Browse Publications Technical Papers 2019-01-1391
2019-03-19

Thermal Analysis of Aircraft Auxiliary Power unit: Potential of Supercritical CO2 Brayton cycle 2019-01-1391

An “APU” (Auxiliary Power Unit) is a small gas turbine engine to provide supplementary power to an aircraft and is located at the tail-section of larger jets. APU generators provide auxiliary electrical power for running aircraft systems on the ground. Applications include powering environmental systems for pre-cooling or preheating the cabin, and providing power for crew functions such as preflight, cabin cleanup, and galley (kitchen) operation and long-haul airliners must be started using pneumatic power of APU compressor. The Honeywell 131-9A gas turbine APU has 440 kW shaft power and 90 kW electric generator consuming 120 kg fuel/hour. Hybrid power systems based on fuel-cell are promising technology for the forthcoming power generation market. A solid oxide fuel cell (SOFC) is the perfect candidate for utilizing/ recovery waste heat. The article deals with waste heat recovery from fuel cell exhaust using Brayton cycle as bottoming cycle for additional power production. The proposed cycle utilizes an SOFC fuel cell acting as the topping cycle for a super-critical carbon dioxide Brayton cycle acting as the bottoming cycle. In this work, carbon dioxide is proposed as the working fluid for the closed supercritical bottoming cycle, which is expected to perform better for intermediate temperature heat recovery applications than the traditional air cycle. The super-critical CO2 power cycle exhibits high power cycle efficiency, small turbo-machinery size (due to high density of carbon –dioxide near the critical point), lower critical pressure (7.38MPa) and temperature (304.25K), stability and non-toxic. At a turbine inlet temperature of 1166.7K and a waste heat input of 316.66kW, the super-critical CO2 power cycle will have an efficiency of around 46% and the hybrid cycle will have a efficiency of around 61% .The main advantage of this kind of hybrid system, is efficiency improvement reduced emissions and negative impacts on the environment.

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