04 Apr 2014

Clean Sky RENERGISE (GA no: 287076)

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During this project, in order to increase system’s efficiency, we studied the introduction of two power generation units, which produce electrical power from waste heat thanks to an energy recovery system. This power generation will be used in replacement of or in addition to usual generation systems that take their power from the Main Gear Box (i.e have a direct cost in fuel burning). There are two ways of converting waste heat into electrical power, named hereafter Static and Dynamic Energy Recovery Systems. First, the heat of the produced gases can be directly converted to electrical energy with the use of a thermoelectric generator. This Thermoelectric generator is to be installed on the engine cover where the temperature difference with the ambient corresponds to a typical thermoelectric module’s operating temperature difference. The generated voltage of the module drops with the increase of its current; hence an MPPT is required in order to achieve the maximum power output. It is worth mentioning that energy recovery using thermoelectric generators has already been implemented in automotive vehicles. On a second level, the kinetic energy of the exhaust gases can be used to rotate a gas turbine connected to an electrical generator, similar to the case of heat-electricity cogeneration units. This way, significant amounts of electric energy can be generated, reducing dramatically fuel consumption. However, the speed and pressure of the gases differ according to the main engine’s power output though the waste heat source remains at very high enthalpy levels over all flight conditions (compared to the recovered electrical power). As a result, the torque/speed characteristic of the turbine may also change, therefore a feedback control would be necessary on the electric generator’s output. Consequently, with the use of the above energy recovery systems, fuel consumption as well as carbon emissions will decrease, improving the efficiency of the aircraft. Another challenge within this project is the introduction of supercapacitor-based energy storage systems, as an intermediate energy bank for the thermoelectric modules generation. Generally, the supercapacitor can store a very large energy amount compared to a common capacitor due to its higher energy density, usually thousands of times greater than an electrolytic capacitor. This higher energy density comes of its unusually high capacitance, which is a result of the unique modern fabrication techniques. The typical nominal voltage is about 3V, therefore supercapacitor banks are produced by a large number of series and parallel connected supercapacitor units, achieving greater capacitance and voltage level. As it will be discussed in next paragraph, common applications of supercapacitors can be found in alternative energy sources, emergency power sources, uninterruptible power supplies and energy recovery systems such as regenerative braking. A comparison with classical battery-based storage systems will take place, highlighting the techno-economically optimum solution.


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