MW per unit). Consumer electricity demands vary widely throughout the day, requiring utility companies to invest substantially in infrastructure to store electricity or otherwise meet peak power demands. Available practices for saving resources include turning off generators when demand is low, only using them for peak hours, but this often backfires due to sharp swings in customer demand and the inability of large power generators to ramp up in time to meet that sudden need. Researchers at the University of Florida have developed a high efficiency, compact humid air turbine that generates electricity at distributed locations. The system runs continuously at a power level dictated by demand for steam with a fast response time and a wide range of efficient generation capacities. The turbine is ideal for meeting fluctuations in demand, lowering the need for energy storage and increasing grid stability. The turbine uses flameless combustion, generating very low emissions and outputting clean water as it runs.
A low-cost, high-efficiency, compact humid air turbine for generating distributed electricity and heat
This semi-closed gas-turbine cycle with an absorption refrigeration cycle creates an efficient system for power generation, heat, refrigeration, and water extraction. It builds upon UF proprietary technology known as the Power, Water Extraction, and Refrigeration (PoWER) cycle, which itself offers significant efficiency, cost, compactness, and emissions benefits. This system combines elements of the humid air turbine (HAT) cycle to further increase efficiency with minimal increase in complexity or cost. It operates more efficiently than available technology, approaching 50 percent efficiency in small plants over a wide range of power output levels. The fast, efficient operation combined with automatic capture of its waste heat makes it an ideal generation system for combined cooling, heat, and power applications and microgrids.
These direct methanol fuel cells can increase the capacity of energy storage in portable electronics, such as laptops and tablets. Methanol is an inexpensive, widely available fuel that can be extracted from both natural gas and renewable plant materials, such as wood. Though long-lasting, existing direct methanol fuel cells (DMFCs) are the size of a briefcase and require bulky fans, exit condensers, and other water management components to function properly.
Researchers at the University of Florida have developed fuel cells that contain microscale passages, eliminating any need for large water management components while supporting operation at high ambient temperature. These DMFCs are two to three times smaller than available batteries capable of 24-hour operation and facilitate low-cost monitoring of methanol concentration.
Direct methanol fuel cells (DMFCs) that are small enough to replace rechargeable batteries in consumer electronics and other mobile devices
Direct methanol fuel cells (DMFCs) continuously require water to react with the methanol fuel at the anode side of the cell; it is generally obtained from the water produced on the cathode side. Available DMFCs utilize a bulky system of fans, exit condensers, and other components to recapture evaporated water from the exiting cathode air stream. This DMFC features an innovative structure that forces water to flow directly from the cathode into the anode stream. Microscale passages within the DMFC reroute water and effectively prevent water losses to the air, all while using much less space. It achieves optimal water balance during fuel cell operation through innovative algorithms that adjust fuel and oxidizer injection rates in response to power load demands. As a result, no excess water is generated. The system also provides inexpensive fuel concentration measurement. Using a computer algorithm, it eliminates the need for expensive in-place fuel sensors and collects information about temperature, fuel-level, stack currents, fan speed, and fuel-injection pump output rates.
Cryogenic power extraction increases fuel efficiency by applying exhaust heat from a vehicle engine to expand a cryogenic liquid (e.g. liquid nitrogen, liquid natural gas) into gas that runs a turbine. Available engine designs waste excess heat and energy. Researchers at the University of Florida have developed a cryogenic power extraction system that uses the exhaust heat to convert cheap, environmentally friendly liquid nitrogen into an extremely high-pressure gas. A car with this engine uses this high-pressure fluid to produce more engine power, more than doubling fuel efficiency. Cheap and abundant, liquid nitrogen provides a cost-efficient and reliable resource. The market for fuel efficient vehicles is one of the fastest growing markets, with a growth rate near 30 percent annually. More than 1.3 million hybrid electric vehicles were sold in 2013. This liquid nitrogen heat extraction is a significant fuel efficiency improvement, positioning it well in this large, dynamic market.
Fuel-efficient engine design dramatically decreases mileage cost with no environmental degradation
In available technologies, the waste heat from vehicle engines produces no work. University of Florida researchers have designed an engine that utilizes a cryogenic working fluid, such as nitrogen (LN2), to extract heat from car exhaust. This design uses the waste heat from an existing engine to convert the cryogen into a high pressure gas, which runs a turbine to recover the stored energy. A vehicle with this system could operate without any cryogen on board or with only cryogen and no fuel. It is also possible to create a system that uses liquid natural gas (LNG) or liquid hydrogen (LH2) in place of, or in combination with an inert cryogen such as LN2. In this case, the engine would use the expanded natural gas or hydrogen as a fuel in the combustion engine.
